Abstract

Ruminal bacterial isolates, 59 from two sheep, five cows and nine buffaloes were used to evaluate sensitivity to the therapeutic antibiotics amikacin, cefadroxil, cefoperazone, cefotaxime, chloramphenicol, ciprofloxacin, erythromycin, gentamicin, piperacillin, polymyxin, roxithromycin, streptomycin and vancomycin. Sensitivity of ruminal bacterial isolates to each was determined by the clearance zone (CZ) in the Kirby-Bauer disc diffusion susceptibility test. Bacterial isolates from sheep exhibited, in general, lower resistance (P=0.040) to antibiotics than buffalo. Irrespective of ruminant species, bacterial isolates had a higher tolerance (P<0.001) to cefadroxil (CZ=3.1 mm), whereas ciprofloxacin (CZ=24.4 mm) followed by erythromycin (CZ=20.9 mm) and amikacin (CZ=20.0 mm) were the most toxic antibiotics to all isolates. Inhibitory effects of other antibiotics to ruminal bacterial isolates were intermediate, with two groups of antibiotics according to CZ size, being those with a CZ of 12-19 mm (gentamicin > roxithromycin > cefotaxime = vancomycin > cefoperazone > piperacillin), and those with CZ size of 7-10 mm (streptomycin > chloramphenicol = polymyxin). Sub-therapeutic antibiotic use in ruminant feeding to optimize rumen fermentation may lead to residues in meat and milk, as well as increase their inhibition to ruminal bacterial populations.

Key words: Antibiotics, buffalo, cattle, sheep, clearance zone, ruminal bacteria isolates.

Abbreviation

CZ, clearance zone.