Survival of Listeria monocytogenes, Listeria innocua, and lactic acid bacteria in chill brines.

Listeria monocytogenes is the pathogen of concern in ready-to-eat (RTE) meat products. Salt brines are used to chill processed meats. L. monocytogenes and lactic acid bacteria (LAB) can grow under saline conditions, and may compete with each other for nutrients. The objective of this study was to determine the effect of lactic acid bacteria (Enterococcus faecalis, Carnobacterium gallinarum, and Lactobacillus plantarum) on the survival of L. monocytogenes and Listeria innocua in brines stored under low temperatures for 10 d. Sterile tap water (STW) and 2 brine solutions (7.9% and 13.2% NaCl) were inoculated with 1 of 5 cocktails (L. monocytogenes, L. innocua, LAB, L. monocytogenes+ LAB, or L. innocua+ LAB) at initial concentrations of 7 log CFU/mL. Brines were stored for 10 d at 4 or 12 degrees C. Three replications of each brine concentration/cocktail/temperature combination were completed. No significant reductions of L. monocytogenes occurred in 7.9%[w/v] or 13.2%[w/v] brines when LAB were present; however, there were significant reductions after 10 d of L. monocytogenes in the STW solution when LAB were present (1.43 log CFU/mL at 4 degrees C and 3.02 log CFU/mL at 12 degrees C). L. innocua was significantly less resilient to environmental stresses of the brines than L. monocytogenes, both with and without LAB present (P< or = 0.05). These strains of lactic acid bacteria are not effective at reducing L. monocytogenes in brines at low temperatures. Furthermore, use of L. innocua as a model for L. monocytogenes is not appropriate under these environmental conditions.

Molecular characterization of Listeria monocytogenes of the serotype 4b complex (4b, 4d, 4e) from two turkey processing plants.

Most foodborne outbreaks of listeriosis have been found to involve a small number of closely related strains of Listeria monocytogenes serotype 4b. The ecology of these organisms and their reservoirs in nature or in the processing plant environment, however, remain poorly understood. Surveys of environmental samples from two turkey processing plants in the United States indicated presence of L. monocytogenes of the serotype 4b complex (serotype 4b and the closely related serotypes 4d and 4e). In addition, environmental and raw product samples from one plant repeatedly yielded isolates with genetic markers typical of two major serotype 4b epidemic clonal groups, ECI and ECII. The pulsed field gel electrophoresis (PFGE) profiles of these isolates, however, were clearly distinct from those of confirmed epidemic-associated strains. Furthermore, we observed minor but consistent differences in PFGE profiles of isolates that harbored ECI- or ECII-specific genetic markers, and that were obtained at different sampling times from the same plant. The findings suggest processing plant persistence (or repeated introductions) and genomic diversification of L. monocytogenes serotype 4b isolates that harbor ECI- or ECII-specific genetic markers. Such diversification would need to be taken into consideration in further efforts to elucidate the evolution and epidemiology of these organisms.

Penetration of surface-inoculated bacteria as a result of electrically generated hydrodynamic shock wave treatment of boneless skinless chicken breasts.

The top surface of boneless skinless chicken breasts was inoculated with either green fluorescent protein (GFP)-labeled Escherichia coli (E. coli-GFP) or rifampicin-resistant E. coli (E. coli-Rif) and subjected to electrically generated hydrodynamic shock wave treatment (HVADH). Cryostat sampling in concert with laser scanning confocal microscopy or plating onto antibiotic selective agar was used to determine if HVADH treatment resulted in the movement of the inoculated bacteria from the outer inoculated surface to the interior of intact boneless skinless chicken breasts. In HVADH-treated boneless skinless chicken breasts, marker bacteria were detected within the first 200 microm below the inoculated surface, 50 to 100 microm beyond the depth of untreated surface inoculated boneless skinless chicken breasts. The exact depth at which the marker bacteria were found was dependent on the cryostat sampling distance used. These results suggest that HVADH treatments affect the movement of surface bacteria.

Comparison of sampling techniques for detection of Arcobacter butzleri from chickens.

Arcobacter butzleri is a causative agent of human enteritis that has been recently differentiated from the genus Campylobacter. Previous work suggests that its transmission to humans is likely through a foodborne route with a substantial tendency to be located on poultry carcasses. For reducing the incidence of this pathogen on commercial poultry, improved protocols are needed to sample and identify A. butzleri from infected birds prior to slaughter. The purpose of this study was to compare sampling methods for this emerging pathogen from chickens that were artificially inoculated per os with A. butzleri. We tested three sampling techniques commonly used to determine the microbiological quality of poultry: cloacal swabs, fecal samples, and environmental surface (drag) swabs collected when birds were 3, 5, or 7 wk old. These samples were cultured in Johnson-Murano enrichment broth and analyzed by PCR. Results indicate that environmental surface swabs yielded the highest recovery percentage. A detection rate of 75 to 100% was observed for each sampling period (age of chicken). Additionally, A. butzleri could not be isolated from the intestinal tract (jejunum, ileum, cecum, colorectum) of inoculated birds.

