A study was carried out to monitor the sequence type of Staphylococcus aureus recovered from bovine mastitic milk in Kaduna State, Nigeria. The dairy cows were analyzed for clinical mastitis, while fresh milk samples were collected from cattle and tested for subclinical mastitis using California Mastitis Test. Isolation of S. aureus was done by culturing the milk onto Baird Parker medium supplemented with egg yolk and potassium tellurite, and antimicrobial susceptibility testing was done as outlined by Clinical Laboratory Standard Institute. Twenty-eight S. aureus were isolated phenotypically from bovine subclinical mastitis which were further examined molecularly for the acquisition of mec A, mec C and fem B genes. All the isolates were negative for mec A and mec C genes, while 3 isolates were positive for fem B gene. Typing using MLST revealed that the 3 fem B positive isolates were MLST type 1 (ST 1) and clonal complex 1, which had similar allelic profiles at all seven loci and showed high degree of monomorphism. The 3 MLST ST 1 isolates were recovered from cases of subclinical mastitis. The antibiotic susceptibility profile showed that the 3 MLST ST 1 isolates were multidrug resistant and resistant to commonly used antimicrobials namely; amoxicillin, ampicillin, cefoxitin, erythromycin, nalidixic acid, oxacillin, penicillin and tetracycline. The phylogenetic relationship established using the nucleotide sequences revealed that the sequence of the strains MT550650, MT550651 and MT550652 had 99 % identity with the S. aureus BX571857, BA000033, AP015012, CP017115 and CP01780 available in the database. The MT550650, MT550651 and MT550652 S. aureus strains obtained were found to be100 % homologous to each other with no divergence within the specie level. The isolation of ST 1 S. aureus strains from milk is of public health significance due to their role in food poisoning. Therefore, the study recommends proper herd, milking environment and milker’s personal hygiene, and proper washing of containers and utensils to reduce the contamination of milk by S. aureus and possible prevention of its spread to other animals and human population.
Keywords: Staphylococcus aureus, MLST, sequence type (ST), subclinical mastitis, settled Fulani herds, Kaduna State