Prevalence, antibiotic resistance, and molecular characterization of Salmonella serovars in retail meat products

The prevalence of Salmonella was determined in chicken meat (n = 26), beef (n = 49), and pork (n = 56) collected from wholesale markets, retail stores, and traditional markets in Seoul, South Korea, in 2009. Antibiotic resistance was assessed, and the molecular subtypes of Salmonella isolates were ascertained using an automated repetitive sequence-based PCR (rep-PCR) system (DiversiLab). A total of 18 Salmonella strains were isolated from 17 of 131 samples: 16 strains from each of 16 samples and 2 strains from the same pork sample. The prevalence of Salmonella from the retail meats was 2.0% in beef, 8.9% in pork, and 42.3% in chicken meat. Among 10 different serotypes, Salmonella enterica Panama was recovered from a beef sample, and Salmonella London and Salmonella Montevideo were the predominant serotypes from pork and chicken meat, respectively. The highest antibiotic resistance observed was to erythromycin (100%) followed by streptomycin (22.2%) and tetracycline and chloramphenicol (16.7%). Of the 18 isolates, 5 (27.8%) were resistant to two or more antibiotics, and 1 isolate from chicken meat was resistant to eight antibiotics, including cephalosporins. Differentiation between all of the Salmonella isolates except between Salmonella Montevideo and Salmonella London was successfully performed with the automated rep-PCR system, indicating that it can be added to the toolbox for source tracking of foodborne pathogens associated with outbreaks.     

Thermal resistance of Salmonella serovars isolated from raw, frozen chicken nuggets/strips, nugget meat and pelleted broiler feed

Raw, frozen chicken nuggets/strips available at retail and prepared at home before consumption have been identified as a significant risk factor in contracting food-borne salmonellosis. Cases of salmonellosis from consumption of these products may be due, in part, to Salmonella strains originating in broiler feed. In this study the thermal resistances of Salmonella strains isolated from chicken nuggets and strips, chicken nugget/strip meat and broiler feed were determined to assess whether they exhibited enhanced thermal resistance. Thermal resistances (D- and z- values) of 7 cocktails (25 isolates, 4 serovars) were determined in commercially prepared irradiation-treated chicken nugget/strip meat blend, and heated in a constant temperature waterbath. The thermal resistances found were lower than those reported for similar strains in the literature. D-values ranged from 6.93 to 0.12 min at 55 and 62 degrees C respectively, with z-values from 4.10 to 5.17 degrees C. Two strains of S. Enteritidis separately isolated from pelleted feed and chicken nugget meat blend, with indistinguishable geno- and phenotypes, had lower (and probably identical) thermal resistances than the other isolates. Results indicated that the strains of Salmonella isolated from raw, frozen chicken nuggets/strips and pelleted broiler feed did not exhibit unusually high thermal resistance, and that normal heating (71 degrees C) prior to consumption should eliminate these organisms from chicken nuggets/strips.     

Phenotypic and genetic characterization of antimicrobial resistance in Salmonella serovars isolated from retail meats in Alberta, Canada

This study determined the prevalence of Salmonella serovars, antimicrobial resistance (AMR) and resistance genes in Salmonella isolated from retail meats purchased in Alberta, Canada. Samples were collected during one year period (May 2007–April 2008) on weekly basis from 19 census divisions in Alberta. A total of 564 samples including chicken (n = 206), turkey (n = 91), beef (n = 134) and pork (n = 133) were purchased. Salmonella were recovered from chicken (40%), turkey (27%) and pork (2%) samples and was not found in ground beef. A total of 21, 8, and 3 different serovars were recovered from chicken, turkey and pork meats, respectively. Salmonella Hadar was most common in chicken whereas S. Heidelberg was common in turkey meat. Overall 29% (32/110) of isolates were susceptible to tested antimicrobials and resistance to ciprofloxacin, amikacin and nalidixic acid was not found in any isolate. Multiresistance (≥2 antimicrobials) was found in 56% of isolates. Resistance to amoxicillin–clavulanic acid (AMC), ceftiofur (TIO), and ceftriaxone (CRO) was found in about 21% of chicken and 25% of turkey isolates. Resistance to either of tetracycline (TET), streptomycin (STR) or ampicillin (AMP) was unconditionally associated with S. Hadar but resistance to either of TET, AMP, AMC, TIO, CRO or cefoxitin was associated with S. Heidelberg. The strA/B (42% isolates), tet(A) (28% isolates), bla_CMY-2 (21% isolates) and bla_TEM (17% isolates) were the most common resistance genes found. The bla_CMY-2 and bla_TEM genes were unconditionally associated with S. Heidelberg; tet(A) and strA/B with S. Hadar and tet(B) gene with S. Kentucky. The strA/B genes were not associated with S. Heidelberg. Our data suggests that the prevalence of Salmonella serovars varied by the meat type and that AMR and resistance genes varied by the Salmonella serovars.     

