Multicenter Clinical Evaluation of Modified Two-Tiered Testing Algorithms for Lyme Disease Using Zeus Scientific Commercial Assays.

Modified two-tiered testing (MTTT) algorithms for Lyme disease (LD), which involve the sequential use of orthogonal enzyme immunoassays (EIAs) without immunoblotting, are acceptable alternatives to standard two-tiered testing (STTT; EIA followed by immunoblots) provided the EIAs have been FDA-cleared for this intended use. We evaluated four Zeus Scientific LD EIAs used in two distinct MTTT algorithms for FDA review. MTTT 1 used a VlsE1/pepC10 polyvalent EIA followed by a whole-cell sonicate (WCS) polyvalent EIA. MTTT 2 used the same first-tier EIA followed by separate IgM and IgG WCS EIAs. In a retrospective phase, we compared each MTTT algorithm to STTT using archived samples from LD patients or control subjects. In a prospective phase, we used the same algorithms to analyze consecutive excess samples submitted for routine LD serology to three clinical laboratories. For the retrospective phase, MTTTs 1 and 2 were more sensitive (56% and 74%) than STTT (41%; P ≤ 0.03) among 61 patients with acute erythema migrans (EM). In LD patients with neuroborreliosis, carditis, or arthritis (n = 75), sensitivity was comparable between algorithms (96 to 100%; P = 1.0). Among 190 control subjects without past LD, all algorithms were highly and comparably specific (≥99%, P = 0.48). For the prospective phase, (n = 2,932), positive percent-agreement (PPA), negative percent-agreement (NPA), and overall agreement of MTTT 1 with STTT were 93%, 97.7% and 97.4% (kappa 0.80). MTTT 2 yielded higher PPA (98%) but lower NPA (96.1%) and overall agreement (96.2%, kappa 0.74; all P < 0.05). Compared with STTT, both MTTT algorithms provided increased sensitivity in EM patients, comparable sensitivity in later disease and non-inferior specificity.

Clinical Laboratory Perspective on Streptococcus halichoeri, an Unusual Nonhemolytic, Lancefield Group B Streptococcus Causing Human Infections.

Streptococcus halichoeri is a relatively newly identified species of pyogenic streptococci that causes zoonotic infection in humans. S. halichoeri was first described in 2004 as indigenous to seals, and only 8 reports of human S. halichoeri infection have been published. S. halichoeri grows as small, white, nonhemolytic colonies and may be strongly catalase-positive on routine blood agar media, which can lead to isolates being misidentified as coagulase-negative staphylococci. S. halichoeri tests positive for Lancefield group B antigen, like S. agalactiae, but can be identified with matrix-assisted laser desorption/ionization time of flight mass spectrometry or partial 16S rRNA sequencing. We describe 3 cases of S. halichoeri bone and joint infections in patients in the United States with underlying health conditions. In addition, we examine the microbiologic characteristics of S. halichoeri and discuss the importance of fully identifying this organism that might otherwise be disregarded as a skin commensal.

Beta-Hemolytic Nongroup A Streptococcal Pharyngitis in Children.

OBJECTIVE: To evaluate the epidemiology, clinical features, and antibiotic prescribing patterns for nongroup A streptococci (NGAS) in children. STUDY DESIGN: Throat cultures obtained for pharyngitis were assessed at a large community-based health system over 10 years. Epidemiologic and clinical features of children with NGAS were compared with children with group A Streptococcus (GAS) and negative cultures. Antibiotic prescribing patterns were evaluated. RESULTS: A total of 224 328 rapid streptococcal antigen tests and 116 578 throat cultures were performed. Clinical analysis was completed for 602 GAS-positive patients, 535 NGAS-positive patients, and 480 patients with negative cultures. Incidence of NGAS did not vary annually or by season but increased with age from 2% at ≤5 years to 7% at 18 years of age. Patients with NGAS were more likely than those with negative cultures to have tonsillar exudate (20.3% vs 13.1%, P = .003) and enlarged tonsils (28.6% vs 19.3%, P < .001). Modified Centor scores did not differ between groups (score ≥2, P = 1.0; score ≥3, P = .50). Patients with GAS were more likely than those with NGAS to have fever (32.6% vs 24.5%, P = .003), palatal petechiae (14.0% vs 3.1%, P < .001), and modified Centor score ≥2 (47.8% vs 27.1%; P < .001). Of patients with NGAS, 65% were prescribed antibiotics. CONCLUSIONS: NGAS likely exist in both carriage and infectious states and incidence increases with age. Infections associated with NGAS are milder than with GAS, and complications are rare. Laboratory reporting of NGAS results in high antibiotic use, despite current recommendations against treatment.

