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Caseous lymphadenitis is a well-known disease caused by Corynebacterium pseudotuberculosis affecting small ruminants with small significance to human health because of its minor zoonotic potential. In both cases, few treatment options are available and conventional antimicrobial therapy is commonly refractory due to development of pyogranulomatous reactions, bringing great interest in discovering novel therapeutics for more suitable approaches. Dideoxynucleotides presented antibacterial action against various bacteria but were never described for C. pseudotuberculosis. Hypothesizing the antimicrobial action of 2',3'-dideoxiadenosine (ddATP) against C. pseudotuberculosis, we performed for the first time an investigation of its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in the ATCC® 19,410 strain and a well-characterized clinical isolate of C. pseudotuberculosis. We also assessed potential synergism with penicillin. ddATP showed a growth delay effect for C. pseudotuberculosis at 2 µmol/mL and a MIC and MBC of 4 µmol/mL against the ATCC® 19,410 strain, but not for the clinical strain. An antimicrobial effect was observed when using concentrations lower than the MIC of ddATP associated with penicillin for both strains tested. Our data suggest the potential of nucleotide analogs, especially adenosine, and its combination with penicillin, as a possible novel treatment for C. pseudotuberculosis-induced infections, and contributes with knowledge regarding alternative drugs to treat C. pseudotuberculosis infections.

Made available in DSpace on 2022-05-01T12:09:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-03-01 Klebsiella species, particularly K. pneumoniae, are well-known opportunistic enterobacteria related to complexity of clinical infections in humans and animals, commonly refractory to conventional therapy. The domestic animals may represent a source of the pathogenic and multidrug-resistant Klebsiella species to humans. Nevertheless, most studies involving Klebsiella-induced infections in domestic animals are restricted to case reports or outbreaks. We retrospectively investigated selected epidemiological data, clinical aspects, and in vitro susceptibility pattern of 697 non-repetitive Klebsiella infections in livestock and companion species (1997–2019). The isolates were obtained from different clinical disorders from dogs (n = 393), cattle (n = 149), horses (n = 98), cats (n = 27), pigs (n = 22), sheep (n = 5), goats (n = 2), and buffalo (n = 1), except four isolates from subclinical bovine mastitis. Urinary (223/697 = 32%), enteric (117/697 = 16.8%), mammary (85/697 = 12.2%), reproductive (85/697 = 12.2%), and respiratory disorders (67/697 = 9.6%) were the most common clinical manifestations. Other miscellaneous clinical pictures (116/697 = 16.6%) included abscesses, otitis, hepatitis, conjunctivitis, pyodermitis, sepsis, and encephalitis. Norfloxacin (183/245 = 74.7%) and gentamicin (226/330 = 68.5%) were the most effective antimicrobials. High in vitro resistance of the isolates was seen to ampicillin (326/355 = 91.8%), amoxicillin/clavulanic acid (25/62 = 40.3%), and trimethoprim/sulfamethoxazole (100/252 = 39.7), and multidrug resistance to ≥ 3 classes of antimicrobials was found in 20.4% (142/697) isolates. Wide variety of clinical manifestations of Klebsiella-induced infections was observed, with a predominance of urinary, enteric, mammary, reproductive, and respiratory tract disorders, reinforcing opportunistic behavior of agent. Poor in vitro efficacy was observed to some conventional antimicrobials and ~ 20% of isolates exhibited resistance pattern, reinforcing the need for proper use of drugs on therapy approaches in domestic animals to avoid multidrug-resistant bacteria, an emergent global concern. Department of Animal Production and Preventive Veterinary Medicine Sao Paulo State University-UNESP, SP School of Veterinary Medicine and Animal Science São Paulo State University-UNESP, SP Department of Veterinary Medicine Faculty of Veterinary Medicine and Animal Sciences Antonio Nariño University Technology Faculty FATEC, SP Department of Animal Production and Preventive Veterinary Medicine Sao Paulo State University-UNESP, SP School of Veterinary Medicine and Animal Science São Paulo State University-UNESP, SP

