Abstract

RIBEIRO, M.G. et al. Virulence factors in Escherichia coli strains isolated from bovine mastitis. Arq. Bras. Med. Vet. Zootec. [online]. 2006, vol.58, n.5, pp. 724-731. ISSN 0102-0935.  http://dx.doi.org/10.1590/S0102-09352006000500004.

The occurrence of different virulence factors and O157:H7 serotype investigation in 120 Escherichia coli strains isolated from clinical (80 cases) and subclinical (40 cases) bovine mastitis was evaluated. Alpha-haemolysin was detected in 8 (6.7%) strains (5 clinical and 3 subclinical cases). None strain showed enterohaemolysin production. E. coli growth under iron restriction conditions (siderophores production) was observed in 11 (9.2%) strains (7 clinical and 4 subclinical cases). STa enterotoxin was detected in 2 (1.7%) strains from subclinical cases. Cytotoxic effect in vero cells compatible with verotoxin-VT production was observed in 5 (4.2%) strains (2 clinical and 3 subclinical cases). One strain (0.8%) isolated from clinical mastitis showed cytophatic effect in vero cells compatible with cytotoxic-necrotic-factor production. None strain showed non-sorbitol fermenting colonies using sorbitol MacConkey agar and agglutination with specific anti-sera for E. coli O157:H7 serotype investigation. Polymixin B (97.5%) and norfloxacin (95.8%) were the most effective drugs. Multiple-drug resistance for 2 or more antimicrobials was observed in 24 (20.0%) strains, mainly with use of ampicillin and ceftiofur.

Keywords : bovine; mastitis; Escherichia coli; virulence; toxin; serotype O157:H7.