Infectious Mononucleosis and Lyme Disease as Confounding Diagnoses: A Report of 2 Cases.

Lyme disease and infectious mononucleosis are common illnesses that share similar clinical presentations. Significant cross-reactivity is known to occur between Lyme and EBV serologic assays complicating the diagnosis. To date, no prior cases of concurrent acute Lyme and EBV infections have been reported. We describe the clinical presentation of two children with confirmed early Lyme disease and features suggestive of infectious mononucleosis, including one case of probable Lyme and EBV co-infection.

Serologic Evidence of Powassan Virus Infection in Patients with Suspected Lyme Disease1.

Powassan virus (POWV) lineage II is an emerging tickborne flavivirus with an unknown seroprevalence in humans. In a Lyme disease-endemic area, we examined the seroreactivity to POWV in 2 patient cohorts and described the clinical features of the POWV-seroreactive patients. POWV disease might be less neuroinvasive than previously thought.

T2 Magnetic Resonance Assay-Based Direct Detection of Three Lyme Disease-Related Borrelia Species in Whole-Blood Samples.

In early Lyme disease (LD), serologic testing is insensitive and seroreactivity may reflect active or past infection. In this study, we evaluated a novel assay for the direct detection of three species of Borrelia spirochetes in whole blood. The T2 magnetic resonance (T2MR) assay platform was used to amplify Borrelia DNA released from intact spirochetes and to detect amplicon. Analytical sensitivity was determined from blood spiked with known concentrations of spirochetes, and the assay's limit of detection was found to be in the single-cell-per-milliliter range: 5 cells/ml for B. afzelii and 8 cells/ml for Borrelia burgdorferi and Borrelia garinii Clinical samples (n = 66) from confirmed or suspected early LD patients were also analyzed. B. burgdorferi was detected using T2MR in 2/2 (100%) of blood samples from patients with confirmed early LD, based on the presence of erythema migrans and documentation of seroconversion or a positive real-time blood PCR. T2MR detected B. burgdorferi in blood samples from 17/54 (31%) of patients with probable LD, based on the presence of erythema migrans without documented seroconversion or of documented seroconversion in patients with a compatible clinical syndrome but without erythema migrans. Out of 21 clinical samples tested by real-time PCR, only 1 was positive and 13 were negative with agreement with T2MR. An additional 7 samples that were negative by real-time PCR were positive with T2MR. Therefore, T2MR enables a low limit of detection (LoD) for Borrelia spp. in whole blood samples and is able to detect B. burgdorferi in clinical samples.

Serologic screening of United States blood donors for Babesia microti using an investigational enzyme immunoassay.

BACKGROUND: The tick-borne pathogen Babesia microti has become recognized as the leading infectious risk associated with blood transfusion in the United States, yet no Food and Drug Administration-licensed screening tests are currently available to mitigate this risk. The aim of this study was to evaluate the performance of an investigational enzyme immunoassay (EIA) for B. microti as a screening test applied to endemic and nonendemic blood donor populations. STUDY DESIGN AND METHODS: The study aimed to test 20,000 blood donors from areas of the United States considered endemic for B. microti and 10,000 donors from a nonendemic area with the investigational B. microti EIA. Repeat-reactive samples were retested by polymerase chain reaction (PCR), blood smear, immunofluorescent assay (IFA), and immunoblot assay. In parallel, serum samples from symptomatic patients with confirmed babesiosis were tested by EIA, IFA, and immunoblot assays. RESULTS: A total of 38 of 13,757 (0.28%) of the donors from New York, 7 of 4583 (0.15%) from Minnesota, and 11 of 8363 (0.13%) from New Mexico were found repeat reactive by EIA. Nine of the 56 EIA repeat-reactive donors (eight from New York and one from Minnesota) were positive by PCR. The specificity of the assay in a nonendemic population was 99.93%. Among IFA-positive clinical babesiosis patients, the sensitivity of the assay was 91.1%. CONCLUSION: The B. microti EIA detected PCR-positive, potentially infectious blood donors in an endemic population and exhibited high specificity among uninfected and unexposed individuals. The EIA promises to provide an effective tool for blood donor screening for B. microti in a format amenable to high-throughput and cost-effective screening.

