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.     

Fecal shedding of Salmonella spp. by dairy cows on farm and at cull cow markets

As part of a national study of the U.S. dairy cow population, fecal samples were collected from representative cows on 91 dairies and 97 cull dairy cow markets in 19 states. Salmonella spp. were recovered from 5.4% of milk cows, 18.1% of milk cows expected to be culled within 7 days, and 14.9% of culled dairy cows at markets. On a premise basis, Salmonella shedding in milk cows was detected on 21.1% of dairies and 66% of cull dairy cow markets. The percentage of herds with at least one cow with detectable Salmonella fecal shedding was higher during the sampling period from May through July, in herds with at least 100 milk cows, and in herds in the South region. The most common Salmonella serogroups isolated were E (30.8% of isolates) and C1 (28.6%); the most common serotypes isolated were Salmonella Montevideo (21.5% of isolates), Salmonella Cerro (13.3%), and Salmonella Kentucky (8.5%). Fecal shedding of Salmonella Typhimurium or Salmonella Typhimurium var. copenhagen was infrequent (2.8% of isolates). Most isolates (88.9%) were susceptible to all 17 antimicrobials evaluated; multiple resistance was an infrequent occurrence. This study provides information describing the distribution of Salmonella fecal shedding from dairy cows on farm and at markets and will serve as a baseline for future studies.     

Survey of Salmonella serotypes shed in feces of beef cows and their antimicrobial susceptibility patterns

Salmonella prevalence on cow-calf operations was studied as a part of a national study of health and management of the U.S. beef cow-calf industry and was conducted as part of the National Animal Health Monitoring System. Within this study, the prevalence of Salmonella spp. shed in feces was determined. A total of 5,049 fecal samples were collected from 187 beef cow-calf operations each visited on a single occasion. The number of fecal samples collected per operation was predetermined based on herd size. Salmonellae were recovered from 1 or more fecal samples collected on 11.2% (21 of 187) of the operations. Overall 78 salmonellae representing 22 serotypes were recovered from 1.4% (70 of 5,049) of samples. Multiple serotypes were recovered from eight samples from a single operation. The five most common serotypes were Salmonella Oranienburg (21.8% of isolates), and Salmonella Cerro (21.8%), followed by Salmonella Anatum (10.3%), Salmonella Bredeney (9.0%), and Salmonella Mbandaka (5.1%). The most common serogroups identified were C1 (33.3%), K (21.8%), B (16.7%), and E (15.4%). Even though the recovery rate of salmonellae from fecal samples was very low, 43.6% (34 of 78) and 38.5% (30 of 78) of the isolates were among the 10 most common serotypes from cattle with clinical signs of disease or isolated from humans, respectively. The majority of the isolates (50 of 78; 64.1%) were recovered from fecal samples from two operations. All isolates were screened for resistance to a panel of 17 antimicrobics, and 87.2% (68 of 78) were susceptible to all of the antimicrobics. The resistant isolates were most commonly resistant to streptomycin (n = 9) and/or sulfamethoxazole (n = 9). Nine isolates showed multiple (> or =2 antimicrobics) resistance most commonly to streptomycin and sulfamethoxazole (n = 6).     

Serotyping and antibiotic resistance profiling of Salmonella in feedlot and nonfeedlot beef cattle

As part of a larger study to assess risk factors associated with hide and carcass contamination of beef cattle during transport to slaughter, a total of 281 salmonellae were isolated from 1,050 rectal, hide, carcass, and environmental samples. For feedlot cattle, salmonellae were recovered from 4.0% of rectal samples, 37.5% of hide samples, 19.0% of carcass samples, and 47.4% of environmental samples. For nonfeedlot cattle, salmonellae were recovered from 10.9% of rectal samples, 37.5% of hide samples, 54.2% of carcass samples, and 50.0% of environmental samples. Overall, the five serotypes most commonly associated with feedlot cattle and their environment were Salmonella Anatum (18.3% of the isolates), Salmonella Kentucky (17.5%), Salmonella Montevideo (9.2%), Salmonella Senftenberg (8.3%), and Salmonella Mbandaka (7.5%). The five serotypes most commonly associated with nonfeedlot cattle and their environment were Salmonella Kentucky (35.4%), Salmonella Montevideo (21.7%). Salmonella Cerro (7.5%), Salmonella Anatum (6.8%), and Salmonella Mbandaka (5.0%). Antimicrobial susceptibility testing of all of the isolates associated with feedlot cattle revealed that 21.7% were resistant to tetracycline, compared with 11.2% of the isolates associated with nonfeedlot cattle. None of the other isolates from feedlot cattle were resistant to any of other antimicrobial agents tested, whereas 6.2% of nonfeedlot cattle isolates were resistant to more than four of the antimicrobial agents tested.     

