The diagnosis of vertebral osteomyelitis is easily missed, particularly for the elderly in whom signs of sepsis may not manifest. The case records of 20 patients with vertebral osteomyelitis who were treated at our hospital between January 1989 and April 1993 were reviewed. The average age of the patients was 72 years. Infection was most commonly due to intravenous cannula-related sepsis. Eighty-five percent of patients presented with back pain, and only 30% had a fever. Computerized tomography and magnetic resonance imaging were the most useful radiological investigations; nuclear scanning was sensitive but insufficiently specific. Staphylococcus aureus was the infecting organism in 13 of 16 patients whose microbiological diagnosis was made by blood or bone cultures. Six (45%) of these 13 patients were infected with methicillin-resistant S. aureus (MRSA). Nosocomial infection occurred in 12 (60%) of the patients studied, including all patients with MRSA infections. Vertebral osteomyelitis may be largely preventable if infection-control aspects of intravenous cannulation are improved, attempts at reducing and preventing MRSA colonization are made, and therapy for bacteremias is optimized.

A new chromogenic plate medium, CHROMagar Orientation, was evaluated for use in the differentiation and presumptive identification of gram-negative bacilli and Enterococcus species by a multipoint inoculation (replicator) technique. In this study, 1,404 gram-negative bacilli and 74 enterococcal isolates were tested on CHROMagar Orientation. Six control American Type Culture Collection strains were also included with the testing to ensure quality control of the media. Of the Escherichia coli isolates (n ‫؍‬ 588) tested, 99.3% produced a pink-to-red color. Only in four isolates that were O-nitrophenyl-␤-D-galactopyranoside (ONPG) negative did this result differ. Proteus mirabilis and P. vulgaris were well differentiated on this medium. P. mirabilis (n ‫؍‬ 184) produced a clear colony with diffusible brown pigment around the periphery. By contrast, 15 of 16 P. vulgaris isolates produced bluish-green colonies with a slight brown background. All Aeromonas hydrophila isolates (n ‫؍‬ 26) tested produced clear to pink colonies at 35 to 37؇C. This colony color changed to blue after 2 to 3 h of incubation at room temperature. A. hydrophila exhibited stronger color and better growth at 30؇C. Serratia marcescens (n ‫؍‬ 29) demonstrated an aqua blue color that deepened to a darker blue when exposed to room temperature. All enterococcal isolates (n ‫؍‬ 74) resulted in a blue color and gave pinpoint colonies on purity subcultures at 35 to 37؇C after 18 h of incubation. Similarity in color resulted in failure to discriminate accurately between Klebsiella, Enterobacter, and Citrobacter species. However, these species could be readily differentiated from other members of the family Enterobacteriaceae. Pseudomonas aeruginosa (n ‫؍‬ 151) was easily differentiated from members of the Enterobacteriaceae but was less easily distinguishable from other gram-negative nonmembers of the Enterobacteriaceae. The medium was found to facilitate easy visual detection of mixed bacterial isolates in culture. When used in a replicator system, it easily detected mixed growths of organisms which may have otherwise led to false antibiotic susceptibility results. These mixed growths were not obvious on the routine susceptibility testing medium (Isosensitest).

Ninety clinical Staphylococcus aureus isolates from separate patients were examined phenotypically and genotypically for susceptibility to methicillin/oxacillin. Thirty were methicillin/oxacillin susceptible and 60 were methicillin and oxacillin resistant (MRSA). The 60 MRSA isolates examined were subdivided into two groups according to their antibiotic profiles and comprised 30 non-multidrug-resistant (NMDR) isolates, resistant to less than two non-beta-lactam antibiotics, and 30 multidrug-resistant (MDR) isolates, resistant to three or more non-beta-lactam antibiotics. Phenotypic and genotypic analysis of methicillin/oxacillin showed that despite use of the guidelines published by the NCCLS for the testing of S. aureus susceptibility to methicillin/oxacillin, MIC values of some NMDR MRSA isolates fell below the NCCLS-recommended breakpoints. Etest strips failed to detect two NMDR MRSA isolates tested with oxacillin and four tested with methicillin. Lowering the NCCLS-recommended oxacillin screen agar concentration from 6 to 2 mg/L and temperature of incubation to 30 degrees C, improved the specificity and sensitivity of NMDR MRSA detection from 87% to 100%. On PFGE analysis these NMDR MRSA strains were genotypically different. Genotypic tests, such as multiplex PCR for the mecA/nuc genes and DNA hybridization for the mecA gene, or phenotypic monoclonal antibody-based tests to detect penicillin-binding protein 2a (PBP2a) offer advantages for problematic isolates in detecting or confirming low-level phenotypic heterogeneous mecA expression of oxacillin and methicillin resistance in NMDR MRSA.

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As toxigenic C. difficile may form part of the normal flora in young children, this study indicates that in the absence of a defined outbreak, C. difficile does not appear to be an important pathogen in pediatric oncology patients.

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While a high rate of MR is not unexpected in patients born in developing countries, the high rate in Australian born patients is surprising and of concern. This may relate to the high local usage of nitroimidazoles as monotherapy and has important implications for the effectiveness of metronidazole containing triple therapies.

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