Background: Invasive listeriosis is a rare, life-threatening foodborne disease. Molecular subtypi... more Background: Invasive listeriosis is a rare, life-threatening foodborne disease. Molecular subtyping and enhanced surveillance identified a cluster of possibly related listeriosis cases from 2006 to 2010 in the Lombardy Region of Northern Italy. Particularly, this major Pulsed-Field Gel Electrophoresis (PFGE) cluster (named 11) grouped 31 isolates, belonging to serotype 1/2a and Sequence Type (ST)38 as defined by Multi-Locus Sequence Typing (MLST). Our study expanded the previous investigation to include cases from 2011 to 2014 and to perform Multi-Virulence-Locus Sequence Typing (MVLST) on isolates in Cluster11/ST38 to better understand their epidemiology and possibly identify a common source outbreak clone. Materials and Methods: All collected human Listeria monocytogenes isolates were serotyped and subtyped with PFGE and MLST. MVLST was performed on all isolates in Cluster11/ST38. Demographic, clinical and microbiological data were collected using a standardized report form. Results: Of 338 L. monocytogenes human isolates collected during the period, 43 (12.7%) belonged to Cluster11/ST38. While this cluster was observed sporadically in 2006, 2008 and 2014 (2 cases/year each), and in 2013 (n=1), cases due to this cluster peaked in 2009, 2010 and 2011 (n=10, 16 and 10 cases respectively). Cases occurred in nine out of twelve Lombardy provinces, with the highest frequency observed in Bergamo and Milan. The 43 isolates in Cluster11/ST38 were split by MVLST into two Virulence Types (VTs), VT80 (n=12) and VT104 (n=31). VT104 cases were concentrated between 2009 and 2011 and in Bergamo and Milan provinces. For all Cluster11/ST38 cases, an epidemiological investigation was performed and in one case, a matching VT104 L. monocytogenes clone was isolated from a cheese sample (Taleggio) retrieved from a patient\u2019s refrigerator. Based on both molecular and epidemiologic data, this cheese was identified as the implicated source. Conclusions: Our findings revealed a major listeriosis outbreak in Northern Italy linked to cheese in 2009-2011, which was undetected by local health authorities. Our study showed that integrating subtyping methods such as PFGE, MLST and MVLST with conventional epidemiologic investigations can help identify the source of outbreak clones of L. monocytogenes. Such information is useful in both terminating ongoing outbreaks and preventing future ones from occurring
Human listeriosis outbreaks in Canada have been predominantly caused by serotype 1/2a isolates wi... more Human listeriosis outbreaks in Canada have been predominantly caused by serotype 1/2a isolates with highly similar pulsed-field gel electrophoresis (PFGE) patterns. Multilocus sequence typing (MLST) and multi-virulence-locus sequence typing (MVLST) each identified a diverse population of Listeria monocytogenes isolates, and within that, both methods had congruent subtypes that substantiated a predominant clone (clonal complex 8; virulence type 59; proposed epidemic clone 5 [ECV]) that has been causing human illness across Canada for more than 2 decades.
High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechan... more High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs withi...
Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-0.6% yeast extract (TSB... more Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-0.6% yeast extract (TSBYE) or sterile, whole milk and heated at 62.8 degrees C in sealed thermal death time tubes. Severely heat-injured cells were recovered in TSBYE within sealed thermal death time tubes because of the formation of reduced conditions in the depths of the TSBYE. Also, the use of strictly anaerobic Hungate techniques significantly increased recovery in TSBYE containing 1.5% agar compared with aerobically incubated controls. The exogenous addition of catalase, but not superoxide dismutase, slightly increased the recovery of heat-injured cells in TSBYE containing 1.5% agar incubated aerobically. Growth of cells at 43 degrees C caused a greater increase in heat resistance as compared with cells heat shocked at 43 degrees C or cells grown at lower temperatures. Growth of L. monocytogenes at 43 degrees C and enumeration by the use of strictly anaerobic Hungate techniques resulted in D62.8 degrees C...
