Emergence of heteroresistance to multiple antibiotics in Gram-negative clinical isolates from two Egyptian hospitals

Background Antimicrobial resistance is a major global threat; the presence of resistance mechanisms in bacteria can provide a correlation between bacterial-genotype and -phenotype. However, exceptions exist where identical bacterial cells in a population can exhibit heterogeneity in terms of antibiotic susceptibility. This response leads to difficulties in unambiguously classifying bacteria as susceptible or resistant. Heteroresistance is an example of this phenomenon that describes a phenotype in which an isolate contains subpopulations with reduced susceptibility compared to its main-population. Heteroresistance emergence led to a diagnostic and therapeutic dilemma. This study aimed to genotypically characterize the difference between the sensitive and the stable heteroresistant isolates (SHI). Methods A total of 151 Enterobacteriaceae isolates from various sources were included. Heteroresistant isolates and their stability were detected by disc-diffusion technique while genotypic analysis was carried out by PCR and efflux activity was assessed by ethidium bromide (EtBr)-agar Cartwheel method. Results A total of 51 heteroresistant subpopulations were detected, producing 16 SHI upon stability-detection. Amplified resistance genes and EtBr-agar Cartwheel method showed a significant difference between resistant subpopulations and their corresponding-sensitive main-populations. Conclusion Genotypic analysis confirmed that genetic mutation can lead to resistance development although the main-populations were sensitive, thereby leading to treatment failure.