In the last few years, phenotypically carbapenem resistant Acinetobacter strains have been identified throughout the world, including in many of the hospitals and intensive care units (ICUs) of Australia. Genotyping of Australian ICU outbreak-associated isolates by pulsed-field gel electrophoresis of whole genomic DNA indicated that different strains were cocirculating within one hospital. The carbapenem-resistant phenotype of these and other Australian isolates was found to be due to carbapenem-hydrolyzing activity associated with the presence of the bla OXA-23 gene. In all resistant strains examined, the bla OXA-23 gene was adjacent to the insertion sequence ISAba1 in a structure that has been found in Acinetobacter baumannii strains of a similar phenotype from around the world; bla OXA-51 -like genes were also found in all A. baumannii strains but were not consistently associated with ISAba1, which is believed to provide the promoter required for expression of linked antibiotic resistance genes. Most isolates were also found to contain additional antibiotic resistance genes within the cassette arrays of class 1 integrons. The same cassette arrays, in addition to the ISAba1-bla OXA-23 structure, were found within unrelated strains, but no common plasmid carrying these accessory genetic elements could be identified. It therefore appears that antibiotic resistance genes are readily exchanged between cocirculating strains in epidemics of phenotypically indistinguishable organisms. Epidemiological investigation of major outbreaks should include whole-genome typing as well as analysis of potentially transmissible resistance genes and their vehicles.Acinetobacter spp. are emerging opportunistic nosocomial pathogens, with increasing prevalence worldwide. Their epidemiology is complex, and genotypic methods or a combination of genotypic and phenotypic methods are required for species identification (28). Differentiation of Acinetobacter baumannii and Acinetobacter genomic species 3 and 13TU (the three most clinically important members of the genus) and the environmental species A. calcoaceticus is impractical in the routine laboratory, and these four species are generally grouped phenotypically as the A. calcoaceticus-A. baumannii complex. DNA fingerprinting by ApaI digestion of total DNA and pulsed-field gel electrophoresis (PFGE) is regarded as the typing method of choice for outbreak investigation and can be used to compare outbreaks in different locations when the methodology is uniform (41).Studies at the species level have shown that the problems of epidemic spread of antibiotic-resistant Acinetobacter strains are mostly due to bacteria belonging to the A. calcoaceticus-A. baumannii complex (3). The potential for acquisition of transferable carbapenem resistance has long been recognized (37a), and the adjusted mortality risk for intensive-care patients infected by carbapenem resistant Acinetobacter may be increased more than threefold (33).Carbapenem resistance in strains of the A. calcoaceticus-A.baumannii comp...

A study of 59 isolates of Bartonella henselae reveals relatively limited diversity among those of human origin (n ‫؍‬ 28). Either of two distinct alleles of both gltA and 16S ribosomal DNA (rDNA) was found in all isolates, with a high level of congruity between 16S and gltA inheritance among proven human pathogens. Human isolates from all over Eastern Australia were most commonly 16S rDNA (Bergmans) type I, with the same gltA allele as the type strain (Houston-1). Comparable feline isolates were more commonly 16S type II, with less congruity of inheritance between 16S and gltA alleles. Previously described arbitrarily primed PCR and EagI-HhaI infrequent restriction site PCR fingerprinting techniques separated Bartonella species effectively but lacked discriminating power within B. henselae. Examination of the 16-23S intergenic spacer region revealed for several strains several point mutations as well as a repeat sequence of unknown significance which is readily detected by HaeIII restriction fragment length polymorphism analysis. The bacteriophage-associated papA gene was present in all isolates. Enterobacterial repetitive intergenic consensus PCR proved to be a useful and robust typing tool and clearly separated human isolates (including imported strains) from the majority of feline isolates. Our data are consistent with published evidence and with previous suggestions of intragenomic rearrangements in the type strain and suggest that human isolates come from a limited subset of B. henselae strains. They strengthen arguments for careful exploration of genotype-phenotype relationships and for the development of a multilocus enzyme electrophoresis and multilocus sequence typing-based approach to the phylogeny of B. henselae.

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