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.     

Associations between on-farm and slaughter plant detection of Salmonella in market-weight pigs

Thirty swine production units in the midwestern United States were studied to assess the relationship of herd-level prevalence of Salmonella on the farm prior to slaughter versus at slaughter. Fecal samples were collected from 30 pigs on each farm within 48 h of slaughter, and 30 ileocecal lymph node samples were collected in the same shipment cohort at slaughter. Samples were cultured by conventional methods, and Salmonella identity was confirmed by serotyping. Overall, 11.7% (n = 105) of the fecal samples and 14.9% (n = 133) of the ileocecal lymph node samples were positive for Salmonella. Seventeen of the farms (56.7%) had one or more positive fecal samples, and 24 (80.0%) had one or more positive ileocecal lymph node samples. Twenty-four recognized serotypes and three additional distinct antigenic types were identified. Among all isolates, 56.5% had serotypes that were duplicated both on the farm and at slaughter for a particular cohort, whereas the remaining samples lacked a duplicate serotype in the other sample type. There was a positive correlation in the prevalence of Salmonella between fecal samples and ileocecal lymph node samples (Spearman's p = 0.75; 95% confidence interval [CI], 0.62 to 0.89). Linear regression analysis was used to identify two farms that biased the regression estimates. Excluding these farms, 62% of the variance in farm slaughter Salmonella prevalence was accounted for by on-farm prevalence. The analyses suggest that the prevalence of Salmonella spp. at slaughter can be predicted from preslaughter on-farm sampling and vice versa.     

Prevalence of Salmonella and Campylobacter in beef cattle from transport to slaughter

The objective of this study was to evaluate the effect of typical production practices during the transport of cattle on the resulting incidence of Salmonella and Campylobacter in the feces, on the hides, and on the carcasses of these cattle and in the environment (trucks, holding pens, and knock boxes). Various factors were evaluated, including the type of animal (feedlot cattle vs. adult pasture cattle), the breed of cattle, the body condition of the animal, the age of the animal, the time of feed and water withdrawal, the contamination level of the transport vehicle at the feedlot or farm, the transport time, the time cattle were held in the holding pen at the plant, and the contamination level of the holding pen. Four groups of each type of animal were sampled on different days. Samples were collected from cattle prior to transport and after transport (rectal and hide swabs) as well as from the carcasses of these cattle. Pre- and posttransit samples were also taken from the transport vehicle and from the holding pen and knock box at the slaughter facility. For feedlot cattle, fecal shedding stayed fairly constant for both organisms before and after transport (3 to 5% for Salmonella and 64 to 68% for Campylobacter). However, the shedding rate for adult cattle increased from 1 to 21% for Salmonella but stayed constant for Campylobacter (6 to 7%). Contamination of hides with Salmonella increased for both animal types from a level of 18 to 20% to a level 50 to 56%. For Campylobacter, the contamination level decreased from 25 to 13% for feedlot cattle but remained unchanged for adult animals (1 to 2%). Nineteen percent of feedlot cattle carcasses and 54% of adult cattle carcasses tested positive for Salmonella, while only2% of feedlot cattle carcasses and none of the adult cattle carcasses tested positive for Campylobacter. Thus, for feedlot cattle, the factors considered in this study did not affect the shedding of either organism but did affect the contamination of hides with both. For adult animals, the factors increased both shedding of and hide contamination with Salmonella only, not Campylobacter.     

