Detection of multiple antibiotic-resistant Salmonella enterica serovar Typhimurium DT104 by phage replication-competitive enzyme-linked immunosorbent assay

A phage replication-competitive enzyme-linked immunosorbent assay (PR-cELISA) was developed for the detection of multiple antibiotic-resistant Salmonella Typhimurium DT104. In the PR-cELISA procedure, a phage, BP1, was inoculated into a log-phase bacterial culture at a ratio of 1:100. After a 3-h incubation of the mixture, BP1 replication was measured by cELISA based on the competitive binding between BP1 and biotinylated BP1 to Salmonella Typhimurium smooth lipopolysaccharide. Among the 84 Salmonella strains and 9 non-Salmonella strains that were tested by PR-cELISA, BP1 detected 39 of 40 Salmonella Typhimurium strains, 2 of 10 Salmonella non-Typhimurium somatic group B strains, and 5 of 18 Salmonella somatic group D1 strains. With the addition of chloramphenicol to the culture medium, PR-cELISA detected all 27 multiple antibiotic-resistant Salmonella Typhimurium DT104 and none of the other Salmonella strains or non-Salmonella strains tested. The results demonstrated that PR-cELISA has potential applications for the detection of multiple antibiotic-resistant Salmonella Typhimurium DT104.     

Salmonella Typhimurium definitive type 104. A multi-resistant Salmonella

The wide variety and the socio-economic and dietary importance of traditional fermented milk products of Ethiopia are discussed in this paper. Information on the microbiology of these products is sparse and has relevance to those organisms associated with spoilage and to those considered desirable for fermentation. There is a clear need to improve the production of African foods and beverages [Int. J. Food Microbiol. 18 (1993) 85]. The objective of this review was to document traditional technology used and information on the microbiology of the products, and to identify various constraints to the development and commercialisation of fermented milk products. Thereby the major problems and potential areas for improvement are pointed out. Ergo, the most important traditional product resembles yoghurt and, as the other traditional products, is prepared by "spontaneous" fermentation, commonly initiated by either "back slopping" or by repeated use of the same utensil. Other products include traditional fermented curd or ititu, traditional butter or kibe, neter kibe or traditional ghee, ayib resembling cottage cheese, arrera or defatted buttermilk and augat or traditional whey.     

Pathogenic potential of Salmonella Typhimurium DT104 following sequential passage through soil, packaged fresh-cut lettuce and a model gastrointestinal tract

From a quantitative microbial risk assessment perspective it is important to know whether certain food environments influence the pathogenic potential of pathogens and to what extent. The purpose of the present study was to examine the pathogenic potential of S. Typhimurium DT104, measured as the capability to survive a simulated gastrointestinal tract system and the capability of adhering to and invading differentiated Caco-2 cells, after sequential incubation (without intermediate culturing) into soil, lettuce and cut lettuce stored under modified atmosphere (MAP) conditions. Two S. Typhimurium DT104 strains were used, one isolated from a pig carcass and one isolated from lettuce. The most important result of the present study is that the sequential incubation of S. Typhimurium in soil and lettuce slightly increased the capability of surviving the simulated gastric fluid, increased the capability to grow in the simulated intestinal fluid but decreased the capability of epithelial attachment and invasion and decreased the overall survival probability of the gastrointestinal tract system. Some variation in responses between the strains was observed, with the lettuce strain maintaining higher epithelial attachment capability and the carcass strains maintaining higher epithelial invasion capability. This study provided quantitative data on the effect of environmental and food matrices on the pathogenic potential of S. Typhimurium DT104 using a realistic system of sequential incubations in environmental and food matrices, followed by simulated gastrointestinal tract passage without intermediate culturing. These results could aid the development of more realistic quantitative microbial risk assessments.     

