bThe emergence of Acinetobacter baumannii as an increasingly multidrug-resistant nosocomial pathogen largely relies on acquisition of resistance genes via horizontal gene transfer. Here, we demonstrate that many clinical isolates of A. baumannii take up DNA while they move along wet surfaces. We show that both motility and DNA uptake are abolished after inactivation of pilT, which putatively encodes the type 4 pilus (T4P) retraction ATPase, and comEC, which putatively encodes the DNA uptake channel, respectively. Inactivation of pilT correlates with an increase in the number and length of pili with an average diameter of 7.2 nm. In the Galleria mellonella infection model, the comEC mutant is significantly attenuated, whereas the pilT mutant is not, dissecting biologically distinct roles of T4P and the DNA uptake channel. Collectively, these findings promote our understanding of the mechanisms of DNA uptake and resistance development in A. baumannii, which may also apply to other important pathogens.

Objectives To investigate the genetic environment of the metallo-β-lactamase gene bla

Novel chatechol/hydroxamate siderophores (named "fimsbactins") were identified in Acinetobacter baumannii ATCC 17978 and Acinetobacter baylyi ADP1. The major compound, fimsbactin A, was isolated from low-iron cultures of A. baylyi ADP1, and its chemical structure was elucidated by mass spectrometry, and detailed (1)H, (13)C and (15)N NMR spectroscopy. From inverse feeding experiments following HPLC-MS analysis, the structures of five additional derivatives were elucidated. The gene cluster encoding the fimsbactin synthetase (fbs) was identified in both genomes, and mutants in fbs genes in A. baylyi were analyzed, thus allowing prediction of the fimsbactin biosynthesis pathway.

The flagellum is believed to be the common ancestor of all type III secretion systems (TTSSs). In Yersinia enterocolitica, expression of the flagellar TTSS and the Ysc (Yop secretion) TTSS are inversely regulated. We therefore hypothesized that the Ysc TTSS may adopt flagellar motor components in order to use the pathogenicity-related translocon in a drill-like manner. As a prerequisite for this hypothesis, we first tested a requirement for the proton motive force by both systems using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP). Motility as well as type III-dependent secretion of Yop proteins was inhibited by CCCP. We deleted motAB, which resulted in an immotile phenotype. This mutant, however, secreted amounts of Yops to the supernatant comparable to those of the wild type. Translocation of Yops into host cells was also not affected by the motAB deletion. Virulence of the mutant was comparable to that of the wild type in the mouse oral infection model. Thus, the hypothesis that the Ysc TTSS might adopt flagellar motor components was not confirmed. The finding that, in addition to consumption of ATP, Ysc TTSS requires the proton motive force is discussed.

SummaryThe natural habitats and potential reservoirs of the nosocomial pathogen Acinetobacter baumannii are poorly defined. Here, we put forth and tested the hypothesis of avian reservoirs of A. baumannii. We screened tracheal and rectal swab samples from livestock (chicken, geese) and wild birds (white stork nestlings) and isolated A. baumannii from 3% of sampled chicken (n 5 220), 8% of geese (n 5 40) and 25% of white stork nestlings (n 5 661). Virulence of selected avian A. baumannii isolates was comparable to that of clinical isolates in the Galleria mellonella infection model. Whole genome sequencing revealed the close relationship of an antibiotic-susceptible chicken isolate from Germany with a multidrug-resistant human clinical isolate from China and additional linkages between livestock isolates and human clinical isolates related to international clonal lineages. Moreover, we identified stork isolates related to human clinical isolates from the United States. Multilocus sequence typing disclosed further kinship between avian and human isolates. Avian isolates do not form a distinct clade within the phylogeny of A. baumannii, instead they diverge into different lineages. Further, we provide evidence that A. baumannii is constantly present in the habitats occupied by storks. Collectively, our study suggests A. baumannii could be a zoonotic organism that may disseminate into livestock.

Acinetobacter baumanniii -motility -1,3-diaminopropane -dat -ddc -A. baylyi ADP1 -52

Acinetobacter baumannii is a Gram-negative bacterium appearing as an opportunistic pathogen in hospital settings. Superoxide dismutase (SOD) contributes to virulence in several pathogenic bacteria by detoxifying reactive oxygen species released in the course of host defense reactions. However, the biological role of SODs in A. baumannii has not yet been elucidated. Here, we inactivated in A. baumannii ATCC 17978 gene A1S_2343, encoding a putative SOD of the Fe-Mn type by transposon insertion, resulting in mutant ATCC 17978 sod2343::Km. The mutation was also introduced in two naturally competent A. baumannii isolates by transformation with chromosomal DNA derived from mutant ATCC 17978 sod2343::Km. We demonstrate that inactivation of sod2343 leads to significant motility defects in all three A. baumannii strains. The mutant strains were more susceptible to oxidative stress compared to their parental strains. Susceptibility to colistin and tetracycline was increased in all mutant strains while susceptibility of the mutants to gentamicin, levofloxacin and imipenem was strain-dependent. In the Galleria mellonella infection model the mutant strains were significantly attenuated. In conclusion, sod2343 plays an important role in motility, resistance to oxidative stress, susceptibility to antibiotics and virulence in A. baumannii.

Pathogenic yersiniae employ a type III secretion system for translocating up to six effector proteins (Yersinia outer proteins (Yops)) into eukaryotic target cells. YopT is a cysteine protease that was shown to remove the C-terminal isoprenoid group of RhoA, Rac, and CDC42Hs. Here we characterized the cell biological and biochemical activities of YopT in cells infected with pathogenic Yersinia enterocolitica. Bacterially injected YopT located to cell membranes from which it released RhoA but not Rac or CDC42Hs. In the infected cells RhoA was dissociated from guanine nucleotide dissociation inhibitor-1 (GDI-1) and accumulated as a monomeric protein in the cytosol, whereas Rac and CDC42Hs remained GDI-bound. Direct transfer of isoprenylated RhoA to YopT and RhoA modification could be reconstituted in vitro by guanosine 5-3-O-(thio)triphosphate loading of a recombinant RhoA⅐GDI-1 complex. Finally, in macrophages infected with a Yersinia strain selectively translocating YopT podosomal adhesion structures required for chemotaxis as well as phagocytic cups mediating uptake of yersiniae were disrupted. These findings indicate that bacterially translocated YopT acts on membrane-bound and GDI-complexed RhoA but not Rac or CDC42, and this is sufficient for disruption of macrophage immune functions.