DETECTION OF ANTIBIOTIC RESISTANCE PROFILES AND ANTIBIOTIC RESISTANCE GENES (ARGs) IN Escherichia coli ISOLATES FROM MASTITIS MILK SAMPLES OF BUFFALOES AND THE ENVIRONMENT
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Date
2023-02
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
The present study is undertaken to investigate the antibiotic resistance patterns
in E. coli isolates from mastitis milk samples of buffaloes and environment (water)
samples in the vicinity of the same dairy animals and to know the distribution of the
selected genetic determinants of antibiotics in these isolates. Based on cultural,
biochemical and molecular (PCR test) tests, 52 samples out of 79 mastitis milk samples
and 31 samples out of 54 water samples were confirmed as E. coli. For isolation of E.
coli presumptively producing ESBL/AmpC, the mastitis milk samples and water
samples were cultured on 1 mg/L of cefotaxime (CTX) supplemented MacConkey agar
(MCA) and Tryptone Bile Glucuronic (TBX) agar, respectively. A total of 27 mastitis
milk samples and 14 water samples were identified as ESBL/AmpC producing E. coli
by cultural, biochemical and molecular tests. With regard to antibiotic resistance pattern of E. coli isolates (including
ESBL/AmpC producing E. coli) from mastitis milk samples in in vitro disc diffusion
based antibiotic sensitivity test (AST) with primary panel of nine antibiotics, majority of
isolates were resistant to cefotaxime followed by ampicillin, cotrimoxazole, imipenem,
enrofloxacin, amoxyclav, tetracycline, chloramphenicol and gentamicin. The E. coli
isolates (including ESBL/AmpC producing E. coli) from water samples also showed
maximum resistance to cefotaxime followed by ampicillin, imipenem, cotrimoxazole,
tetracycline, amoxyclav, enrofloxacin, chloramphenicol and gentamicin. Further, AST
with secondary panel of five antibiotic discs for presumptive ESBL/AmpC producing
E. coli isolates from mastitis milk samples and water samples showed that all the
isolates were ESBL/AmpC producers and showed highest resistance to ceftazidime
followed by cefoxitin and meropenem. In PCR test for detecting the genetic
determinants of antibiotic resistance genes, 91.9% of the E. coli isolates (including
ESBL/AmpC producers) from mastitis milk samples and water samples possessed
AmpC gene followed by SHV, NDM-1, TEM and OXA genes.
In the present study, AmpC gene was detected in all E. coli isolates that were
showing resistance to third generation cephalosporins in AST except three E. coli
isolates from water samples (W41, W48 and W52). In some (A6, A9, A16, A25, A34,
A49 and A64) of the E. coli isolates, although AmpC gene was detected in PCR test,
phenotypically it was not correlated in ASTs as these isolates have shown only
sensitivity/intermediate resistance to third generation of cephalosporins. Further, some
of the E. coli isolates that were detected with AmpC gene also didn’t show resistance to
clavulanic acid. This might be due to the lack of expression of AmpC gene in those
isolates.
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