Prevalence and Molecular Diagnosis of Staphylococcus aureus Subclinical Mastitis in Lactating Nili-Ravi Buffaloes (Bubalus Bubalis) at Livestock Experiment Station, Bahadurnagar, Okara, Pakistan

Subclinical mastitis is 3 to 40 times more common than clinical mastitis and causes great losses in the dairy herds. Staphylococcus aureus (S. aureus) is one of the most common causative agents of subclinical bovine mastitis in dairy cattle worldwide and it has been observed that up to 50 - 100% of herds are infected with this pathogen. To determine prevalence and compare bacterial culture methods and polymerase chain reaction (PCR) for diagnosis of subclinical mastitis caused by S. aureus, milk samples from 164 apparently mastitis free Nili-Ravi buffaloes were collected from lactating herd at Livestock Experiment Station, Bahadurnagar Okara. These samples were initially tested by using subclinical mastitis detection kit "CMT Test" and eighteen milk samples (10.97%) were found positive for subclinical mastitis by using this kit. To compare cultural technique with PCR, all these 164 milk samples were cultured on blood agar and the bacteria were identified by standard methods. Ten out of 164 samples showed cultural growth of the organism, thus showing prevalence 6.09 % (10 /164) of S. aureus by using conventional culturing technique. DNA was extracted from all 164 milk samples as well as from samples cultured in broth & blood agar plate colonies. All these were then subjected to PCR test with primers STAA-AUI and STAA-AVII, for a 420 bp amplicon specific for S. aureus. Thirty two (19.51 %) out of 164 milk samples, 18 broth culturing and 10 bacterial colonies were found positive for S. aureus by PCR. The results of this study indicate that PCR is sensitive and specific for diagnosis of S. aureus subclinical mastitis and can detect this pathogen in milk samples within few hours in Nili-Ravi buffaloes.