Antibiotic resistance of Salmonella spp. from animal sources in Spain in 1996 and 2000

Emergence of resistant and multiresistant bacteria has become an important worldwide sanitary problem. International agencies recommend improving resistance surveillance studies in not only human but also animal origin strains. Because of its ubiquitous characteristics and zoonotic agent consideration, Salmonella spp. can be used as a good indicator microorganism for resistance surveillance studies. Salmonella spp. strains from animal sources isolated in 1996 (107) and 2000 (474) in Spain were tested against 12 different antimicrobials agents, using the disc diffusion method. Results were interpreted following the NCCLS criteria. Data showed that Salmonella spp. strains (61.7% in 1996 and 81.5% in 2000) were resistant to at least one antibiotic. Pig-related strains were considerably more resistant than strains from other sources. Enteritidis serotype was less resistant than other serotypes, except for ampicillin in 1996 (50% resistant) and nalidixic acid in 2000 (65.1% resistant). An emergent monophasic serotype, 4,5,12:i:-, first detected in 1997 in Spain was 100% resistant and 90% multiresistant. Typhimurium serotype was the most common Salmonella serotype from animal sources in both years. It was widely distributed among animals and was among the serotypes with a higher degree of resistance. The ampicillin, chloramphenicol, sulfonamides, streptomycin, and tetracycline resistance pattern, commonly associated with Salmonella serotype Typhimurium DT 104, had spread among other Typhimurium phage types and other Salmonella serotypes. Salmonella spp. strains isolated from feeding stuffs were considerably more susceptible than animal source strains, suggesting that the high Salmonella spp. resistance percentage was probably due to the use of antibiotics in animal farms rather than the consumption of contaminated feeding stuffs.     

Impact of transportation and lairage on hide contamination with Escherichia coli O157 in finished beef cattle

Transportation of cattle from the feedlot to the slaughter plant could influence hide contamination of Escherichia coli O157. A study was initiated to investigate the influence of transportation and lairage on shedding and hide contamination of E. coli O157. Fecal and hide samples were obtained from 40 pens of harvest-ready beef cattle at the feedlot prior to transport and again at the slaughter plant immediately after slaughter. Potential risk factors for hide contamination at the feedlot, during transport, and at slaughter were evaluated. A multilevel Poisson regression model was used to evaluate if transportation and lairage were associated with hide contamination by E. coli O157 in finished beef cattle. Lots of cattle held in E. coli O157-positive lairage pens had eight times greater risk of having positive slaughter hide samples compared with cattle held in culture-negative pens (relative risk, 8.0; 95% confidence interval, 1.6 to 38.8). Lots of cattle that were held in lairage pens contaminated with feces had three times greater risk for positive slaughter hide samples compared with cattle held in clean pens (relative risk, 3.1; 95% confidence interval, 1.2 to 7.9). Lots of cattle that were transported for long distances (> 160.9 km) had twice the risk of having positive hide samples at slaughter compared with cattle transported a shorter distance (relative risk, 2.4; 95% confidence interval, 1.1 to 5.1). These findings suggest that transportation and lairage should be considered in E. coli O157 control strategies.     

Salmonella in dairy operations in the United States: prevalence and antimicrobial drug susceptibility

Salmonella serotypes are important foodborne pathogens of humans that can be acquired through consumption of contaminated meat and dairy products. Salmonella infection also can be a significant animal health issue. As part of a national study of U.S. dairy operations conducted between March and September 2002, fecal samples were collected from representative cows in 97 dairy herds in 21 states and were cultured to determine the prevalence of Salmonella shedding. Salmonella was recovered from the feces of at least one cow in 30.9% of the herds. Overall, 7.3% of fecal samples were culture positive for Salmonella. The three most frequently recovered serotypes were Salmonella Meleagridis (24.1%), Salmonella Montevideo (11.9%), and Salmonella Typhimurium (9.9%). The susceptibilities of Salmonella isolates recovered were determined using a panel of 16 antimicrobial drugs. Salmonella isolates recovered from dairy cows had relatively little resistance to these antimicrobial agents; 83.0% of the isolates were susceptible to all antimicrobials tested. This study provides updated information on the prevalence and susceptibility patterns of Salmonella in dairy herds and on cow and herd characteristics. These data contribute to our understanding of the ecology of Salmonella in the dairy farm environment.     

