Plasmid-Mediated Aminoglycosides Resistance Among Clinical Isolates Of Escherichia Coli

Escherichia coli is a component of the normal bacterial flora of the human digestive tract, but, on the other hand, it is an important opportunistic pathogen, which can cause infections at various locations such as the urinary tract, respiratory tract, or surgical sites. Treatment of these infections is becoming more and more difficult because of the increase in bacterial resistance against antibiotics and the reduction of therapeutic options.

One of the most prevalent mechanisms of resistance among E. coli isolates is the production of extended-spectrum β-lactamases (ESBLs), which determine resistance to β-lactam antibiotics. One of the therapeutic options for treating infections with such bacteria is aminoglycosides. Unfortunately, E. coli has developed effective resistance mechanisms against this group of antibiotics as well. It may be a result of antibiotic modification by enzymes, decreased intracellular drug accumulation, and the mutation of rRNA or the substitution of ribosomal proteins.

One of the most prevalent mechanisms of resistance to aminoglycosides in E. coli is the production of aminoglycoside-modifying enzymes (AMEs). AMEs include acetyltransferases (ACC) which inactivate antibiotics by acetylation, O-nucleotidyltransferases (ANT) which cause the process of adenylation, and O-phosphotransferases (APH) which can phosphorylate aminoglycosides. It is worth noting that genes responsible for AMEs production often are contained within plasmids harboring also genes for ESBLs. The simultaneous resistance of E. coli against aminoglycosides as well as extended-spectrum cephalosporins remains a serious therapeutic challenge.

The changing epidemiology of ESBLs and aminoglycosides resistance was the reason why we decided to study the occurrence of the aph(3”)-Ib, ant(2”)-Ia, aac(6’)-Ib, aac (3)-Ia, and ant(4”)-IIa genes, responsible for AMEs production, among both ESBL-producing and  ESBL-non-producing E. coli isolates.

We evaluated the resistance phenotypes against aminoglycosides with the presence of genes responsible for this resistance. The study was prepared on 44 nonduplicated E. coli strains isolated from various clinical materials originated from patients hospitalized at University Hospital of Bialystok. Bacterial susceptibility to amikacin, gentamicin, netilmycin, and tobramycin was determined using  MIC values. Moreover, all isolates undergone analysis for the presence of the aph(3”)-Ib, ant(2”)-Ia, aac(6’)-Ib, aac (3)-Ia, and ant(4”)-IIa  genes with using of specific primers and the PCR technique.

In our study, we found that 79.5% of tested isolates presented resistance against aminoglycosides. The highest percentage of resistant strains (70.5%) was observed for tobramycin. The resistance of tested strains to gentamicin, netilmycin, and amikacin was at the level of 59%, 43.2%, and 11.4%, respectively. Moreover, the presence of aac(6’)-Ib gene was observed among 59.2% isolates, aph(3”)-Ib among 36.2%,  aac(3)-Ia among 15.9%, and ant(2”)-Ia among 4.6% isolates.

Concluding, the aac(6’)-Ib and aph(3”)-Ib genes are mainly responsible for the enzymatic resistance of clinical isolates of E. coli to aminoglycosides.

These findings are described in the article entitled Genetic basis of enzymatic resistance of E. coli to aminoglycosides, recently published in the journal Advances in Medical Sciences. This work was conducted by Dominika Ojdana, Anna Sieńko,  Paweł Sacha, Piotr Majewski, Piotr Wieczorek, Anna Wieczorek, and Elżbieta Tryniszewska from the Medical University of Białystok, Poland.