Much uncertainty remains about the origin and public health implications of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA). This study aimed to investigate the occurrence and prevalence of MRSA in general and LA-MRSA in particular in pigs and farm workers in five states. We collected nasal swabs from pigs and farm workers at 45 swine herds (21 antibiotic-free herds; 24 conventional herds) in Illinois, Iowa, Minnesota, North Carolina and Ohio. MRSA was isolated from 50 of 1085 pigs (4.6%) and 31 of 148 (20.9%) of farm workers. MRSA-positive pigs and people were clustered in four conventional swine farms in Iowa and Illinois. Based on genotyping, spa type t034, a common livestock associated variant, was predominant among both human and swine isolates. These results confirm the presence of LA-MRSA in pigs and swine farm workers in the USA, but the prevalence found is relatively low compared with European studies.

The main goal of this study was to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA), particularly livestock-associated MRSA (LA-MRSA) in pigs and pork. The genotypic relatedness of isolates on the farm, at slaughter, and at the retail level was assessed. Paired nasal and perianal swab samples were collected from 10 cohorts of market-age pigs (24 pigs per cohort) and carcasses at slaughterhouse, and pork samples were collected at retail. Staphylococci were isolated using selective enrichment method. Isolates were tested for antimicrobial resistance by broth microdilution. Duplex PCR was used to confirm MRSA using species-specific (nuc) and methicillin resistance (mecA) genes. The clonal relatedness of isolates was determined using pulsed-field gel electrophoresis (PFGE), Staphylococcus protein A (spa) typing, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec element (SCCmec) typing. MRSA was detected in 5 of the 10 cohorts (50%), with the prevalence ranging from 0% to 12.5% per cohort. Of all the pigs sampled on the farm before they went to market, 3% (7/240) were MRSA positive. A higher prevalence of MRSA was detected at holding pens at the slaughterhouse (11% [27/240]). MRSA was also detected in 2% (4/235) of the carcasses and 4% (5/135) of the retail pork. While the isolates appear predominantly to be highly clonal, PFGE had a relatively higher discriminatory power (discriminatory index [DI] ‫؍‬ 0.624). Four genotypic clusters were identified by PFGE; of the four clusters, clonal type B was predominant across the farm-to-retail continuum. MLST findings revealed that sequence type 5 (ST5) was the most predominant subtype (32/50). The livestock-associated MRSA (clonal complex 398 [CC398] or sequence type 398 [ST398]) was the second common type (12/50) and was detected at all stages from farm to retail. Nine of the 50 (18%) MRSA isolates belonged to spa type 539/t034 that were of ST398 based on MLST. The results of this study confirm that MRSA, including LA-MRSA, is common in herds of swine in Ohio and hereby shown to persist in the farm to processing and retail continuum.

CTX-M extended-spectrum β-lactamases are enzymes produced by bacteria that are capable of inhibiting the antimicrobial effects of cephalosporin drugs. Recently, the first domestically acquired Salmonella in the United States expressing bla(CTX-M) was reported. This is a concern because expanded-spectrum cephalosporins are the treatment of choice for invasive Gram-negative infections, including salmonellosis in children. Because Salmonella transmission is primarily foodborne, there is also concern that resistant enteric bacteria from livestock can be transferred through the food supply chain to consumers. bla(CTX-M) has not been previously identified in bacterial isolates from food animal populations in the United States. We report the recovery of CTX-M-type extended-spectrum β-lactamases from fecal Escherichia coli of sick and healthy dairy cattle in Ohio. Four individual fecal samples yielded E. coli isolates representing three clonal strains that carried bla(CTX-M) on transferable plasmids. Two distinguishable plasmids were identified, each encoding bla(CTX-M-1) or bla(CTX-M-79). Transferrable bla(CTX-M) genes in bovine E. coli have the potential to serve as a reservoir of resistance for pathogens and may represent a public health concern.

ABSTRACTblaCTX-Mbeta-lactamases confer resistance to critically important cephalosporin drugs. Recovered from both hospital- and community-acquired infections,blaCTX-Mwas first reported in U.S. livestock in 2010. It has been hypothesized that veterinary use of cephalosporins in livestock populations may lead to the dissemination of beta-lactamase-encoding genes. Therefore, our objectives were to estimate the frequency and distribution of coliform bacteria harboringblaCTX-Min the fecal flora of Ohio dairy cattle populations. In addition, we characterized the CTX-M alleles carried by the isolates, their plasmidic contexts, and the genetic diversity of the bacterial isolates themselves. We also evaluated the association between ceftiofur use and the likelihood of recovering cephalosporinase-producing bacteria. Thirty fresh fecal samples and owner-reported ceftiofur use data were collected from each of 25 Ohio dairy farms. Fecal samples (n= 747) yielded 70blaCTX-M-positiveEscherichia coliisolates from 5/25 herds, 715blaCMY-2E. coliisolates from 25/25 herds, and 274Salmonellaspp. from 20/25 herds. The within-herd prevalence amongblaCTX-M-positive herds ranged from 3.3 to 100% of samples. Multiple pulsed-field gel electrophoresis (PFGE) patterns, plasmid replicon types, and CTX-M genes were detected. Plasmids with CTX-M-1, -15, and -14 alleles were clonal by restriction fragment length polymorphism (RFLP) within herds, and specific plasmid incompatibility group markers were consistently associated with eachblaCTX-Mallele. PFGE of total bacterial DNA showed similar within-herd clustering, with the exception of one herd, which revealed at least 6 different PFGE signatures. We were unable to detect an association between owner-reported ceftiofur use and the probability of recoveringE. colicarryingblaCTX-MorblaCMY-2.

The purpose of this study was to determine the occurrence and genotypic relatedness of Salmonella enterica isolates recovered from feed and fecal samples in commercial swine production units. Of 275 feed samples, Salmonella was detected in 10 feed samples that originated from 8 of 36 (22.2%) barns, with a prevalence of 3.6% (10/275 samples). In fecal samples, a prevalence of 17.2% was found at the early finishing stage (1,180/6,880 samples), with a significant reduction in prevalence (7.4%) when pigs reached market age (392/5,321 samples). Of the 280 Salmonella isolates systematically selected for further characterization, 50% of the feed isolates and 55.3% of the isolates of fecal origin showed similar phenotypes based on antimicrobial resistance patterns and serogrouping. About 44% of the isolates were multidrug resistant. Pulsed-field gel electrophoresis (PFGE) genotyping grouped the 46 representative isolates into five genotypic clusters, of which four of the clusters consisted of genotypically related isolates recovered from feed and fecal samples. The occurrence of genotypically related and, in some cases, clonal strains, including multidrug-resistant isolates in commercially processed feed and fecal samples, suggests the high significance of commercial feed as a potential vehicle of Salmonella transmission.