Diarrhea is a prevalent and economically impactful ailment in cattle herds, resulting in substantial losses attributed to mortality, treatment expenses, and impaired calf growth. The aim of this study was to establish data about the occurrence of the main bacterial agents involved in diarrhea in dairy calves in the state of Maranhão, as well as to determine the most effective and/or resistant antibiotics, establishing a foundation for treatment and prevention protocols. The samples were collected with rectal swabs and initially cultivated on sheep blood agar (5%) and MacConkey agar and later on Salmonella-Shigella agar and eosin-methylene blue agar. Gram staining, biochemical tests, and antibiograms were performed on the obtained colonies. Ten municipalities were studied, with 230 calves evaluated from ten dairy farms. A total of 21 animals exhibited clinical signs of diarrhea, representing a frequency of 9.13%. The frequency of positive farms was 35%, and in 50% of municipalities. Bacteria isolated belonged to the Enterobacteriaceae family, with 71.4% Escherichia coli, 14.3% Enterobacter sp., 9.5% Proteus sp. and 4.8% Klebsiella sp. On the antibiogram, the bacteria that showed the highest resistance levels were those of the Proteus genus, followed by Enterobacter sp. and E. coli. The bacteria found are relevant for both animal and human health due to their zoonotic potential and serve as a public health alert since the isolates in this study showed in vitro resistance to several antibiotics, which predisposes them to the emergence of multidrug-resistant bacteria.
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