Bayleyegn Z. Molla

Methicillin-resistant Staphylococcus aureus in pigs and farm workers on conventional and antibiotic-free swine farms in the USA.

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.

Epidemiology and Genotypic Characteristics of Methicillin-Resistant Staphylococcus aureus Strains of Porcine Origin

ABSTRACT 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.

Salmonella enterica in Commercial Swine Feed and Subsequent Isolation of Phenotypically and Genotypically Related Strains from Fecal Samples

ABSTRACT 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.

Prevalence of Porcine Noroviruses, Molecular Characterization of Emerging Porcine Sapoviruses from Finisher Swine in the United States, and Unified Classification Scheme for Sapoviruses

ABSTRACT Noroviruses (NoVs) and sapoviruses (SaVs) are important human pathogens. Although the involvement of porcine NoVs in disease in pigs is unclear, they are genetically and antigenically closely related to human NoVs. Human NoV-like strains have been detected in pigs, raising public health concerns of potential interspecies transmission. Porcine SaVs are highly diverse and emerging in swine populations. Recently, at least three new genogroups of porcine SaVs have been proposed. In this study, we tested 413 pooled fecal samples collected from apparently healthy finisher pigs in North Carolina swine farms during 2009. Reverse transcription (RT)-PCR coupled hybridization assays were performed to detect known porcine NoVs. The overall prevalence of porcine NoVs determined was 18.9% based on this method. Samples were then tested by RT-PCR targeting the 5′ end of the capsid region for genogroup II (GII) NoVs, a group which includes human NoVs, followed by sequence analysis. All NoVs identified belonged to typical porcine NoV genotypes, and no human NoV-like strains were detected in specimens from these pigs. Porcine NoV-negative samples (n = 335) were subsequently screened using universal calicivirus primers, and 17 SaV strains were confirmed by sequencing. Based on the partial RNA-dependent RNA polymerase (RdRp) region, they clustered with GIII, GVII, and GVIII and with currently unclassified SaVs. According to analysis of the complete capsid sequences, 7 representative strains clustered with GVII, GVIII, and GIX? SaVs. We tentatively classified SaVs into 14 genogroups based on the complete capsid protein VP1. In summary, porcine NoVs and highly divergent SaVs were present in North Carolina finisher pigs.

Tracking Salmonella Contamination in Various Watersheds and Phenotypic and Genotypic Diversity

Salmonella enterica is an important foodborne pathogen, and contamination of surface and ground water that may result from various human activities, such as animal production and urbanization, may contribute to the public health burden. The aims of this study was to determine the sources of Salmonella contamination in four different types of watersheds and to assess the relative contribution of multidrug-resistant strains. Eighty-six water samples collected from four different watershed systems, including those impacted by swine production (n = 12), residential/industrial (n = 34), crop agriculture (n = 12), and forestry (n = 28), were cultured for Salmonella and further characterized by serotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis genotyping. Salmonella prevalence was high in all four watersheds: residential/industrial area (58.8%), forestry (57.1%), crop agriculture (50%), and swine production (41.7%). Majority of the Salmonella isolates (87.1%) were pansusceptible. Multidrug resistance up to eight antimicrobials (R-type: AmStTeAxChCeKmGm) was detected in water samples that originated from swine production systems only. Serovars identified included Anatum, Gaminara, and Inverness (18.3% each) and Muenchen and Newport (8.7% each), Bredeny (7.6%), and Montevideo (6.8%). Pulsed-field gel electrophoresis analysis indicated genotypic relatedness among Salmonella recovered from residential/industrial and forestry-associated watersheds (genotypic cluster types A, C, D, E, F, G, H, and J), sites with relatively close geographic proximity. Swine-production-associated isolates were distinctly different from the others (genotypic cluster types B and I), corroborating the phenotypic findings. Overall, the findings suggest that all the various watersheds, including natural forest, remain important contributors of Salmonella contamination. While swine-production-associated water samples were not found to have a disproportionately high prevalence, it was the most important reservoir of multidrug-resistant strains.