市售鸡肉中沙门菌分离株多重耐药谱测定

为了解我国市售鸡肉中沙门菌多重耐药状况及耐药程度，对国家食源性疾病监测网从市售鸡肉中分离到的51株沙门菌进行耐药检测，并对多重耐药谱进行分析。利用NccLs(National Committee of Clinical Labaratory Standard)推荐的纸片法进行耐药检测，51株分离菌株全部对至少3种以上的抗生素耐药，属多重耐药株，耐5种抗生素的9株(17.6％)，耐6～9种抗生素的12株(23．5％)，耐10种以上抗生素的9株(17．6％)。51株沙门菌对万古霉素、红霉素、苯唑西林都具有耐药性(100％)，对其它抗生素的耐药情况是：萘啶酮酸(52.9％)、磺胺(35．3％)、链霉素(33．3％)、四环素(29.4％)、氨苄青霉素(23．5％)、羧苄西林(21.6％)、阿莫西林(19．6％)、吡拉西林(19．6％)、美唑西林(17．6％)、强力霉素(17．6％)、氯霉素(13．7)和头孢噻吩(9．8％)。有3株菌对庆大霉素耐药，有2株菌对丁胺卡那霉素和甲氧苄胺嘧啶耐药，有1株菌对复方新诺明耐药。分离出1株耐15种抗生素的鼠伤寒沙门菌，其耐药谱与超级耐药鼠伤寒沙门菌DTl04的耐药谱类似。从8省市市售鸡肉中分离的51株沙门菌均为多重耐药株，提示我国畜牧养殖业在使用抗生素方面存在严重问题，应加强对饲料添加剂使用的安全性管理，合理使用抗生素。     

Salmonella serotypes isolated from chicken meat in Albania.

A total of 31 salmonellae, belonging to four different serogroups and nine serotypes, were isolated from 30 out of 461 (6.5%) chicken meat samples, taken during a 3-year period, from 1996 to 1998. There were no significant differences among years in Salmonella positive samples, ranging from 5.1% to 8%. The most frequently encountered serotype was Salmonella enteritidis, isolated in 16 out of 30 Salmonella positive samples (53.3%), but its predomination was clearly evident only in 1996. The other isolated serotypes were S. senftenberg (three isolates), S. newport (two isolates), and S. abony, S. agona, S. banana, S. brancaster, S. infantis and S. oslo with only one isolate each. Four other Salmonella strains were not fully serotyped.     

Prevalence of antibiotic-resistant enterobacteriaceae isolated from chicken and pork meat purchased at the slaughterhouse and at retail in Bavaria, Germany

The purpose of this study was to investigate chicken and pork meat sampled at the slaughterhouse and at retail for differences in the presence of antibiotic resistant Gram-negative bacteria. For this aim, Escherichia coli (n=677), Enterobacter spp. (n=167), Citrobacter spp. (n=83), Serratia spp. (n=116), Klebsiella spp. (n=125), and Salmonella spp. (n=89) were isolated from 500 chicken and 500 pork samples purchased at the slaughterhouse and at retail (in the same amounts) in Germany. Salmonella were present in 17% of the chicken, and in 0.4% of the pork meat samples. There was a clear shift in the spectrum of coliforms from slaughterhouse to retail: Enterobacter, Citrobacter and Klebsiella were the most frequently detected coliforms (other than E. coli) from slaughterhouse samples, whereas the prevalence of Serratia spp. was up to eight times higher in retail samples. The prevalence of E. coli was higher in slaughterhouse samples, whereas the prevalence of other coliforms and Salmonella spp. was higher in retail samples. E. coli strains were often resistant to penicillins, streptomycin, spectinomycin, doxycycline and sulfamethoxazole/trimethoprim. Resistance rates of the other coliforms were generally low. Resistant and multi-resistant isolates were significantly more common in chicken meat. Compared to samples from the slaughterhouse, the prevalence of resistant bacteria tended to be higher in retail samples, probably due to good conditions for resistant bacteria on the matrix meat and/or due to secondary contamination with resistant strains. Therefore, stringent hygiene measures should be observed to reduce the risk of transmission of resistant bacteria from food to humans.     

