Journal of Advances in Microbiology

Aims: The study was carried out to assess the occurrence and biofilm production ability of mastitis causing streptococci and its antimicrobial resistance pattern from cases of clinical bovine mastitis in dairy cows of Wayanad district, Kerala.

Study Design: A cross-sectional study based on bacteriological and laboratory investigation of milk samples.

Place and Duration of Study: Milk samples were collected from dairy farms and rural households in Wayanad district, Kerala. The samples were processed in the Department of Veterinary Epidemiology and Preventive Medicine, College of Veterinary and Animal Sciences, Pookode, Wayanad, Kerala during the study period.

Methodology: A total of 104 milk samples were aseptically collected from cows showing clinical signs of mastitis. Samples were cultured on Brain Heart Infusion agar and examined using standard microbiological procedures. Presumptive identification of Streptococcus spp. was done based on colony characteristics, Gram staining and standard biochemical tests, followed by molecular confirmation by polymerase chain reaction targeting the 16S rRNA gene. Biofilm formation was detected using the Congo Red Agar method. Antimicrobial susceptibility testing was performed using the Kirby–Bauer disc diffusion method on Mueller–Hinton agar according to Clinical and Laboratory Standards Institute guidelines and the resultant patterns were analysed. Isolates showing resistance to three or more antimicrobial classes were considered multidrug resistant.

Results: Among the 104 bacterial isolates obtained, 90 (86.54%) were Gram-positive cocci, of which 19 (18.26%) were identified as Streptococcus spp. on PCR (317bp amplicons). Biofilm production was observed in 17 isolates (89.47%), although the intensity of biofilm formation varied. Antibiotic sensitivity test showed that isolates showed the 78.95% of the isolates were resistant to tetracycline, followed by enrofloxacin and amoxicillin–clavulanate (57.89%). Thirteen out of the nineteen streptococci were found to be multidrug resistant.

Conclusion: The findings indicate that mastitis due to biofilm-forming haemolytic streptococci is widely prevalent in the study area. Majority of the isolates were multidrug resistant, which may contribute to reduced response to therapy. Routine antimicrobial susceptibility testing and rational use of antibiotics are therefore essential for effective mastitis management.