Antimicrobial susceptibility of broilers enterococci to enrofloxacin (ENR), gentamicin (GEN), oxytetracyclin (OXT), streptomycin (S) and vancomycin (VAN) was evaluated by both methods. Three types of discrepancies were considered: minor error (one test is intermediate, the other is positive or negative); major error (false"resistant DD result) and very major error (false"susceptible DD result). Levels of agreement between methods to ENR, GEN, OXT, S and VAN were, respectively, 32.4%, 52.9%, 70.6%, 79.4% and 100%. Minor errors were the most frequent. Major errors were found for ENR, S and OXT while very major errors were found for S and GEN. False susceptibility and resistance levels in DD testing may lead to the antimicrobial drug inadequate choice. Specific breakpoints for poultry pathogens and their correspondence in DD testing should be established.

Enterococci, major broiler intestinal colonizers, play a recognized role in antimicrobial resistance transmission. Several virulence mechanisms, such as biofilm expression, have been identified. Minimum inhibitory concentrations of vancomycin, enrofloxacin, oxytetracycline, streptomycin, and gentamicin and biofilm production of 34 isolates from intensive and extensive farming system broilers were evaluated. All isolates were susceptible to vancomycin. In extensive-reared broilers (n = 18), resistance to enrofloxacin, oxytetracycline, streptomycin, and gentamicin was high (83.33, 55.56, 100, and 83.33%, respectively). Intensive farming broilers (n = 16) showed a lower resistance level for enrofloxacin and streptomycin and a higher resistance level for oxytetracycline and gentamicin. The relation between antimicrobial susceptibility and farming system was not significant for all drugs tested (P > or = 0.05). Enterococci produced biofilm at 24 h (47.0%), 48 h (55.9%), and 72 h (58.8%). Resistance to gentamicin and streptomycin was related to biofilm production at all time points (P < or = 0.05), whereas resistance to enrofloxacin was only related to biofilm at 24 h (P < or = 0.05; Friedman's test). No relation was found between susceptibility to oxytetracyclin and biofilm formation at any of the 3 time points studied (P > or = 0.05). Poultry are colonized by biofilm-producing and antimicrobial-resistant enterococci, independently of the farming system. Results show a relation between resistance to the majority of the drugs tested and biofilm production, which reenforces the importance of these virulence factors in animal and public health.