A simple well-plate technique was utilized to determine the effect of various metals on the growt... more A simple well-plate technique was utilized to determine the effect of various metals on the growth of microorganisms in media containing different polyphosphates. Aspergillus flavus and four gram-positive bacteria were completely inhibited by media containing 1% of various alkaline polyphosphates, whereas four gram-negative bacteria were not. Significant differences were observed between the type of polyphosphate added, the type of metal added, and the species of gram-positive bacterium inhibited. The addition of Mg2+ stimulated growth of A. flavus and Bacillus cereus in the presence of tetrasodium pyrophosphate, whereas Mn2+ permitted growth of A. flavus and Staphylococcus aureus in the presence of sodium hexametaphosphate. Iron supplementation allowed the growth of S. aureus and Listeria monocytogenes on media containing 1 % tetrasodium pyrophosphate. A method for determining the amount of calcium and magnesium in water was modified to detect free Mg2+ by replacing EDTA with phosp...
Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convect... more Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convection at an air speed of 30.5 m/min. Upon rapid cooling using forced convection and when brought back to room temperature, eggs were more prone to penetration by Salmonella enteritidis (strain PS8NSR). Eggs cooled using forced convection had 100% penetration by PS8NSR; eggs cooled using natural convection had 91.3% penetration; and uncooled eggs had 48% penetration. Scanning electron microscopy revealed that shells of both cooled and uncooled eggs had microscopic cracks; however, cracks were more numerous and larger in shells of cooled eggs.
Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and su... more Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg contents. Egg contents were then incubated at 37 degrees C, and Salmonella Enteritidis colonies were enumerated for up to 106 h. Iron supplementation significantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth in egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. After 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in eggs supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reached approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts in eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of type of preenrichment and level of iron supplementation on the growth of Salmonella Enteritidis in...
Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do no... more Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do not exceed 48.8 degrees C (120 degrees F). Therefore, it is important to study parameters that influence the destruction of Escherichia coli O157:H7 in Lebanon bologna. The objective of the present study was to determine the influence of curing salts (NaCl and NaNO2) on the destruction of E. coli O157:H7 during Lebanon bologna processing. Fermentation to pH 4.7 at 37.7 degrees C reduced populations of E. coli O157:H7 by approximately 0.3 log10, either in the presence or absence of curing salts. Subsequent destruction of E. coli O157:H7 during heating of fermented product to 46.1 degrees C was significantly reduced by the presence of 3.5% NaCl and 156 ppm NaNO2, compared to product without curing salts (P < 0.01). The presence of a higher level of NaCl (5%) in Lebanon bologna inhibited the growth of lactic acid bacteria (LAB), which yielded product with higher pH (approximately 5.0) and ...
Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes was spread onto the s... more Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes was spread onto the surface of Lebanon bologna luncheon slices using sterile glass rods. The inoculated slices were stacked and vacuum packaged. The packages were stored at 3.6 or 13 degrees C. The foodborne pathogens. E. coli O157:H7, Salmonella Typhimurium, or L. monocytogenes were reduced in Lebanon bologna during storage at 3.6 or 13 degrees C. The higher storage temperature (13.0 degrees C) resulted in significantly faster destruction of E. coli O157:H7 and L. monocytogenes, compared to storage at refrigeration temperature (3.6 degrees C) (P < 0.005). E. coli O157:H7 was the most resistant to destruction among the three foodborne pathogens. A linear destruction of E. coli O157:H7 occurred only after an initial lag period. Storage temperature did not have a significant effect on the rate of destruction of Salmonella Typhimurium. Foodborne pathogens inoculated prior to fermentation did not show any enh...
