Abstract
Staphylococcus aureus is a major etiological agent of clinical and subclinical bovine mastitis. Owing to the mostly backyard dairy practices, we hypothesized that genetic diversity among mastitis-associated S. aureus from India would be high, and investigated 166 isolates obtained mostly from the Southern State of Karnataka, but also from a few other states. The results revealed (a) 8 to 13 fragments in pulsed-field gel electrophoresis (PFGE), forming 31 distinct patterns, and (b) 34 spa types, of which three (t17680, t18314, and t18320) were newly identified. Multi-locus sequencing typing (MLST) identified 39 sequence types (STs), with ST2454 (34.4%) and ST2459 (24%) being the most commonly represented, which clustered to clonal complexes (CC) CC9 and CC97, respectively; 12 STs were newly identified. Thirty-four (20.5%) of the 166 isolates displayed oxacillin resistance. On the other hand, whereas none were mecC+, 44 (26.5%) isolates were mecA+, with a predominance of SCCmecIVb (26/32 isolates, others being untypeable); 24 isolates (14.46%) were oxacillin-susceptible methicillin-resistant S. aureus (OS-MRSA; mecA+ but OS). Integrated analysis revealed that CC9-ST2454- and CC97-ST2459-SCCmecIVb were the predominant MRSA, although the distribution of CC9 and CC97 was similar between methicillin-resistant and -susceptible isolates. By PCR, 56.25%, 28.75% and 47.5% of the 166 isolates were positive for hlg, tsst and pvl genes, respectively. Our results, for the first time describe the application of a combination of various molecular methods to bovine mastitis-associated S. aureus isolates from India, corroborate the worldwide distribution of CC97 and CC9, and suggest pathogenic potential of the isolates.
Highlights
Staphylococcus aureus is a major etiological agent of clinical and subclinical bovine mastitis
The results showed that 56.25%, 28.75% and 47.5% of the isolates harboured hlg, tsst and pvl genes, respectively (Table 1)
Infection with S. aureus can lead to a wide range of manifestations including clinical as well as subclinical, chronic, persistent and recurrent mastitis
Summary
Staphylococcus aureus is a major etiological agent of clinical and subclinical bovine mastitis. To gain knowledge about similarities among strains, sources of infection, modes of transmission and carriage of virulence and resistance genes, one can employ molecular typing methods which can reveal genetic diversity of the isolates of a particular pathogen. MLST analyses the sequence polymorphism of seven housekeeping genes of each isolate; MLST facilitates comparisons of population structures with high levels of discrimination and r eproducibility[28] These typing methods provide tools to examine the epidemiological picture in terms of diversity and clonality of S. aureus. We analysed 166 isolates of S. aureus obtained from bovine mastitis cases from six different states of India using spa, MLST and PFGE, and found the existence of limited CCs with diversity at genotype level
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