Cross-Sectional And Longitudinal Studies On Antimicrobial Susceptibility Profiles And The Genomic Diversity Of Acinetobacter Baumannii Isolates From Senile Patients

Background: To date, little data is available on the antimicrobial susceptibility profiles and molecular characteristics of Acinetobacter baumannii clinical isolates from senile patients. Herein, cross-sectional and longitudinal studies on antimicrobial susceptibility and genomic diversity were conducted to investigate the susceptibility patterns and clonal relatedness of A. baumannii isolates in our gerontal wards. Methods: Cross-sectional analysis was performed on 170 non-repetitive A. baumannii isolates recovered from senile patients (aged 61-99 years, mean = 86.8) over a 2-year period (2012-2013). The longitudinal study examined 77 repetitive A. baumannii isolates recovered from 8 senile patients (aged 87-98 years, mean = 92) with long-time hospitalization. Results: The majority of the 170 isolates (128/170, 75.3%) were non-susceptible to carbapenems (CRAB), and all CRAB were extensively drug-resistant (XDR) or multidrug-resistant (MDR), which were spread evenly over the different departments. The isolates belonged to 36 pulsotypes, as determined by pulsed-field gel electrophoresis. Groups I to IV (containing 119, 4, 1, and 2 isolates, respectively) were major epidemic strains with similar clonal relatedness (similarity > 80%); 98.4% (124/126) of which were CRAB with the XDR phenotype. In the longitudinal study, all 77 isolates were XDR. A comparison of pulsotypes was performed for each patient. All isolates clustered in Group I except for one isolate, which belonged to a new group. Conclusions: Extensive drug-resistance of A. baumannii was more serious in gerontal wards than in regular wards. Clone dissemination was the most important type of XDR strains spread and the XDR clones were responsible for long-term infection of A. baumannii. Therefore, more preventive measures should be reinforced in gerontal wards.