Antibiogram Pattern of Bacterial Isolates Identified from Bovine Clinical Mastitis

A total of 65 milk samples from bovine clinical mastitis were collected from villages of Sabarkantha Milk Union and were subjected to bacterial isolation and identification. Out of 74 recovered isolates, Str. agalactiae was the most frequent, followed by E. coli and Str. dysgalactiae. The in-vitro antibiogram revealed that most isolates were sensitive to ceftriaxone/tazobactam, followed by gentamicin, tetracycline and cefoperazone/sulbactam. Ampicillin/cloxacillin combination was found least effective.

Mastitis is one of the major diseases of bovines that seriously affecting the profitability of dairy farmers. Around 70% of the avoidable losses in productivity are reported due to mastitis alone (Sumathi et al., 2008). In India, annual economic losses due to mastitis has been estimated ` 7165.51 crores (Bansal and Gupta, 2009). The economic losses associated with clinical mastitis are mainly due to decreased milk production, milk discard during the withholding period after antibiotic usage (together accounting for 25%), veterinary and labour cost, decreased milk quality, culling and, fatalities. Antibiotic usage in dairy animals is by and large attributed to the treatment of mastitis. The emergence of antibiotic resistance is an important issue that has public health implications. Identification of organism and their antibiogram pattern needs to monitor on a regular basis. The present study was conducted to assess the prevalence of bacterial pathogens associated with clinical mastitis in bovines and, to study their antibiogram pattern.
Sixty-five quarter milk samples were collected from bovines with clinical mastitis from different villages of Gujarat. The milk samples were collected aseptically from milch animals by standard milk sampling technique using sterile vials and stored at 4°C until processed (NMC, 2017).
For bacteriology, milk samples were examined by standard protocol (Quinn et al., 2004). For isolation of Gram negative organisms, MacConkey's agar was used. After obtaining growth on MacConkey's agar, Eosine Methylene Blue (EMB) agar was used as the selective media. Mannitol Salt Agar and Edwards medium were used for the isolation of Staphylococcus and Streptococcus, respectively. For isolation of Klebsiella spp., Klebsiella special agar was used. The bacterial isolates were identified based on the cultural, morphological and biochemical characteristics (Edward and Ewing, 1972). Catalase, coagulase, oxidase, latex agglutination test, IMViC (Indole test, methyl-red test, Voges-Proskauer test, citrate utilization test), urease production, glucuronidase, lysine utilization, ortho-Nitrophenyl-β-galactoside (ONPG) test were performed for identification of the bacterial isolates.
In-vitro antibiotic sensitivity of the isolates was assessed by disc diffusion method (Bauer et al., 1996) using six antibiotic discs (Hi-Media) namely, gentamicin, enrofloxacin, ampicillin/cloxacillin, ceftriaxone/ tazobactam, cefoperazone/sulbactam and tetracycline. The antibiotic discs were chosen as per the pattern of use by the veterinarians. Sensitivity was determined on the basis zone of inhibition as per the manufacturer's instructions (Hi-Media).
In an earlier study, Staphylococcus spp., Streptococcus spp. and E. coli were found sensitive to gentamicin, tetracycline and enrofloxacin (Kaur et al., 2015). In another research study, S. aureus, Str. dysgalactiae and E. coli were reported to be sensitive to ceftriaxone/tazobactam (Bhat et al., 2017). Jhambh et al. (2012) reported low sensitivity of coliforms to ampicillin/cloxacillin combination. These observations are in accordance with the findings of the present study. The lower sensitivity of most antimicrobials could be attributed to the indiscriminate use of these antibiotics in the field which is an important factor for antibiotic resistance.

CONCLUSION
Bacteriological isolation, biochemical characterization of mastitis causing organisms and subsequently determining their antibiotic susceptibility is important in the therapeutic management of bovine clinical mastitis.