Antimicrobial susceptibility of lactamase-positive and lactamase-negative bacteria strains isolated from mastitis in cows [Polish]

摘要

The purpose of the study was to examine 120 Staph. aureus strains, 196 coagulase-negative staphylococci (CNS) strains, and 84 Gram-negative bacteria strains isolated from clinical and subclinical cases of mastitis for their susceptibility in-vitro to antimicrobial drugs depending on the strain's ability to produce beta-lacatamase. Antimicrobial sensitivity was tested by the disk diffusion method and performed according to NCCLS guidelines in Mueller-Hinton agar. The detection of beta-lactamase production was determined by Oxoid sticks impregnated with Nitrocefin, a chromogenic cephalosporin where a positive reaction is shown by the development of a pink-red colour of the tip of the stick. 54.2% of Staph. aureus tested strains, 29.1% CNS strains and 91.7% Gram-negative bacteria strains were lactamase-positive. All the lactamase-positive Staph. aureus strains were resistant to penicillin and 96.9% of them were resistant to ampicillin. Their resistance to cloxacillin (18.5%), cefoperazone (20%) and cephalexine 1 (7.6%) was relatively low but it was high to amoxicillin (52.3%). Clavulanic acid caused an in-vitro increase of activity of amoxicillin from 47.7% up to 81.5%. The lactamase-negative coagulase-positive staphylococci were susceptible to beta-lactam antibiotics in 90-100% of cases. The sensitivity of lactamaso-positive CNS strains to antibiotics was very similar to Staph. aureus strains. The sensitivity of lactamase-positive and lactamase-negative strains of Gram-negative bacteria to beta-lactam antibiotics did not differ. The combination of amoxicillin with clavulanic acid increased its activity in-vitro compared to pure amoxicillin. No connection between beta-lactamase production of 1 staphylococci and Gram-negative bacteria strains and their sensitivity to streptomycin, neomycin, gentamycin, erythromycin, tylosin tetracycline, bacitracine, lincomycine, novobiocin and norfloxacin was noted.