Hospital-acquired Stenotrophomonas maltophilia infection in Western Australia: epidemology, antibiotic susceptibilities and virulence factors

[Truncated abstract] Stenotrophol11onas l11altophilia is a Gram-negative bacillus commonly isolated in clinical microbiology laboratories. Although this organism usually causes disease only in immunocompromised patients, infection is often clinically significant and treatment can be difficult due to antibiotic resistance. Little is known about the epidemiology of S. l11altophilia in Australia or the characteristics of local strains. Furthermore, the pathogenesis of S. maltophilia infections is poorly understood. The aims of this thesis were: to describe the epidemiology of hospital-acquired S. maltophilia infections in Western Australia (W A) and identify environmental reservoirs; to characterise a collection of local clinical and environmental S. maltophilia isolates; to examine the antibiotic susceptibilities of local clinical and environmental S. maltophilia isolates and investigate susceptibility testing protocols; and to investigate mechanisms of pathogenicity of S. maltophilia. A retrospective matched case-control study was conducted on patients admitted to either of two WA hospitals between Februmy 1999 and Janumy 2004. Cases that had hospitalacquired S. maltophilia infections were compared to controls of the same gender and hospital, similar age and date of hospital admission, and longer length of stay than the matched case prior to infection, that were free from bacterial infection during their hospital stay. Independent risk factors identified included admission to an intensive care unit (lCU), previous hospitalisation, ~-lactam/~-lactamase inhibitor use and antifungal use. These factors may be useful for identifying patients particularly susceptible to S. maltophilia infection so that measures can be taken to reduce risk or, if an infection develops, early treatment could include an agent active against this organism. To obtain environmental S. maltophilia isolates for comparison with clinical strains to identify bacterial characteristics associate