A prospective multicenter study on the evaluation of antimicrobial resistance and molecular epidemiology of multidrug-resistant Acinetobacter baumannii infections in intensive care units with clinical and environmental features

Abstract

Background: Multidrug-resistant (MDR) Acinetobacter baumannii infections are considered as emerging nosocomial infections particularly in patients hospitalized in intensive care units (ICUs). Therefore, reliable detection of MDR strains is crucial for management of treatment but also for epidemiological data collections. The purpose of this study was to compare antimicrobial resistance and the clonal distribution of MDR clinical and environmental A. baumannii isolates obtained from the ICUs of 10 different hospitals from five geographical regions of Turkey in the context of the demographic and clinical characteristics of the patients.

Methods: A multicenter-prospective study was conducted in 10 medical centers of Turkey over a 6 month period. A total of 164 clinical and 12 environmental MDR A. baumannii isolates were included in the study. Antimicrobial susceptibility testing was performed for amikacin (AN), ampicillin-sulbactam (SAM), ceftazidime (CAZ), ciprofloxacin (CIP), imipenem (IMP) and colistin (COL) by microdilution method and by antibiotic gradient test for tigecycline (TIG). Pulsed-field gel electrophoresis (PFGE) was performed to determine the clonal relationship between the isolates. The detection of the resistance genes, bla_OXA-23, bla_OXA-24, bla_OXA-51, bla_OXA-58, bla_IMP, bla_NDM, bla_KPC, bla_OXA-48 and bla_PER-1 was carried out using the PCR method.

Results: The mortality rate of the 164 patients was 58.5%. The risk factors for mortality included diabetes mellitus, liv1er failure, the use of chemotherapy and previous use of quinolones. Antimicrobial resistance rates for AN, SAM, CAZ, CIP, IMP, COL and TIG were 91.8%, 99.4%, 99.4%, 100%, 99.4%, 1.2% and 1.7% respectively. Colistin showed the highest susceptibility rate. Four isolates did not grow on the culture and were excluded from the analyses. Of 172 isolates, 166 (96.5%) carried bla_OXA-23, 5 (2.9%) bla_OXA-58 and one isolate (0.6%) was positive for both genes. The frequency of bla_PER-1 was found to be 2.9%. None of the isolates had bla_IMP, bla_KPC, bla_NDM and bla_OXA-48 genes. PFGE analysis showed 88 pulsotypes. Fifteen isolates were clonally unrelated. One hundred fifty-seven (91.2%) of the isolates were involved in 14 different clusters.

Conclusions: Colistin is still the most effective antibiotic for A. baumannii infections. The gene bla_OXA-23 has become the most prevalent carbapenemase in Turkey. The distribution of invasive A. baumannii isolates from different regions of Turkey is not diverse so, infection control measures at medical centers should be revised to decrease the MDR A. baumannii infections across the country. The results of this study are expected to provide an important baseline to assess the future prophylactic and therapeutic options.

Keywords: Acinetobacter baumannii; Antimicrobial resistance genes; Clonal relatedness; Polymerase chain reaction; Pulsed field gel electrophoresis; Risk factors.

Fig. 1

Distribution of centers collaborating in the study

Fig. 2

The frequency of resistance genes according to centers

Fig. 3

A cross-sectional example of PFGE dendogram representing the largest PFGE group (Group VI, n = 27). PFGE types; the strains having indistinguishable DNA band profile were clustered in the same PFGE types and labeled with a same number such as PFGE type 42 included 3 stains, any difference in PFGE patterns was defined as unique and labeled with different number. PFGE group VI included the strains having PFGE patterns that were similar to each other ≥ 85%