Interventions for the reduction of Salmonella Typhimurium DT 104 and non-O157:H7 enterohemorrhagic Escherichia coli on beef surfaces

A study was conducted to determine if slaughter interventions currently used by the meat industry are effective against Salmonella Typhimurium definitive type 104 (DT 104) and two non-O157:H7 enterohemorrhagic Escherichia coli (EHEC). Three separate experiments were conducted by inoculating prerigor beef surfaces with a bovine fecal slurry containing Salmonella Typhimurium and Salmonella Typhimurium DT 104 (experiment 1), E. coli O157:H7 and E. coli O111:H8 (experiment 2), or E. coli O157:H7 and E. coli O26:H11 (experiment 3) and spray washing with water, hot water (72 degrees C), 2% acetic acid, 2% lactic acid, or 10% trisodium phosphate (15 s, 125 +/- 5 psi, 35 +/- 2 degrees C). Remaining bacterial populations were determined immediately after treatments (day 0), after 2 days of aerobic storage at 4 degrees C, and after 7, 21, and 35 days of vacuum-packaged storage at 4 degrees C. In addition to enumeration, confirmation of pathogen serotypes was performed for all treatments on all days. Of the interventions investigated, spray treatments with trisodium phosphate were the most effective, resulting in pathogen reductions of >3 log10 CFU/cm2, followed by 2% lactic acid and 2% acetic acid (>2 log10 CFU/cm2). Results also indicated that interventions used to reduce Salmonella Typhimurium on beef surfaces were equally effective against Salmonella Typhimurium DT 104 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. Similarly, E. coli O111:H8 and E. coli O26:H11 associated with beef surfaces were reduced by the interventions to approximately the same extent as E. coli O157:H7 immediately after treatment and again after long-term, refrigerated, vacuum-packaged storage. It was also demonstrated that phenotypic characterization may not be sufficient to identify EHECs and that the organisms should be further confirmed with antibody- or genetic-based techniques. Based on these findings, interventions used by the meat industry to reduce Salmonella spp. and E. coli O157:H7 appear to be effective against DT 104 and other EHEC.     

Tolerance to stress and ability of acid-adapted and non-acid-adapted Salmonella enterica serovar Typhimurium DT104 to invade and survive in mammalian cells in vitro

The ability of acid-adapted (AA) and non-acid-adapted (NA) Salmonella enterica serovar Typhimurium definitive type 104 (DT104) strains to invade and multiply in mammalian cells in vitro and to survive stress conditions was examined. DT104 and non-DT104 strains were grown in tryptic soy broth without glucose (NA) or in tryptic soy broth containing 1% glucose (AA) for 18 h at 37 degrees C. The invasiveness of DT104 strains in J774A.1 macrophage and Int407 intestinal cell lines was not more extensive than that of non-DT104 strains. In most cases, AA bacteria were less invasive than NA bacteria in both cell lines. Confocal microscopy showed that both DT104 and non-DT104 strains replicated in the two cell lines. In related studies, the survival levels of three strains of AA and NA DT104 and a non-DT104 (LT2) strain in 150 and 15 mM H2O2, 170 and 43 mM acetic acid, 2.6 M NaCl, 2.6 M NaCl containing 170 mM acetic acid, synthetic gastric fluid (SGF) at pH 2 and pH 3, and apple cider were compared. For all four strains, acid adaptation did not result in increased survival in apple cider. After 15 days of storage at 4 degrees C, reductions ranged from 1.96 to 4.1 log10 CFU/ml for AA bacteria and from 0.48 to 1.34 log10 CFU/ml for NA bacteria from a starting level of ca. 7.00 log10 CFU/ml of cider. Neither AA nor NA DT104 strains were more resistant to NaCl, acetic acid, H2O2, or SGF solutions than non-DT104 strain LT2. The level of AA bacteria was not appreciably reduced after exposure to SGF; however, the level of NA bacteria decreased to nondetectable levels in SGF at pH 2 within 3 h of exposure. These results indicate that the DT104 strains examined were not more invasive, nor did they display increased survival in mammalian cells or increased resistance to food environment stresses compared with non-DT104 strains. However, acid adaptation resulted in increased resistance to a low-pH gastric environment for all strains tested. These data indicate that DT104 strains are likely not more virulent or resistant to stresses relevant to foods than are non-DT104 Salmonella and that procedures used to inactivate or inhibit the growth of Salmonella in foods are likely adequate for DT104 strains.     

