The objective of this study was to determine the prevalence and molecular typing of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in food-producing animals and retail meat in Fargo, North Dakota. A two-step enrichment followed by culture methods were used to isolate S. aureus from 167 nasal swabs from animals, 145 samples of retail raw meat, and 46 samples of deli meat. Positive isolates were subjected to multiplex polymerase chain reaction in order to identify the genes 16S rRNA, mecA, and Panton-Valentine Leukocidin. Pulsed-field gel electrophoresis and multilocus sequence typing were used for molecular typing of S. aureus strains. Antimicrobial susceptibility testing was carried out using the broth microdilution method. The overall prevalence of S. aureus was 37.2% (n=133), with 34.7% (n=58) of the animals positive for the organism, and the highest prevalence observed in pigs (50.0%) and sheep (40.6%) (p<0.05); 47.6% (n=69) of raw meat samples were positive, with the highest prevalence in chicken (67.6%) and pork (49.3%) (p<0.05); and 13.0% (n=6) of deli meat was positive. Five pork samples (7.0%) were positive for MRSA, of which three were ST398 and two were ST5. All exhibited penicillin resistance and four were multidrug resistant (MDR). The Panton-Valentine Leukocidin gene was not detected in any sample by multiplex polymerase chain reaction. The most common clones in sheep were ST398 and ST133, in pigs and pork both ST398 and ST9, and in chicken ST5. Most susceptible S. aureus strains were ST5 isolated from chicken. The MDR isolates were found in pigs, pork, and sheep. The presence of MRSA, MDR, and the subtype ST398 in the meat production chain and the genetic similarity between strains of porcine origin (meat and animals) suggest the possible contamination of meat during slaughtering and its potential transmission to humans.

Different clones of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus have been found in humans as well as in animals and retail meat. However, more information about the genetic characteristics and similarities between strains is needed. The aim of this study was to identify and characterize Staphylococcus aureus from humans, and to compare their characteristics with isolates of animal origin. A total of 550 nasal swabs were taken from healthy humans, and S. aureus was isolated and identified. Positive S. aureus isolates were subjected to molecular typing and susceptibility testing. In addition, 108 MRSA isolates recovered from clinical patients in the state of North Dakota and 133 S. aureus isolates from animals and meat previously analyzed were included. The nasal carriage of S. aureus in healthy people was 7.6% and, in general, clones were genetically diverse. None of the S. aureus strains obtained from healthy people were mecA- or PVL-positive. A total of 105 (97.2%) MRSA isolates from clinical cases harbored the mecA gene and 11 (10.2%) isolated from blood stream infections harbored the PVL gene. The most common resistance profile among S. aureus from healthy people was penicillin, and from clinical cases were erythromycin-penicillin-ciprofloxacin. The rate of multidrug resistance (MDR) was 70% in humans. Most of the S. aureus harboring mecA and PVL genes were identified as ST5 and ST8, and exhibited MDR. However, S. aureus isolates of animal origin used for comparison exhibited a lower rate of MDR. The most common resistance profiles in isolates of animal origin were penicillin-tetracycline and penicillin-tetracycline-erythromycin, in animals and raw meat, respectively. The ST5 was also found in animals and meat, with ST9 and ST398 being the major clones. The genetic similarity between clones from humans and meat suggests the risk of spread of S. aureus in the food chain.

BackgroundSalmonella species are recognized worldwide as a significant cause of human and animal disease. In this study the molecular profiles and characteristics of Salmonella enterica Senftenberg isolated from human cases of illness and those recovered from healthy or diagnostic cases in animals were assessed. Included in the study was a comparison with our own sequenced strain of S. Senfteberg recovered from production turkeys in North Dakota. Isolates examined in this study were subjected to antimicrobial susceptibility profiling using the National Antimicrobial Resistance Monitoring System (NARMS) panel which tested susceptibility to 15 different antimicrobial agents. The molecular profiles of all isolates were determined using Pulsed Field Gel Electrophoresis (PFGE) and the sequence types of the strains were obtained using Multi-Locus Sequence Type (MLST) analysis based on amplification and sequence interrogation of seven housekeeping genes (aroC, dnaN, hemD, hisD, purE, sucA, and thrA). PFGE data was input into BioNumerics analysis software to generate a dendrogram of relatedness among the strains.ResultsThe study found 93 profiles among 98 S. Senftenberg isolates tested and there were primarily two sequence types associated with humans and animals (ST185 and ST14) with overlap observed in all host types suggesting that the distribution of S. Senftenberg sequence types is not host dependent. Antimicrobial resistance was observed among the animal strains, however no resistance was detected in human isolates suggesting that animal husbandry has a significant influence on the selection and promotion of antimicrobial resistance.ConclusionThe data demonstrates the circulation of at least two strain types in both animal and human health suggesting that S. Senftenberg is relatively homogeneous in its distribution. The data generated in this study could be used towards defining a pathotype for this serovar.