Staphylococcal species associated with bovine mastitis in the North West of Iran: Emerging of coagulase-negative staphylococci

Staphylococcal mastitis is a major and costly problem of dairy cattle all over the world. The objective of this study was to isolate and identify the main staphylococcal species causing bovine mastitis in 7 dairy herds located in 4 different areas of East and West Azerbaijan provinces, Iran. Of the 158 mastitic milk samples collected, 113 staphylococcal isolates were identified (71.5%) on the basis of cultural and biochemical features as well as by genus specific PCR. Then, species level identification of staphylococcal isolates was carried out using restriction fragment length polymorphism (RFLP) analysis of the gap gene (933 bp). On the basis of polymerase chain reaction-RFLP, 10 different patterns were identified. Of 113 isolates, 5 (4.4%) were Staphylococcus aureus and 108 (95.6%) were coagulase-negative staphylococci (CoNS). Overall, nine different species of CoNS were identified as: 44 Staphylococcus haemolyticus (40.7%), 17 Staphylococcus chromogenes (15.7%), 11 Staphylococcus epidermidis, Staphylococcus warneri and Staphylococcus cohnii each (10.2%), 6 Staphylococcus simulans (5.5%), 4 Staphylococcus hominis (3.7%), 3 Staphylococcus capitis (2.7%) and 1 Staphylococcus xylosus (0.9%). S. haemolyticus, S. chromogenes and S. warneri were the only species identified from clinical mastitis. No significant difference in staphylococcal IMI was found among the studied herds and regions. This study demonstrated that CoNS, especially S. haemolyticus and S. chromogenes, were predominant and thus be considered as emerging pathogens causing mastitis in the North West of Iran. Our results also revealed that the gap PCR-RFLP was useful for identifying staphylococcal isolates derived from bovine mastitis at species level.