Occurrence of Salmonella enterica serotype typhimurium DT104A in retail ground beef

Surveillance data of cattle and human isolates of Salmonella enterica serovar Typhimurium DT104 indicate that this pathogen emerged worldwide in the 1980s, particularly in cattle. Studies were conducted to determine the prevalence of Salmonella Typhimurium DT104 in ground beef. Samples were also tested for the presence of generic Escherichia coli. A total of 404 fresh ground beef samples obtained at retail stores from New York, San Francisco, Philadelphia, Denver, Atlanta, Houston, and Chicago were shipped overnight to Georgia for processing. Salmonella spp. were isolated from 14 (3.5%) samples. Eight different serotypes were identified among the isolates, including Salmonella Typhimurium (5), Salmonella Lille (3), Salmonella Montevideo (1), Salmonella Hadar (1), Salmonella Meleagridis (1), Salmonella Cerro (1), Salmonella Kentucky (1), and Salmonella Muenster (1). Antibiotic resistance profiles indicated that all five Salmonella Typhimurium isolates were resistant to ampicillin, streptomycin, sulfamethoxazole, ticarcillin, and tetracycline but that they were sensitive to chloramphenicol. Phage typing revealed that all five Salmonella Typhimurium isolates were DT104A, a subtype of DT104. All five Salmonella Typhimurium DT104A isolates were obtained from ground beef sampled from retail outlets in San Francisco. Pulsed-field gel electrophoresis (PFGE) genomic DNA profiles of the five Salmonella Typhimurium DT104A isolates from ground beef were indistinguishable from those of four control Salmonella Typhimurium DT104 penta-resistant isolates from cattle that were used for comparison. A total of 102 generic E. coli isolates were obtained, only three of which were multiresistant to antibiotics. In addition, three E. coli isolates were recovered from samples that were positive for Salmonella Typhimurium DT104A. No correlation of antibiotic resistance profiles was observed between Salmonella Typhimurium DT104A and generic E. coli, as two of the three E. coli isolates were susceptible to all of the antibiotics tested, and the third isolate was resistant only to cephalothin. These data indicate that Salmonella Typhimurium DT104A can be isolated from retail ground beef, and because there was little overlap in antibiotic resistance patterns between Salmonella Typhimurium DT104A and E. coli isolates from the same ground beef samples, these limited data suggest that the transfer of antibiotic resistance genes among enteric bacteria in ground beef may not be common. This latter observation is further supported by the limited isolation of multiantibiotic-resistant E. coli from retail ground beef.     

Effect of gamma or beta radiation on Salmonella DT 104 in ground pork

Mixtures of six Salmonella Typhimurium DT 104 strains were inoculated into three ground pork products to determine the effect of fat content on the radiation resistance of Salmonella DT 104. The ground pork products were 90% lean, 50:50 fat:lean, and 100% fat. Inoculated products were irradiated using a gamma radiation source in a self-contained 137Cesium irradiator or a 10 MeV accelerator producing electrons (e-beam). The radiation D10-values (dose required for a 90% inactivation of viable CFU) for Salmonella DT 104 inoculated into 90% lean ground pork, 50:50 fat/lean ground pork, and 100% pork fat and subjected to beta radiation were 0.42 kGy, 0.43 kGy, and 0.43 kGy, respectively. The corresponding radiation D10-values for Salmonella DT 104 subject to gamma radiation were 0.56, 0.62, and 0.62 kGy, respectively. There was no statistical significant difference (P = 0.3) in radiation D10-values for Salmonella in the three products subject to either radiation treatment. Therefore, fat content had no effect. There was a significant difference (P = 0.001) between the radiation D10-values obtained with the two radiation sources. The radiation D10-values were within the reported range for irradiation destruction of Salmonella contaminated raw meat products.     

Prevalence of Salmonella serotypes S. Enteritidis and S. Typhimurium in poultry and poultry products

Salmonella continues to be a major food safety and public health threat. In the present study, Salmonella enterica subsp. enterica serotypes Enteritidis (SE) and Typhimurium (ST) were isolated from poultry and characterized for virulence, antimicrobial susceptibility, and biofilm formation. Prevalence of Salmonella serotypes in poultry was 3.35%; predominant serotypes isolated were S. Enteritidis (68.1%) and S. Typhimurium (31.8%). Source-wise, Salmonella were isolated from retail market chicken meat (4.8%), live chicken at farm (2.5%), and table eggs (2.1%). Salmonella isolates produced invA gene of 284 bp (100%), spvR gene of 310 bp (77.27%), spvC gene of 571 bp (22.72%), and stn gene of 260 bp (100%) as virulence/ pathogenicity determinants. Salmonella isolates exhibited resistance to common antimicrobials; 72.7% isolates showed multiple resistance (≥3 antimicrobial class), highest resistance was observed for polymyxin-B (81.8%) followed by nalidixic acid (72.7%), colistin (59.1%), ampicillin/tetracyline (45.5%), ampicillin + sulbactam (40.9%), cefodroxil (18.2%), streptomycin (9.1%), and cefazidine/ceftriaxone-tazobactam (4.5%). Multiple antimicrobial resistance (MAR) index of poultry Salmonella isolates ranged from 0.11 to 0.35; wherein, 59.1% isolates showed MAR of >0.2. About 81.8% Salmonella isolates produced biofilm and were categorized as strong (13.6%), moderate (45.4%), and weak (22.7%) biofilm producers. Occurrence of antimicrobial resistant virulent Salmonella strains in poultry requires implementation of suitable strategies so as to protect the public health.     