Surveillance of Wisconsin Antibacterial Susceptibility Patterns.

BACKGROUND: Antimicrobial resistance presents a threat to quality patient care. Knowledge of localantibacterial susceptibility patterns can guide clinicians in empiric antibacterial administration andassist pharmacists and infectious disease physicians in development of appropriate therapeutic pathways. METHODS: To characterize Wisconsin antibacterial susceptibility patterns and elucidate geographicor temporal variation in antibacterial resistance, a retrospective, observational analysis of antibiogram data was performed. Seventy-two members of the Wisconsin Clinical Laboratory Network(WCLN) submitted antibiograms describing clinically significant isolates tested in calendar year 2013 to the WCLN Laboratory Technical Advisory Group. RESULTS: In the context of commonly reported antibacterial agents, data were compiled for approximately 75,800 isolates of Escherichia coi; 13,300 Klebsiella pneumoniae; 6300 Proteus mirobilis;2800 Enterobacter cloacae; 8400 Pseudomonas aeruginosa; 30,000 S aureus; 11,200 coagulase-negative Staphylococcus spp; and 13,800 Enterococcus spp. P mirobilis isolates from northern Wisconsin were more likely to demonstrate resistance than those in the southern region. In contrast, P aeruginosa isolates from southern Wisconsin had decreased susceptibility to a number ofagents when compared to other regions. Temporal trending in decreased E coli and P mirabilis susceptibility to fluoroquinolones and trimethoprimsulfamethoxazole was observed. Increased methicillin-resistant Staphylococcus oureus (MRSA) rates were observed in northwest and southeastWisconsin. In general, northeast Wisconsin exhibited less frequency of antibacterial resistance. CONCLUSIONS: Geographic variation exists with respect to antibacterial resistance, particularly inareas of Wisconsin adjacent to large population centers of neighboring states. Antibacterial surveillance in Wisconsin is indicated on a regular basis to assess emerging trends in antibacterial resistance. Existing WCLN infrastructure allows for such investigations.

Human Infection with Ehrlichia muris-like Pathogen, United States, 2007-2013(1).

An Ehrlichia muris-like (EML) pathogen was detected among 4 patients in Minnesota and Wisconsin during 2009. We characterized additional cases clinically and epidemiologically. During 2004-2013, blood samples from 75,077 patients from all 50 United States were tested by PCR from the groEL gene for Ehrlichia spp. and Anaplasma phagocytophilum. During 2007-2013, samples from 69 (0.1%) patients were positive for the EML pathogen; patients were from 5 states: Indiana (1), Michigan (1), Minnesota (33), North Dakota (3), and Wisconsin (31). Most (64%) patients were male; median age was 63 (range 15-94) years; and all 69 patients reported likely tick exposure in Minnesota or Wisconsin. Fever, malaise, thrombocytopenia, and lymphopenia were the most common symptoms. Sixteen (23%) patients were hospitalized (median 4 days); all recovered, and 96% received doxycycline. Infection with the EML pathogen should be considered for persons reporting tick exposure in Minnesota or Wisconsin.

Appearances are Deceptive: Staphylococcus Superinfection of Clavicular Tuberculous Osteomyelitis.

A man, aged 25 years, presented with pain, swelling, and drainage from the right clavicular area. He had a past history of abscess at the sternoclavicular joint. The cultures from the drainage site grew methicillin-sensitive Staphylococcus aureus, and he was placed on appropriate antibiotics. As S. aureus infection of the clavicle is often secondary in nature, particularly in adults, a thorough workup was done to identify the underlying cause. Quantiferon gold, done as a part of the workup, came back positive, while the bone cultures grew S. aureus and Mycobacterium tuberculosis. He was placed on 9 months of combination therapy for tuberculosis osteomyelitis with a good clinical outcome.

High diversity of plasmids harbouring blaCMY-2 among clinical Escherichia coli isolates from humans and companion animals in the upper Midwestern USA.