In-Feed Use of Heavy Metal Micronutrients in U.S. Swine Production Systems and Its Role in Persistence of Multidrug-Resistant Salmonellae

ABSTRACT The study aimed to characterize the role of heavy metal micronutrients in swine feed in emergence of heavy-metal-tolerant and multidrug-resistant Salmonella organisms. We conducted a longitudinal study in 36 swine barns over a 2-year period. The feed and fecal levels of Cu2+ and Zn2+ were measured. Salmonella was isolated at early and late finishing. MICs of copper sulfate and zinc chloride were measured using agar dilution. Antimicrobial susceptibility was tested using the Kirby-Bauer method, and 283 isolates were serotyped. We amplified pcoA and czcD genes that encode Cu2+ and Zn2+ tolerance, respectively. Of the 283 isolates, 113 (48%) showed Cu2+ tolerance at 24 mM and 164 (58%) showed Zn2+ tolerance at 8 mM. In multivariate analysis, serotype and source of isolates were significantly associated with Cu2+ tolerance (P < 0.001). Fecal isolates were more likely to be Cu2+ tolerant than those of feed origin (odds ratio [OR], 27.0; 95% confidence interval [CI], 2.8 to 250; P = 0.0042) or environmental origin (OR, 5.8), implying the significance of gastrointestinal selective pressure. Salmonella enterica serotypes Typhimurium and Heidelberg, highly significant for public health, had higher odds of having >20 mM MICs of Cu2+ than did “other” serotypes. More than 60% of Salmonella isolates with resistance type (R-type) AmStTeKm (32 of 53) carried pcoA; only 5% with R-type AmClStSuTe carried this gene. czcD gene carriage was significantly associated with a higher Zn2+ MIC (P < 0.05). The odds of having a high Zn2+ MIC (≥8 mM) were 14.66 times higher in isolates with R-type AmClStSuTe than in those with R-type AmStTeKm (P < 0.05). The findings demonstrate strong association between heavy metal tolerance and antimicrobial resistance, particularly among Salmonella serotypes important in public health.

Characterization and prevalence of a new porcine Calicivirus in Swine, United States.

Real-time reverse transcription PCR revealed that new St-Valerien–like porcine caliciviruses are prevalent (2.6%–80%; 23.8% overall) in finisher pigs in North Carolina. One strain, NC-WGP93C, shares 89.3%–89.7% genomic nucleotide identity with Canadian strains. Whether these viruses cause disease in pigs or humans or are of food safety concern requires further investigation.

Association of multicellular behaviour and drug resistance in Salmonella enterica serovars isolated from animals and humans in Ethiopia.

To determine the association between multicellular behaviour, integron status and antibiotic resistance among 87 Ethiopian Salmonella enterica isolates of animal and human origin.

Distribution, quantitative load and characterization of Salmonella associated with swine farms in upper-northern Thailand.

This study was conducted to analyze the prevalence and quantitative loads of Salmonella spp. on pig farms in Chiang Mai, Lamphun, Thailand to assess loading levels before slaughtering. The serotype diversity, antimicrobial-resistance pattern and pulse-field type of Salmonella spp. were also characterized to assess the dynamic propagation of the pathogen. The Salmonella-positive prevalence was 246/805 (30.56%), and the quantitative loads varied from 1.48~4.04 Log10MPN/g, with a mean ± standard deviation of 2.11 ± 0.57. AMP/S/TE (ampicillin/streptomycin/tetracycline) was the highest frequency antimicrobial resistance pattern found in this study. In addition, Salmonella Rissen was the primary serotype in this region. PFGE results indicated the occurrence of infection by cross contamination among pig farms. Our study showed that pork is easily contaminated with this pathogen. Farm control programs must be based on strict biosecurity and hygienic measures, which could further reduce the contamination pressure at slaughterhouses or retail shops.