Inactivation of Salmonella typhimurium DT 104 in UHT whole milk by high hydrostatic pressure

Cell suspensions of Salmonella typhimurium DT 104 in ultra-high temperature (UHT) whole milk were exposed to high hydrostatic pressure at 350, 400, 450, 500, 550, and 600 MPa at ambient temperature (ca. 21 degrees C). Tailing was observed in all survival curves, and sigmoidal survival curves were observed at relatively high pressure (500-600 MPa). Four modeling methods (linear and nonlinear including Weibull, modified Gompertz, and log-logistic models) were fitted to these data at 500, 550, and 600 MPa. Performances of the modeling methods were compared using mean square error (MSE). The linear regression model at these three pressure levels had a mean square error (MSE) of 1.260-2.263. Nonlinear regressions using Weibull, modified Gompertz, and log-logistic models had MSE values in the range of 0.334-0.764, 0.601-1.479, and 0.359-0.523, respectively. Modeling results indicated that first-order kinetics could not accurately describe pressure inactivation of S. typhimurium DT 104 in UHT milk; the log-logistic model produced the best fit to data.     

Extrapolation of a predictive model for growth of a low inoculum size of Salmonella Typhimurium DT104 on chicken skin to higher inoculum sizes

Validation of model predictions for independent variables not included during model development can save time and money by identifying conditions for which new models are not needed. A single strain of Salmonella Typhimurium DT104 was used to develop a general regression neural network (GRNN) model for growth of a low inoculum size (0.9 log) on chicken skin with native microflora as a function of time (0 to 8 h) and temperature (20 to 45°C). The ability of the GRNN model to predict growth of higher inoculum sizes (2, 3, or 4.1 log) was evaluated. When the proportion of residuals in an acceptable prediction zone (pAPZ) from -1 log (fail-safe) to 0.5 log (fail-dangerous) was ≥0.7, the GRNN model was classified as providing acceptable predictions of the test data. The pAPZ for dependent data was 0.93 and for independent data for interpolation was 0.88. The pAPZs for extrapolation to higher inoculum sizes of 2, 3, or 4.1 log were 0.92, 0.73, and 0.77, respectively. However, residual plots indicated local prediction problems with pAPZs of < 0.7 for an inoculum size of 3 log at 30, 35, and 40°C and for an inoculum size of 4.1 log at 35 and 40°C where predictions were fail-dangerous, indicating faster growth at higher inoculum sizes. The model provided valid predictions of Salmonella Typhimurium DT104 growth on chicken skin from inoculum sizes of 0.9 and 2 log at all temperatures investigated and from inoculum sizes of 3 and 4.1 log at some but not all temperatures investigated. Thus, the model can be improved by including inoculum size as an independent variable.     

Antimicrobial effect of Thai spices against Listeria monocytogenes and Salmonella typhimurium DT104

The objective of this study was to determine the potential antimicrobial activity of extracts and essential oils of spices from Thailand against foodborne pathogenic bacteria. The antimicrobial efficacy of ginger (Zingiber officinale), fingerroot (Boesenbergia pandurata), and turmeric (Curcuma longa) was evaluated against five strains of Listeria monocytogenes and four strains of Salmonella enterica ssp. enterica serovar Typhimurium DT104. Antimicrobial activity was investigated in microbiological media by using an agar dilution assay and enumeration over time and a model food system, apple juice, by monitoring growth over time. In the agar dilution assay, water extracts of the three spices had no effect on L. monocytogenes. Similarly, 50% ethanol extracts of ginger or turmeric had no effect. In contrast, ethanolic fingerroot extracts at 5 to 10% (vol/ vol) inhibited most L. monocytogenes strains for 24 h in the agar dilution assay. Commercial essential oils (EO) of ginger or turmeric inhibited all L. monocytogenes at < or = 0.6 or < or = 10%, respectively. Fingerroot EO inhibited all strains at < or = 0.4%. In the enumeration-over-time assay, a 5% fingerroot ethanol extract reduced ca. 4 log CFU/ml Listeria by around 2 log in 24 h while 10% inactivated the microorganism in 9 h. Fingerroot EO at 0.2% inactivated 4 log CFU/ml L. monocytogenes in 6 to 9 h. Neither extracts nor commercial EO had any effect on Salmonella Typhimurium DT 104 with the exception of fingerroot EO, which inhibited all strains at < or = 0.7%. Addition of 0.2% fingerroot EO to apple juice reduced 4 log of L. monocytogenes Scott A and both strains of Salmonella Typhimurium to an undetectable level within 1 to 2 days. It was concluded that fingerroot EO and extract have potential for inhibiting pathogens in food systems.     

