Molecular and phenotypic investigations of enzyme mediated resistance profiles against aminoglycoside antibiotics in gram-negative clinical isolates in Dhaka, Bangladesh

Abstract

In recent decades, focus has shifted from notorious Gram-positive pathogens to Gram-negative threats, the majority of which comprise members of the Enterobacteriaceae and Pseudomonadaceae families. These, often commensal bacteria, co-inhabit our environment and within us, however have the propensity to develop opportunistic infections in immunocompromised individuals, especially in intensive care units (ICUs) of hospitals. Aminoglycoside antibiotics are often reserved for severe bacterial infections. Therefore, we conducted surveillance on their resistance phenotypes by antibiotic susceptibility testing (AST) and have found a total of 83.3% of strains to be multidrug resistant (MDR) forms. Among a range of clinical isolates as collected from three major hospitals in Dhaka, ETEC; Klebsiella pneumoniae; Pantoea agglomerans; Pseudomonas spp. and Aeromonas spp. were interrogated against five commercially popular aminoglycoside antibiotics, finding phenotypic resistance towards streptomycin (50%); tobramycin (50%); gentamicin (44.4%); amikacin (33.3%), and netilmicin (28%). Molecular methods were then employed, where three aminoglycoside resistance enzyme (AME) encoding genes were prominent: aac(6’)-Ib (27.8%), aac(3’)-II (16.7%) and ant(3”)-Ia (5.6%) among a total of seven genes investigated. Phylogenetic analysis revealed these genes had previous origins in Australia, France and China respectively. These comprised identifical clones which have dispersed world-wide, demonstrating the high possibility for dissemination via horizontal gene transfer using mobile genetic elements. We therefore recommend sparse, cycled use of these drugs in pragmatic combinations with other antibiotic classes for synergistic effects, and report the greatest efficacy remaining towards amikacin and netilmicin amongstthe aminoglycosides.