Molecular Epidemiology of Salmonella enterica and Subtyping Using Phenotypic and Genotypic Approaches

The aim of this study was to evaluate the discriminatory power of two phenotyping and three genotyping methods commonly used to subtype Salmonella in swine and other hosts. We found AFLP and PFGE to have the highest and comparable discriminatory power to each other. Among the 202 isolates analyzed in this study, using AFLP, 16 cluster types of S. Typhimurium were identified. Vertical spread in the production chain, from nursery to finishing farms and vertical as well as horizontal spread among finishing farms appeared to be important means of Salmonella serovar Typhimurium dissemination in swine units

Antimicrobial resistance profile and genetic diversity of Salmonella enterica serotypes Typhimurium and Muenchen

The aim of this study was to compare the antimicrobial resistance pattern and genetic diversity of Salmonella enterica serotypes Typhimurium and Muenchen from human and swine. Previously, we reported two predominant multi-drug resistant (MDR) patterns common among Salmonella isolates from swine. In this study we report serovar Muenchen, to have MDR pattern similar to Typhimurium and with expanded spectrum in swine (AmCmStSuTeKm). This pattern is more frequent among isolates from swine (with 46% frequency) while most of isolates from human were pansusceptible (only one isolate with MDR to 10 antimicrobials). Genotyping using PFGE revealed swine and human isolates clustered separately from each other. We identified class-I integrons among nine S. Muenchen isolates from swine and single isolate from human using polymerase chain reaction (PCR). We propose that interserovar exchange of resistance genes might be responsible for emergence of MDR strains among serovars not previously showing MDR. Further molecular investigations are underway

The role of truck wash practices in dissemination of Salmonella and Campylobacter in commercial swine production

This study investigated the sources of two foodborne pathogens, Salmonella and Campylobacter in a commercial swine production system. Pathogens were characterized using conventional culture and isolation techniques and antibiograms

Evaluation of phenotypic and genotypic approaches as predictors of Salmonella strains of clinical and non-clinical origin

This study investigated the possible phenotypic and genotypic similarities and differences between Salmonella isolates obtained from swine with clinical salmonellosis to isolates obtained from swine showing no clinical disease. Phenotypic analysis was done by antimicrobial resistance profiling and amplified fragment length polymorphism (AFLP) fingerprinting was employed for genotypic analysis

Developing real-time PCR assay for detection of multi-drug Salmonella strains in pigs

The main objective of this study was to develop a rapid, sensitive and accurate real-time detection assay for multi-drug resistant (MDR) Salmonella strains isolated from pigs. Initially, standardized procedures for use with real-time PCR using SYBR green were developed to evaluate selected primers, detection limitations using two predominant strains: S. typhimurium phage types DT104 and DT193

Differential translocation of Salmonella serovars to mesenteric lymph nodes of pigs

In observational studies of growing pigs in North Carolina, we cultured paired samples of mesenteric lymph nodes (MLN) and cecal contents for Salmonella using standard methods for selective enrichment and plating. Apparent Salmonella prevalence was higher among cecal (39.2%) than MLN (20.5%) samples from the same animals. Salmonella Typhimurium var. Copenhagen (STC) and S. Derby comprised 84% of all isolates at slaughter. For these two serovars we found an association between serovar and sample type. The odds of isolating STC from MLN rather than cecum were 5.7 (95%CI 3.0 to 10.7) times higher than the odds for S. Derby. The odds for isolating STC from MLN versus cecum were 58 times higher for groups where STC had been isolated from the pigs on farm than for groups where it was had not been detected on farm. These findings suggest biological differences among common group B Salmonella serovars in the pig

Prevalence and antimicrobial resistance of Salmonella isolated from conventional and antimicrobial-free (ABF) swine herds in North Carolina

The main objective of this stdy was to compare prevalence and antimicrobial resistance of Salmonella isolated from swine reared in antimicrobial-free (ABF) and conventional production systems in North Carolina

Three-Year Trend in Antimicrobial Resistance and Genotypes among Salmonella in Swine and Humans

The aim of this study was to determine antimicrobial resistance among Salmonella isolated from swine and humans in North Carolina, compare genotypes among isolates from humans originated from pig-producing areas and characterize important genes. Resistance to 9 and 11 of the 12 antimicrobial agents tested was detected among isolates from swine and humans respectively. Frequency of resistance to tetracycline and b-lactams was significantly higher among isolates from swine than humans (p \u3c0.05). Two common multi-drug resistance (MDR) patterns were found among isolates from apparently healthy swine: AmKmStSuTe and AmCmStSuTe. However, the former MDR pattern was rare among clinical isolates. Genotyping revealed that two predominant genotypes, one composed of clinical isolates and the other non-clinical were noticed. Further characterization using Salmonella plasmid virulence; spvA gene also revealed that this gene is absent among the most common MDR pattern, AmKmStSuTe, in swine

Comparison of multidrug resistant Salmonella between intensively - and extensively-reared antimicrobial - free (ABF) swine herds

This cross-sectional study was conducted to determine the prevalence and antimicrobial resistance of Salmonella species in swine reared in the intensive (indoor) and extensive (outdoor) ABF production systems at farm and slaughter in North Carolina, U.S.A. We sampled a total of 279 pigs at farm (Extensive 107; Intensive 172) and collected 274 carcass swabs (Extensive 124; Intensive 150) at slaughter. Salmonella species were tested for their susceptibility against 12 antimicrobial agents using the Kirby-Bauer disk diffusion method. Serogrouping was done using polyvalent and group specific antisera. A total of 400 salmonellae were isolated in this study with a significantly higher Salmonella prevalence from the Intensive (30%) than the extensive farms (0.9%) (P \u3c 0.001 ). At slaughter, significantly higher Salmonella was isolated at the pre and post-evisceration stages from extensively (29 % pre-evisceration and 33.3 % post-evisceration) than the intensively (2 % pre-ev1sceration and 6 % post-evisceration) reared swine (P \u3c 0.001 ). The isolates were clustered in six serogroups including B, C, E1, E4, G and R. Highest frequency of antimicrobial resistance was observed against tetracycline (78.5%) and streptomycin (31 .5%). A total of 13 antimicrobial resistance patterns were observed including the pentaresistant strains with ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline resistance pattern observed only among isolates from the intensive farms (n=28) and all belonged to serogroup B. This study shows that multidrug resistant Salmonella are prevalent in ABF production systems despite the absence of antimicrobial selection pressure

Salmonella prevalence in pigs reared on farms with and without antimicrobials

A convenience sample of farms using antimicrobials (antimicrobial-using, AMU) post-weaning for therapy and/or growth promotion (n=21) were contrasted to a convenience sample of farms not using antimicrobials post-weaning (antimicrobial-free, AMF, n=21) distributed across three US geographic areas