Kinetics of growth and inactivation of Salmonella enterica serotype Typhimurium DT104 in pasteurised liquid egg products

The potential impact of post-pasteurisation contamination of liquid egg products with the multi-antibiotic resistant pathogen Salmonella enterica serotype Typhimurium definitive type 104 (DT104) was assessed by determining the viability of this bacterium in whole egg, albumen and 10% w/w sugared and salted yolk incubated at 4–42 °C. Results indicated that populations of S. Typhimurium DT104 were slowly inactivated in all four products when stored at 4 °C. However, based on the typical shelf-lives of cold-stored liquid egg, less than 0.6 log-kill would be achieved in those products prior to their use. Incubation at temperatures pertaining to abuse situations (10, 15, 20 and 25 °C) revealed an increasing potential for growth of S. Typhimurium DT104 in whole egg, albumen and sugared yolk, as indicated by trends in growth rate, lag duration and maximum population density. At even higher temperatures (30, 37 and 42 °C), growth rates of S. Typhimurium DT104 in whole egg and sugared yolk continued to increase. The same was true for S. Typhimurium DT104 in albumen except that growth was not observed at 42 °C and instead populations were inactivated within 30 h. At no temperature tested was S. Typhimurium DT104 able to grow in salted yolk. The influence of these growth and inactivation patterns on the risk of salmonellosis in relation to product type and storage temperature is discussed.     

Biofilm formation by multidrug-resistant Salmonella enterica serotype typhimurium phage type DT104 and other pathogens

The biofilm-forming capability of Salmonella enterica serotypes Typhimurium and Heidelberg, Pseudomonas aeruginosa, Listeria monocytogenes, Escherichia coli O157:H7, Klebsiella pneumoniae, and Acinetobacter baumannii isolated from humans, animal farms, and retail meat products was evaluated by using a microplate assay. The tested bacterial species showed interstrain variation in their capabilities to form biofilms. Strong biofilm-forming strains of S. enterica serotypes, E. coli O157: H7, P. aeruginosa, K. pneumoniae, and A. baumannii were resistant to at least four of the tested antibiotics. To understand their potential in forming biofilms in food-processing environments, the strong biofilm formers grown in beef, turkey, and lettuce broths were further investigated on stainless steel and glass surfaces. Among the tested strains, Salmonella Typhimurium phage type DT104 (Salmonella Typhimurium DT104) isolated from retail beef formed the strongest biofilm on stainless steel and glass in beef and turkey broths. K. pneumoniae, L. monocytogenes, and P. aeruginosa were also able to form strong biofilms on the tested surface materials. Salmonella Typhimurium DT104 developed a biofilm on stainless steel in beef and turkey broths through (i) initial attachment to the surface, (ii) formation of microcolonies, and (iii) biofilm maturation. These findings indicated that Salmonella Typhimurium DT104 alongwith other bacterial pathogens could be a source of cross-contamination during handling and processing of food.     

Thermal Inactivation of Salmonella spp., Salmonella typhimurium DT104, and Escherichia coli 0157:H7 in Ground Beef

ABSTRACT: In 19.1% fat ground beef, Escherichia coli 0157:H7 was less heat- resistant at ≥58°C than the Salmonella typhimurium DT104 and Salmonella senftenberg , but at 55°C the D value was similar to DT104 strains and higher than an eight-strain Salmonella cocktail. Inactivation of E. coli 0157:H7 was more temperature-dependent than the cocktail and DT104 strains. E. coli and DT104 strains were more heat-resistant in beef containing 19% fat than 4.8% fat. The cocktail was more thermally stable in stationary as compared to log phase. Freezing of inoculated raw meat decreased heat resistance of the cocktail. The pathogenic strain, growth phase of the organism, state of the meat (fresh or frozen) and meat composition must be considered when designing protocols to verify thermal processes.     

Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organic acids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of four S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5·4, 4·4, and 3·7. Significantly (P<0·05) higher numbers of S. typhimurium DT104 cells were detected at pH 4·4 and 4·0 in TSB acidified with acetic acid and at pH 4·4 and 3·7 in TSB acidified with lactic acid compared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7·3) acidified with lactic acid at pH 5·4, 4·4, and 4·0 and on TSA (pH 7·0±0·2) containing 0·5, 2·5, and 5% sodium chloride. Populations of acid-shockedS. typhimurium DT104 and non DT104 cells recovered on acidified or salt-supplemented TSA were significantly (P<0·05) lower than those of non-shocked cells. A significantly lower number of acid-shocked non-DT104 cells recovered on TSA at pH 5·4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and subsequent exposure to acid pH. D values and z values of acid-shocked or non-shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE), egg yolk (EY), egg white (EW), whole egg+10% salt (WES), and egg yolk+10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S. typhimurium DT104 cells indicate that the USDA pasteurization process would eliminate >8 log₁₀cfu ml⁻¹of EW heated at 57°C and >11 log₁₀cfu ml⁻¹of WE, EY, WES, or EYS heated at 61°C. D values of acid-shocked DT104 and non-DT104 cells heated in liquid egg products were significantly (P<0·05) lower than those of respective non-shocked cells.     

Survival of multidrug-resistant Salmonella typhimurium DT104 in egg powders as affected by water activity and temperature.

A study was done to determine if a four-strain mixture of multidrug-resistant Salmonella typhimurium definitive type 104 (DT104) cells and a four-strain mixture of S. typhimurium non-DT104 cells differed in ability to survive in whole egg powder, whole egg powder supplemented with corn syrup solids (38%) and salt (1.9%), egg yolk powder, and egg white powder as affected by a(w)(0.29-0.37 and 0.51-0.61) during storage at 13 or 37 degrees C for 8 weeks. Rates of inactivation of S. typhimurium DT104 and non-DT104 cells were similar within each set of test parameters. With the exception of whole egg powder supplemented with corn syrup solids and salt, death was enhanced at a(w) 0.29-0.37 compared to a(w) 0.51-0.61 when powders were stored at 13 degrees C. Survival of cells in whole egg powder supplemented with corn syrup solids and salt was significantly (P < or = 0.05) higher compared to survival in other egg powders stored at 13 degrees C. The opposite trend occurred in powders at a(w) 0.5-0.61 stored at 37 degrees C. Survival of S. typhimurium DT104 and non-DT104 cells at initial populations of 5.01-5.39 log10 cfu/g of egg white powder containing 4.9, 6.1, or 8.2% moisture at 54 or 82 degrees C for 7 days or 8 h, respectively, was determined. Rates of inactivation of DT104 and non-DT104 cells did not differ. Both cell types were detected in egg white powder containing 4.9% moisture but not in powder containing 8.2% moisture when held at 54 degrees C for 7 days. Heating at 82 degrees C for 8 h failed to eliminate 5 log10 S. typhimurium per g of egg white powder, regardless of the moisture content.     

A rapid most-probable-number-based enzyme-linked immunosorbent assay for the detection and enumeration of Salmonella Typhimurium in poultry wastewater

The rapid and accurate detection and enumeration of low levels of Salmonella Typhimurium in food processing facilities are critical components of an effective hazard analysis critical control point program. The objective of this study was to develop a rapid (8 h) most probable number (MPN)-enzyme-linked immunosorbent assay (ELISA) for the detection and enumeration of Salmonella Typhimurium in wastewater. The specific objectives were to (i) characterize poly- and monoclonal Salmonella Typhimurium-specific antibodies in order to select the most specific and sensitive antibody for Salmonella Typhimurium detection, and (ii) validate the MPN assay through a correlation between the 8-h MPN-ELISA and the traditional 48-h Salmonella Typhimurium MPN method in poultry scald water. Poultry scald water samples were spiked with 10 and 50 CFU/ml of Salmonella Typhimurium. The traditional MPN method used a 48-h enrichment period followed by an analysis, while the MPN-ELISA used a 5-h enrichment period followed by a 3-h ELISA analysis. No differences (P < 0.05) were found between the traditional MPN and the MPN-ELISA, indicating the promise of the MPN-ELISA for the rapid detection and enumeration of Salmonella Typhimurium within an 8-h shift. This abbreviated assay will permit increased product sampling and more rapid movement of food between production and processing, resulting in reduced spoilage and quality losses.     

