ANTIMICROBIAL RESISTANCE IN BRAZILIAN ISOLATES OF SHIGA TOXIN-ENCODING ESCHERICHIA COLI FROM COWS WITH MASTITIS

Antimicrobial resistance is a matter of growing concern in public and animal health. Public health can be threatened by the transfer of pathogens from animals to people via indirect contact through food or directly by contact with animals. The potential transfer of resistance determinants from animals to humans through Escherichia coli strains is an additional cause of concern. From February to November 2004, 670 samples of bovine mastitic milk were collected in two Brazilian states. The 231 E. coli strains isolated from the samples were screened for the presence of genes encoding Shiga toxin (stx 1 and stx 2) and intimin (eae). Twenty (8.6%) strains were shown by PCR to harbor the Shiga toxin genes (8 harbored the stx 1 gene, 12 the stx 2 gene and none both of them). Two (0.8%) strains were eae positive; however, they did not carry the stx 1 or stx 2. These strains were also screened for resistance to 12 antimicrobial agents. Predominant resistance was to amikacin (60.0%), gentamicin (50.0%), streptomycin (50.0%) and ampicillin (45.0%). Multidrug resistance was found among 7 isolates (35.0%). These results indicate that dairy cattle from the region surveyed may be a source of STEC potentially pathogenic for humans. KEY-WORDS: Escherichia coli. STEC strains. Antimicrobial resistance. Bovines. Mastitis