Made available in DSpace on 2022-05-01T07:58:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Bloody diarrhea is a common condition in dogs, but studies evaluating the enteropathogens involved specifically in adult dogs are scarce. In the present study, stool samples from 45 adult dogs with bloody diarrhea were evaluated for the four enteric organisms mainly reported in these cases: canine parvovirus type 2 (CPV-2), Clostridioides difficile, Clostridium perfringens, and Salmonella spp. In addition, the samples were also tested for coronavirus, rotavirus, Giardia spp., and Escherichia coli pathotypes to provide a better understanding of possible co-occurrence. Vaccination status, diet, and clinical outcome were also obtained when available. CPV-2b was identified in 17 dogs (37.8%), being the most frequent cause of bloody diarrhea, including completely vaccinated adult dogs. Toxigenic C. difficile and C. perfringens netF+ were detected in 6 (13.3%) and 5 (11.1%) dogs, in some cases in a co-occurrence with other enteric organisms. Three fatal cases of salmonellosis were identified in dogs fed a raw meat-based diet, raising the risks associated with this increasing practice. Veterinary School. Universidade Federal de Minas Gerais (UFMG) UNESP-São Paulo State University - Department of Animal Production and Preventive Veterinary Medicine Universidade Federal do Rio Grande do Sul (UFRGS) Clínica Veterinária MedVet Clínica Veterinária VetMaster UNESP-São Paulo State University - Department of Animal Production and Preventive Veterinary Medicine CAPES: CAPES – Prêmio CAPES 2015 - 0774/2017 CNPq: CNPq - 406402/2018-3 FAPEMIG: FAPEMIG - APQ-00524-17

Made available in DSpace on 2020-12-12T02:36:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-04-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Pró-Reitoria de Pesquisa, Universidade Federal de Minas Gerais The occurrence and characteristics of Clostridioides (previously Clostridium) difficile and Clostridium perfringens in the feces of diarrheic and non-diarrheic cats was investigated. Apparently healthy animals were more likely to be positive for C. perfringens type A (p = 0.009). Two isolates (0.7%), one each from a diarrheic and an apparently healthy cat, were positive for the enterotoxin-encoding gene but negative for the NetF-encoding gene. Six toxigenic C. difficile isolates were isolated, all RT106 and ST42, which is commonly reported in humans with C. difficile infection. Veterinary School Universidade Federal de Minas Gerais (UFMG), Av. Antônio Carlos, 6627 UNESP-São Paulo State University - Department of Veterinary Hygiene and Public Health UNESP-São Paulo State University - Department of Veterinary Hygiene and Public Health

As espécies Tayassu tajacu e o Tayassu pecari conhecidos popularmente como cateto equeixada, respectivamente, ou também denominados porcos-do-mato, pertencem à famíliaTayassuidae. A criação em cativeiro destas espécies tem-se difundido em vários países nasúltimas décadas, em razão da demanda de carnes exóticas, principalmente em restaurantesespecializados. Devido ao crescente consumo deste tipo de carne, há a necessidade deimplantação de programas de manejo, reprodutivos e de saúde, visando à criação em cativeirode modo sustentável, economicamente viável e com níveis adequados de biosseguridade. Acriação em cativeiro dos catetos e queixadas pode gerar produtos de grande valor comercial erepresentam uma alternativa proteica ao consumo humano, bem como pode minimizar osefeitos da caça predatória, fragmentação de habitat, tráfico e extinção das espécies, quepoderiam resultar em desequilíbrios ecológicos. Os Tayassuídeos de vida livre ou de cativeirosão susceptíveis a maioria dos agentes infecciosos que acometem os suínos domésticos,incluindo micro-organismos de potencial zoonótico, apesar de certa variação geográfica naprevalência das doenças. O presente estudo revisou os principais aspectos da criação deTayassuídeos no Brasil, com ênfase as principais doenças de origem bacteriana, viral eparasitárias que acometem essas espécies.

Os patógenos de eliminação fecal figuram como uma das principais classes de microorganismos patogênicos para os humanos e animais, causando graves doenças entéricas e,ocasionalmente, extra-entéricas. Este grupo de organismos caracteriza–se por manterem–seviáveis e com capacidade infectante em condições hostis do ambiente, após a eliminaçãopelas fezes dos animais com e sem sinais entéricos. Devido ao contato cada vez mais estreitocom os humanos, os animais de companhia são elos importantes na cadeia de transmissão depatógenos entéricos. Os gatos domésticos representam um grupo importante de animaiscarreadores de patógenos entéricos com potencial zoonótico, uma vez que possuem hábitos decaça, de estabelecer territorialidade e de auto-limpeza. Dentre os patógenos de veiculaçãofecal de gatos domésticos de potencial zoonótico para humanos, merecem destaque:Escherichia coli, Salmonella spp., Campylobacter spp., Clostridium spp. Rhodococcus equi,Giardia spp. e Cryptosporidium spp. O presente estudo revisou os principais patógenosbacterianos e parasitários de gatos domésticos com ênfase aos aspectos de virulência,epidemiológicos, sinais clínicos, controle e reflexos em Saúde Pública

