Characterisation of Staphylococcus species from subclinical mastitis dairy cattle in Free State Province, South Africa

Abstract

Background: Mastitis is an important disease in dairy industry causing major economic burden. Subclinical mastitis (SCM) is regarded as one of the most economically important diseases affecting the dairy industry due to the financial constraints incurred by it. Subclinical mastitis as compared to clinical mastitis does not cause visible changes in the udder or physical changes of the milk hence the need for routine testing and surveillance. Materials and methods: The aim of this study was to assess the prevalence of subclinical mastitis in dairy cows of small-holder farms in the Free State province using California mastitis test (CMT) and somatic cell counts (SCC) and further characterise staphylococcal species isolated by using Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and Polymerase chain reaction (PCR). Results: The CMT results revealed that out of 166 cows, only 55 (33%) were positive for intramammary infection. The quarter level prevalence based on SCC was 87 (54%) for intramammary infections. Out of 50 bacterial culture isolates, 48 (96%) were identified as S. aureus (76%), S. epidermidis (4%), S. chromogenes (12%) and S. haemolyticus (4%) by MALDI-TOF MS. The 16S rDNA PCR products and obtained sequences indicated that S. aureus was the dominant species infecting tested cows at 76%, followed by S. chromogenes, S. agnetis, S. argenteus and S. devriesei at 10%, 4%, 4%) and 1% respectively. Conclusions: This study has shown the presence of diverse Staphylococcusspecies infecting subclinical mastitis cows in sampled areas of the Free State province. It further indicated the importance of using various diagnostic tools for bacterial infection surveillance involved in subclinical mastitis to ensure accurate species identification.