Frequency and antimicrobial resistance of Salmonella serotypes on beef carcasses at small abattoirs in Jalisco State, Mexico

The prevalence and antimicrobial resistance of Salmonella serotypes on beef carcasses from four small abattoirs in Jalisco State, Mexico, were investigated during a 10-month period. Following U.S. Department of Agriculture Food Safety and Inspection Service protocols, Salmonella was isolated from 78 (15.4%) beef carcasses (n = 505) after the final carcass water wash. Isolation frequency differed by establishment (P < 0.05) and was higher (P < 0.05) during the wet season (May through September) for all establishments. Thirteen Salmonella serotypes and four serogroups (partially serotyped isolates) were identified. The most prevalent were Salmonella enterica Give (24.4%), Salmonella Typhimurium (17.9%), and Salmonella Group B (14.1%). Antimicrobial susceptibility was tested against 11 drugs, and results indicated that 46.2% of the isolates were resistant to tetracycline, 42.3% were resistant to streptomycin, 23.1% were resistant to chloramphenicol, 21.8% were resistant to trimethoprim-sulfamethoxazole, and 19.2% were resistant to gentamicin. No resistance to ceftriaxone or ciprofloxacin was observed, and 33% of the isolates were resistant to three or more antimicrobials. Although Salmonella Give was the most prevalent serotype, 95% of the isolates of this serotype were susceptible to all antimicrobials tested. Antimicrobial resistance was more common in Salmonella Typhimurium, and 93% (13 of 14) of the isolates of this serotype were resistant to at least five antimicrobials. The frequency of multidrug-resistant Salmonella isolates differed among establishments (P < 0.05) and may be related to the origin of the cattle presented for harvesting. These findings highlight the need for control measures to reduce Salmonella prevalence on beef carcasses in small abattoirs in Mexico and for strategies to ensure the cautious use of antimicrobials in animal production to prevent and control the spread of antimicrobial-resistant foodborne pathogens.     

Competitive inhibition bacteria of bovine origin against Salmonella serovars

Studies were conducted to isolate bacteria inhibitory to Salmonella enterica serovar Typhimurium definitive type (DT) 104 in vitro from cattle not carrying Salmonella and to determine the inhibitory activity of the isolated bacteria through competitive growth in cattle feces artificially contaminated with Salmonella Typhimurium DT104 and S. enterica serovar Newport. Fecal samples (108) were obtained from dairy and beef cows. S. enterica serovars were isolated from 9.25% of the samples and included Salmonella Newport (4), Salmonella Bareilly (1), Salmonella Mbandaka (1), Salmonella Montevideo (1), Salmonella Meleagridis (1), and monophasic Salmonella (2). All four Salmonella Newport isolates were resistant to at least nine antibiotics. Of 1,097 bacterial isolates from cattle feces screened, 30 were inhibitory to Salmonella Typhimurium DT104 in vitro. The inhibitory isolates included 22 Escherichia coli, 6 Bacillus circulans, 1 Serratia fonticola, and 1 Enterobacter cloacae. Typing by pulsed-field gel electrophoresis showed 17 distinguishable profiles among the 22 E. coli. Competitive inhibition isolates did not significantly reduce Salmonella Typhimurium DT104 during 21 days of storage at 37 degrees C in cattle feces. B. circulans (10(5) CFU/g of inoculum) significantly reduced Salmonella Newport on days 3 and 5 and on day 21 with 10(8) CFU/g of inoculum at 37 degrees C. At 21degrees C, significant reductions of Salmonella Typhimurium DT104 occurred with 10(8) CFU of gram-negative competitive inhibition bacteria per g and 10(5) CFU of B. circulans per g on day 5 only. No significant reductions were observed with Salmonella Newport at 21 degrees C. The 25 competitive inhibition bacteria identified in this study offer a first step in identifying competitive inhibition bacteria that may reduce the level of intestinal carriage and fecal shedding of Salmonella Typhimurium DT104 and Salmonella Newport in cattle.     

A study of the prevalence and enumeration of Salmonella enterica in cattle and on carcasses during processing