Proteus spp. are opportunistic multidrug resistant enterobacteria associated with diverse clinical diseases in domestic animals. However, Proteus infections in domestic animals are often misdiagnosed or considered contaminants in microbiological cultures rather than a primary agent of disease. Descriptions of Proteus infections in domestic animals are typically restricted to case reports, retrospective studies, or surveillance of other microorganisms. The present study investigated multiple antibiotic resistance indices, minimum inhibitory concentrations (MICs), and ESBL production in 73 strains of Proteus mirabilis (n = 69) and Proteus vulgaris (n = 4) isolated from domestic animals with various clinical manifestations. In dogs, the pathogen was most commonly associated with cystitis (48.21), enteritis (21.42%), otitis (14.29%), and conjunctivitis (3.57%). In bovines, the microorganism was predominant in cases of enteritis (22.22%), abscess (11.11%), otitis (11.11%), omphalitis (11.11%), and peritonitis (11.11%), and in organ fragments (11.11%). In equines (50.0%) and cats (100.0%), diarrhea was the main clinical sign. In vitro standard disk diffusion assay showed that the most effective antimicrobials against the isolates were imipenem (98.63), norfloxacin (95.89), amikacin (95.89), levofloxacin (90.41), ceftriaxone (87.64), and florfenicol (87.67). In contrast, the isolates commonly showed resistance to novobiocin (95.89), azithromycin (57.53), and trimethropim/sulfamethoxazole (39.73). Among the 73 isolates, the efficacy of amoxicillin/clavulanic acid, gentamicin, ceftriaxone, and ciprofloxacin according to MICs was 87.67%, 86.30%, 84.93%, and 82.19%, respectively. The MIC50 values of amoxicillin/clavulanic acid, ceftriaxone, ciprofloxacin, and gentamicin were, respectively, 1.0, 0.004, 0.03, and 1.0 µg/mL. Thirty-three strains (45.21%) showed a antimicrobial multiple resistance index of ? 0.3. Multidrug resistance profiles of isolates were observed most frequently in dogs (n = 25; 75.76%), particularly in those with cystitis (n = 13; 52.0%), followed by bovines (n = 4; 12.12%), equines (n = 2; 6.06%), and cats (n = 2; 6.06%). Two (2.7%) strains, obtained from canine skin and feces, were diagnosed phenotypically as ESBL-producers. Here, we observed the diversity of Proteus infections in domestic animals. The presence of multidrug-resistant isolates and ESBL-producers reinforces the need for appropriate antimicrobial use and in vitro antimicrobial tests to support therapy.

Escherichia coli is a normal inhabitant of the enteric microflora of human and animal. Intestinal and extra-intestinal infections caused by E. coli in mammals are characterized by the presence of diversity of virulence factors. In addition it can be isolated from environment surrounding human and animal farms. E. coli is the main environmental pathogen causing clinical mastitis in dairy cattle. It causes a wide range of disease severity, from changes seen exclusively in milk to severe systemic signs. The severity of clinical mastitis has been conventionally classified into three levels: mild (grade 1), moderate (score 2), and severe (score 3). Recently, reports of cases of bovine mastitis caused by environmental agents have been on the rise, in particular in countries that have succeeded in controlling contagious microorganisms. Unlike enteric and certain extra-enteric conditions in domestic animals and humans, the impact of virulence factors on the occurrence of bovine mastitis due to E. coli, as well as the clinical severity of the cases, is not fully understood. In this regard, the present study reviewed the most relevant virulence factors of E. coli in human and animals, with emphasis in bovine mastitis. Escherichia coli (E. coli) é um micro-organismo que pertence a microbiota entérica de humanos e animais. As afecções entéricas e extra-entéricas causadas por E.coli em mamíferos são caracterizadas pela presença de ampla diversidade de fatores de virulência. Além disso, este micro-organismo também pode ser isolado em ambientes de produção animal. E. coli é o principal agente ambiental que causa mastite clínica em vacas leiteiras, provocando sinais clínicos que podem variar desde mudanças observadas exclusivamente no leite até sinais sistêmicos graves. A gravidade da mastite clínica é convencionalmente classificada em três níveis: leve (grau 1), moderada (grau 2), e grave (grau 3). Atualmente, os relatos de casos de mastite bovina causada por agentes ambientais têm aumentando, principalmente nos países que conseguiram controlar os micro-organismos contagiosos. Diferentemente de infecções entéricas e certas extra-entéricas em humanos e animais, o impacto dos fatores de virulência de E. coli na ocorrência de mastite bovina não é totalmente compreendido, assim como na gravidade clínica dos casos. Neste contexto, o presente estudo revisou os fatores de virulência de E. coli mais relevantes para humanos e animais, com ênfase na mastite bovina.