Prevalence of Salmonella on retail broiler chicken meat carcasses in Colombia

A cross-sectional study was performed to estimate the prevalence of Salmonella on retail market chicken carcasses in Colombia. A total of 1,003 broiler chicken carcasses from 23 departments (one city per department) were collected via a stratified sampling method. Carcass rinses were tested for the presence of Salmonella by conventional culture methods. Salmonella strains were isolated from 27 % of the carcasses sampled. Logistic regression analysis was used to determine potential risk factors for Salmonella contamination associated with the chicken production system (conventional versus free-range), storage condition (chilled versus frozen), retail store type (supermarket, independent, and wet market), poultry company (integrated company versus nonintegrated company), and socioeconomic stratum. Chickens from a nonintegrated poultry company were associated with a significantly (P < 0.05) greater risk of Salmonella contamination (odds ratio, 2.0) than were chickens from an integrated company. Chilled chickens had a significantly (P < 0.05) higher risk of Salmonella contamination (odds ratio, 4.3) than did frozen chicken carcasses.     

Prevalence and antimicrobial resistance of Campylobacter isolated from retail raw chicken and beef meat, Tehran, Iran

Campylobacter spp. is a leading cause of human diarrhea. The common source of infection is contaminated food, particularly poultry. The veterinary use of antimicrobial drugs has been suggested to be largely responsible for resistance in human isolates of this zoonotic pathogen. From April to October 2004, 241 samples of chicken and beef meat for sale in retail outlets in Tehran (Iran) were analyzed for the presence of Campylobacter. Totally, 88 (36.5%) Campylobacter strains were isolated. Campylobacter was isolated from a significantly larger number of chicken (63%) than beef (10%) meat (P < 0.0001). Susceptibilities of 72 strains were determined for eight antimicrobial drugs using the disk diffusion assay. Resistance to nalidixic acid was the most common finding (75%), followed by resistance to ciprofloxacin (69.4%), tetracycline (45.8%), amoxicillin (11.1%), streptomycin (4.2%), chloramphenicol (2.8%) and gentamicin (1.4%). None of the isolates was resistant to erythromycin. Multidrug resistance was seen in 75% of the Campylobacter strains.     

Antimicrobial resistance types and genes in Salmonella enterica infantis isolates from retail raw chicken meat and broiler chickens on farms

Salmonella enterica subsp. enterica serotype Infantis isolates from retail raw chicken meat (n = 98) and broiler chickens on farms (n = 70) were examined for antimicrobial susceptibility and antimicrobial resistance genes. A total of 15 antimicrobial resistance types, 14 in meat and 10 in broiler isolates, were identified, and 9 of the 15 types were indistinguishable between meat and broiler isolates. Resistance to both oxytetracycline and dihydrostreptomycin accounted for 94.0% of the resistance types in meat and broiler isolates, and each type harbored aadA1 within 1.0 kb of class 1 integron and tetA. Of nalidixic acid resistance types, point mutations at 87Asp (GAC) to Tyr (TAC) in the quinolone resistance-determining region of gyrA was detected in 10 of 13 meat isolates and at 87Asp to Asn (AAC) in four of seven broiler isolates. These findings suggest that the antimicrobial resistance of Salmonella Infantis in retail chicken meat predominantly originates from broiler chickens.     

Mutations in gyrase and topoisomerase genes associated with fluoroquinolone resistance in Salmonella serovars from retail meats

