Occurrence and antibiotic resistance of coliform bacteria and antimicrobial residues in pasteurized cow's milk from Brazil.

In this study we examined the hygienic and sanitary quality of pasteurized cow's milk in the state of Paraná, Brazil, by determining the presence of coliforms and occurrence of antimicrobial residues. A total of 260 milk samples were collected from commercial establishments in different regions of the state. Coliform populations were estimated by the multiple-tube test, and antimicrobial residues were detected by enzyme-linked immunosorbent assay. Overall, 105 samples (40.4%) were unsuitable for consumption according to Brazilian legal standards. Among the coliforms, Escherichia coli and Klebsiella pneumoniae were respectively identified in 77.05 and 36.07% of the samples. The highest rates of resistance to antimicrobial agents were observed for ampicillin (19.2%), cephalothin (18.9%), and tetracycline (17.1%). Antimicrobial residues were detected in 80 samples (30.8%). Forty-eight samples (18.5%) were positive for tetracycline, 29 (17.4%) for neomycin, 9 (3.5%) for beta-lactams, 6 (2.3%) for gentamicin, 4 (1.5%) for chloramphenicol, and 1 (0.4%) for streptomycin-dihydrostreptomycin. The results demonstrate a high prevalence of coliforms and also a high occurrence of antimicrobial residues in pasteurized cow's milk from Paraná, Brazil.