OCCURRENCE OF MASTITIS AND METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS IN GOATS IN ZARIA, NIGERIA
A cross sectional study was conducted to determine the occurrence of mastitis and \methicillin resistant Staphylococcus aureus (MRSA) in milk samples obtained from lactating goats in Zaria, Kaduna state, Nigeria. The specific objectives of the study were to determine the occurrence of mastitis in goats in Zaria, determine the prevalence of S. aureus in goat milk, document the antimicrobial susceptibility profiles of S. aureus isolates to commonly used antibiotics and finally to detect mecA gene by PCR in phenotypically confirmed MRSA isolates. A total of 386 fresh milk samples from both right and left halves of 198 lactating goats from farms and households were examined for the occurrence of mastitis and MRSA. The observed prevalence of mastitis in goats, defined by positive (≥+1) California Mastitis Test (CMT) was 119 (60.1%). From a total of 386 fresh goat milk samples examined, 60 strains of staphylococci were isolated and identified using the conventional biochemical tests and 32 of which were identified as Staphylococcus aureus using the MicrogenTMSTAPH-ID system. Furthermore, 12 of these 32 showed agglutination with the PBP-2a Latex agglutination test reagent. The susceptibilities of the isolates to 14 antimicrobial agents were evaluated using the Kirby-Bauer disc diffusion method and interpreted as sensitive, intermediate or resistant following the Clinical and Laboratory Standards Institute (CLSI, 2011). Out of the 32 isolates of S. aureus ; 90.63% were resistant to cefoxitin, penicillin G (93.75%), ampicillin (100%), amoxicillin-clavulanic acid (34.38%), ceftriaxone (71.88%), vancomycin (31.25%), gentamicin (31.25%), kanamycin (46.88%), erythromycin (43.75%), tetracycline (40.63%), ciprofloxacin (3.13%), nitrofurantoin (15.63%), trimethoprim-sulfamethoxazole (25%) and chloramphenicol (15.63%). All the isolates were resistant to 2 or more antimicrobial agents, but none was simultaneously resistant to all. There were 30 antimicrobial resistant patterns in which resistance to ampicillin, penicillin G, vii cefoxitin were the most frequent. Methicillin resistance was determined using cefoxitin discs as a surrogate marker of mecA gene as recommended by Clinical Laboratory Standards International (CLSI). A total of 19 Staphylococcus aureus isolates that showed phenotypic resistance to methicillin (cefoxitin) and showing multiple antibiotic resistance (resistance to 3 antibiotic classes apart from beta-lactams) were selected for molecular detection of mecA by Polymerase Chain Reaction (PCR). The results of the PCR showed that none of the 19 S. aureus harboured the methicillin resistance mecA gene. The findings of this study confirm the importance of S. aureus as a mastitis causing organism and the possible role of goats in the transmission of multiple drug resistant S. aureus, and it is recommended that microbiological examination of udder of lactating goats should be carried out at regular intervals to detect and treat mastitis and goat milk should be pasteurized before consumption.