Identification of coagulase-negative staphylococci isolated from caprine milk samples by PCR-RFLP of groEL gene

Abstract

Coagulase-negative staphylococci (CNS) are the most common cause of intramammary infection (IMI) in small ruminants. In this study, 143 CNS isolates were collected from 1385 sarda goats belonging to 29 herds with high somatic cell count scores. In order to make light of the role of CNS species in goat mastitis, all isolates were subjected to identification with the API Staph ID test, and then to amplification of staphylococcal groEL gene by PCR assay. Amplicons of groEL gene were submitted to restriction fragment length polymorphism analysis with the enzyme AluI. When PCR-RFLP patterns of CNS isolates were different from those of their reference strains, groEL gene amplicons were sequenced for definitive identification. The API Staph ID test, in alternative to the genotypic identification method, produced considerably different results in terms of species identified within each group. Using the PCR-RFLP assay, most of the isolates clustered together with the Staphylococcus epidermidis type strain (53, corresponding to 37%), followed by S. caprae (45, corresponding to 31.4%), S. chromogenes (19, corresponding to 13.2%) and S. simulans (7 corresponding to 4.8%). In conclusion, the PCR-RFLP assay of groEL gene is a more reliable and reproducible method than the API Staph ID test for the identification of CNS causing goats mastitis.