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BackgroundA giant protein called BAP (biofilm-associated protein) plays a role in biofilm formation and adhesion to host cells in A. baumannii. Most of the protein is made by arrays of 80–110 aa modules featuring immunoglobulin-like (Ig-like) motifs.ResultsThe survey of 541 A. baumannii sequenced strains belonging to 108 STs (sequence types) revealed that BAP is highly polymorphic, distinguishable in three main types for changes both in the repetitive and the COOH region. Analyzing the different STs, we found that 29 % feature type-1, 40 % type-2 BAP, 11 % type-3 BAP, 20 % lack BAP. The type-3 variant is restricted to A. baumannii, type-1 and type-2 BAP have been identified also in other species of the Acinetobacter calcoaceticus-baumannii (ACB) complex. A. calcoaceticus and A. pittii also encode BAP-like proteins in which Ig-like repeats are replaced by long tracts of alternating serine and aspartic acid residues. We have identified in species of the ACB complex two additional proteins, BLP1 and BLP2 (BAP-like proteins 1 and 2) which feature Ig-like repeats, share with BAP a sequence motif at the NH2 terminus, and are similarly expressed in stationary growth phase. The knock-out of either BLP1 or BLP2 genes of the A. baumannii ST1 AYE strain severely affected biofilm formation, as measured by comparing biofilm biomass and thickness, and adherence to epithelial cells. BLP1 is missing in the majority of type-3 BAP strains. BLP2 is largely conserved, but is frequently missing in BAP-negative cells.ConclusionsMultiple proteins sharing Ig-like repeats seem to be involved in biofilm formation. The uneven distribution of the different BAP types, BLP1, and BLP2 is highly indicative that alternative protein complexes involved in biofilm formation are assembled in different A. baumannii strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2136-6) contains supplementary material, which is available to authorized users.

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Staphylococcus aureus is a microorganism capable of causing numerous diseases of the human skin. The incidence of S. aureus skin infections reflects the conflict between the host skin′s immune defenses and the S. aureus’ virulence elements. Antimicrobial peptides (AMPs) are small protein molecules involved in numerous biological activities, playing a very important role in the innate immunity. They constitute the defense of the host′s skin, which prevents harmful microorganisms from entering the epithelial barrier, including S. aureus. However, S. aureus uses ambiguous mechanisms against host defenses by promoting colonization and skin infections. Our review aims to provide a reference collection on host-pathogen interactions in skin disorders, including S. aureus infections and its resistance to methicillin (MRSA). In addition to these, we discuss the involvement of defensins and other innate immunity mediators (i.e., toll receptors, interleukin-1, and interleukin-17), involved in the defense of the host against the skin disorders caused by S. aureus, and then focus on the evasion mechanisms developed by the pathogenic microorganism under analysis. This review provides the “state of the art” on molecular mechanisms underlying S. aureus skin infection and the pharmacological potential of AMPs as a new therapeutic strategy, in order to define alternative directions in the fight against cutaneous disease.

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