Recently, numerous product recalls and one devastating outbreak that claimed 21 lives were attrib... more Recently, numerous product recalls and one devastating outbreak that claimed 21 lives were attributed to Listeria monocytogenes in ready-to-eat meat products. Consequently, the Food Safety and Inspection Service published a federal register notice requiring manufacturers of ready-to-eat meat and poultry products to reassess their hazard analysis and critical control point plans for these products as specified in 9 CFR 417.4(a). Lebanon bologna is a moist, fermented ready-to-eat sausage. Because of undesirable quality changes. Lebanon bologna is often not processed above 48.9 degrees C (120 degrees F). Therefore, the present research was conducted to validate the destruction of L. monocytogenes in Lebanon bologna batter in a model system. During production, fermentation of Lebanon bologna to pH 4.7 alone significantly reduced L. monocytogenes by 2.3 log10 CFU/g of the sausage mix (P < 0.01). Heating the fermented mix to 48.9 degrees C in 10.5 h destroyed at least 7.0 log10 CFU of ...
The effect of different reducing agents (L-cysteine, Oxyrase, and Enterococcus faecium) and their... more The effect of different reducing agents (L-cysteine, Oxyrase, and Enterococcus faecium) and their combinations on the detection of heat-injured (62.8 degrees C, 7.5 min or 10 min) Listeria monocytogenes was examined. The incorporation of L-Cysteine (0.5 g/liter) yielded higher percentage detection than any of the other reducing agents (P < 0.05). The combination of Oxyrase (10 U/ml) and E. faecium (10(3) CFU/ml) synergistically enhanced the detection of L. monocytogenes heat-injured for 10 min at 62.8 degrees C (P < 0.05). Simultaneous addition of L-cysteine (0.5 g/liter) and Oxyrase (10 U/ml) significantly lowered the recovery of heat-injured L. monocytogenes (P < 0.05). Higher activities of Oxyrase (50 U/ml) inhibited the detection of heat-injured L. monocytogenes (P < 0.05). The rates of depletion of relative percentage O2 were in the order: L-cysteine (0.5 g/liter; 6.63%/ min) > Oxyrase (10 U/ml; 5.00%/min) > E. faecium (10(8) CFU/ml; 1.66%/min) > E. faecium...
A simple anaerobic recovery-enrichment system, semisolid Penn State University (ssPSU) broth, tha... more A simple anaerobic recovery-enrichment system, semisolid Penn State University (ssPSU) broth, that enhances recovery of heat-injured Listeria monocytogenes, was rapidly achieved in 10-ml screw-capped tubes by adding Bacto-agar (2.5 g/liter) and L-cysteine (0.5 g/liter) to Penn State University broth. Glucose was removed from the formulation for ssPSU broth to prevent the growth of thermoduric lactobacilli. Ferric ammonium citrate was added to ssPSU broth to detect esculin hydrolysis and to indicate the presumptive presence of L. monocytogenes. Replacement of phosphate buffer with 3-[N-morpholino]propanesulfonic acid (MOPS) buffer and addition of magnesium sulfate (15 mM) enhanced recovery and detection of L. monocytogenes heat treated at 62.8 degrees C for 20 min. D-Serine, at a concentration of 150 mM, was found to inhibit germination of Bacillus spp. spores but did not inhibit severely heat-injured L. monocytogenes. Finally, ssPSU broth was modified (to mPSU broth) to contain the ...
This study was undertaken to determine if association with collagen enables Escherichia coli O157... more This study was undertaken to determine if association with collagen enables Escherichia coli O157:H7 to resist high-pH treatments and to determine the effects of high pH on the survival of E. coli O157:H7 within different layers of beef tissue. E. coli O157:H7 was inoculated onto purified bovine type I collagen on 12-mm2 circular glass coverslips, plain 12-mm2 circular glass coverslips (control), and 12-mm2 irradiated (cobalt-60) lean beef tissue. The rates of destruction of E. coli O157:H7 inoculated on coverslips in pH 10.5 NaHCO3-NaOH buffer at 35 degrees C were determined at various sampling times. E. coli O157:H7 cells associated with collagen and treated in the same manner were also examined using scanning electron microscopy to determine if association with collagen enabled the organism to resist high-pH treatments. The inoculated tissue was treated in pH 13.0 NaHCO3-NaOH buffer at 25 degrees C, and penetrating cells of E. coli O157:H7 were recovered using a cryostat techniqu...
Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne ... more Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne illness outbreaks, including those traced back to pasteurized fluid milk and milk products. This microorganism is especially important because it can grow at storage temperatures recommended for milk (< or =7 degrees C). Growth of L. monocytogenes in fluid milk depends to a large extent on the varying temperatures it is exposed to in the postpasteurization phase, i.e., during in-plant storage, transportation, and storage at retail stores. Growth data for L. monocytogenes in sterilized whole milk were collected at 4, 6, 8, 10, 15, 20, 25, 30, and 35 degrees C. Specific growth rate and maximum population density were calculated at each temperature using these data. The data for growth rates versus temperature were fitted to the Zwietering square root model. This equation was used to develop a dynamic growth model (i.e., the Baranyi dynamic growth model or BDGM) for L. monocytogenes base...
Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consump... more Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consumption of Lebanon bologna was epidemiologically associated wit a recent outbreak of salmonellosis. The present study was conducted to determine the effect of pH (after the fermentation step), final heating temperature, and time on destruction of E. coli O157:H7 and Salmonella typhimurium in Lebanon bologna. Raw Lebanon bologna mix was inoculate with either of the pathogens (ca.10(8) CFR/g and fermented for 12 h at 80 degrees F (26.7 degrees C) and then at 100 degrees F (37.8 degrees C) unit the pH reached wither 5.2 or 4.7. The mix was then heated to 110, 115, or 120 degrees F (43.3, 46.1, or 48.9 degrees C). The bologna was sampled at various times, decimally diluted, and plated on either McConkey sorbitol agar or XLD agar to enumerate E. coli O157:H7 and S. typhimurium, respectively. Fermentation alone reduced populations of both pathogens by < 2 log units and heating alone reduced po...
The Difco EZ Coli Rapid Detection System was compared to the 3M Petrifilm method for detection of... more The Difco EZ Coli Rapid Detection System was compared to the 3M Petrifilm method for detection of Escherichia coli O157:H7 in raw ground beef. Raw meatballs (25 g) were inoculated with 10 to 15 cells of Escherichia coli O157:H7, stored for various times and at different temperatures, and then stomached for 2 min in 225 ml of EZ Coli enrichment broth, which was then incubated at 42 degrees C for 18 to 24 h. A 1-ml sample of the enrichment broth was loaded into the top of the detector tips and the remaining EZ Coli broth held at 35 degrees C before streaking onto MacConkey sorbitol agar and tryptic soy agar with yeast extract. A duplicate set of meatballs were tested using the 3M Petrifilm Test Kit-HEC for hemorrhagic Escherichia coli O157:H7. In this method raw meatballs (25 g) were enriched for 6 h in modified EC broth containing novobiocin at 37 degrees C prior to inoculation of the Petrifilm E. coli Count Plates, which were incubated at 42 degrees C for 18 h. The immunoblot ELISA ...
High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechan... more High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs withi...