Rhodococcus equi is responsible for infections in multiple-host animals. In humans, the prevalence of rhodococcus has increased worldwide and represents an emergent risk. R. equi is a soil-borne opportunistic bacterium isolated from feces of a wide variety of domestic species, except cats; thus, there is no known potential risk of its transmission from humans. Here, the mono- and cooccurrence of Rhodococcus equi and other bacteria and selected virulence markers were investigated in feces of nondiarrheic cats from urban (n=100) and rural (n=100) areas. Seven (7/200=3.5%) R. equi isolates were recovered in ceftazidime, novobiocin, and cycloheximide (CAZ-NB) selective media, exclusively of cats from three distinct farms (p=0.01), and these cats had a history of contact with horses and their environment (p=0.0002). None of the R. equi isolates harbored hosted-adapted plasmid types associated with virulence (pVAPA, pVAPB, and pVAPN). One hundred seventy-five E. coli isolates were identified, and 23 atypical enteropathogenic E. coli (aEPEC), 1 STEC (Shiga-toxin producing E. coli), and 1 EAEC (enteroaggregative E. coli) were detected. Eighty-six C. perfringens type A isolates were identified, and beta-2 and enterotoxin were detected in 21 and 1 isolates, respectively. Five C. difficile isolates were identified, one of which was toxigenic and ribotype 106. The main cooccurring isolates in cats from urban areas were E. coli and C. perfringens A (26/100=26%), E. coli and C. perfringens type A cpb2+ (8/100=8%), and aEPEC (eae+/escN+) and C. perfringens type A (5/100=5%). In cats from farms, the main cooccurring isolates were E. coli and C. perfringens type A (21/100=21%), E. coli and C. perfringens type A cpb2+ 8/100=8%), and E. coli and R. equi (4/100=4%). We identified, for the first time, R. equi in nondiarrheic cats, a finding that represents a public health issue because rhodococcus has been reported in both immunosuppressed and immunocompetent humans, particularly people living with HIV/AIDS.

Made available in DSpace on 2019-10-06T16:16:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-04-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Canine morbillivirus (previously, canine distemper virus, CDV) is a highly contagious infectious disease-causing agent that produces immunosuppressive infections and multiple clinical signs. Canine toxoplasmosis is an opportunistic disease characterized by enteric, pulmonary, and neuromuscular signs that might be confused with CDV-induced infections. Rhodococcus equi is a Gram-positive intracellular facultative bacterium that is also opportunistic in nature, and causes pyogranulomatous infections in humans and multiple host animals, although canine rhodococcosis is rare or unrecognized. The pathogenicity of R. equi is intimately related to the presence of plasmid-encoded virulence-associated proteins (Vap). Three host-adapted virulence plasmid types of R. equi have been recognized: the circular pVAPA and pVAPB are associated with equine and porcine strains, respectively, and the recently detected linear pVAPN virulence plasmid is related to bovine isolates. Nevertheless, data regarding the detection of host-adapted virulence plasmid types of R. equi isolated from companion animals are scarce. This report describes a case of an uncommon coinfection due to R. equi, T. gondii and CDV, which was diagnosed in a pet dog with respiratory distress. In this case, CDV most likely induced immunosuppression, which facilitated opportunistic infections by R. equi and T. gondii. The analysis of the virulence profile of R. equi revealed the novel pVAPN plasmid type, initially related to bovine strains. This is the second report of the bovine-associated pVAPN type in a pet dog, with an unusual coinfection with T. gondii and CDV. These findings represent a public health concern due to the close contact between pet animals and their owners, particularly because the pVAPN plasmid type was recently detected in people with HIV/AIDS from the same geographical region. UNESP-São Paulo State University Department of Veterinary Hygiene and Public Health School of Veterinary Medicine and Animal Sciences UNESP Department of Veterinary Clinical Sciences VetMol Laboratory UEL-Londrina State University Department of Preventive Veterinary Medicine Kitasato University Department of Animal Hygiene UNESP-São Paulo State University Department of Veterinary Hygiene and Public Health School of Veterinary Medicine and Animal Sciences UNESP Department of Veterinary Clinical Sciences FAPESP: 2015/20585-9 CNPq: 306116/2016-2