OBJECTIVES: To determine the population structure and genetic relatedness of plasmids encoding CMY-2 ß-lactamase in clinical Escherichia coli from humans and companion animals within a defined geographical area. METHODS: In total, 42 human and 73 companion animal isolates displaying an AmpC phenotype were isolated at a regional diagnostic reference laboratory in the upper Midwestern USA during 2009-11. Following PCR screening for transferable AmpC genes and plasmid transformation, blaCMY-2-positive plasmids were characterized by S1 nuclease PFGE, PCR-based replicon typing, antimicrobial susceptibility testing of transformants, conjugation experiments, plasmid multilocus sequence typing and restriction fragment length polymorphism. RESULTS: blaCMY-2 occurred in 6 (14%), 56 (86%) and 6 (75%) isolates from humans, dogs and cats, respectively. Usually plasmids carrying blaCMY-2 were conjugative (78%) and did not contain additional resistance genes (82%). The replicon types were IncI1 (52%), IncA/C (13%), IncFII (10%), IncI2 (5%), IncL/M (3%), IncB/O (2%) or non-typeable (15%). Related IncI1/ST12 plasmids were detected in one human and five canine isolates, while the remaining plasmids did not show similarity across host species. A novel epidemiological linkage of blaCMY-2 with IncL/M plasmids and a new CMY gene variant (blaCMY-108) were found in human isolates. CONCLUSIONS: This study is one of the first One Health attempts to compare plasmids encoding CMY-2 ß-lactamase among clinical isolates from humans and companion animals in the same region. The results indicate an unforeseen heterogeneity of plasmid backgrounds and suggest limited exchange between the two populations, in which blaCMY-2 occurred at very different frequencies and was harboured by distinct plasmid types.

A clinical, diagnostic, and ecologic perspective on human anaplasmosis in the Upper Midwest.

INTRODUCTION: Human anaplasmosis caused by the bacterial pathogen Anaplasma phagocytophilum was first discovered in the Upper Midwest in 1990. Since that time the number of cases in the region has steadily increased, such that today, the pathogen rivals that of Lyme disease in causing human tick-borne-related illness. OBJECTIVE: We provide an overview of the biology, clinical characteristics, and epidemiology of the disease in the Upper Midwest and discuss currently available diagnostic methods. FINDINGS: Rapid differentiation of anaplasmosis from other acute febrile illnesses and targeted treatment are important for preventing severe disease and potentially fatal outcomes in infected individuals. Beyond blood smear analysis and serology, the development of real-time polymerase chain reaction (PCR) assays for clinical use holds promise in improving our ability to make rapid diagnoses and to differentiate A phagocytophilum infections from those produced by closely related Ehrlichia pathogens, which are also present in the region. CONCLUSION: Continuing expansion of the range of the black-legged tick (Ixodes scapuloris), the principal vector of the disease, into areas heavily populated or visited by humans in the region likely will result in this pathogen becoming an even greater burden on human health. Efforts are needed to better characterize the current geographic distribution of human Anaplasma and Ehrlichia cases to identify emerging foci and to better understand the enzootic cycles that maintain the pathogens in the region. Improved diagnostics may assist with such efforts.

In vitro activity of ozenoxacin against Staphylococcus aureus and Streptococcus pyogenes clinical isolates recovered in a worldwide multicentre study (2020-2022).

Objectives: We performed a multicentre study (2020-2022) to compare the in vitro activity of ozenoxacin and comparator agents against Staphylococcus aureus and Streptococcus pyogenes clinical isolates from skin and soft-tissue infections (SSTI). Methods: A total of 1725 isolates (1454 S. aureus and 271 S. pyogenes) were collected in 10 centres from eight countries between January 2020 and December 2022. Antimicrobial susceptibility testing was determined (microdilution-SENSITITRE). Results were interpreted following European Committee on Antimicrobial Susceptibility Testing (EUCAST) 2023 (clinical breakpoints, ECOFF) and CLSI criteria. Results: Ozenoxacin exhibited high in vitro activity against S. aureus (MIC50/90 = 0.002/0.12 mg/L) and S. pyogenes (MIC50/90 = 0.015/0.03 mg/L), inhibiting 99% of the isolates at MIC ≤ 0.5 mg/L and at MIC ≤ 0.06, respectively. The most active comparators against S. aureus were retapamulin (MIC90 = 0.12 mg/L), fusidic acid (MIC90 = 0.25 mg/L) and mupirocin (MIC90 = 0.5 mg/L); and against S. pyogenes were retapamulin (MIC90 = 0.03 mg/L), clindamycin (MIC90 = 0.12 mg/L) and mupirocin (MIC90 = 0.25 mg/L). Ciprofloxacin and methicillin resistant rates for S. aureus were 31.3% (455/1454) and 41% (598/1454), respectively. Additionally, 62% (373/598) of the MRSA were also ciprofloxacin non-susceptible, whereas only 10% (23/271) of the MSSA were ciprofloxacin resistant. Ozenoxacin was more active against ciprofloxacin-susceptible S. aureus than against ciprofloxacin-resistant isolates, and showed a slightly higher MIC in MRSA isolates than in MSSA. However, ozenoxacin activity was comparable in both ciprofloxacin-resistant MSSA and MRSA subsets. On the other hand, ozenoxacin had similar activity in ciprofloxacin-susceptible and resistant S. pyogenes isolates. Conclusions: Ozenoxacin is a potent antimicrobial agent of topic use against Gram-positive bacteria causing SSTI, including MRSA isolates non-susceptible to ciprofloxacin.