Background: Invasive listeriosis is a rare, life-threatening foodborne disease. Molecular subtypi... more Background: Invasive listeriosis is a rare, life-threatening foodborne disease. Molecular subtyping and enhanced surveillance identified a cluster of possibly related listeriosis cases from 2006 to 2010 in the Lombardy Region of Northern Italy. Particularly, this major Pulsed-Field Gel Electrophoresis (PFGE) cluster (named 11) grouped 31 isolates, belonging to serotype 1/2a and Sequence Type (ST)38 as defined by Multi-Locus Sequence Typing (MLST). Our study expanded the previous investigation to include cases from 2011 to 2014 and to perform Multi-Virulence-Locus Sequence Typing (MVLST) on isolates in Cluster11/ST38 to better understand their epidemiology and possibly identify a common source outbreak clone. Materials and Methods: All collected human Listeria monocytogenes isolates were serotyped and subtyped with PFGE and MLST. MVLST was performed on all isolates in Cluster11/ST38. Demographic, clinical and microbiological data were collected using a standardized report form. Results: Of 338 L. monocytogenes human isolates collected during the period, 43 (12.7%) belonged to Cluster11/ST38. While this cluster was observed sporadically in 2006, 2008 and 2014 (2 cases/year each), and in 2013 (n=1), cases due to this cluster peaked in 2009, 2010 and 2011 (n=10, 16 and 10 cases respectively). Cases occurred in nine out of twelve Lombardy provinces, with the highest frequency observed in Bergamo and Milan. The 43 isolates in Cluster11/ST38 were split by MVLST into two Virulence Types (VTs), VT80 (n=12) and VT104 (n=31). VT104 cases were concentrated between 2009 and 2011 and in Bergamo and Milan provinces. For all Cluster11/ST38 cases, an epidemiological investigation was performed and in one case, a matching VT104 L. monocytogenes clone was isolated from a cheese sample (Taleggio) retrieved from a patient\u2019s refrigerator. Based on both molecular and epidemiologic data, this cheese was identified as the implicated source. Conclusions: Our findings revealed a major listeriosis outbreak in Northern Italy linked to cheese in 2009-2011, which was undetected by local health authorities. Our study showed that integrating subtyping methods such as PFGE, MLST and MVLST with conventional epidemiologic investigations can help identify the source of outbreak clones of L. monocytogenes. Such information is useful in both terminating ongoing outbreaks and preventing future ones from occurring
Human listeriosis outbreaks in Canada have been predominantly caused by serotype 1/2a isolates wi... more Human listeriosis outbreaks in Canada have been predominantly caused by serotype 1/2a isolates with highly similar pulsed-field gel electrophoresis (PFGE) patterns. Multilocus sequence typing (MLST) and multi-virulence-locus sequence typing (MVLST) each identified a diverse population of Listeria monocytogenes isolates, and within that, both methods had congruent subtypes that substantiated a predominant clone (clonal complex 8; virulence type 59; proposed epidemic clone 5 [ECV]) that has been causing human illness across Canada for more than 2 decades.
High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechan... more High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs withi...
Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-0.6% yeast extract (TSB... more Listeria monocytogenes F5069 was suspended in either Trypticase soy broth-0.6% yeast extract (TSBYE) or sterile, whole milk and heated at 62.8 degrees C in sealed thermal death time tubes. Severely heat-injured cells were recovered in TSBYE within sealed thermal death time tubes because of the formation of reduced conditions in the depths of the TSBYE. Also, the use of strictly anaerobic Hungate techniques significantly increased recovery in TSBYE containing 1.5% agar compared with aerobically incubated controls. The exogenous addition of catalase, but not superoxide dismutase, slightly increased the recovery of heat-injured cells in TSBYE containing 1.5% agar incubated aerobically. Growth of cells at 43 degrees C caused a greater increase in heat resistance as compared with cells heat shocked at 43 degrees C or cells grown at lower temperatures. Growth of L. monocytogenes at 43 degrees C and enumeration by the use of strictly anaerobic Hungate techniques resulted in D62.8 degrees C...
A simple well-plate technique was utilized to determine the effect of various metals on the growt... more A simple well-plate technique was utilized to determine the effect of various metals on the growth of microorganisms in media containing different polyphosphates. Aspergillus flavus and four gram-positive bacteria were completely inhibited by media containing 1% of various alkaline polyphosphates, whereas four gram-negative bacteria were not. Significant differences were observed between the type of polyphosphate added, the type of metal added, and the species of gram-positive bacterium inhibited. The addition of Mg2+ stimulated growth of A. flavus and Bacillus cereus in the presence of tetrasodium pyrophosphate, whereas Mn2+ permitted growth of A. flavus and Staphylococcus aureus in the presence of sodium hexametaphosphate. Iron supplementation allowed the growth of S. aureus and Listeria monocytogenes on media containing 1 % tetrasodium pyrophosphate. A method for determining the amount of calcium and magnesium in water was modified to detect free Mg2+ by replacing EDTA with phosp...
Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convect... more Eggs were cooled to 0°C using two different cooling rates, natural convection, and forced convection at an air speed of 30.5 m/min. Upon rapid cooling using forced convection and when brought back to room temperature, eggs were more prone to penetration by Salmonella enteritidis (strain PS8NSR). Eggs cooled using forced convection had 100% penetration by PS8NSR; eggs cooled using natural convection had 91.3% penetration; and uncooled eggs had 48% penetration. Scanning electron microscopy revealed that shells of both cooled and uncooled eggs had microscopic cracks; however, cracks were more numerous and larger in shells of cooled eggs.
Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and su... more Mixed raw egg contents were inoculated with approximately 10 CFU of Salmonella Enteritidis and supplemented with 0 to 7 mg of FeSO4 per g of egg contents. Egg contents were then incubated at 37 degrees C, and Salmonella Enteritidis colonies were enumerated for up to 106 h. Iron supplementation significantly enhanced the growth of Salmonella Enteritidis. Within the first 24 h of incubation, the optimum iron level for Salmonella Enteritidis growth in egg contents was between 0.2 and 2 mg of FeSO4 per g of egg contents. After 24 h of incubation at 37 degrees C. Salmonella Enteritidis counts in eggs supplemented with 0.5 mg of FeSO4 per g of egg contents consistently reached approximately 1 x 10(9) CFU/ml, whereas Salmonella Enteritidis counts in eggs without iron supplementation varied from less than 5 CFU/ml to 8.4 x 10(6) CFU/ml. A 3 by 3 factorial design was used to study the effect of type of preenrichment and level of iron supplementation on the growth of Salmonella Enteritidis in...
Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do no... more Due to undesirable quality changes, Lebanon bologna is often processed at temperatures that do not exceed 48.8 degrees C (120 degrees F). Therefore, it is important to study parameters that influence the destruction of Escherichia coli O157:H7 in Lebanon bologna. The objective of the present study was to determine the influence of curing salts (NaCl and NaNO2) on the destruction of E. coli O157:H7 during Lebanon bologna processing. Fermentation to pH 4.7 at 37.7 degrees C reduced populations of E. coli O157:H7 by approximately 0.3 log10, either in the presence or absence of curing salts. Subsequent destruction of E. coli O157:H7 during heating of fermented product to 46.1 degrees C was significantly reduced by the presence of 3.5% NaCl and 156 ppm NaNO2, compared to product without curing salts (P < 0.01). The presence of a higher level of NaCl (5%) in Lebanon bologna inhibited the growth of lactic acid bacteria (LAB), which yielded product with higher pH (approximately 5.0) and ...
Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes was spread onto the s... more Escherichia coli O157:H7, Salmonella Typhimurium, or Listeria monocytogenes was spread onto the surface of Lebanon bologna luncheon slices using sterile glass rods. The inoculated slices were stacked and vacuum packaged. The packages were stored at 3.6 or 13 degrees C. The foodborne pathogens. E. coli O157:H7, Salmonella Typhimurium, or L. monocytogenes were reduced in Lebanon bologna during storage at 3.6 or 13 degrees C. The higher storage temperature (13.0 degrees C) resulted in significantly faster destruction of E. coli O157:H7 and L. monocytogenes, compared to storage at refrigeration temperature (3.6 degrees C) (P < 0.005). E. coli O157:H7 was the most resistant to destruction among the three foodborne pathogens. A linear destruction of E. coli O157:H7 occurred only after an initial lag period. Storage temperature did not have a significant effect on the rate of destruction of Salmonella Typhimurium. Foodborne pathogens inoculated prior to fermentation did not show any enh...