Mutations in gyrase and topoisomerase genes (gyrA, gyrB, parC and parE) were examined among 30 multidrug-resistant (MDR) Salmonella isolates recovered from retail meats using PCR and DNA sequencing analysis. Six isolates had a single gyrA mutation (Ser83 → Phe or Ser83 → Tyr or Asp87 → Asn) with ciprofloxacin (Cip) minimum inhibitory concentrations (MICs) ranging from 0.125 to 0.5 μg/ml except 1 with 16 μg/ml. Three isolates had both a gyrA mutation (Ser83 → Tyr or Ser83 → Phe) and a parC mutation (Ser80 → Arg) (Cip MICs, 8 to 16 μg/ml). Fifteen isolates had both double mutations in gyrA (Ser83 → Phe and Asp87 → Gly or Asp87 → Asn) and a single mutation (Ser80 → Arg) in parC (Cip MICs, 8 to ≥ 16 μg/ml). Three had double gyrA mutations (Ser83 → Phe, Asp87 → Gly or Asp87 → Asn), one parC mutation (Ser80 → Arg), and 1 parE mutation (Lys428 → Gln or Gly442 → Ser) (Cip MICs, 8 to ≥ 16 μg/ml). One had double gyrA mutations (Ser83 → Phe, Asp87 → Gly or Asp87 → Asn), one parC mutation (Ser80 → Arg), and 2 parE mutations (Lys441 → Ile and Asp494 → Asn) (Cip MICs, 8 to ≥ 16 μg/ml). Isolates with single gyrA mutations were less resistant to quinolone and fluoroquinolones than those together with additional parC and/or parE mutations in Salmonella. Our findings confirmed the importance of point mutations in gyrase and topoisomerase in reduced susceptibility to quinolone and fluoroquinolones. Mutations in gyrA confer low-level quinolone and fluoroquinolone resistance, while additional gyrA mutation(s) together with parC and/or parE mutations increase the resistance to a high level.     

Antimicrobial-resistant Salmonella serovars isolated from imported foods

A total of 187 Salmonella isolates representing 82 serotypes recovered from 4072 imported foods in the year 2000 by the U.S. Food and Drug Administration field laboratories were tested for their susceptibility to 17 antimicrobials of human and veterinary importance. Fifteen (8%) isolates were resistant to at least one antimicrobial, and five (2.7%) were resistant to three or more antimicrobials. Most of the isolates (n=9) exhibited resistance to tetracycline. Four isolates from catfish or tilapia from Taiwan or Thailand also demonstrated resistance to nalidixic acid. These nalidixic acid-resistant Salmonella isolates possessed a point mutation at the Ser83 or Asp87 position in DNA gryase, resulting in amino acid substitutions to phenylalanine, tyrosine, or asparagine. One Salmonella Derby isolated from frozen anchovies imported from Cambodia was resistant to six antimicrobials including ampicillin, amoxicillin/clavulanic acid, chloramphenicol, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. Of seven isolates displaying resistance to sulfonamides, only one S. Derby and one Salmonella Agona contained class 1 integrons that were further shown to possess the aadA and pse-1 genes conferring resistance to streptomycin and ampicillin, respectively. This study indicates that antimicrobial-resistant Salmonella are present in imported foods, primarily of seafood origin, and stresses the need for continued surveillance of foodborne zoonotic bacterial pathogens from imported foods entering the United States.     

Antibiotic resistance of Salmonella isolated from hog, beef, and chicken carcass samples from provincially inspected abattoirs in Ontario

The emergence of antimicrobial-resistant Salmonella organisms, especially Salmonella Typhimurium DT104, has been reported in many countries, including the United States and Canada. The purposes of this study were to determine the antimicrobial resistance patterns of Salmonella isolated from hog, beef, and chicken carcasses from provincially inspected abattoirs in Ontario and to determine the agreement between the agar dilution method and the microbroth dilution method for measurement of antimicrobial resistance of the isolates. Antimicrobial resistance of Salmonella isolates from hogs (n = 71), beef (n = 24), and chicken (n = 295) to amikacin, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, streptomycin, sulfamethoxazole, and tetracycline was determined using the two methods. None of the 390 isolates were resistant to ciprofloxacin at levels of 0.125 microg/ml. All chicken and hog isolates were sensitive to amikacin, whereas all beef isolates were sensitive to both amikacin and gentamicin. Multiple antimicrobial resistance (resistance to more than one antimicrobial) was found in 29% of bovine isolates and 42% of porcine isolates using both methods for testing and in 42% by the agar dilution and 33% by the microbroth dilution methods in the chicken isolates. Overall, there was good agreement between the two test methods for resistance to most of the antimicrobials, with disagreement found in the results in 1.3% of the isolates for ampicillin and sulfamethoxazole, 8.2% for streptomycin, 5.6% for cephalothin, and 1.0% of the isolates for tetracycline. The lack of agreement between the two test methods was found mostly among the chicken isolates.     

