Biofilm formation at the solid-liquid and air-liquid interfaces by Acinetobacter species

Abstract Background: The members of the genus Acinetobacter are Gram-negative cocobacilli that are frequently found in the environment but also in the hospital setting where they have been associated with outbreaks of nosocomial infections. Among them, Acinetobacter baumannii has emerged as the most common pathogenic species involved in hospital-acquired infections. One reason for this emergence may be its persistence in the hospital wards, in particular in the intensive care unit; this persistence could be partially explained by the capacity of these microorganisms to form biofilm. Therefore, our main objective was to study the prevalence of the two main types of biofilm formed by the most relevant Acinetobacter species, comparing biofilm formation between the different species. Findings: Biofilm formation at the air-liquid and solid-liquid interfaces was investigated in different Acinetobacter spp. and it appeared to be generally more important at 25°C than at 37°C. The biofilm formation at the solid-liquid interface by the members of the ACB-complex was at least 3 times higher than the other species (80-91% versus 5-24%). In addition, only the isolates belonging to this complex were able to form biofilm at the air-liquid interface; between 9% and 36% of the tested isolates formed this type of pellicle. Finally, within the ACB-complex, the biofilm formed at the air-liquid interface was almost 4 times higher for A. baumannii and Acinetobacter G13TU than for Acinetobacter G3 (36%, 27% & 9% respectively). Conclusions: Overall, this study has shown the capacity of the Acinetobacter spp to form two different types of biofilm: solid-liquid and air-liquid interfaces. This ability was generally higher at 25°C which might contribute to their persistence in the inanimate hospital environment. Our work has also demonstrated for the first time the ability of the members of the ACB-complex to form biofilm at the air-liquid interface, a feature that was not observed in other Acinetobacter species

Reduced membrane fluidity of a sigX deficient strain results in altered carbon catabolic repression response in Pseudomonas aeruginosa.

International audienceThe extracytoplasmic sigma factor SigX is a master regulator of bacterial adaptation that is involved in fatty acids biosynthesis and membrane homeostasis in P. aeruginosa. The growth of a sigX mutant was strongly affected in LB broth, but not in M9-glucose minimal medium. Through comparative transcriptomics and proteomics conducted in LB medium, we show that the absence of SigX results in strong dysregulation of genes, the products of which are mainly involved in transport, carbon and energy metabolisms. The CbrA/B two components system was strongly activated in a sigX mutant, leading to a higher production of crcZ and a reduced activity of the major translational repressors Hfq and Crc compared to the wildtype strain. Remarkably, growth as well as genes, the expression of which was dysregulated in the mutant strain, were restored when the C18ω9-structurally related detergent Polysorbate 80 was supplemented to LB medium. Anisotropy data further showed that the sigX mutant displayed a less fluid membrane than the WT strain, a phenotype that was restored by adding Polysorbate 80. Altogether, our data show that the altered membrane of the sigX mutant strain was probably the leading cause of the strong metabolic alterations and the reduced carbon catabolic repression response (CCR) encountered by this mutant strain. Thus, by controlling membrane homeostasis, SigX behaves as a master regulator of the nutritional response, in addition to its involvement in P. aeruginosa adaptation, virulence and biofilm formation

The outer membrane porin OmpW of Acinetobacter baumannii is involved in iron uptake and colistin binding.

This study was undertaken to characterize functions of the outer membrane protein OmpW, which potentially contributes to the development of colistin- and imipenem-resistance in Acinetobacter baumannii. Reconstitution of OmpW in artificial lipid bilayers showed that it forms small channels (23 pS in 1 m KCl) and markedly interacts with iron and colistin, but not with imipenem. In vivo, (55) Fe uptake assays comparing the behaviours of ΔompW mutant and wild-type strains confirmed a role for OmpW in A. baumannii iron homeostasis. However, the loss of OmpW expression did not have an impact on A. baumannii susceptibilities to colistin or imipenem.journal articleresearch support, non-u.s. gov't2016 Jan2016 01 11importe