Recently, numerous product recalls and one devastating outbreak that claimed 21 lives were attrib... more Recently, numerous product recalls and one devastating outbreak that claimed 21 lives were attributed to Listeria monocytogenes in ready-to-eat meat products. Consequently, the Food Safety and Inspection Service published a federal register notice requiring manufacturers of ready-to-eat meat and poultry products to reassess their hazard analysis and critical control point plans for these products as specified in 9 CFR 417.4(a). Lebanon bologna is a moist, fermented ready-to-eat sausage. Because of undesirable quality changes. Lebanon bologna is often not processed above 48.9 degrees C (120 degrees F). Therefore, the present research was conducted to validate the destruction of L. monocytogenes in Lebanon bologna batter in a model system. During production, fermentation of Lebanon bologna to pH 4.7 alone significantly reduced L. monocytogenes by 2.3 log10 CFU/g of the sausage mix (P < 0.01). Heating the fermented mix to 48.9 degrees C in 10.5 h destroyed at least 7.0 log10 CFU of ...
The effect of different reducing agents (L-cysteine, Oxyrase, and Enterococcus faecium) and their... more The effect of different reducing agents (L-cysteine, Oxyrase, and Enterococcus faecium) and their combinations on the detection of heat-injured (62.8 degrees C, 7.5 min or 10 min) Listeria monocytogenes was examined. The incorporation of L-Cysteine (0.5 g/liter) yielded higher percentage detection than any of the other reducing agents (P < 0.05). The combination of Oxyrase (10 U/ml) and E. faecium (10(3) CFU/ml) synergistically enhanced the detection of L. monocytogenes heat-injured for 10 min at 62.8 degrees C (P < 0.05). Simultaneous addition of L-cysteine (0.5 g/liter) and Oxyrase (10 U/ml) significantly lowered the recovery of heat-injured L. monocytogenes (P < 0.05). Higher activities of Oxyrase (50 U/ml) inhibited the detection of heat-injured L. monocytogenes (P < 0.05). The rates of depletion of relative percentage O2 were in the order: L-cysteine (0.5 g/liter; 6.63%/ min) > Oxyrase (10 U/ml; 5.00%/min) > E. faecium (10(8) CFU/ml; 1.66%/min) > E. faecium...
A simple anaerobic recovery-enrichment system, semisolid Penn State University (ssPSU) broth, tha... more A simple anaerobic recovery-enrichment system, semisolid Penn State University (ssPSU) broth, that enhances recovery of heat-injured Listeria monocytogenes, was rapidly achieved in 10-ml screw-capped tubes by adding Bacto-agar (2.5 g/liter) and L-cysteine (0.5 g/liter) to Penn State University broth. Glucose was removed from the formulation for ssPSU broth to prevent the growth of thermoduric lactobacilli. Ferric ammonium citrate was added to ssPSU broth to detect esculin hydrolysis and to indicate the presumptive presence of L. monocytogenes. Replacement of phosphate buffer with 3-[N-morpholino]propanesulfonic acid (MOPS) buffer and addition of magnesium sulfate (15 mM) enhanced recovery and detection of L. monocytogenes heat treated at 62.8 degrees C for 20 min. D-Serine, at a concentration of 150 mM, was found to inhibit germination of Bacillus spp. spores but did not inhibit severely heat-injured L. monocytogenes. Finally, ssPSU broth was modified (to mPSU broth) to contain the ...
This study was undertaken to determine if association with collagen enables Escherichia coli O157... more This study was undertaken to determine if association with collagen enables Escherichia coli O157:H7 to resist high-pH treatments and to determine the effects of high pH on the survival of E. coli O157:H7 within different layers of beef tissue. E. coli O157:H7 was inoculated onto purified bovine type I collagen on 12-mm2 circular glass coverslips, plain 12-mm2 circular glass coverslips (control), and 12-mm2 irradiated (cobalt-60) lean beef tissue. The rates of destruction of E. coli O157:H7 inoculated on coverslips in pH 10.5 NaHCO3-NaOH buffer at 35 degrees C were determined at various sampling times. E. coli O157:H7 cells associated with collagen and treated in the same manner were also examined using scanning electron microscopy to determine if association with collagen enabled the organism to resist high-pH treatments. The inoculated tissue was treated in pH 13.0 NaHCO3-NaOH buffer at 25 degrees C, and penetrating cells of E. coli O157:H7 were recovered using a cryostat techniqu...
Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne ... more Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne illness outbreaks, including those traced back to pasteurized fluid milk and milk products. This microorganism is especially important because it can grow at storage temperatures recommended for milk (< or =7 degrees C). Growth of L. monocytogenes in fluid milk depends to a large extent on the varying temperatures it is exposed to in the postpasteurization phase, i.e., during in-plant storage, transportation, and storage at retail stores. Growth data for L. monocytogenes in sterilized whole milk were collected at 4, 6, 8, 10, 15, 20, 25, 30, and 35 degrees C. Specific growth rate and maximum population density were calculated at each temperature using these data. The data for growth rates versus temperature were fitted to the Zwietering square root model. This equation was used to develop a dynamic growth model (i.e., the Baranyi dynamic growth model or BDGM) for L. monocytogenes base...
Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consump... more Fermented meats have caused food-borne illness due to enterohemorrhagic Escherichia coli. Consumption of Lebanon bologna was epidemiologically associated wit a recent outbreak of salmonellosis. The present study was conducted to determine the effect of pH (after the fermentation step), final heating temperature, and time on destruction of E. coli O157:H7 and Salmonella typhimurium in Lebanon bologna. Raw Lebanon bologna mix was inoculate with either of the pathogens (ca.10(8) CFR/g and fermented for 12 h at 80 degrees F (26.7 degrees C) and then at 100 degrees F (37.8 degrees C) unit the pH reached wither 5.2 or 4.7. The mix was then heated to 110, 115, or 120 degrees F (43.3, 46.1, or 48.9 degrees C). The bologna was sampled at various times, decimally diluted, and plated on either McConkey sorbitol agar or XLD agar to enumerate E. coli O157:H7 and S. typhimurium, respectively. Fermentation alone reduced populations of both pathogens by < 2 log units and heating alone reduced po...
The Difco EZ Coli Rapid Detection System was compared to the 3M Petrifilm method for detection of... more The Difco EZ Coli Rapid Detection System was compared to the 3M Petrifilm method for detection of Escherichia coli O157:H7 in raw ground beef. Raw meatballs (25 g) were inoculated with 10 to 15 cells of Escherichia coli O157:H7, stored for various times and at different temperatures, and then stomached for 2 min in 225 ml of EZ Coli enrichment broth, which was then incubated at 42 degrees C for 18 to 24 h. A 1-ml sample of the enrichment broth was loaded into the top of the detector tips and the remaining EZ Coli broth held at 35 degrees C before streaking onto MacConkey sorbitol agar and tryptic soy agar with yeast extract. A duplicate set of meatballs were tested using the 3M Petrifilm Test Kit-HEC for hemorrhagic Escherichia coli O157:H7. In this method raw meatballs (25 g) were enriched for 6 h in modified EC broth containing novobiocin at 37 degrees C prior to inoculation of the Petrifilm E. coli Count Plates, which were incubated at 42 degrees C for 18 h. The immunoblot ELISA ...
High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechan... more High pH has been shown to rapidly destroy gram-negative food-borne pathogens; however, the mechanism of destruction has not yet been elucidated. Escherichia coli O157:H7, Salmonella enteritidis ATCC 13706, and Listeria monocytogenes F5069 were suspended in NaHCO3-NaOH buffer solutions at pH 9, 10, 11, or 12 to give a final cell concentration of approximately 5.2 x 10(8) CFU/ml and then held at 37 or 45 degrees C. At 0, 5, 10, and 15 min the suspensions were sterilely filtered and each filtrate was analyzed for material with A260. Viability of the cell suspensions was evaluated by enumeration on nonselective and selective agars. Cell morphology was evaluated by scanning electron microscopy and transmission electron microscopy. A260 increased dramatically with pH and temperature for both E. coli and S. enteritidis; however, with L. monocytogenes material with A260 was not detected at any of the pHs tested. At pH 12, numbers of E. coli and S. enteritidis decreased at least 8 logs withi...
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