Salmonella prevalence and counts were estimated for samples from the oral cavity, hide, rumen, and feces of 100 cattle at slaughter and from the pre- and postchill carcasses of these cattle. Samples were collected from 25 consecutively slaughtered cattle from each of four unrelated groups slaughtered at a single abattoir on different days. Ten additional fecal samples from each group were collected from their respective abattoir holding pens prior to slaughter. The prevalence of Salmonella was estimated using automated immunomagnetic separation, and the counts were estimated using a combination of most probable number (MPN) and automated immunomagnetic separation. A total of 606 samples were collected with Salmonella isolated from 157 (26%), including 29% of oral cavities, 68% of hides, 16% of feces collected after evisceration, 25% of rumen samples, 2% of prechill carcasses, 3% of postchill carcasses, and 48% of feces collected from holding pens. The prevalence and count of Salmonella varied between the different groups of animals tested. The highest count obtained was from a rumen sample (1.1 x 10(4) MPN/g). Other counts were generally low, with a maximum count in feces collected after evisceration and in the abattoir holding pens of 93 and 23 MPN/g, respectively. The highest count on hides, in oral cavities, and on carcasses was 4.8 MPN/cm2, 23 MPN/g, and 0.31 MPN/cm2, respectively. Even though Salmonella was present on the hides and in the rumen and feces of at least one animal from each group of cattle, the processing of animals at this abattoir resulted in few contaminated carcasses, and when contamination occurred, Salmonella was detected at low numbers.     

Salmonella spp. on chicken carcasses in processing plants in Poland

Chickens at selected points in the slaughter process and after slaughter on the dressing line in poultry plants were sampled and analyzed for Salmonella. These chickens came from the northeast part of Poland. The examinations were carried out in quarters I, II, III, and IV of 1999. All the birds were determined to be healthy by a veterinary inspection. Swab samples were taken from the cloaca after stunning and from the skin surface and body cavity of the whole bird after evisceration, after rinsing at the final rinse station but before chilling in the spin-chiller, and after cooling in the continuous cooling plant at the end of the production day. In 1999, 400 whole chickens were examined. The percentage of these 400 chickens from which Salmonella spp. were isolated was relatively high (23.75%; Salmonella-positive results were observed in 95 cases). Salmonella spp. were found after stunning in 6% of the chickens (6 of 100 samples), after evisceration in 24% (24 of 100), before cooling in 52% (52 of 100), and after cooling in 13% (13 of 100). These results show that Salmonella spp. were found more often at some processing points than at others. The lowest Salmonella spp. contamination rate (6%) for slaughter birds was found after stunning, and the highest contamination rate was found before chilling (52%). The serological types of Salmonella spp. isolated from whole chickens were Salmonella Enteritidis, Salmonella Typhimurium, Salmonella Saintpaul, Salmonella Agona, and Salmonella Infantis. The results of these investigations indicate that Salmonella Enteritidis is the dominant serological type in infections of slaughter chickens, as it is in many countries.     

Fecal shedding of Escherichia coli O157, Salmonella, and Campylobacter in Swiss cattle at slaughter

Fecal samples from 2,930 slaughtered healthy cattle were examined with the following goals: (i) to monitor the shedding of Escherichia coli O157, Salmonella, and Campylobacter in cattle; and (ii) to further characterize the isolated strains. The percentage of the 2,930 samples that tested positive for E. coli O157 by PCR was 1.6%. Thirty-eight strains from different animals that agglutinated with Wellcolex E. coli O157 were isolated. Of the six sorbitol-negative strains, five tested positive for stx2 genes (two times for stx2c and three times for stx2), and one strain tested positive for stx1 and stx2c genes. All sorbitol-negative strains belonged to the serotypes O157:H7- and O157:H7 and harbored the eae type gamma 1 and ehxA genes. The 32 sorbitol-positive strains tested negative for stx genes and belonged to the serotypes O157:H2, O157:H7, O157:H8, O157:H12, O157:H19, O157:H25, O157:H27, O157:H38, O157:H43, O157:H45, and O157:H-. All O157:H45 strains harbored the eae subtype alpha 1 and therefore seem to be atypical enteropathogenic E. coli strains. Whereas none of 1,000 examined samples was positive for Salmonella, 95 of 935 (10.2%) samples were positive for Campylobacter, and all strains were identified as C. jejuni. Sixteen Campylobacter strains were resistant to tetracycline, five were resistant to nalidixic acid/ciprofloxacin, four were resistant to streptomycin, and one was resistant to nalidixic acid/ciprofloxacin and streptomycin. Fecal shedding of zoonotic pathogens in slaughter animals is strongly correlated with the hazard of carcass contamination. Therefore, the maintenance of slaughter hygiene is of crucial importance.     

