The livestock sector plays a critical role in strengthening the economy of Pakistan. Control of livestock diseases is the primary objective of government livestock departments. Bovine mastitis is among the most significant diseases of livestock as reported by various field surveys in Pakistan. Despite considerable knowledge about mastitis and its etiology, this disease is still prevalent in many dairy herds; it remains most difficult to eradicate or control. It is an inflammation of mammary gland resulting in decreased milk production, veterinary care costs and culling losses.
In animal health improvement, there is a paradigm shift from treatment of clinical illness to disease prevention. Recognition of disease is the foundation of disease control and prevention. California mastitis test and somatic cell counting are the most commonly used methods for diagnosis of bovine mastitis. These methods are unable to identify the causative agent. Detection of pathogen is critically important for better control of mastitis. Microbial culturing and biochemical tests are traditionally used methods for pathogen identification. But, these methods are very time consuming and can only detect viable bacteria from the sample and can lead to false negative results. The progress in molecular methods based on PCR has improved the veterinary diagnostics.
For the identification of bovine mastitis pathogens, an economical, rapid and sensitive molecular diagnostic assay was developed using multiplex PCR, detecting the pathogenic species-specific DNA. The target species areS. aureus,E. coli, S. uberis, S. agalactiae, S. dysagalactia, S. haemolyticus, S. epidermidis, S. chromogenes andM. bovis. Multiplex PCR assay was developed for the detection of these significantly important bacterial pathogen
causing bovine mastitis. Species specific primers were designed which have the ability to specifically amplify the particular gene in the target species. For this purpose various gene regions were selected for different bacterial species which included 16S rRNA, cpn60, phoA and rdr. Initially monoplex PCRs were optimized individually for each target species. For optimizing multiplex PCR assay, various combinations of individual PCRs with varying concentrations of primers and template DNA were used. The final protocol included all the nine sets of primer pairs, every set targeting a unique mastitic pathogen. Multiplex PCR assay was checked for its specificity and analytic sensitivity was calculated. Mastitic milk samples were collected aseptically from various farms. Initial screening was based on Surf field mastitis test and California mastitis test. Milk samples were cultured on nutrient agar, blood sheep agar and MacConkey’s agar. The bacterial isolates were identified and further sub-cultured in nutrient broth. All the isolates were identified on the basis of 16S rRNA sequencing analysis.
The developed multiplex PCR assay was used to detect the target bacterial pathogens from the collected milk samples. Limit of detection of developed assay was up to 50 pg for DNA isolated from pure cultures and 104 CFU/ml for spiked milk samples. The results obtained by 16S rRNA sequencing, bacterial culture based identification and multiplex PCR assay were compared. Sensitivity and specificity were calculated using latent class analysis, specificity was up to 88% and sensitivity was up to 98% for targeted mastitic pathogens. The developed multiplex PCR detected nine bacterial species in a single reaction. Multiplex PCR assay has also detected the bacterial pathogens in a few culture-negative mastitis milk samples. This is the first multiplex PCR assay which can efficiently detect nine important mastitic bacterial pathogens in a single reaction. The development of multiplex PCR assay is useful in early diagnosis and prevention & control of bovine mastitis.
Mycoplasma is often ignored as a major mastitis-causing pathogen due to lack of rapid and accurate diagnostic tools. In this study a LAMP assay was developed for the identification of M. bovis from clinical mastitic milk samples. LAMP primers were designed from three gene regions including uvrC, 16S rRNA and gyrB. Bacterial reference strains and mastitic milk samples positive for M. bovis were collected from Quality Milk Production Services, Cornell University, Ithaca, NY. Bacterial strains were further cultured on Hayflick medium containing 15% horse serum and incubated for up to 7 d at 37°C with CO2 enrichment. DNA was isolated from mastitic milk samples and bacterial culture using Qiagen DNeasy Blood and Tissue Kit (Life Technologies, Carlsbad, CA) according to the manufacturer’s instructions with few modifications. PCR and LAMP assay was performed for all the samples obtained. Analytic sensitivity was calculated and the limit of detection was up to 50pg/reaction for LAMP assay which is higher as compared to PCR.
Sensitivity and specificity was calculated for each of the three tests. Cohen’s kappa values obtained were 0.940 for uvrC, 0.970 for gyrB and 0.807 for 16S rRNA. All three tests showed a high level of agreement between test results and the true mastitis status, indicated by the receiver operating characteristic (ROC) curve. A robust, sensitive and specific LAMP assay has been developed for the detection of M. bovis from mastitic milk. These novel molecular assays could be helpful for correct and timely identification of bovine mastitic pathogens, which is crucial for the control and treatment of the disease.Molecular diagnostic assayshave been developed in the current study based on multiplex PCR assay and loop-mediated isothermal amplification assay.