Real-time PCR Based Assay Offers High Resolution in Detecting Bacterial Species from Bovine Sub-clinical Mastitis for Prudent Antimicrobial Treatment

Quick and reliable detection of bacterial species causing bovine sub-clinical mastitis is pivotal in determination of the antimicrobial treatment to minimize economic losses and ensure re-establishment of cattle health. The performance of conventional bacterial culture examination and real-time PCR based assay while screening cattle for sub-clinical mastitis is evaluated. 156 quarter milk samples (qms) (103 from sub-clinically affected (SCM) quarters and 53 from healthy quarters) were simultaneously subjected to PathoProof mastitis PCR assay and bacterial culture examination. On bacteriological culture examination, 93 (90.29 %) out of 103 qms from SCM quarters showed positive results, revealing either the presence of 1, 2 or 3 bacterial species. However, PathoProof mastitis PCR assay showed presence of one or more bacterial species in all 103 SCM quarters. From healthy quarters, out of a total of 53 qms, 8 (15.09 %) were positive bacteriologically and by PathoProof mastitis PCR assay. Out of remaining 45 (84.91 %) qms, 42 (79.25 %) which showed negative results on bacterial culture showed presence of one or more bacterial species on PathoProof mastitis PCR assay. Overall, in 18 (11.54 %) out of 156 milk samples from healthy and sub-clinically mastitic quarters, both techniques provided identical results. In 78 (50%) qms, PathoProof mastitis PCR assay detected the species identified by bacterial culture, however, it also detected one or more additional species. In 8 (5.13 %) qms, both tests identified different species, while in 52 (33.33 %) qms which were negative on bacterial culture, PathoProof mastitis PCR assay detected one or more species. Thus, common mastitis causing bacteria may be present in large numbers, but are not detected by conventional bacterial culturing. The real-time PCR kit exemplified the advantages over conventional culturing in terms of speed, automated interpretation and increased sensitivity. Hence, this kit proves to be an indispensible parallel component in identification of pathogens. Quick and reliable identification of mastitis causing microorganism is central in management of disease and deciding the treatment with antimicrobials. In future, a similar kit can be designed which is affordable to dairy farmers across the world.