Streptococcus agalactiae is a major health concern in tilapia farming worldwide. In contrast to the availability of susceptibility profile results, interpretative criteria for disk diffusion assays and the influence of serotypes on resistance profiles are not available. To address this, sixty isolates (thirty of each serotype, Ib and III) were evaluated using the disk diffusion assay against six antibiotics, and the epidemiological cut-off value (ECV) was calculated. All the isolates were classified as non-wild type (NWT) for sulfamethoxazole (SUT) and norfloxacin (NOR). The inhibition zones for oxytetracycline (OXY) and doxycycline (DOX) were largely distinct; all serotype Ib and III isolates were classified as wild-type (WT) and NWT, respectively. The results for serotype III of fish group B Streptococcus (GBS) were comparable to the NWT tetracycline profile of human GBS available in EUCAST, suggesting the presence of resistance mechanisms in these fish isolates. The calculation of the cut-off wild type (CO_WT) values for OXY and DOX was appropriate for both serotypes. Differences between the distribution of florfenicol (FLO) and amoxicillin (AMO) were found, and we attribute this to the faster growth rate of serotype III, which promotes smaller inhibition zones. Therefore, using separate CO_WT for each serotype is necessary. In conclusion, the serotype of fish GBS affects its susceptibility profile, and it is recommended to use serotype-specific CO_WT values as interpretative criteria for disk diffusion assays against FLO and AMO.

Edwardsiella tarda is a crucial pathogenic bacterium in tropical aquaculture. This bacterium was recently isolated from tambaqui (Colossoma macropomum), a commercially important fish species in Brazil. This study assessed the antimicrobial susceptibility, pathogenicity, and genetic diversity of the tambaqui-derived E. tarda isolates. Fourteen bacterial isolates isolated from tambaqui were identified as E. tarda by using matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry and dnaJ gene sequencing. Antimicrobial susceptibility tests were conducted against seven drugs using the disc diffusion assay. The pathogenicity test conducted by intraperitoneal injection of 2.4 × 10⁷ colony-forming units (CFU) fish⁻¹ of E. tarda (ED38-17) into tambaqui juveniles eventually revealed that neither clinical signs nor death were present. However, splenomegaly and whitish areas in the spleen and kidneys were observed. The histological investigation also revealed granulomatous splenitis, nephritis, and hepatitis occurring internally. Repetitive extragenic palindromic-PCR fingerprinting separated the 14 isolates into three genetic groups. The antibiogram revealed that all E. tarda isolates were wild-type (WT) to florfenicol (FLO), norfloxacin (NOR), neomycin (NEO), erythromycin (ERY), and oxytetracycline (OXY); however, some were non-wild-type to sulfamethoxazole/trimethoprim (7.1%) and amoxicillin (21.4%). Therefore, through experimental infection, E. tarda ED38-17 could induce pathogenic effects in C. macropomum. Additionally, three distinct genetic types were found, and the E. tarda isolates were WT to FLO, NOR, NEO, ERY, and OXY. These findings raise awareness of a bacteria causing unseen lesions, a pathogen that will potentially impact tambaqui aquaculture in the future.

Recently, this microorganism has emerged as a pathogen of humans and livestock, being mainly associated with acute infections in the genitourinary tract of these hosts (^{LEITE et al., 2010}; ^{TOHNO et al., 2014}), as well as related to sepsis in pigs (^{MARTÍN et al., 2007}), subclinical mastitis (^{LIU et al., 2015}) and septicemia in human neonates (accession number Genbank MG576151.1).

In the last few decades, there has been a global increase in the adoption of reptiles as companion animals, mainly turtles and tortoises. Considering the popularity of reptiles as pets in Brazil, and a notable lack of data about potentially pathogenic staphylococci in these animals, this study isolated and evaluate the antimicrobial susceptibility of staphylococcal species from healthy tortoises (Chelonoidis carbonaria) in Brazil. During a 12-month period (February 2019 to February 2020), cloacal swabs from 66 healthy tortoises were collected at the Wild Animals Screening Center in Belo Horizonte, Minas Gerais, Brazil. The swabs were plated onto mannitol salt agar for staphylococci isolation, and species identification was performed using MALDI-TOF MS. Antimicrobial susceptibility was investigated using the disk diffusion method, and the presence of the mecA gene was investigated by PCR to detect methicillin resistance. Of the tested animals, 72.7% were positive for staphylococcal isolation. All isolates were coagulase-negative staphylococci (CoNS), and Staphylococcus sciuri (81.3%), and S. xylosus (12.5%) were the most frequently isolated species. The majority of the isolates (56%) were resistant to at least one antimicrobial agent. A high frequency of resistance was observed for penicillin (35.5%) and tetracycline (29.1 %). All strains were susceptible to cefoxitin, chloramphenicol, ciprofloxacin, erythromycin, and gentamicin. All isolates were negative for the mecA gene. The present work suggests that healthy tortoises are mainly colonized by CoNS, especially S. sciuri. Half of the isolates were resistant to at least one antimicrobial, raising questions regarding the possible role of these animals as reservoirs of antimicrobial resistance genes.

Paratuberculosis (PTB) or Johne’s disease is an infection characterized by chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP), which affects cattle, sheep, goats and wild ruminants (^{Fecteau, 2017}). Enzootic bovine leukosis EBL is caused by an RNA virus of the Retroviridae family, the bovine leukemia virus (BLV). Considering the economic impact of PTB and EBL and the importance of an epidemiological analysis to support prophylactic measures, our objective here was to conduct a seroepidemiological study of PTB and EBL in cattle herds in the largest dairy basin in the state of Minas Gerais, Brazil. This research was approved by the Ethics Committee on Animal Use of the University Center of Patos de Minas (UNIPAM), under Protocol no. 54/17. The study was carried out in the municipality of Lagoa Formosa, located in the region of Alto Paranaíba, state of Minas Gerais, Brazil. To determine the sample size, the prevalence estimation method was used on a simple random sample. Estimated prevalence was 75.8% for paratuberculosis (Fernández-Silva et al., 2014) and 80.89% for leukosis (^{Ambrósio, 2015}). Thus, for the sample size an expected prevalence of 81%was adopted with a 95% confidence level and a statistical error of 5%, indicating a minimum total sample size of 236 samples.