Survival ofAcinetobacter baumanniion Dry Surfaces: Comparison of Outbreak and Sporadic Isolates

Abstract

Acinetobacterspp. are important nosocomial pathogens reported with increasing frequency in outbreaks of cross-infection during the past 2 decades. The majority of such outbreaks are caused byAcinetobacter baumannii. To investigate whether desiccation tolerance may be involved in the ability of certain strains ofA. baumanniito cause hospital outbreaks, a blind study was carried out with 39 epidemiologically well-characterized clinical isolates ofA. baumanniifor which survival times were determined under simulated hospital conditions. The survival times on glass coverslips of 22 strains isolated from eight well-defined hospital outbreaks in a German metropolitan area were compared with the survival times of 17 sporadic strains not involved in outbreaks but rather isolated from inpatients in the same geographic area. All sporadic isolates have been shown by pulsed-field gel electrophoresis to represent different strain types. There was no statistically significant difference between the survival times of sporadic strains ofA. baumanniiand outbreak strains (27.2 versus 26.5 days, respectively;P≤ 0.44) by the Wilcoxon-Mann-Whitney test. All investigatedA. baumanniistrains, irrespective of their areas of endemicity or epidemic occurrence, have the ability to survive for a long time on dry surfaces. Antimicrobial susceptibility testing showed thatA. baumanniioutbreak strains were significantly more resistant to various broad-spectrum antimicrobial agents than sporadic strains. Both desiccation tolerance and multidrug resistance may contribute to their maintenance in the hospital setting and may explain in part their propensity to cause prolonged outbreaks of nosocomial infection.