Regular ArticleGrowth of Listeria monocytogenes, Aeromonas hydrophila and Yersinia enterocolitica on cooked beef under refrigeration and mild temperature abuse
Abstract
Strains of the cold-tolerant bacteria Listeria monocytogenes, Aeromonas hydrophila and Yersinia enterocolitica were inoculated onto samples of cooked beef and incubated at 5 and 10°C under both aerobic and vacuum-packaged (anaerobic) conditions. These organisms were enumerated over a time course and data were analysed to give values for the generation and lag times. All species grew well under all conditions except for A. hydrophila at 10°C under anaerobic conditions where inhibition by lactic acid bacteria may have occurred. Growth rates were similar for L. monocytogenes and A. hydrophila whether the samples were stored aerobically or anaerobically, but Y. enterocolitica grew more slowly under anaerobic conditions. However, the growth of lactic acid bacteria in samples stored aerobically indicated that metabolic activity resulted in the formation of anaerobic conditions during the incubation period. Growth rates predicted by response surface models and measured growth rates were not in agreement for L. monocytogenes or A. hydrophila, but similar comparisons for Y. enterocolitica showed good agreement.
References (0)
Cited by (26)
The prevalence of Listeria, Salmonella, Escherichia coli and E. coli O157:H7 on bison carcasses during processing
2004, Food MicrobiologyBison meat is a relatively new, emerging meat species gaining increased popularity in the US and European meat markets, but little is known of its microflora or pathogens that may be present. This study was carried out to determine the incidence of the foodborne pathogens Listeria, Salmonella, Escherichia coli/E. coli O157:H7 on slaughtered bison and to evaluate the bison slaughter process. Bison carcass sampling was carried out at monthly intervals over a period of 1 year at a Bison processing facility in the Midwestern United States. A total of 355 Bison carcasses were sampled by surface swabbing the carcasses at five points on the production line: pre-dehiding, post-evisceration, post-USDA inspection, post-washing and 24 h chilled carcass. Overall, the prevalence of Listeria spp., Salmonella spp., E. coli and E. coli O157:H7 was 18.3%, 3.94%, 38.3% and 1.13%, respectively. The prevalence of Listeria spp. at each sampling point tested was 42.24%, 18.1%, 6.03%, 1.72% and 3.77% while the prevalence of E. coli at each sampling point was: 88.79%, 73.28%, 52.59%, 56.89% and 11.3%, respectively. The data obtained suggests that current antimicrobial intervention strategies used at the plant are relatively effective in reducing Listeria and E. coli contamination on bison carcasses to some extent, however further study is required to determine the influence of current slaughter practices on carcass contamination. The data reported in this study to the authors’ knowledge is some of the first information reporting on the bacteriological status of Bison, and provides some useful baseline information for future research.
Incidence and pathogenicity of Yersinia spp. isolates from poultry in Spain
2002, Food MicrobiologyForty eviscerated and refrigerated chicken carcasses were collected from retail outlets in León (Spain) and investigated for the presence of Yersinia spp. Following a two-step enrichment procedure (phosphate buffer saline was used as primary enrichment and bile oxalate sorbose as secondary enrichment), yersiniae were isolated on cefsulodin-irgasan-novobiocin (CIN) and MacConkey agar. Yersinia spp., Y. enterocolitica and Y. frederiksenii were detected in 26 (65%), 22 (55%) and six (15%) samples, respectively. The incidence ofYersinia and Y. enterocolitica was greater than that obtained in poultry meat by the majority of the consulted authors. Of the 68 Yersinia isolates, 52 were identified as Y. enterocolitica and 16 as Y. frederiksenii. Biotyping of Y. enterocolitica revealed that 45 (86·5%) strains corresponded to biotype 1A, and three (5·8%) to biotype 3. Four (7·7%) strains could not be classified. Two biotype 3 strains were found to be presumptively virulent according to the dye (Congo red and crystal violet) binding, low-calcium response, and pyrazinamidase activity techniques. It is suggested from results that the presence of Yersinia in poultry could represent a health risk for consumers in Spain. The education of people involved in production, processing and final preparation of poultry products are required in order to assure adequate cooking and to avoid cross-contamination.
