ANTIMICROBIAL SUSCEPTIBILITY AND MOLECULAR CHARACTERIZATION OF STAPHYLOCOCCUS AUREUS FROM MASTITIC COWS

ABSTRACT

This study investigated the antimicrobial susceptibility and molecular characterization of Staphylococcus aureus in mastitic cows in southern part of Kano State of Nigeria. A total of two hundred and thirty four (234) milk and swab samples were collected from six (6) local government areas of Kano State in northern part of Nigeria. Staphylococcus aureus was isolated from samples and identified using standard microbiological procedures. The antimicrobial susceptibility of the isolates was determined using Kirby- Bauer disc diffusion technique as described by the Clinical and Laboratory standards institute (CLSI). Resistant isolates were tested for Beta-lactamase production. A total of 200 (85.5%) have staphylococcal isolates, of which 141 (70.5%) were Staphylococcus aureus (coagulase positive staphylococci, CPS), 59 (29.5%) were coagulase negative staphylococci (CoNS) and 6 (2.9%) were non- Staphylococcal (rods) isolates. The antibiotic susceptibilities of the Staphylococcus aureus isolates were in the following order: ofloxacin (99.3%) > ciprofloxacin (98.6%) > gentamicin (91.5%) > cephalexine (56%) >

sulphamethoxazole/trimethoprim (46.1%) > tetracycline (43.3%) > cefuroxime (33.3%) > cefoxitin (2.1%) > amoxicillin (1.4%) > ampicillin (1.4%). Resistance to three or more antimicrobials was presented in 98.6% of the Staphylococcus aureus isolates. Of the 141 Staphylococcus aureus isolates tested for β-lactamase production, 31 (22.5%) were β lactamase producers. However, of the 31 β-lactamase producers, only 13 (41.9%) were multidrug resistant to cefoxitin, Ampicillin and cephalexine. PCR assay was used to detect mecA and blaZ genes in multi-drug resistant Staphylococcus aureus isolates that were β-lactamase producers. The MDR- Staphylococcus aureus was also tested by latex agglutination for presence of PBP2a. PCR results indicated none of the isolates showed any amplification to both mecA gene and blaZ gene. All the Beta-lactamase producing MDR- Staphylococcus aureus isolates tested showed negative reaction to latex agglutination test which was also an indication of absence of Pinicillin binding protein

(PBP2a). In conclusion, high isolation of Staphylococcus aureus (70.5%) causing bovine mastitis was observed in this study in which both mecA and blaZ genes were absent.

Key words: Staphylococcus aureus, CoNS, CPS, Mastitis, β-lactamase, PCR, Disk diffusion test