Overproduction of outer membrane protein A (OmpA) by Acinetobacter baumannii is a risk factor for nosocomial pneumonia, bacteremia and mortality increase.

BACKGROUND: OmpA is a porin involved in Acinetobacter baumannii pathogenesis. However, OmpA clinical implication in hospital-acquired infections remains unknown. We aimed to determine whether OmpA overproduction was a risk factor associated with pneumonia, bacteremia, and mortalilty.

METHODS: Demographic, microbiological and clinical data from 100 and 246 patients included, respectively, in a unicenter cohort (UC) and a multicenter cohort (MC) were analyzed. Representative isolates were classified in two groups: i-16 UC and 20 MC isolates from colonized patients (CP) by A. baumannii, and ii-13 UC and 23 MC isolates from patients with pneumonia (PP) without bacteremia (NBPP) or with bacteremia (BPP) by A. baumannii. ompA expression was determined by qRT-PCR.

RESULTS: PP isolates overexpressed more ompA than CP isolates (ratio=1.76 vs. 0.36 (P<0.001)) for UC and (ratio=1.36 vs. 0.91 (P=0.029)) for MC. Among PP, BPP isolates overexpressed non-significantly more ompA than NBPP isolates (ratio=2.37 vs. 1.43 (P=0.058)), for UC and (ratio=2.03 vs. 0.91 (P=0.137)) for MC. The multivariate analysis in both cohorts together showed ompA overexpression as independent risk factor for pneumonia (P<0.001), bacteremia (P=0.005), and mortality (P=0.049).

CONCLUSIONS: These data suggest that ompA overexpression is an associated factor for pneumonia and bacteremia development, and mortality by A. baumannii.