A quantitative approach towards a better understanding of the dynamics of Salmonella spp. in a pork slaughter-line

Pork contributes significantly to the public health disease burden caused by Salmonella infections. During the slaughter process pig carcasses can become contaminated with Salmonella. Contamination at the slaughter-line is initiated by pigs carrying Salmonella on their skin or in their faeces. Another contamination route could be resident flora present on the slaughter equipment. To unravel the contribution of these two potential sources of Salmonella a quantitative study was conducted. Process equipment (belly openers and carcass splitters), faeces and carcasses (skin and cutting surfaces) along the slaughter-line were sampled at 11 sampling days spanning a period of 4 months. Most samples taken directly after killing were positive for Salmonella. On 96.6% of the skin samples Salmonella was identified, whereas a lower number of animals tested positive in their rectum (62.5%). The prevalence of Salmonella clearly declined on the carcasses at the re-work station, either on the cut section or on the skin of the carcass or both (35.9%). Throughout the sampling period of the slaughter-line the total number of Salmonella per animal was almost 2 log lower at the re-work station in comparison to directly after slaughter. Seven different serovars were identified during the study with S. Derby (41%) and S. Typhimurium (29%) as the most prominent types. A recurring S. Rissen contamination of one of the carcass splitters indicated the presence of an endemic 'house flora' in the slaughterhouse studied. On many instances several serotypes per individual sample were found. The enumeration of Salmonella and the genotyping data gave unique insight in the dynamics of transmission of this pathogen in a slaughter-line. The data of the presented study support the hypothesis that resident flora on slaughter equipment was a relevant source for contamination of pork.     

Salmonella prevalence and antimicrobial susceptibility from the National Animal Health Monitoring System Swine 2000 and 2006 studies

Concern about Salmonella contamination of food is compounded by fear that antimicrobials traditionally used to combat the infection will become useless due to rising antibiotic resistance. Livestock, in particular swine, often are blamed for illnesses caused by Salmonella and for increasing antibiotic resistance due to use of antibiotics in pigs. As part of the National Animal Health Monitoring System Swine 2000 and 2006 studies, swine fecal samples were cultured for Salmonella. These samples were collected from 123 operations in 17 states in 2000 and from 135 operations in 17 states in 2006. At each operation, 50 and 60 fecal samples were collected from late finisher pig pens in 2000 and 2006, respectively. Salmonella isolates were characterized to determine serogroup and serotype and were tested for susceptibility to a panel of 17 and 15 antimicrobial drugs in 2000 and 2006, respectively. A total of 5,470 and 7,788 samples were cultured for Salmonella in 2000 and 2006, respectively. Overall, 6.2% of the samples and 34.2% of the farms were positive for Salmonella in 2000. In 2006, 7.2% of the samples and 52.6% of the farms were positive. Salmonella Derby, Salmonella Typhimurium var. 5- (formerly Salmonella Typhimurium var. Copenhagen), and Salmonella Agona were the three serotypes most often recovered in both study years. The most common antimicrobial resistance pattern for Salmonella Derby in the two study years was resistance to streptomycin, sulfisoxazole, and tetracycline. Most isolates were resistant to tetracycline, sulfisoxazole, and streptomycin in both study years. The proportion of Salmonella isolates that were susceptible to all antimicrobials (pansusceptible) was 38.1% in 2000 and 20.4% in 2006. The proportion of Salmonella isolates that were resistant to three or more antimicrobials (multidrug resistant) was similar in 2000 and in 2006 (52.8 and 57.7%, respectively).     

Fecal shedding of foodborne pathogens by Florida-born heifers and steers in U.S. beef production segments

The objective in this study was to assess breed effects in fecal prevalence of Escherichia coli O157:H7 in heifers on a development program in Florida and in their steer half siblings in stocker and feedlot phases in Oklahoma. A secondary objective was to characterize fecal shedding of Campylobacter and Salmonella in subsets of the same samples. After weaning, heifers (n = 501; purebreds and F1 crosses of Angus, Brahman, and Romosinuano) were preconditioned and placed in a local development program. Steers (n = 481) were transported to Oklahoma, where they grazed wheat for 6 months and then were placed in feedlot pens. Fecal samples were obtained at least every 28 days for 12 months on most animals. None of the 10,982 samples tested positive for E. coli O157:H7. Overall fecal prevalences of Campylobacter and Salmonella in heifers were 1.7 and 0.04%, respectively. Corresponding overall prevalences in steer samples were 27.2 and 0.6%. Campylobacter isolates were mostly C. jejuni and were tetracycline resistant. Eight Salmonella isolates were Salmonella Typhimurium that were either quad or penta resistant, most often to ampicillin, chloramphenicol, sulfamexathole, and tetracycline. Feedlot steers had greater odds of positive detection of Campylobacter (odds ratio, 8.5; confidence interval, 3.7, 19.5) than when grazing winter wheat. No breed effect was detected for fecal prevalence of these pathogens.     

