Overproduction of Outer Membrane Protein A by Acinetobacter baumannii as a Risk Factor for Nosocomial Pneumonia, Bacteremia, and Mortality Rate Increase.

Background: Outer membrane protein A (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 mortality. Methods: We analyzed demographic, microbiological, and clinical data from 100 patients included in a unicenter cohort and 246 included in a unicenter cohort and a multicenter cohort. Representative isolates were classified into 2 groups: (1) isolates from patients colonized by A. baumannii (16 from the unicenter and 20 from the multicenter cohort) and (2) isolates from bacteremic or nonbacteremic patients with pneumonia (PP) caused by A. baumannii (13 from the unicenter and 23 from the multicenter cohort) Expression of ompA was determined with quantitative reverse-transcription polymerase chain reaction. Results: Isolates from PP overexpressed more ompA than those from colonized patients from the unicenter (ratio, 1.76 vs 0.36; P < .001) and the multicenter (1.36 vs 0.91; P = .03) cohorts. Among isolates from PP, those from bacteremic patients overexpressed nonsignificantly more ompA than those from nonbacteremic patients in the unicenter (ratio, 2.37 vs 1.43; P = .06) and the multicenter (2.03 vs 0.91; P = .14) cohorts. Multivariate analysis in both cohorts together showed ompA overexpression as independent risk factor for pneumonia (P < .001), bacteremia (P = .005), and death (P = .049). Conclusions: These data suggest that ompA overexpression is an associated factor for pneumonia, bacteremia, and death due to A. baumannii.

Interspecies spread of CTX-M-32 extended-spectrum beta-lactamase and the role of the insertion sequence IS1 in down-regulating bla CTX-M gene expression.

OBJECTIVES: To characterize the extended-spectrum beta-lactamases (ESBLs) as well as their genetic environment in different isolates of Enterobacteriaceae from a patient with repeated urinary tract infections. METHODS: Two isolates of Escherichia coli and one Proteus mirabilis, all with ESBL phenotypes, were studied. Conjugation experiments and restriction fragment length polymorphisms (RFLPs) were performed. Cloning of the bla genes was by plasmid restriction and fragments ligation. Antibiotic susceptibility testing was by Etest. The genetic environment was analysed by direct sequencing of the DNA surrounding the bla gene. RT-PCR was performed to study the differences in the bla(CTX-M) gene expression. RESULTS: The bla gene was transferred by conjugation from the three clinical isolates, which by RFLP showed the same plasmid. The bla gene and surrounding sequences were cloned, an approximately 9 kbp AccI fragment was sequenced and the bla(CTX-M-32) gene was identified. The MICs of ceftazidime for transconjugants and transformants bearing the bla(CTX-M-32) gene were lower than those previously reported. Analysis of the DNA surrounding the ESBL gene revealed a new genetic structure with two insertion sequences, IS5 and IS1, located immediately upstream of the bla(CTX-M-32) gene; IS1 was located between the bla gene and IS5, and within the -10 and -35 promoter boxes of the bla(CTX-M-32) gene. Microbiological and biochemical studies revealed lower bla(CTX-M-32) gene expression in bacterial isolates with IS1 between the promoter boxes. CONCLUSIONS: Data suggest putative in vivo horizontal bla(CTX-M-32) gene transfer between two different genera of Enterobacteriaceae. A new complex structure, IS5-IS1, was detected upstream of the bla gene and IS1 negatively modulated expression of the bla(CTX-M-32) gene because its location modified the bla promoter region.