Modeling the inactivation of Salmonella Typhimurium, Listeria monocytogenes, and Salmonella Enteritidis on poultry products exposed to pulsed UV light

Pulsed UV light inactivation of Salmonella Typhimurium on unpackaged and vacuum-packaged chicken breast, Listeria monocytogenes on unpackaged and vacuum-packaged chicken frankfurters, and Salmonella Enteritidis on shell eggs was explained by log-linear and Weibull models using inactivation data from previous studies. This study demonstrated that the survival curves of Salmonella Typhimurium and L. monocytogenes were nonlinear exhibiting concavity. The Weibull model was more successful than the log-linear model in estimating the inactivations for all poultry products evaluated, except for Salmonella Enteritidis on shell eggs, for which the survival curve was sigmoidal rather than concave, and the use of the Weibull model resulted in slightly better fit than the log-linear model. The analyses for the goodness of fit and performance of the Weibull model produced root mean square errors of 0.059 to 0.824, percent root mean square errors of 3.105 to 21.182, determination coefficients of 0.747 to 0.989, slopes of 0.842 to 1.042, bias factor values of 0.505 to 1.309, and accuracy factor values of 1.263 to 6.874. Overall, this study suggests that the survival curves of pathogens on poultry products exposed to pulsed UV light are nonlinear and that the Weibull model may generally be a useful tool to describe the inactivation patterns for pathogenic microorganisms affiliated with poultry products.     

Improving recovery of Salmonella enterica serovar typhimurium DT104 cells injured by heating at different water activity values

This study describes the evaluation of potentially more sensitive methods for the recovery of Salmonella cells injured by heating (54 to 60 degrees C) at different water activity values (0.65 to 0.90, reduced using equal portions of glucose and fructose). These methods included gradual rehydration, the use of diluting media with added solutes or blood, the addition of blood to plating agar, and the use of different incubation temperatures and times. Gradual rehydration of cells that had been challenged at low water activity (0.65 and 0.70) and high temperature markedly improved recovery, measured as a >50% increase in the time to obtain a 3-log10 reduction in cell numbers, compared to dilution into media with a high water activity. Adding sucrose, glycerol, or blood to the diluting media (maximal recovery diluent) did not improve recovery, but a plating agar containing blood recovered approximately 38% more cells than nutrient agar. Prolonged incubation of agar plates allowed recovery of injured Salmonella cells that presumably had extended lag periods, with significantly higher recovery rates after 48 h incubation at 37 degrees C than after 24 h (P = 0.05). This work highlights that by recovering Salmonella using a method specific to the nature of the injury, a better prediction of food safety and the success of food processing can be made.     

Efficacy of Neutral pH Electrolyzed Water in Reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on Fresh Produce Items using an Automated Washer at Simulated Food Service Conditions

The objective of this study was to determine the efficacy of neutral pH electrolyzed (NEO) water (155 mg/L free chlorine, pH 7.5) in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce, iceberg lettuce, and tomatoes washed in an automated produce washer for different times and washing speeds. Tomatoes and lettuce leaves were spot inoculated with 100 μL of a 5 strain cocktail mixture of either pathogen and washed with 10 or 8 L of NEO water, respectively. Washing lettuce for 30 min at 65 rpm led to the greatest reductions, with 4.2 and 5.9 log CFU/g reductions achieved for E. coli O157:H7 and S. Typhimurium respectively on romaine, whereas iceberg lettuce reductions were 3.2 and 4.6 log CFU/g for E. coli O157:H7 and S. Typhimurium respectively. Washing tomatoes for 10 min at 65 rpm achieved reductions greater than 8 and 6 log CFU/tomato on S. Typhimurium and E. coli O157:H7 respectively. All pathogens were completely inactivated in NEO water wash solutions. No detrimental effects on the visual quality of the produce studied were observed under all treatment conditions. Results show the adoption of this washing procedure in food service operations could be useful in ensuring produce safety.