Antimicrobial resistance in Campylobacter, Salmonella, and Escherichia coli isolated from retail grain-fed veal meat from Southern Ontario, Canada

This study estimated the prevalence of Salmonella, Campylobacter, and Escherichia coli isolates in fresh retail grain-fed veal obtained in Ontario, Canada. The prevalence and antimicrobial resistance patterns were examined for points of public health significance. Veal samples (n = 528) were collected from February 2003 through May 2004. Twenty-one Salmonella isolates were recovered from 18 (4%) of 438 samples and underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was found in 6 (29%) of 21 Salmonella isolates; 5 (24%) of 21 isolates were resistant to five or more antimicrobials. No resistance to antimicrobials of very high human health importance was observed. Ampicillin-chloramphenicolstreptomycin-sulfamethoxazole-tetracycline resistance was found in 5 (3%) of 21 Salmonella isolates. Campylobacter isolates were recovered from 5 (1%) of 438 samples; 6 isolates underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was documented in 3 (50%) of 6 Campylobacter isolates. No Campylobacter isolates were resistant to five or more antimicrobials or category I antimicrobials. E. coli isolates were recovered from 387 (88%) of 438 samples; 1,258 isolates underwent antimicrobial susceptibility testing. Resistance to one or more antimicrobials was found in 678 (54%) of 1,258 E. coli isolates; 128 (10%) of 1,258 were resistant to five or more antimicrobials. Five (0.4%) and 7 (0.6%) of 1,258 E. coli isolates were resistant to ceftiofur and ceftriaxone, respectively, while 34 (3%) of 1,258 were resistant to nalidixic acid. Ciprofloxacin resistance was not detected. There were 101 different resistance patterns observed among E. coli isolates; resistance to tetracycline alone (12.7%, 161 of 1,258) was most frequently observed. This study provides baseline prevalence and antimicrobial resistance data and highlights potential public health concerns.     

The antibiotic resistance characteristics of non-typhoidal Salmonella enterica isolated from food-producing animals, retail meat and humans in South East Asia

Antimicrobial resistance is a global problem. It is most prevalent in developing countries where infectious diseases remain common, the use of antibiotics in humans and animals is widespread, and the replacement of older antibiotics with new generation antibiotics is not easy due to the high cost. Information on antibiotic resistance phenotypes and genotypes of Salmonella spp. in food animals and humans in different countries and geographic regions is necessary to combat the spread of resistance. This will improve the understanding of antibiotic resistance epidemiology, tracing of new emerging pathogens, assisting in disease treatment, and enhancing prudent use of antibiotics. However, the extent of antibiotic resistance in food-borne pathogens and humans in many developing countries remains unknown. The goal of this review is to discuss the current state of antibiotic resistance of non-typhoid Salmonella spp. in food-producing animals, retail meat and humans from South East Asia. It is focused on resistance characteristics of traditional and "critically important" antibiotics in this region, and the emergence of multidrug resistant strains and genetic elements that contribute to the development of multidrug resistance, including integrons and the Salmonella Genomic Island (SGI).     

Genotypes, serotypes, and antibiotic resistance profiles of Salmonella isolated from commercial North Carolina turkey farms

This study was designed to determine the serotypes, genotypes, and antibiotic resistance (AbR) patterns of 42 Salmonella isolates recovered from either fecal or litter samples of 12 commercial turkey farms across two seasons (summer and winter) and two ages (3 and 19 weeks). Isolates were serotyped on the basis of the Kauffmann-White scheme. Genotyping was done by restriction digestion of cDNA (XbaI) and subsequent pulsed-field gel electrophoresis (PFGE). The AbR was determined with Sensititre susceptibility plates. Serovar Kentucky was the most prevalent serotype (26%), followed by Senftenberg (19%), Muenster (17%), Mbandaka (10%), Javiana (7%), Hadar (5%), Heidelberg (5%), 8,(20):nonmotile (5%), Agona (2%), Infantis (2%), and 4,12:r:-(2%). Serovars Kentucky, Heidelberg, Hadar, and 8,(20):nonmotile were isolated only from the 19-week-old bird samples, whereas Senftenberg and Muenster were isolated only from the young birds (3 weeks old). Isolates within any one serotype showed minor PFGE banding pattern differences, but dendogram analysis indicated that sequence variability between serotypes was more significant than within serotypes. Isolates were resistant to tetracycline (86%), sulfisoxazole (71%), streptomycin (64%), gentamicin (41%), ampicillin (36%), kanamycin (26%), sulfamethoxazole-trimethoprim (7%), nalidixic acid (5%), cefoxitin (2%), and ceftiofur (2%). One isolate (Muenster) was resistant to nine antibiotics (2%), and the others were resistant to six (7%), five (12%), four (10%), three (21%), two (24%), and one (10%) antibiotic. Only two isolates (5%) were susceptible to all antibiotics tested. The AbR patterns were affected by age; on average, strains recovered from young birds were resistant to more than four drugs compared with fewer than three in older birds (P < 0.05). This study showed that Salmonella enterica subsp. enterica serotypes, genotypes and AbR patterns were affected by bird age but not by season or farm.     