Development of a model meat system and investigation of the growth characteristics and genetic stability of Escherichia coli O157:H7, in the absence of meat microflora
2002, Journal of Microbiological MethodsModel meat systems were produced using both aseptically procured and irradiated raw minced beef to initially compare the growth characteristics of a three-strain mixture of Escherichia coli O157:H7 in each medium. A multiplex PCR assay (detecting VT1, VT2 and eae genes) was used to determine the proportion of individual strains recovered at each sampling time by virtue of the different combinations of these virulence factors encoded by each strain, and to investigate their genetic stability. No differences in the growth characteristics of the pathogen (P>0.05) were recorded in the meat matrices, irrespective of the preparation method, thus validating the use of irradiation to sterilise (42 kGy, in vacuo at <−5°C) minced meat in the production of control meat matrices for application to further research investigations. A novel plating method, incorporating a period of catalase-induced resuscitation, was found to give significantly higher recovery of the pathogen (P<0.05) from these meat matrices when compared to conventional spread-plating on Trypticase Soy Agar (TSA). A proportion of the recovered populations, however, was found to be failing to produce an amplicon relating to a Verotoxin (VT) gene. A further investigation demonstrated that O157:H7 strain E 90197 (VT2 and eae positive) was displaying genetic instability during growth in and recovery from meat matrices with the apparent loss of the VT2 gene. An alternative VT2 and eae positive strain (ATCC 43889) demonstrated no such genetic instability, demonstrating inter-strain variation for this phenomenon. Thus, it should be considered that an essential pre-requisite to studies relying upon the maintenance of the pathogenic potential of E. coli O157:H7 should be an evaluation of the genetic stability of proposed strains of this serotype.
Mathematical modelling of the growth rate and lag time for Listeria monocytogenes
2000, International Journal of Food MicrobiologyGrowth data for Listeria monocytogenes were collected from the literature and a global model built with existing secondary models describing independently the effects of environmental factors on the growth rate and lag time was based on these data. The growth rates calculated with this model were consistent with the published ones but the fit was poor near the limits of growth of the micro-organism. The model was also less accurate to describe the lag time. It seems then that reliable predictions of the growth rate of L. monocytogenes could be obtained in a wide range of growth conditions, but models should take into account interactions between environmental factors. Furthermore, it is necessary to better model the lag phase duration and particularly to model the effect of the history of the inoculum on the subsequent lag time.
Predictive model of the effect of CO<inf>2</inf>, pH, temperature and NaCl on the growth of Listeria monocytogenes
1997, International Journal of Food MicrobiologyThe growth responses of L. monocytogenes as affected by CO2 concentration (0–100% , balance nitrogen), NaCl concentration (0.5–8.0% ), pH (4.5–7.0) and temperature (4–20 °C) were studied in laboratory medium. Growth curves were fitted using the model of Baranyi and Roberts, and specific growth rates derived from the curve fit were modelled. Predictions for specific growth rate, doubling time and time to a 1000-fold increase could be made for any combination of conditions within the matrix. Predictions of growth from the model were compared with published data and this showed the model to be suitable for predicting growth of L. monocytogenes in a range of foods packaged under a modified atmosphere.
Yersinia spp. and numbers, with particular reference to Y. enterocolitica bio/serotypes, occurring on Irish meat and meat products, and the influence of alkali treatment on their isolation
1996, International Journal of Food MicrobiologySamples (n = 340) of Irish meat and meat products were examined to determine the incidence and initial numbers of Yersinia spp. present. In cases where no typical Yersinia colonies were observed, samples were cold enriched up to 21 days at 4 °C and streaked out on CIN agar with and without post-enrichment alkali treatment. The highest isolation rates of Yersinia were found using post-enrichment alkali treatment and an incubation temperature of 37 °C. All Yersinia isolates were identified to species level and Y. enter ocolitica isolates were biotyped and serotyped. Pathogenic isolates (biotypes 1B-5) were examined for the presence of a virulence plasmid using dye binding reactions and agglutination tests. The incidence of Yersinia spp. was high on raw (89%) and cooked meats (49%) obtained fromdelicatessen counters but lower in pre-packaged cooked meats (18.8%). Initial numbers of Yersinia were generally <2.7 log10 on raw meats and <0.7 log10 on cooked meats. Pathogenic Y. enterocolitica were recovered from both raw (9%) and cooked meats (2%). Y. enterocolitica serotypes O:3 and O:5,27 were the most common pathogenic species found on Irish meats.