INCIDENCE OF STAPHYLOCOCCUS AUREUS IN COW MILK AND ASSESSMENT OF CHARACTERISTICS ASSOCIATED WITH ITS VIRULENCE
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Date
1991
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AAU, Anand
Abstract
The present study was undertaken with a view to knowing the occurrence of Staphylococcus aureus in cow milk in relation to location breed, involvement of quarters, method of milking, stage of lactation, and lactation numbers and to study the characteristics responsible for its virulence. Phage typing of the isolates was also carried out to know the possible origin. The milk samples were collected from the normal lactating cows maintained at three different farms of Gujarat Agricultural University, Anand and from mastitic cows located around Nadiad town of Kheda district. A total of 4-19 quarter milk samples were collected, of which 369 quarter milk samples were from 95 normal lactating cows and 50 quarter milk samples were from 23 mastitic cows. All the sample s were primarily inoculated on mannitol salt agar to isolate S.aureus. Out of 419 quarter milk samples, totally 128 cultures were isolated and identified as S,aureus by O-F test , catalase test , glucose fermentation and coagulase test. The incidence of S. aureus was 56.84 and 26.28 per cent in normal lactating cows, whereas it was 100.0 and 62.00 per cent in clinical cases on cow basis and quarter basis respectively. Out of 369 quarter milk samples from farm animals, 10 (2.71 per cent) samples were found positive by GMT and a l l GMT positive samples yielded S.aureus. All the 50 milk samples from clinical cases of mastitis were found positive by GMT, of which 31 (62,00 per cent) samples resulted into cultural isolation of S.aureus. The difference in the incidence of S. aureus in cow milk in relation to farms, breed and method of milking was found to be non-significant, whereas significant difference was found in quarter involvement and parity and stage of lactation . One quarter involvement was found higher (50.00 and 86.96 per cent) in both normal lactating cows as well as clinical cases. Similarly in farm animals, significant difference was found between hind half quarter (30.86 per cent) and fore half quarter (20.69 per cent). Higher incidence of S.aureus (76.47 and 42.86 'per cent) was observed during last lactation which was statistically significant on cow b a s i s and quarter basis respectively. Coagulase production was studied using four different plasma , viz., rabbit plasma, human plasma, poultry plaana and bovine plasma. Remarkable variation was observed in the incidence of coagulase production by S. aureus using rabbit plasma (100.00 per cent), human plasma (94.53 per cent) and poultry plasma (33.59 per cent), whereas bovine plasma was not found to be useful to determine coagulase production. Haemolytic activity of S,aureus was determined using human, horse, rabbit, bovine, sheep arv3 guinea pig blood agar media. Beta haemolytic activity was most commonly observed on all the blood agar media except on guinea pig blood agar medium. Forty Isolates of S, aureus (31.25 per cent) showed haeraolysin produotion on Crystal violet blood agar. Pigment production was observed in 103 (80.46 per cent) S. aureus isolates, whereas DNAase and TDNAase production was detected in 88 (68.75 per cent) and 44 (34.37 per cent) isolates of S.aureus respectively. Hone of the isolates was found to be enterotoxigenic as ascertained by absence of fried egg appeareince of colony on Carter's medium. Cent per cent correlation was observed between mannitol fermentation and coagulase production (with rabbit plasma) by Staphylococci. Out of 103 pigment producing isolates of S.aureus, 67.96, 6B.05 and 22.33 per cent isolates produced beta haemolysis, PNAase and TDNAase respectively. Out of the 70 beta haemolytic S.aureus isolates , 61.43 and 32.86 per cent produced DNAase and TDNAase respectively. The relationship of TDNAase to DNAase production was only 50.00 per cent. All the 128 coagulase positive Staphylococci were sent to the phage typing centre, I.C.M.R,, Maul ana Azad Medical College, New Delhi, where none of the isolates was found to be typable with International basic set and Basic bovine set of phages.
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VERTINARY MICROBIOLOGY, A STUDY