No abstract

Mastitis is a major constraint that severely affects milk production in dairy animals. The California Mastitis Test (CMT) is a reliable and rapid field test for the diagnosis of subclinical mastitis (SCM) which gives an indirect estimate of somatic cell count (SCC). Based on the results of CMT screening and SCC of the milk of 105 crossbred animals located in different farms in Wayanad and Calicut districts of Kerala state, the present study attempts to find the estimates of sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV), false discovery rate (FDR) and false omission rate (FOR) of CMT relative to SCC as the reference standard. The correlation and agreement between CMT and SCC were also analysed. The estimated Spearman and Kendall Tau b correlation coefficients were 0.88 and 0.76, respectively, which indicated a strong positive relationship between CMT and SCC. The sensitivity and specificity values of CMT were 1.000±0.000 and 0.510±0.071, respectively. These values indicate that the probability for an animal with mastitis to be identified using CMT is 100 per cent and the probability of correctly identifying an animal without mastitis animal is 51 per cent. The high sensitivity value of CMT in this study indicated that CMT could be used to find out the true prevalence of SCM in crossbred animals. Analysis of the data also revealed that CMT had a PPV of 0.700±0.051 and an NPV of 1.000±0.000. The calculated accuracy of CMT was 0.771±0.041. The estimated FDR and FOR were 0.300±0.051 and 0.000±0.000, respectively. Kappa statistic was used to determine the level of agreement between CMT and SCC and the kappa coefficient value was 0.53±0.07 which indicated moderate agreement.

Quaternary ammonium compounds (QAC) are widely used biocides in the field of medical and veterinary practice. Resistance to QACs is an emerging problem due to this widespread use. The present study was undertaken to detect the presence of genes that contribute to resistance to QACs in Staphylococcus aureus isolates obtained from udder surface and mastitis milk. A total 22 isolates of S. aureus were obtained from udder washings and milk of bovine mastitis cases. Among these, seventeen isolates were from udder wash samples and five isolates from clinical and subclinical cases of mastitis. Broth microdilution assay was performed to assess the minimum inhibitory concentration (MIC) of the isolates against Cetyltrimethylammonium bromide (CTAB), a QAC. Polymerase chain reaction (PCR) was done targeting qac A/B gene which codes for efflux pump which targets QACs. In the present study qac A/B gene was detected in seven out of 22 isolates of S. aureus. Three of these isolates were obtained from udder washings before milking and four, after milking. None of the S. aureus isolates from mastitis milk possessed the gene. The average minimum inhibitory concentration of qac A/B positive isolates against CTAB was 0.63 ± 0.55 μg/ml. The average MIC between qac A/B positive and negative isolates were statistically insignificant. The study points to the fact that multiple factors could be contributing to biocide resistance in S. aureus.