Acinetobacter baumannii is an opportunistic nosocomial pathogen and one of the six most important multidrug-resistant microorganisms in hospitals worldwide. This human pathogen is responsible for a vast array of infections, of which ventilator-associated pneumonia and bloodstream infections are the most common, and mortality rates can reach 35%. Community-acquired infections have also been reported, but few strains have been recovered from environmental sources and infection reservoirs external to the hospital have not been identified. The majority of A. baumannii infections are caused by two main population clones with worldwide distribution. Infection outbreaks are often associated with multidrug resistance, including the recent emergence of strains resistant to all available antibiotics. Nevertheless, A. baumannii virulence traits and pathogenic potential have mostly remained elusive. The recent expansion of A. baumannii sequenced genomes has permitted the development of large-array phylogenomic and phenotypic analyses, which can offer valuable insights into the evolution and adaptation of A. baumannii as a human pathogen. This review summarises these recent advances, with particular focus on A. baumannii evolutionary and genomic aspects, and proposes new avenues of research.

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These evidence-based guidelines have been produced after a literature review of the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA). We have considered the detection of MRSA in screening samples and the detection of reduced susceptibility to glycopeptides in S. aureus. Recommendations are given for the identification of S. aureus and for suitable methods of susceptibility testing and screening for MRSA and for S. aureus with reduced susceptibility to glycopeptides. These guidelines indicate what tests should be used but not when the tests are applicable, as aspects of this are dealt with in guidelines on control of MRSA. There are currently several developments in screening media and molecular methods. It is likely that some of our recommendations will require modification as the new methods become available.

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SummaryThe genus Acinetobacter comprises a complex and heterogeneous group of bacteria, many of which are capable of causing a range of opportunistic, often catheter-related, infections in humans. However, Acinetobacter baumannii, as well as its close relatives belonging to genomic species 3 (''Acinetobacter pittii'') and 13TU (''Acinetobacter nosocomialis''), are important nosocomial pathogens, often associated with epidemic outbreaks of infection, that are only rarely found outside of a clinical setting. These organisms are frequently pandrug-resistant and are capable of causing substantial morbidity and mortality in patients with severe underlying disease, both in the hospital and in the community. Several epidemic clonal lineages of A. baumannii have disseminated worldwide and seem to have a selective advantage over non-epidemic strains. The reasons for the success of these epidemic lineages remain to be elucidated, but could be related to the potential of these organisms to achieve very dynamic reorganization and rapid evolution of their genome, including the acquisition and expression of additional antibiotic resistance determinants, under fluctuating environmental and selective conditions.

A survey was conducted of the antimicrobial susceptibilities of 595 Acinetobacter spp. isolated from routine clinical specimens in 54 sentinel laboratories throughout the UK during 2000. Isolates of the Acinetobacter baumannii complex (genomic groups 2, 3 and 13TU; n = 443) were distinguished from other genomic groups (n = 152) by PCR fingerprinting of tDNA spacer regions. MICs of amikacin, cefotaxime, ceftazidime, ciprofloxacin, colistin, gentamicin, imipenem, meropenem, minocycline, piperacillin, piperacillin/tazobactam, rifampicin, sulbactam and tetracycline were determined on IsoSensitest agar and interpreted, wherever possible, using BSAC breakpoints. Tigecycline (GAR-936), a new glycylcycline, was also tested. Resistance to cephalosporins, aminoglycosides and ciprofloxacin was widespread, but carbapenems, colistin, sulbactam, minocycline and tigecycline were each active against >80% of the isolates. Isolates of A. baumannii were more often resistant to cefotaxime, ceftazidime, piperacillin, piperacillin/tazobactam, ciprofloxacin, gentamicin and tetracyclines than those belonging to other genomic groups, but were less often resistant to colistin; no significant differences between genomic groups were noted in the susceptibilities to amikacin, carbapenems, rifampicin or sulbactam. The relative activities of the tetracyclines were minocycline > tigecycline > tetracycline. Thirteen carbapenem-resistant isolates (MICs > or =8 mg/L; 2.2%) were received from six centres; four centres sent single isolates; one sent three and one sent six. An allele of bla(IMP) was detected in one of these isolates, but the other 12 isolates either had carbapenemase-independent resistance, or undetectable carbapenemase activity combined with other resistance mechanisms. In conclusion, carbapenems, colistin and minocycline retained greatest activity against the Acinetobacter isolates collected. Tigecycline was less active than minocycline, but both agents overcame most tetracycline resistance.