Diversity of aminoglycoside modifying enzymes and 16S rRNA methylases in Acinetobacter baumannii and Acinetobacter nosocomialis species in Iran; wide distribution of aadA1 and armA.

PURPOSE: Acinetobacter baumannii-calcoaceticus complex (ABC) make a great burden on health-care systems due to hospital-acquired infections and antibacterial resistance. Aminoglycoside in combination with other antibacterials used as treatment options. However, ABC species overcome this class of antibacterials in different ways. This study provides a comprehensive report on the distribution of aminoglycoside modifying enzymes (AMEs) and 16S rRNA methylase in Acinetobacter baumannii and Acinetobacter nosocomialis isolated from various provinces in Iran. METHODS: During six month of study, from eight referral centers in seven provinces across the country, Iran, 178 A. baumannii and 43 A. nosocomialis isolates were collected. The minimum inhibitory concentration of amikacin, gentamicin, netilmicin, kanamycin and tobramycin were measured by microbroth dilution method. AMEs and 16S rRNA methylase variants were sought by PCR. RESULTS: High rates of resistance were seen in all centers. MIC50 and MIC90 for all A. baumannii and A. nosocomialis isolates from different centers were > 512 mg/L. The most frequent AME was ant(3″)-Ia (aadA1) in both of A. baumannii (74.1%) and A. nosocomialis (86%). armA was detected in A. baumannii and A. nosocomialis at the frequency of 41.6% and 67.4%, respectively. rmtA, B, C, D, aac(3)-Ia (aacC1) and aac(6')-Im were not detected, neither in A. baumannii nor A. nosocomialis. Moreover, aac(6')-Ih was only found in A. baumannii isolates. The distribution of some of the ARGs was limited to a definite center. CONCLUSION: The overall high-level carriage of ARGs in Acinetobacter species may limited usage of this class of antibacterials as a treatment option.

Molecular characterization and genetic relatedness of clinically Acinetobacter baumanii isolates conferring increased resistance to the first and second generations of tetracyclines in Iran.

BACKGROUND: The increasing resistance of Acinetobacter baumannii to antibiotics has recently been regarded as a notable therapeutic difficulty. Evaluating resistance rates of some A. baumannii isolates to tetracyclines had an impact on understanding the antibiotic resistance dissemination. By comparing genetic characteristics and relatedness of A. baumannii isolates, we are able to determine the transition dynamics of outbreak isolates. METHODS: A total of 72 non-duplicate isolates of A. baumannii were recovered in 2011 and 2015 and minimum inhibitory concentration (MIC) range distribution of the isolates to tetracyclines was performed by broth micro dilution (BMD) assay, and to determine the lineage relatedness of the outbreak isolates repetitive extragenic palindromic element based on polymerase chain reaction (rep-PCR) and international clonal (ICs) investigations were performed. RESULTS: Resistance rates to tetracycline, doxycycline and minocycline in 2011 were 73, 2 and 0%, while these rates in 2015 increased up to 90, 84 and 52%, respectively. The tetB existed in 100% of all the isolates of both years. tetA was not found in any of the isolates. According to the rep-PCR assays, up to 83% of all isolates clustered distinctly and only 6% of isolates had a common root. The percentage rates of IC1 decreased from 42% in 2011 to 22% in 2015, while those of IC2 increased from 28 to 36%, from 2011 to 2015. CONCLUSIONS: Our data showed that resistance to the first and second generations of tetracyclines is on the rise and the clonal transition dynamics of isolates are in progress in our hospital.