Rhodococcus equiis responsible for infections in multiple-host animals. In humans, the prevalence of rhodococcus has increased worldwide and represents an emergent risk.R. equiis a soil-borne opportunistic bacterium isolated from feces of a wide variety of domestic species, except cats; thus, there is no known potential risk of its transmission from humans. Here, the mono- and cooccurrence ofRhodococcus equiand other bacteria and selected virulence markers were investigated in feces of nondiarrheic cats from urban (n=100) and rural (n=100) areas. Seven (7/200=3.5%)R. equiisolates were recovered in ceftazidime, novobiocin, and cycloheximide (CAZ-NB) selective media, exclusively of cats from three distinct farms (p=0.01), and these cats had a history of contact with horses and their environment (p=0.0002). None of theR. equiisolates harbored hosted-adapted plasmid types associated with virulence (pVAPA, pVAPB, and pVAPN). One hundred seventy-fiveE. coliisolates were identified, and 23 atypical enteropathogenicE. coli(aEPEC), 1 STEC (Shiga-toxin producingE. coli), and 1 EAEC (enteroaggregativeE. coli) were detected. Eighty-sixC. perfringenstype A isolates were identified, and beta-2 and enterotoxin were detected in 21 and 1 isolates, respectively. FiveC. difficileisolates were identified, one of which was toxigenic and ribotype 106. The main cooccurring isolates in cats from urban areas wereE. coliandC. perfringensA (26/100=26%),E. coliandC. perfringenstype Acpb2+(8/100=8%), and aEPEC (eae+/escN+) andC. perfringenstype A (5/100=5%). In cats from farms, the main cooccurring isolates wereE. coliandC. perfringenstype A (21/100=21%),E. coliandC. perfringenstype Acpb2+8/100=8%), andE. coliandR. equi(4/100=4%). We identified, for the first time,R. equiin nondiarrheic cats, a finding that represents a public health issue because rhodococcus has been reported in both immunosuppressed and immunocompetent humans, particularly people living with HIV/AIDS.

Made available in DSpace on 2018-11-12T17:28:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2018. Added 1 bitstream(s) on 2018-11-12T17:36:25Z : No. of bitstreams: 1 S0036-46652018005000602.pdf: 432009 bytes, checksum: 1a143450dcdaac86bfa9abe9436f4f3d (MD5) ABSTRACT Although the tuberculin test represents the main in vivo diagnostic method used in the control and eradication of bovine tuberculosis, few studies have focused on the identification of mycobacteria in the milk from cows positive to the tuberculin test. The aim of this study was to identify Mycobacterium species in milk samples from cows positive to the comparative intradermal test. Milk samples from 142 cows positive to the comparative intradermal test carried out in 4,766 animals were aseptically collected, cultivated on Lowenstein-Jensen and Stonebrink media and incubated for up to 90 days. Colonies compatible with mycobacteria were stained by Ziehl-Neelsen to detect acid-fast bacilli, while to confirm the Mycobacterium genus, conventional PCR was performed. Fourteen mycobacterial strains were isolated from 12 cows (8.4%). The hsp65 gene sequencing identified M. engbaekii (n=5), M. arupense (n=4), M. nonchromogenicum (n=3), and M. heraklionense (n=2) species belong to the Mycobacterium terrae complex. Despite the absence of M. tuberculosis complex species in the milk samples, identification of these mycobacteria highlights the risk of pathogen transmission from bovines to humans throughout milk or dairy products, since many of mycobacterial species described here have been reported in pulmonary and extrapulmonary diseases both in immunocompetent and immunocompromised people. Universidade Estadual Paulista Faculdade de Medicina Veterinária e Zootecnia Departamento de Higiene Veterinária e Saúde Pública Universidade de São Paulo Faculdade de Medicina Veterinária e Zootecnia Departamento de Medicina Veterinária Preventiva e Saúde Animal Universidade de Nariño Departamento de Biología Universidade do Rio Verde Universidade Estadual Paulista Faculdade de Medicina Veterinária e Zootecnia Departamento de Higiene Veterinária e Saúde Pública