Prevalence of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in two geographically distant commercial beef processing plants in the United States

For two large beef processing plants, one located in the southern United States (plant A) and one located in the northern United States (plant B), prevalence of Escherichia coli O157:H7, Listeria spp., Listeria monocytogenes, and Salmonella was determined for hide, carcass, and facility environmental samples over the course of 5 months. The prevalence of E. coli O157:H7 (68.1 versus 55.9%) and Salmonella (91.8 versus 50.3%) was higher (P < 0.05), and the prevalence of Listeria spp. (37.7 versus 75.5%) and L. monocytogenes (0.8 versus 18.7%) was lower (P < 0.05) for the hides of cattle slaughtered at plant A versus plant B. Similarly, the prevalence of Salmonella (52.0 versus 25.3%) was higher (P < 0.05) and the prevalence of Listeria spp. (12.0 versus 40.0%) and L. monocytogenes (1.3 versus 14.7%) was lower (P < 0.05) for the fence panels of the holding pens of plant A versus plant B. The prevalence of E. coli O157:H7 (3.1 versus 10.9%), Listeria spp. (4.5 versus 14.6%), and L. monocytogenes (0.0 versus 1.1%) was lower (P < 0.05) for preevisceration carcasses sampled at plant A versus plant B. Salmonella (both plants), Listeria spp. (plant B), and L. monocytogenes (plant B) were detected on fabrication floor conveyor belts (product contact surfaces) late during the production day. For plant B, 21 of 148 (14.2%) late-operational fabrication floor conveyor belt samples were L. monocytogenes positive. For plant B, E. coli O157:H7 and L. monocytogenes were detected in preoperational fabrication floor conveyor belt samples. Overall results suggest that there are regional differences in the prevalence of pathogens on the hides of cattle presented for harvest at commercial beef processing plants. While hide data may reflect the regional prevalence, the carcass data is indicative of differences in harvest practices and procedures in these plants.     

Prevalence and characteristics of Shiga toxin-producing Escherichia coli, Salmonella spp. and Campylobacter spp. isolated from slaughtered sheep in Switzerland

Caecum samples collected from 653 slaughtered sheep from two Swiss abattoirs were examined. The aim of this study was: (i) to determine the prevalence of Shiga toxin-producing Escherichia coli (STEC), Salmonella spp. and Campylobacter spp.; (ii) to further characterize isolated strains; and (iii) to discuss the results obtained with their relevance to food safety. The percentage of samples testing positive for STEC by a polymerase chain reaction was 29.9%. The prevalence of positive Salmonella spp. samples was 11.0% and of Campylobacter spp. 17.5%. In 55.3% of the 76 isolated non-O157 STEC strains, stx2 variants (mostly stx2d) were detected. Additional virulence factors were harbored by 55.3% of the STEC strains, 10.5% of them being eae positive, 55.3% ehxA positive and 2.6% astA positive. All isolated salmonella were identified as Salmonella enterica subsp. diarizonae serovar 61:k:1,5,(7). Pulsed-field gel electrophoresis (PFGE) was performed for genotyping and 22 different restriction endonuclease digestion profiles were found among these strains for the different farms of origin. Of the 114 isolated Campylobacter spp. strains, 64.9% were shown to be Campylobacter jejuni and 35.1% Campylobacter coli, nine strains showed resistance against tetracycline, ciprofloxacin/nalidixic acid or streptomycin. In conclusion, sheep are a reservoir for the pathogens of latent zoonoses as non-O157 STEC, S. enterica subsp. diarizonae and Campylobacter spp. The maintenance of slaughter hygiene is consequently of crucial importance. It can be measured in daily practice by "slaughter-process-controls" and regular microbiological monitoring of carcasses. These are valuable tools for verifying slaughter hygiene according to hazard analysis critical control point principles.