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).

Bronchial mucosal biopsy specimens were obtained during fibreoptic bronchoscopy in 30 patients receiving a new oral cephalosporin antibiotic, cefaclor (10 had 250 mg, 10 had 500 mg, and 10 had 1000 mg every eight hours). In 10 patients (from all dosage groups) cefaclor was undetectable in the bronchial mucosa but in every case the serum concentration was low, suggesting incomplete absorption. The mean (SD) bronchial mucosal concentration after 250 mg was 3-78 (1-77) ,ug/g (range 2-1-5-8 pug/g, n = 4), after 500 mg 4-43 (2.04) ug/g (range 2-0-7-1 ,ug/g, n = 8), and after 1000 mg 7*73 (2.76) ug/g (range 5-012-7 ,ug/g, n = 6). A significantly higher concentration in the bronchial mucosa was achieved with 1000 mg than with 250 mg (p < 0.05) or 500 mg (p < 0-025). These concentrations should be effective against Streptococcus pneumoniae, most strains being inhibited below 10 ,ug/ml. The concentrations were within one dilution of the minimal inhibitory concentration for Haemophilus infuenzae, most strains being inhibited below 4 0 Zg/ml. Some strains of H injflenzae will not be inhibited by the concentrations of cefaclor found in the bronchial mucosa, particularly those that are ampicillin resistant.

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An outbreak of an unusual tetracycline-sensitive, rifampicin-and ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus (MRSA) strain at a large teaching hospital was investigated. Two typing methods, phage typing and restriction fragment length polymorphism (RFLP) by pulsed-field gel electrophoresis (RFLP-PFGE), gave conflicting results which were clarified by phylogenetic analysis. Phage typing identified all the ''epidemic-associated'' strains as identical, while RFLP-PFGE further divided these strains into four pulsotypes. Phylogenetic analysis showed these four pulsotypes were related genetically and also recognized a second strain of MRSA causing a continuing cross-infection problem. Variation in the RFLP-PFGE pattern was shown to occur following lysogenization of phage-sensitive MRSA. These results indicate that in analyzing outbreaks caused by subgroups of clonal organisms like MRSA, it is necessary to use at least two typing methods and that conflicts between these could be resolved by phylogenetic analysis.

Autobac I, a recently introduced semiautomated method for rapid antibiotic susceptibility testing, has been evaluated by comparison with the calibrated dichotomous sensitivity disk diffusion technique, which is routinely used in many Australian hospitals. Only the most common clinical isolates, Staphylococcus aureus, Escherichia coli, Klebsiella sp., and Proteus mirabilis, were included in this evaluation, and an overall interpretive agreement of 93% was obtained. However, an unusually high rate of discrepancy was noted in several organismantibiotic combinations, in particular E. coli and P. mirabilis with ampicillin, S. aureus with penicillin, and methicillin-resistant S. aureus with methicillin, erythromycin, and clindamycin. The discrepancies associated with ampicillin have been reduced from 29 and 24% for E. coli and P. mirabilis, respectively, to less than 5% after the utilization of commercial 10-jug diffusion disks, in preference to the lower antibiotic content disks supplied by the Autobac manufacturer. Furthermore, modifications in the interpretive procedure have eliminated discrepancies associated with S. aureus and penicillin.The manufacturers of Autobac I, Pfizer Diagnostics Inc., claim that their product offers high interpretive agreement (average, 90%; range, 80 to 100%) with the results of the BauerKirby agar diffusion method. These figur6s were confirmed in a collaborative study performed at several United States hospitals (7). Since the Autobac in the Division of Microbiology, Repatriation General Hospital, Concord, was the first to be installed in Australia, a similar evaluation was undertaken to compare Autobac I susceptibility results with those obtained by the calibrated dichotomous sensitivity (CDS) disk diffusion technique. Organism-antibiotic combinations which showed poor correlation were studied in greater detail.MATERILS AND METHODS OrganiSm8. Clinical isolates of S. aureus, E. coli, Klebsiella sp., and P. mirabilis were used. The staphylococci were differentiated into three groups according to their susceptibility to methicillin as determined by the disk diffusion technique, and to their ability to produce penicillinase, this being determined by direct observation of the inhibitory zone surrounding the penicillin disk. A sharp well-defined border or large, discreet colonies at the zone edge indicated penicillinase production (1,5,8