Staphylococcus aureus is one of the major causes of mastitis in dairy animals and its resistance against multiple antimicrobials always remains crucial concern. Present investigation was carried out to detect the distribution of antibiotic-resistant genes of S. aureus isolates. Isolates (128) of S. aureus from mastitic milk were collected, tested for antibiotics with disc-diffusion method, and resistant genes mecA, linA, msrA msrB, vatA, vatB, vatC ermA, ermC tetK, tetM and aacA-D were detected by PCR. The phenotypic antibiotics resistance percent in S. aureus isolates was classified as tetracycline (36.7), gentamycin (30.5), streptomycin (26.6), kanamycin (25.8) and penicillin G (22.7). All the isolates were susceptible to vancomycin. Among isolates, 10.2% were observed as methicillin-resistant. The distribution of antibiotic-resistant genes was linA (51.6) followed by msrB (46.1), tetK + M (34.4), msrA and aacA-D (26.6%). Different antibiotic-resistant genes combinations (mecA/linA-2; mecA/aacA-D/tetK/linA/msrB-3; mecA/linA/msrA/msrB-3; aacA-D/linA/msrA/msrB-4; aacA-D/linA/msrB-7; linA/msrA/msrB-10; tetK/linA/msrA/msrB-11; aacA/tetK/linA/msrB-12 isolates) were observed. All the isolates lacked amplification of vatA, vatB, ermA and ermC genes. Molecular typing resulted genetic variation in protein A (6-12 repeats) and coagulase genes (A-E patterns) were observed. Coagulase A and D genotypes were more prevalent in antibiotic-resistant isolates, while E, B and C in susceptible ones. The significant observation was the prevalence of methicillin-resistant S. aureus, which were resistant to multiple antibiotics. Findings revealed the status of resistant isolates in herd that might be helpful in treatment, controlling of resistant strains and culling of cows for mastitis reduction.

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious problem in dairy animals suffering from mastitis. In the present study, the distribution of mastitic MRSA and antibiotic resistance was studied in 107 strains of S. aureus isolated from milk samples from 195 infected udders. The characterizations pathogenic factors (adhesin and toxin genes) and antibiotic susceptibility of isolates were carried out using gene amplification and disc diffusion assays, respectively. A high prevalence of MRSA was observed in the tested isolates (13.1%). The isolates were also highly resistant to antibiotics, i.e. 36.4% were resistant to streptomycin, 33.6% to oxytetracycline, 29.9% to gentamicin and 26.2% each to chloramphenicol, pristinomycin and ciprofloxacin. A significant variation in the expression of pathogenic factors (Ig, coa and clf) was observed in these isolates. The overall distribution of adhesin genes ebp, fib, bbp, fnbB, cap5, cap8, map and cna in the isolates was found to be 69.1, 67.2, 6.5, 20.5, 60.7, 26.1, 81.3 and 8.4%, respectively. The presence of fib, fnbB, bbp and map genes was considerably greater in MRSA than in methicillin-susceptible S. aureus (MSSA) isolates. The proportions of toxin genes, namely, hlb, seb, sec, sed, seg and sei, in the isolates were found to be 94.3, 0.9, 8.4, 0.9, 10.2 and 49.5%, respectively. The proportions of agr genes I, II, III and IV were found to be 39.2, 27.1, 21.5 and 12.1%, respectively. A few isolates showed similar antibiotic-resistance patterns, which could be due to identical strains or the dissemination of the same strains among animals. These findings can be utilized in mastitis treatment programmes and antimicrobials strategies in organized herd.

To keep the concept of a safe food supply to the consumers, animal feed industries world over are showing an increasing interest in the direct-fed microbials (DFM) for improved animal performance in terms of growth or productivity. This becomes all the more essential in a situation, where a number of the residues of antibiotics and/or other growth stimulants reach in milk and meat with a number of associated potential risks for the consumers. Hence, in the absence of growth stimulants, a positive manipulation of the rumen microbial ecosystem to enhance the feedstuff utilization for improved production efficiency by ruminants has become of much interest to the researchers and entrepreneurs. A few genera of live microbes (i.e., bacteria, fungi and yeasts in different types of formulations from paste to powder) are infrequently used as DFM for the domestic ruminants. These DFM products are live microbial feed supplements containing naturally occurring microbes in the rumen. Among different DFM possibilities, anaerobic rumen fungi (ARF) based additives have been found to improve ruminant productivity consistently during feeding trials. Administration of ARF during the few trials conducted, led to the increased weight gain, milk production, and total tract digestibility of feed components in ruminants. Anaerobic fungi in the rumen display very strong cell-wall degrading cellulolytic and xylanolytic activities through rhizoid development, resulting in the physical disruption of feed structure paving the way for bacterial action. Significant improvements in the fiber digestibility were found to coincide with increases in ARF in the rumen indicating their role. Most of the researches based on DFM have indicated a positive response in nutrient digestion and methane reducing potential during in vivo and/or in vitro supplementation of ARF as DFM. Therefore, DFM especially ARF will gain popularity but it is necessary that all the strains are thoroughly studied for their beneficial properties to have a confirmed ?generally regarded as safe? status for ruminants.authorsversionPeer reviewe