Tuberculosis remains as the world’s biggest threat. In 2014, human tuberculosis ranked as a major infectious disease by the first time, overcoming HIV death rates. Bovine tuberculosis is a chronic disease of global distribution that affects animals and can be transmitted to humans by the consumption of raw milk, representing a serious public health concern. Despite the efforts of different countries to control and eradicate bovine tuberculosis, the high negative economic impact on meat and milk production chains remains, given the decreased production efficiency (approximately 25%), the high number of condemned carcasses, and increased animal culling rates. This scenario has motivated the establishment of official programs based on regulations and diagnostic procedures. Although Mycobacterium tuberculosis and Mycobacterium bovis are the major pathogenic species to humans and bovines, respectively, nontuberculous mycobacteria within the Mycobacterium genus have become increasingly important in recent decades due to human infections, including the ones that occur in immunocompetent people. Diagnosis of mycobacteria can be performed by microbiological culture from tissue samples (lymph nodes, lungs) and secretions (sputum, milk). In general, these pathogens demand special nutrient requirements for isolation/growth, and the use of selective and rich culture media. Indeed, within these genera, mycobacteria are classified as either fast- or slow-growth microorganisms. Regarding the latter ones, incubation times can vary from 45 to 90 days. Although microbiological culture is still considered the gold standard method for diagnosis, molecular approaches have been increasingly used. We describe here an overview of the diagnosis of Mycobacterium species in bovine milk.

Made available in DSpace on 2018-12-11T17:13:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-01. Added 1 bitstream(s) on 2019-10-09T18:31:10Z : No. of bitstreams: 1 S0100-736X2017000400325.pdf: 863385 bytes, checksum: 499cb32239b1b6557dea17a7022ed660 (MD5) Septic arthritis is a debilitating joint infectious disease of equines that requires early diagnosis and immediate therapeutic intervention to prevent degenerative effects on the articular cartilage, as well as loss of athletic ability and work performance of the animals. Few studies have investigated the etiological complexity of this disease, as well as multidrug resistance of isolates. In this study, 60 horses with arthritis had synovial fluid samples aseptically collected, and tested by microbiological culture and in vitro susceptibility test (disk diffusion) using nine antimicrobials belonging to six different pharmacological groups. Bacteria were isolated in 45 (75.0%) samples, as follows: Streptococcus equi subsp. equi (11=18.3%), Escherichia coli (9=15.0%), Staphylococcus aureus (6=10.0%), Streptococcus equi subsp. zooepidemicus (5=8.3%), Staphylococcus intermedius (2=3.3%), Proteus vulgaris (2=3.3%), Trueperella pyogenes (2=3.3%), Pseudomonas aeruginosa (2=3.3%), Klebsiella pneumoniae (1=1.7%), Rhodococcus equi (1=1.7%), Staphylococcus epidermidis (1=1.7%), Klebsiella oxytoca (1=1.7%), Nocardia asteroides (1=1.7%), and Enterobacter cloacae (1=1.7%). Ceftiofur was the most effective drug (> 70% efficacy) against the pathogens in the disk diffusion test. In contrast, high resistance rate (> 70% resistance) was observed to penicillin (42.2%), enrofloxacin (33.3%), and amikacin (31.2%). Eleven (24.4%) isolates were resistant to three or more different pharmacological groups and were considered multidrug resistant strains. The present study emphasizes the etiological complexity of equine septic arthritis, and highlights the need to institute treatment based on the in vitro susceptibility pattern, due to the multidrug resistance of isolates. According to the available literature, this is the first report in Brazil on the investigation of the etiology. of the septic arthritis in a great number of horses associated with multidrug resistance of the isolates. Departamento de Higiene Veterinária e Saúde Pública Faculdade de Medicina Veterinária e Zootecnia (FMVZ) Universidade Estadual Paulista (Unesp), Cx. Postal 560 Departamento de Clínica Médica de Grandes Animais Universidade de Rio Verde (UniRV), Cx. Postal 104 Programa de Pós-Graduação em Reprodução Animal Faculdade de Medicina Veterinária e Zootecnia (FMVZ) Universidade de São Pulo (USP), Cx. Postal 225 Médica Veterinária Autônoma, Av. Panamericana, Carrera 13, dBarrio Ciudad Jardin Pós-doutor pela Mississippi State University USA. Department of Pathobiology and Population Medicine College of Veterinary Medicine Departamento de Higiene Veterinária e Saúde Pública Faculdade de Medicina Veterinária e Zootecnia (FMVZ) Universidade Estadual Paulista (Unesp), Cx. Postal 560