Screening of bovine milk samples for sub-clinical mastitis and antibiogram of bacterial isolates

Abstract

The study was undertaken to find out the incidence of subclinical mastitis (SCM) and to assess the antibiotic sensitivity pattern of the causative organisms in lactating cows in and around Kanakapura taluk, Ramanagara district of Karnataka state. The prevalence of subclinical mastitis was assessed by the results of 3 different screening tests and bacteriological evaluation was done for the milk samples that were found positive. The predominant bacterial isolates recovered were Staphylococcus aureus (58%) and Escherichia coli (23.5%) followed by Staphylococcus epidermidis (8%), Streptococcus sp. (5.5%), Klebsiella sp. (3%) and Bacillus sp. (2%). The in vitro antibiogram studies of bacterial isolates revealed higher sensitivity for ciprofloxacin (89%), ofloxacin (85%), enrofloxacin (82%), gentamicin (80%) and chloramphenicol (75%), resistant to colistin, neomycin, streptomycin, penicillin and tetracycline. Subclinical Mastitis causes higher economic Hi Media Laboratories Ltd., Mumbai) plates against losses to farmers. Subclinical mastitis goes without commonly used antibiotics in the field as per the diagnosis. So, The study was undertaken to find out method of Bauer et al. (1966). Minimal Inhibitory the incidence of subclinical mastitis (SCM) and to Concentration (MIC) values of the bacterial organisms assess the antibiotic sensitivity pattern of the causative were analyzed against common antibiotic discs (M/s organisms in lactating cows in and around Kanakapura Hi Media Laboratories Ltd., Mumbai). The following taluk, Ramanagara district of Karnataka state. antibiotic discs namely chloramphenicol (30µg), ofloxacin (10µg), ciprofloxacin (10µg), colistin (Methane Materials and Methods sulphonate (25 µg), enrofloxacin (10 µg), penicillin gentamicin (30 µg), tetracycline (30 µg), Sources of milk samples (10 I.U.), : A total of 250 milk neomycin (30 µg), streptomycin (10 µg) were used. samples from lactating cows in and around Kanakapura taluk, Ramanagaram district were Results and Discussion screened for subclinical mastitis by white side test, california mastitis test and chloride test (Schalm et al., Screening of milk samples from 250 cows by the 1971). The samples were subjected to bacteriological three tests revealed 75% (175) cows to be affected study in the regional laboratory by inoculating with SCM. Cultural examination of positive samples approximately 0.01 ml of milk sample on to blood revealed higher incidence of Staphylococcal mastitis. agar, nutrient agar, MacConkey's agar and Eosine Out of 175 samples, 105 samples (60%) yielded pure Methylene Blue agar plates and the plates were and the remaining 70 (40%) yielded mixed cultures. 0 incubated “under aerobic conditions” at 37 C for 24 to Totally 200 bacterial cultures were recovered. The 48 hours. The staining and cellular morphological predominant bacterial isolates were Staphylococcus features of organisms were ascertained by microscopic aureus (58%) and Escherichia coli (23.5%) followed examination of Gram stained smears. The bacteria by Staphylococcus epidermidis (8%), Streptococcus isolated were identified on the basis of their cultural, sp. (5.5%), Klebsiella sp. (3%) and Bacillus sp. (2%). morphological and biochemical characteristics as per The frequency of isolation of different bacterial species the method of (Cruickshank et al., 1975).