Background: A study was carried out to screen milk borne Staphylococcus aureus for resistance against Beta lactam antibiotics. Methods: A total of 45 milk samples were collected over a period of three months from large animal outpatient unit of Madras Veterinary College Hospital, Chennai. Upon collection of samples, ABST followed by its growth in Mannitol Salt Agar was carried out as part of the phenotypic screening. Genotypic screening for Staphylococcus screening was done with the help of PCR by using nuc and mec A primers. MIC for ceftriaxone and cloxacillin was carried out with the samples that were found positive for Staphylococcus aureus. The antibiotic sensitivity pattern is presented: Fluoroquinolones (87.5% sensitive), aminoglycosides (72.5% sensitive), Amoxicillin-Clavulanic acid (Amoxyclave) (72.5% sensitive). The MSA positive samples were subjected to molecular identification with the help of PCR. Result: The results revealed 10 samples positive for Staphylococcus aureus and 5 among them positive for mecA gene. The MIC results were as follows: MIC50-10.95µg/ml and MIC90- 87.510.95µg/ml for ceftriaxone and MIC50- 43.75 µg/ml and MIC90- 87.5µg/ml for cloxacillin, indicating emergence of resistance. However, further studies are required in a larger sample size that can help us to attain more conclusive results.

Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus (MRSA) presence in milk is of significant importance as they are often involved in food borne intoxications. Effective surveillance and detection are the most important tools in outbreak investigation and control. Our study was designed to ascertain the occurrence Staphylococcus aureus and Methicillin-Resistant S. aureus (MRSA) from raw milk collected from apparently healthy cattle in Chennai city, Tamil Nadu, India. A total of 89 (89/258; 34.49%) positive isolates of Staphylococcus aureus obtained from 258 raw milk samples screened. Of which 24 (24/258; 9.3%) isolates positive for MRSA. Studying the antimicrobial resistance and its patterns in foods of animal origin will be of immense help to various regulatory agencies and authorities to devise and implement control measures and to note the compliance of our foods with the prescribed standards.