Flap infection associated with medicinal leeches in reconstructive surgery: two new drug-resistant organisms.

The use of medicinal leeches in reconstructive surgery has proven value for the salvage of flaps with venous congestion but is associated with a risk of leech-acquired infection. The most common leech-associated organism is Aeromonas hydrophila, which antibiotic prophylaxis is typically directed against. The authors describe two new multidrug-resistant organisms acquired from medicinal leech therapy that resulted in flap infection. The evaluation of suspected leech-borne infection and management protocol for this leech-acquired resistant multi-organism infection is presented.

Direct Tissue PCR and Genotyping for Species Identification in a Case of Laryngeal Blastomycosis.

Otolaryngologic manifestations of infection with Blastomyces species are extremely rare and restricted geographically to recognized endemic regions. Here, we describe a case of laryngeal blastomycosis that presented as slowly progressive dysphonia. While a preliminary diagnosis was made using routine histopathology, a species identification of Blastomyces dermatitidis was made using polymerase chain reaction amplification and rapid genotyping without the need for fungal culture. All symptoms resolved following 1 month of antifungal therapy. Rapid molecular differentiation of B dermatitidis from Blastomyces gilchristii provides important insights into pathogenesis given recent recognition of differences in clinical spectra.

A geospatial approach to identify patterns of antibiotic susceptibility at a neighborhood level in Wisconsin, United States.

The global threat of antimicrobial resistance (AMR) varies regionally. This study explores whether geospatial analysis and data visualization methods detect both clinically and statistically significant variations in antibiotic susceptibility rates at a neighborhood level. This observational multicenter geospatial study collected 10 years of patient-level antibiotic susceptibility data and patient addresses from three regionally distinct Wisconsin health systems (UW Health, Fort HealthCare, Marshfield Clinic Health System [MCHS]). We included the initial Escherichia coli isolate per patient per year per sample source with a patient address in Wisconsin (N = 100,176). Isolates from U.S. Census Block Groups with less than 30 isolates were excluded (n = 13,709), resulting in 86,467 E. coli isolates. The primary study outcomes were the results of Moran's I spatial autocorrelation analyses to quantify antibiotic susceptibility as spatially dispersed, randomly distributed, or clustered by a range of - 1 to + 1, and the detection of statistically significant local hot (high susceptibility) and cold spots (low susceptibility) for variations in antibiotic susceptibility by U.S. Census Block Group. UW Health isolates collected represented greater isolate geographic density (n = 36,279 E. coli, 389 = blocks, 2009-2018), compared to Fort HealthCare (n = 5110 isolates, 48 = blocks, 2012-2018) and MCHS (45,078 isolates, 480 blocks, 2009-2018). Choropleth maps enabled a spatial AMR data visualization. A positive spatially-clustered pattern was identified from the UW Health data for ciprofloxacin (Moran's I = 0.096, p = 0.005) and trimethoprim/sulfamethoxazole susceptibility (Moran's I = 0.180, p < 0.001). Fort HealthCare and MCHS distributions were likely random. At the local level, we identified hot and cold spots at all three health systems (90%, 95%, and 99% CIs). AMR spatial clustering was observed in urban areas but not rural areas. Unique identification of AMR hot spots at the Block Group level provides a foundation for future analyses and hypotheses. Clinically meaningful differences in AMR could inform clinical decision support tools and warrants further investigation for informing therapy options.

What Is Your Diagnosis?

In collaboration with the American College of Veterinary Radiology.

Sternal osteomyelitis caused by Gordonia bronchialis in an immunocompetent patient following coronary artery bypass surgery.