Salmonella in raw meat and by-products from pork and beef

After campylobacteriosis, salmonellosis is the second main cause of human bacterial enteritis in Germany. Salmonella is known to colonize the gastrointestinal tract of animals without producing any clinical signs. Therefore, carcasses can become contaminated with Salmonella at the time of slaughter. During an 11-month period, a total of 4,170 raw meat samples and by-products from beef and pork, obtained from seven different slaughterhouses in Southern Germany, were screened by the VIDAS system for Salmonella in this study. Positive results were confirmed by isolation of the pathogen on selective agars. The overall percentage of Salmonella-positive samples was 1.4% by the VIDAS system and 0.7% by culture confirmation. Salmonella was detected in 1.8% of pork samples by the VIDAS system and in 1.1% of samples by culture. In beef samples the presence of Salmonella was verified in 0.6% of samples by the VIDAS system and in 0.1% by culture on selective agars. The highest contamination rates were found in porcine and bovine tongue samples. Salmonella was detected in porcine samples throughout the year, except in samples collected in July, and a slight increase was observed in the colder months. The VIDAS system was shown to be an efficient screening method for the detection of Salmonella, with the advantage of a reduced analysis time.     

Salmonella enterica serotypes isolated from imported frozen chicken meat in the Canary islands

To determine the prevalence of Salmonella enterica serotypes in imported frozen chicken meat, 406 samples (whole chicken, legs, and breast meat) were analyzed for Salmonella according to ISO6579 rules, serotypes were assigned, and phage typing was conducted for Salmonella serotypes Enteritidis, Typhimurium, and Heidelberg. The overall frequency of Salmonella isolation was 16.5%. By country of origin, the highest percentage of cases was found among the samples from France followed by samples from Brazil. The differences between legs and breast meat were significant. The most frequently isolated serotype of Salmonella was Enteritidis, followed by Salmonella Heidelberg, Salmonella Typhimurium, and Salmonella Virchow. By country of origin, we identified a large percentage of serotype Salmonella Enteritidis in the samples imported from Brazil. There was a greater diversity of serotypes isolated from the French samples, and Salmonella Enteritidis was not the dominant strain. In the samples from the United States, the only serotype isolated was Salmonella Kentucky, although a smaller number of samples was analyzed. The Salmonella Enteritidis phage type that prevailed in both France and Brazil was 4. Phage types 204c and 204 were identified for Salmonella Typhimurium, and phage types 8, 31, and 37 were identified for Salmonella Virchow.     

Genetic characterization of antimicrobial resistance in Salmonella enterica serovars isolated from dairy cattle in Wisconsin

Salmonella enterica is a pathogen of humans and animals, and is one of the most frequent causes of bacterial foodborne illness worldwide. People consuming contaminated foods or working with infected livestock have the potential to become infected with Salmonella and may require antimicrobial therapy. Antimicrobial resistance in Salmonella has become a problem worldwide due in part to the inappropriate use of antimicrobial agents in human and veterinary medicine. In this study, forty-five Salmonella isolates from diagnostic fecal samples of Wisconsin dairy cattle were serotyped and characterized by antimicrobial susceptibility testing using agar disk diffusion, antimicrobial resistance gene detection by PCR, plasmid analysis and conjugation studies. The predominant serovars detected were Kentucky, Newport, Typhimurium, Cerro, Dublin and Montevideo. Over half (51%) of all isolates were resistant to at least one antimicrobial agent, and 29% were resistant to 8–10 drugs. The most commonly observed resistance phenotypes were to streptomycin (44%), tetracycline (42%), sulfisoxazole (40%), chloramphenicol (35%), ampicillin (33%), and cefoxitin (33%). When resistance was detected phenotypically, a corresponding resistance gene was detected 86.2% of the time. Plasmids ranging in size from < 8 to 165 kb were detected in 45% of the isolates. A greater understanding of the factors associated with antimicrobial resistance in Salmonella should provide insights into the factors that contribute to the development of resistant pathogens during dairy production, which in turn can lead to strategies to minimize the spread of antimicrobial resistant Salmonella in the food supply.