Molecular analysis of the Acinetobacter baumannii biofilm-associated protein.

Acinetobacter baumannii is a multidrug-resistant pathogen associated with hospital outbreaks of infection across the globe, particularly in the intensive care unit. The ability of A. baumannii to survive in the hospital environment for long periods is linked to antibiotic resistance and its capacity to form biofilms. Here we studied the prevalence, expression, and function of the A. baumannii biofilm-associated protein (Bap) in 24 carbapenem-resistant A. baumannii ST92 strains isolated from a single institution over a 10-year period. The bap gene was highly prevalent, with 22/24 strains being positive for bap by PCR. Partial sequencing of bap was performed on the index case strain MS1968 and revealed it to be a large and highly repetitive gene approximately 16 kb in size. Phylogenetic analysis employing a 1,948-amino-acid region corresponding to the C terminus of Bap showed that BapMS1968 clusters with Bap sequences from clonal complex 2 (CC2) strains ACICU, TCDC-AB0715, and 1656-2 and is distinct from Bap in CC1 strains. By using overlapping PCR, the bapMS1968 gene was cloned, and its expression in a recombinant Escherichia coli strain resulted in increased biofilm formation. A Bap-specific antibody was generated, and Western blot analysis showed that the majority of A. baumannii strains expressed an ∼200-kDa Bap protein. Further analysis of three Bap-positive A. baumannii strains demonstrated that Bap is expressed at the cell surface and is associated with biofilm formation. Finally, biofilm formation by these Bap-positive strains could be inhibited by affinity-purified Bap antibodies, demonstrating the direct contribution of Bap to biofilm growth by A. baumannii clinical isolates.

Molecular epidemiology of multidrug-resistant Acinetobacter baumannii in a single institution over a 10-year period.

Multidrug-resistant Acinetobacter baumannii is a worldwide nosocomial menace. We sought to better understand its behavior through studying the molecular epidemiology of this organism at the Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia, over a 10-year period. Multilocus sequence typing (MLST), semiautomated repetitive sequence-based PCR (rep-PCR), and pulsed-field gel electrophoresis (PFGE) were performed on a selection of 31 A. baumannii isolates collected over the 10-year period to determine their relationships to one another. MLST also allowed us to put this information in a global context. The presence or absence of bla(OXA-23) was also established. The presence of bla(OXA-23) closely correlated with carbapenem resistance in our collection. Sequence type 92 (ST92) was the dominant sequence type and was present in the hospital for 9 years. There was also evidence of the spread of ST69, ST73, and ST125 (novel) within the hospital, but this was not sustained over long periods. There were only single examples of the novel sequence types ST126 and ST127. The different typing methods clustered the isolates similarly; however, PFGE and rep-PCR were more discriminatory than MLST. Worldwide, ST92 and the associated clonal complex 92 represent the most sampled and widespread sequence type(s) and are also known as European clone 2 and worldwide clonal lineage 2. Antibiotic susceptibility within ST92 is variable, suggesting a role for mechanisms other than antibiotic resistance in its success.

Model systems for the study of Enterococcal colonization and infection.

Enterococcus faecalis and Enterococcus faecium are common inhabitants of the human gastrointestinal tract, as well as frequent opportunistic pathogens. Enterococci cause a range of infections including, most frequently, infections of the urinary tract, catheterized urinary tract, bloodstream, wounds and surgical sites, and heart valves in endocarditis. Enterococcal infections are often biofilm-associated, polymicrobial in nature, and resistant to antibiotics of last resort. Understanding Enterococcal mechanisms of colonization and pathogenesis are important for identifying new ways to manage and intervene with these infections. We review vertebrate and invertebrate model systems applied to study the most common E. faecalis and E. faecium infections, with emphasis on recent findings examining Enterococcal-host interactions using these models. We discuss strengths and shortcomings of each model, propose future animal models not yet applied to study mono- and polymicrobial infections involving E. faecalis and E. faecium, and comment on the significance of anti-virulence strategies derived from a fundamental understanding of host-pathogen interactions in model systems.

Bladder catheterization increases susceptibility to infection that can be prevented by prophylactic antibiotic treatment.

Catheter-associated urinary tract infections (CAUTI) are the most common hospital-associated infections. Here, we report that bladder catheterization initiated a persistent sterile inflammatory reaction within minutes of catheter implantation. Catheterization resulted in increased expression of genes associated with defense responses and cellular migration, with ensuing rapid and sustained innate immune cell infiltration into the bladder. Catheterization also resulted in hypersensitivity to Enterococcus faecalis and uropathogenic Escherichia coli (UPEC) infection, in which colonization was achieved using an inoculum 100-fold lower than the ID90 for infection of an undamaged urothelium with the same uropathogens. As the time of catheterization increased, however, colonization by the Gram-positive uropathogen E. faecalis was reduced, whereas catheterization created a sustained window of vulnerability to infection for Gram-negative UPEC over time. As CAUTI contributes to poorer patient outcomes and increased health care expenditures, we tested whether a single prophylactic antibiotic treatment, concurrent with catheterization, would prevent infection. We observed that antibiotic treatment protected against UPEC and E. faecalis bladder and catheter colonization as late as 6 hours after implantation. Thus, our study has revealed a simple, safe, and immediately employable intervention, with the potential to decrease one of the most costly hospital-incurred infections, thereby improving patient and health care economic outcome.