Skin commensals, especially gram-positive cocci, are the usual microbial organisms that cause post-operative sternal wound infections. Rarely, environmental bacteria such as Gordonia spp. have been implicated as etiological agents in post-cardiac procedure surgical site infections. We report a case of a patient who presented with post-coronary artery bypass sternal osteomyelitis caused by this uncommon pathogen, and review relevant medical literature to identify commonalities in presentation, diagnosis and management. Repeat isolation of Gordonia bronchialis in the setting of post-procedure wound infection should raise suspicion for a real pathogenicity. Definitive identification requires a broad range of bacterial PCR DNA amplification and sequencing followed by susceptibility testing as treatment may require a prolonged course of antibiotics.

Surveillance for multidrug resistant Escherichia coli carriage in cattle, dogs and humans reveals predominance of CMY-2, CTX-M-15 and CTX-M-9 groups of ß-lactamases.

Global spread of antimicrobial multidrug resistance (MDR) in human and veterinary medicine relies upon diagnostics, surveillance and stewardship to guide mitigation. Utilizing surveillance of fecal samples from our service area for detecting MDR Escherichia coli carriage in humans (2143), dogs (627), and cattle (130), we found isolates resistant to third/fourth generation cephems present in 3.7 %, 13.1 %, and 51.5 %, respectively. CMY-2, CTX-M-15-like and CTX-M9 group genes in descending order were predominant in all hosts and accounted for 83.3 % of non-wild-type gene targets. MDR carriage mirrored cephem non-susceptibility rates as published in annual antibiograms for humans and dogs; notably, no carbapenem-resistant carriage isolates were detected. Given the scale of MDR E. coli carriage in cattle (14X) and dogs (3.5X) compared to humans, bench-marking of the resistance gene pool by host species utilizing regional One Health surveillance may aid in assessing occupational and geographic risks for acquiring resistance and for monitoring of mitigation strategies.

Evidence of multiple virulence subtypes in nosocomial and community-associated MRSA genotypes in companion animals from the upper midwestern and northeastern United States.

OBJECTIVE: Not much is known about the zoonotic transmission of methicillin-resistant Staphylococcus aureus (MRSA) in companion animals in the United States. We report the rate of prevalence of S. aureus and MRSA recovered from clinical samples of animals requiring treatment at veterinary clinics throughout the upper midwestern and northeastern United States. DESIGN: We compared phenotypes, genotypes, and virulence profiles of the MRSA isolates identified in companion animals, such as cats, dogs, horses, and pigs, with typical human nosocomial and community-associated MRSA (CA-MRSA) genotypes to assess implied zoonotic transmission or zooanthroponosis. Five hundred thirty-three coagulase-positive staphylococci (CPS) isolates recovered between 2006 and 2008 from a variety of animal-source samples were screened for S. aureus by S. aureus-specific 16S rDNA primers and were screened for methicillin-resistance. All MRSA isolates were genotyped by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and spa typing. They were also screened for common staphylococcal enterotoxin and adhesion genes by multiplex and singleplex PCR. RESULTS: Among the 533 CPS isolates recovered, 66 (12.4%) were determined to be S. aureus and 24 (4.5%) were MRSA. The percent of animals that were positive for S. aureus were as follows: 6.6% (32 of 487) dogs, 39.6% (19 of 48) cats, 83.3% (10 of 12) horses, and 100% of pigs, rabbits, hamsters and rats. Notably, 36.4% of all S. aureus identified were MRSA. Methicillin-resistant S. aureus was present in clinical samples from 12 of 487 dogs (2.5%), 6 of 48 cats (12.5%), 5 of 12 horses (42%), and 1 of 2 pigs (50%). The 24 MRSA isolates resolved into 4 PFGE clones: USA100 (50%), USA300 (16.7%), USA500 (20.8%) and USA800 (12.5%) and 6 sequence types (ST5, ST8, ST105, ST830, and ST986) or 2 clonal complexes, CC5 and CC8. Five major virulence profiles (clusters A to E) were observed in these MRSA isolates. Genotypic and virulence profiles of cats and dogs were more similar to each other than to those of horses. A Panton-Valentine leukocidin positive isolate with ST8:USA300 background was identified in a pig causing skin and soft infection. CONCLUSION: The presence of human MRSA clones in these animals suggests possible reverse zoonotic transmission. This study reports the first case of a USA300 genotype in a pig. Presence of multiple virulence profiles within a MRSA genotype in these animals suggests the potential of emergence of new MRSA clones by gaining or losing additional virulence genes.