ABSTRACT
BACKGROUND: Tuberculosis (TB) continues to pose a threat to communities worldwide and remains a significant public health issue in several countries. We assessed the role of heteroresistance and efflux pumps in bedaquiline (BDQ)-resistant Mycobacterium tuberculosis isolates. METHODS: Nineteen clinical isolates were included in the study, of which fifteen isolates were classified as MDR or XDR, while four isolates were fully susceptible. To evaluate BDQ heteroresistance, the Microplate Alamar Blue Assay (MABA) method was employed. For screening mixed infections, MIRU-VNTR was performed on clinical isolates. Mutations in the atpE and Rv0678 genes were determined based on next-generation sequencing data. Additionally, real-time PCR was applied to assess the expression of efflux pump genes in the absence and presence of verapamil (VP). RESULTS: All 15 drug-resistant isolates displayed resistance to BDQ. Among the 19 total isolates, 21.05% (4/19) exhibited a heteroresistance pattern to BDQ. None of the isolates carried a mutation of the atpE and Rv0678 genes associated with BDQ resistance. Regarding the MIRU-VNTR analysis, most isolates (94.73%) showed the Beijing genotype. Fifteen (78.9%) isolates showed a significant reduction in BDQ MIC after VP treatment. The efflux pump genes of Rv0676c, Rv1258c, Rv1410c, Rv1634, Rv1819, Rv2459, Rv2846, and Rv3065 were overexpressed in the presence of BDQ. CONCLUSIONS: Our results clearly demonstrated the crucial role of heteroresistance and efflux pumps in BDQ resistance. Additionally, we established a direct link between the Rv0676c gene and BDQ resistance. The inclusion of VP significantly reduced the MIC of BDQ in both drug-susceptible and drug-resistant clinical isolates.
Subject(s)
Antitubercular Agents , Diarylquinolines , Microbial Sensitivity Tests , Mycobacterium tuberculosis , Tuberculosis, Multidrug-Resistant , Mycobacterium tuberculosis/genetics , Mycobacterium tuberculosis/drug effects , Diarylquinolines/pharmacology , Humans , Antitubercular Agents/pharmacology , Iran , Tuberculosis, Multidrug-Resistant/microbiology , Mutation , Membrane Transport Proteins/genetics , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Drug Resistance, Multiple, Bacterial/genetics , Verapamil/pharmacologyABSTRACT
Background: Enterobacter cloacae (E. cloacae) is one of the most common Enterobacteriaceae causing nosocomial infections. Plasmid-mediated quinolone resistance (PMQR) determinants have been considered recently. This study evaluated the abundance of PMQR genes in strains of E. cloacae obtained from clinical samples in Kermanshah, Iran. Methods: In this descriptive cross-sectional study, after collecting 113 isolates of E. cloacae, their identity was confirmed using specific biochemical tests. After determining their drug resistance patterns using disc diffusion, the phenotypic frequency of extended-spectrum beta-lactamase (ESBL)-producing isolates was measured by the double-disk synergy test (DDST) method. The isolates were examined for the presence of qnrA, qnrB, qnrS, and aac(6')-Ib-cr genes by the polymerase chain reaction (PCR) assay. Results: The antibiotic resistance rate of E. cloacae isolates varied from 9.7% to 60.2%; among them, 78% were multidrug-resistant (MDR). The highest quinolone resistance was observed in ESBL-producing strains of E. cloacae. The frequency of positive isolates for PMQR and ESBL was 79.6% and 57.5%, respectively. The genes aac(6')-ib-cr (70.8%) and qnrB (38.1%) had the highest frequency among other genes. The number of isolates simultaneously carrying 2 and 3 genes was 64 and 5 isolates, respectively. Conclusion: The obtained results indicate a high degree of quinolone resistance among ESBL-producing E. cloacae strains. Nevertheless, there was a significant relationship between the PMQR gene and ESBL-positive isolates. Therefore, special attention should be paid to molecular epidemiological studies on antibiotic resistance to quinolones and beta-lactamases in these strains.
ABSTRACT
BACKGROUND AND OBJECTIVES: The selection of alternative treatment options with antibiotic combinations may be used for successful managing of multidrug-resistant Acinetobacter baumannii. The aim of this study was to determine the synergistic effects of ampicillin-sulbactam combined with either levofloxacin or tigecycline against MDR A. baumannii. MATERIALS AND METHODS: A total 124 of A.baumannii isolates collected from clinical samples of hospitalized patients which assessed for antibiotic susceptibility using disk diffusion method. E-test was used on 10 MDR A. baumannii isolates to determine the minimum inhibitory concentration (MIC) of ampicillin-sulbactam, levofloxacin and tigecycline. Any synergistic effects were evaluated at their own MIC using E-test assay at 37°C for 24 hours. Synergy was defined as a fractional inhibitory concentration index (FICI) of ≤0.5. RESULTS: Levofloxacin plus ampicillin-sulbactam combination was found to have synergistic effects (FIC index: ≤0.5) in 90% of the isolates, but there was no synergistic effect for ampicillin-sulbactam/tigecycline and tigecycline/levofloxacin combination. The antagonist effect in 50% of isolates (FIC index: >2) showed in combination of levofloxacin/tigecycline. CONCLUSION: The emergence of multidrug A. baumannii isolates requires evaluating by combination therapy. The combination of levofloxacin plus a bactericidal antibiotic such as ampicillin-sulbactam is recommended. Results should be confirmed by clinical studies.
