Staphylococcusspp. associated with subclinical bovine mastitis in central and northeast provinces of Thailand

Abstract

BackgroundStaphylococcusspp. are major cause of bovine mastitis (BM) worldwide leading to economic damage to dairy farms and public health threat. Recently, a newly emergedStaphylococcus argenteushas been found as a human and animal pathogen. Molecular characteristics, virulence and antibiotic resistant phenotypes of bacteria causing BM in Thailand are rare. This study aimed to investigatedStaphylococcusspp. associated with subclinical bovine mastitis (SCM) in Thailand.MethodsMilk samples were collected from 224 cows of 52 dairy herds in four central and northeast provinces. Total somatic cell counts (SCC) and California mastitis test (CMT) were used to identify SCM cows. Milk samples were cultured forStaphylococcusspp. Coagulase-positive isolates were subjected to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Organisms suspected asS. argenteuswere verified by detecting nonribosomal peptide synthetase gene. All isolates were checked for antibiograms and the presence of various virulence genes.ResultsFrom the 224 milk samples of 224 cows, 132 (59%) were positive for SCM by SCC and CMT and 229 staphylococcal isolates were recovered. They were 32 coagulase-positive (24S. aureusand eightS. argenteus) and 197 coagulase-negative. PFGE of theS. aureusandS. argenteusrevealed 11 clusters and a non-typeable pattern. MLST of representatives of the 11 PFGE clusters, three PFGE non-typeableS. aureusisolates from different locations andS. argenteusshowed 12 sequence types. The eightS. argenteusisolates belonged to ST1223 (three isolates), ST2250 (two isolates), and ST2793 (two isolates). The antimicrobial tests identified 11 (46%) methicillin-resistantS. aureusand 25 (13%) methicillin-resistant coagulase-negative isolates, while sevenS. argenteuswere methicillin-susceptible and one isolate was methicillin-resistant. All of the 229 isolates were multiply resistant to other antibiotics. The most prevalent virulence genes of the 24S. aureusisolates wereclfA,coaandspa(X and IgG-binding region) (100%),hla(96%),pvl(96%) andsec(79%). SixS. argenteusisolates carried one enterotoxin gene each and other virulence genes includingcoa, clfA, hla/hlb, spa, tsstandpvl, indicating their pathogenic potential.Conclusion and perspectiveThis is the first report on theS. argenteusfrom cow milk samples with SCM. Data on the molecular characteristics, virulence genes and antibiograms of theStaphylococcusspp. obtained from the present study showed a wide spread and increasing trend of methicillin-resistance and multiple resistance to other antibiotics. This suggests that the “One Health” practice should be nurtured, not only at the dairy farm level, but also at the national or even the international levels through cooperation of different sectors (dairy farmers, veterinarians, medical and public health personnel and scientists) in order to effectively combat and control the spread of these pathogens.