Pathogenic and fecal Escherichia coil strains from turkeys in a commercial operation.

The biochemical phenotypes and antimicrobial susceptibility patterns of 105 clinical Escherichia coli isolates from flocks with colibacillosis in a turkey operation were compared with 1104 fecal E. coli isolates from 20 flocks in that operation. Clinical isolates and 194 fecal isolates with biochemical phenotypes or minimum inhibitory concentrations for gentamicin and sulfamethoxazole similar to clinical isolates were tested for somatic antigens and the potential virulence genes hylE, iss, tsh, and K1. The predominant biochemical phenotype of clinical isolates contained 21 isolates including 14 isolates belonging to serogroup 078 with barely detectable beta-D-glucuronidase activity. Thirty-five fecal isolates had biochemical phenotypes matching common phenotypes of clinical isolates. Sixty-six (63%) clinical isolates exhibited intermediate susceptibility or resistance to gentamicin and sulfamethoxazole compared with 265 (24%) fecal isolates (P < 0.001). Seventy-seven clinical isolates reacted with O-antisera, of which 51 (66%) belonged to the following serogroups: O1, O2, O8, O25, O78, O114, and O119. In comparison, 8 of 35 (23%) fecal isolates subtyped on the basis of biochemical phenotype belonged to these serogroups and four of 167 (2%) fecal isolates subtyped on the basis of their antimicrobial resistance patterns belonged to these serogroups. Iss, K1, and tsh genes were detected more often among clinical isolates than these fecal isolates (P < 0.05). In summary, a small subgroup of E. coli strains caused most colibacillosis infections in this operation. These strains existed at low concentration in normal fecal flora of healthy turkeys in intensively raised flocks. The data suggest that colibacillosis in turkey operations may be due to endogenous infections caused by specialized pathogens.

Penetration of surface-inoculated bacteria as a result of hydrodynamic shock wave treatment of beef steaks.

The top surface of the raw eye of round steaks was inoculated with either green fluorescent protein (GFP)-labeled Escherichia coli (E. coli-GFP) or rifampin-resistant E. coli (E. coli-rif). Cryostat sampling in concert with laser scanning confocal microscopy (LSCM) or plating onto antibiotic selective agar was used to determine if hydrodynamic shock wave (HSW) treatment resulted in the movement of the inoculated bacteria from the outer inoculated surface to the interior of intact beef steaks. HSW treatment induced the movement of both marker bacteria into the steaks to a maximum depth of 300 microm (0.3 mm). Because popular steak-cooking techniques involve the application of heat from the exterior surface of the steak to achieve internal temperatures ranging from 55 to 82 degrees C, the extent of bacterial penetration observed in HSW-treated steaks does not appear to pose a safety hazard to consumers.

Use of a Modified Gompertz Equation to Predict the Effects of Temperature, pH, and NaCl on the Inactivation of Listeria monocytogenes Scott A Heated in Infant Formula.

The heat resistance of Listeria monocytogenes was determined in infant formula for all possible combinations of temperature (50, 55, and 60°C), pH level (5, 6, and 7), and NaCl concentration (0, 2, and 4%). Survival curves were fit using nonlinear regression with a Gompertz equation. The Gompertz equation was flexible enough to fit the three most commonly observed survival curves: linear curves, those with an initial lag region followed by a linear region, and sigmoidal shaped. Parameter estimates obtained by the method of nonlinear least squares were used to describe the effect(s) of different heating treatments on the lag region, death rate, and tailing region of survival curves. These estimates were further used to predict single and interactive effects of temperature, pH, and percentage of NaCl on the log of the surviving fraction (LSF) of bacteria. Interactions among these variables significantly (P ≤ .05) affected the LSF. Generally, increased pH or NaCl concentration lead to an increased LSF, whereas increased time or temperature lead to a decreased LSF. All multiple-factor interactions significantly (P ≤ .05) affected the LSF. The correlation of observed LSF versus predicted LSF (R2 = .92) indicated that the estimated Gompertz equation was in close agreement with the observation. This study demonstrated that the Gompertz equation and nonlinear regression can be used as an effective means to predict survival curve shape and response to heat of L. monocytogenes under many different environmental conditions.