Mice pathology study of toxA and exoS genes bearing Pseudomonas aeruginosa isolated from bovine Sub-clinical mastitis in West Begal with their Antibiogram

Abstract

Sub-clinical Mastitis is one of the major problems in India which is among the largest milk producing countries in the world, hampering national economy. Among 422 bovine milk samples screened from different cattle farms of West Bengal with history of infection and drop in milk yield by on-spot bromothymol blue (BTB) test, 371 samples were considered for collection and secondary screening by somatic cell count study. The collected milk samples showed significantly high average SCC value of 3.26-4.88 lakh cells/ml of milk which was indicative of infection. Samples (23, 6.53%) were found to be positive for Pseudomonas sp. showing distinct bluish-green pigmentation on cetrimide agar, typical results on morphological and in biochemical characterization. Presence of 19 (5.39%) Pseudomonas aeruginosa isolates were confirmed by fluorescent technique for detection of characteristic blue-green fluorescence by the pigment pyoverdin. PCR of these positive isolates revealed that 11 isolates were positive for toxA and 6 isolates for exoS genes with 2 isolates possessing both the genes. In Mice pathogenicity test, highest fatality (100%) was shown by the isolates with both the genes followed by isolates with toxA (66.67%) and exoS (41.67%) respectively with successful re-isolation of P. aeruginosa from the dead mice. Post-mortem examination of the dead mice showed marked haemorrhages on liver, blackish discoloration of intestines and haemorrhages on lungs. Antibiogram revealed that the isolates were highly sensitive to drugs like amikacin (89.47%), imipenem (84.21%), meropenem (78.95%) and cefoperazone-sulbactam (84.21%) but resistant to tetracycline (68.42%), piperacillin (63.16%), oxacillin (52.63%), mecilinam (47.37%) and others.