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Bovine mastitis is a multifactorial disease, caused mainly by bacteria, whose most traditional method of treatment is the use of antibiotics. However, incorrect administration of these drugs may lead to the emergence of resistant strains. The objective of this study was to identify the most common pathogens causing subclinical mastitis in the northwest State of Paraná, Brazil and establish their antimicrobial susceptibility profiles. A total of 507 foremilk samples were collected in 13 municipalities. Bacteria were identified and their profile of antimicrobial susceptibility were tested. The distribution of positive samples was not homogeneous among the cities. Streptococci were the most frequently genus observed (61%), followed by staphylococci (28%) and other genera (11%). Among streptococci and staphylococci, Streptococcus uberis and Staphylococcus aureus were the most frequently identified species, respectively. Overall, 40% of the isolates showed resistance to at least one of the antibiotics used in this study. A high proportion of cefoperazone resistant Staphylococcus spp. and bacitracin resistant Streptococcus were observed. The isolated microorganisms showed little resistance to enrofloxaxin. The results obtained show the importance of isolating the microorganism causing mastitis and testing its resistance to antibiotics before performing the treatment of the disease.

Considering the high prevalence of subclinical mastitis and its impacts on milk production, thematic studies are need to provide strategic data for its control. This study aimed at investigating the most frequent microorganisms associated with subclinical mastitis in dairy cows in Brazil through compiling the occurrence of the etiological agents and their sensitivity to antibiotics. The systematic review includes articles published between 2009 and 2019. Fiftyseven articles evaluating 22,287 milk samples were selected. The number of publications and the sample size were not homogeneous among Brazilian regions. Most of the studies and sampling were conducted in Rio Grande do Sul, whereas no studies were found in some states in the north and mid‑west regions. The most frequent pathogen was Staphylococcus spp. It was isolated in all studies and had an average prevalence of 49% in the analyzed samples. Resistance to penicillin was the most frequent microbial resistance found in Brazil, with an average of 66% among the isolates evaluated. Moreover, bacterial resistance to cephalexin, cefoperazone, erythromycin, gentamicin, neomycin, penicillin, tetracycline, and trimethoprim increased over the research period. Given the territorial extension, the etiological diversity, and the lack of studies with a representative sample, the compilation of scientific data must be interpreted with caution. Regions where a greater number of studies were conducted and with numerous samples, such as the South, provided a comprehensive scenario that is closer to reality. Nevertheless, although decision making on the farm cannot be replaced by scientific studies, it can be supported by such efforts.