Caracterização da resistência antimicrobiana e estudo fenogenotípico da produção de betalactamases em enterobactérias associadas à etiologia da mastite bovina

Abstract

The use of antibiotic in the prophylaxis of intramammary infections and in the elimination of its possible sources in dairy farms is an important control measure. However, the inappropriate use of antibiotics can result in the appearance of resistant strains. Enterobacteriaceae are the main etiological agents of environment bovine mastitis and are often resistant to antimicrobials, especially to beta-lactam antibiotics due to the production of beta-lactamases. Some Enterobacteriaceae can produce broad-spectrum beta-lactamases such as AmpC, TEM, SHV, CTX-M and carbapenemase and can be classified into several groups according the molecular structure and substrate activity. Furthermore, these bacteria may develop resistance to other antimicrobial agents which are used in the treatment of infections caused by enteric bacteria. The present study evaluated the profile fenogenotipic resistance to β-lactams, with emphasis on the detection of beta-lactamases, and other classes of antimicrobials in 42 isolates from 381 milk samples obtained from nine farms located in the middle region of the Rio de Janeiro-RJ so to contribute data to help in the grant for the implementation of measures to control this disease. Farms A and D had poor sanitary conditions, much fecal contamination and the highest rates of prevalence of Enterobacteriaceae in mastitic milk. The AmpC production was confirmed by disk approach that also was performed in addition to Etest for suspected ESBL (2be) producing. The Three-Dimensional Extract Test was conducted for all these suspects. The carbapenemase production was performed using the Modified Hodge Test and all isolates were subjected to PCR searching aacC2, qnr, blaTEM, blaSHV, blaCTX-M and blaampC. The enterobacteria prevalent in milk samples were Proteus mirabilis and Escherichia coli. The higher percentage of the resistance was to ciproflaxin and aacC2 and qnr were detected in 25% and 66.7% of isolates resistant to these antibiotics, respectively. We observed a high variability in phenotypic profile and multidrug resistance was detected in 97.6% of isolates. The group 1 was predominant and 30% of betalactamases of this group were classified as inducible type. No isolate showed phenotypic profile for ESBL (2be) or carbapenemase. The TET confirmed the negativity of ESBL (2be) production but proved to be less sensitive in the detection of AmpC. The blaTEM, blaSHV, blaCTX-M and blaampC genes were detected in 61.9%, 42.8%, 23.8%, 9.5% of isolates, respectively. Any isolate showed all bla genes simultaneously. The P. mirabilis blaTEM + belonging to a group 1e and E. coli negative for all genes belonging to a group 2a are prevalent. A total 66% of the isolates classified as group 2 presented blaTEM and blaSHV genes and 15% belonging to the group 1 showed blaampC gene. The pheno-genotypic variability detected indicates multiple mechanisms of antimicrobial resistance which is worrying due of the resistance bacterial spread determining a clinical and epidemiological impact for veterinary and human medicine.