Coexistence of aminoglycoside resistance genes in CTX-M-producing isolates of Klebsiella pneumoniae in Bushehr province, Iran

BACKGROUND AND OBJECTIVES: Increasing the rate of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae has given rise to a major healthcare issue in clinical settings over the past few years. Treatment of these strains is hardly effective since the plasmid encoding ESBL may also carry other resistance genes including aminoglycosides. The current study aimed to evaluate the prevalence of ESBL-producing K. pneumoniae and investigate the coexistence of Cefoxitamase-Munich (bla(CTX-M)) with aminoglycoside-modifying enzyme (AME) genes, aac(3)IIa as well as aac(6′)Ib, in CTX-M-producing K. pneumoniae isolated from patients in Bushehr province, Iran. MATERIALS AND METHODS: A total of 212 K. pneumoniae isolates were collected and confirmed using polymerase chain reaction (PCR) of the malate dehydrogenase gene. Isolates were screened for production of ESBL. Phenotypic confirmatory test was performed using combined disk test. The genes encoding CTX-M groups and AME genes, aac(3)IIa and aac(6′)Ib, were investigated by PCR. RESULTS: The ESBL phenotype was detected in 56 (26.4%) K. pneumoniae isolates. Moreover, 83.9% of ESBL-producing isolates carried the genes for CTX-M type β-lactamases, which were distributed into the two genetic groups of CTX-M-1 (97.8%)- and CTX-M-2 (2.1%)-related enzymes. Notably, among K. pneumoniae isolates containing the bla(CTX-M) gene, 68.08% of isolates harbored AME genes. In addition, the coexistence of bla(CTX-M) with aac(3)-IIa and aac(6′)-Ib was observed in 46.8% of CTX-M-producing K. pneumoniae isolates. CONCLUSION: This study provides evidence of a high prevalence of AME genes in CTX-M-producing K. pneumoniae isolates; therefore, in the initial empirical treatment of infections caused by ESBL-KP in regions with such antibiotic resistance patterns, aminoglycoside combination therapy should be undertaken carefully.