RESUMO
Background and Objectives: Plasmid-mediated AmpC producers are considered an increasing concern. The aim of this study was to investigate the prevalence of plasmid-mediated AmpC ß-lactamases (pAmpCs) in Klebsiella pneumoniae isolates. Materials and Methods: A total of 228 clinical isolates of K. pneumoniae were collected in Bushehr province, Iran, from December 2017 to February 2019. Cefoxitin disks were applied for screening AmpC-producing isolates. Furthermore, 3 phenotypic confirmatory tests including combine disk test (CDT), double disk synergy test (DDST) and modified three dimensional test (M3DT) were used. Finally, the presence of pAmpC genes was tested by multiplex PCR. Results: We identified 18 pAmpC-KP isolates among the 228 isolates (7.9%): 12 DHA (66.6%) and 6 CMY (33.3%). In the present study only 47% of cefoxitin-resistant isolates were pAmpC producers. The sensitivity of CDT, DDST, and M3DT was 89%, 67% and 100% and the specificity was 90%, 90% and 85%, respectively. In addition, M3DT displayed a higher rate of efficiency (92%) than CDT (89%) and DDST (79%) in detecting plasmid-meditated AmpC producers. Conclusion: DHA was the most prevalent pAmpC beta-lactamase in this study. DDST and CDT tests proved inefficient to detect two and six pAmpC producers, respectively, while M3DT represented the best overall performance.
RESUMO
BACKGROUND AND OBJECTIVES: Increasing the rate of extended-spectrum ß-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 ß-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.