The in vitro activity of fosfomycin in combination with ceftazidime, imipenem, amikacin, or ciprofloxacin was studied by an agar plate checkerboard method against 40 clinical isolates of Pseudomonas aeruginosa with various antibiotic resistance profiles. Fosfomycin/ciprofloxacin appeared to be the most effective combination (synergy 15%, addition 80%, indifference 5%), followed by fosfomycin/amikacin (synergy 7.5%, addition 52.5%, indifference 40%), fosfomycin/imipenem (addition 37%, indifference 63%), and fosfomycin/ceftazidime (addition 20%, indifference 80%). The effects of the combinations were not significantly influenced by the antibiotic susceptibility patterns of the strains.

A clinical isolate of Morganella morganii, with reduced susceptibility to expanded-spectrum cephalosporins and aztreonam, was found to produce an extended-spectrum β-lactamase with a pI of 6.4. The nucleotide sequence of the encoding gene was that of the gene encoding TEM-21. This is the first molecular characterization of an extended-spectrum β-lactamase in M. morganii.

Antigenic relationships among the 10 Bacteroides species, Porphyromonas gingivalis, Prevotella bivia, and Prevotella intermedia were investigated by rocket-line immunoelectrophoresis, using antigenic extracts prepared from type strains and antisera to Bacteroides fragilis, Bacteroides distasonis, Bacteroides thetaiotaomicron, Porphyromonas gingivalis, and Prevotella intermedia. Among the members of the genus Bacteroides, B. fragdis, Bacteroides caccae, Bacteroides stercoris, Bacteroides vulgatus, B. thetaiotaomicron, and Bacteroides ovatus were found to be closely related, and B. distasonis and Bacteroides merdue were the species that were most distantly related to B. fragilis; Bacteroides eggerthii and Bacteroides uniformis were in an intermediate position. Porphyromonas gingivalis, Prevotella bivia, and Prevotella intermedia shared very low percentages of common antigens with the Bacteroides species. Detection of enzymic activities in immunoprecipitates allowed us to identify some antigens to enzymes and to study the immunological similarities of the enzymes. The malate dehydrogenases of the Bacteroides species were genus specific, and the glucose-6-phosphate dehydrogenases of most species exhibited antigenic similarities, The esterases of B. distasonis and B. thehiohomicron appeared to be species specific, whereas the esterases and phosphatases of B. fragilis cross-reacted with the esterases and phosphatases of B. stercoris and B. vulgatus, as did the phosphatases of B. distasonis and B. merdae. The phosphatases of B. eggerthii, B. uniformis, Porphyromonas gingivalis, and Prevotella intermedia were antigenically similar.Organisms belonging to the genus Bacteroides Castellani and Chalmers 1919 are obligately anaerobic, gram-negative, nonsporing, rod-shaped bacteria (7, 8). However, this genus is known to be phenotypically and phylogenetically extremely heterogeneous. Thus, the 39 species included in the genus in Betgey's Manual of Systematic Bacteriology (7) exhibit a variety of cellular morphologies and saccharolytic and proteolytic activities and have DNA base compositions ranging from 28 to 61 mol% guanine plus cytosine.On the basis of biochemical, chemical, and molecular biological criteria (10,18,20), the majority of the more typical Bacteroides species form three broad groups. The first group consists of Bacteroides frasilis and related saccharolytic intestinal species. This group includes five species which at one time were described as subspecies of a single species, B. fragdis (8) Shah and Collins (20) have proposed that the genus Bacteroides should be restricted to the 10 species belonging to the B. fragiis group and that the members of the second and third groups should be transferred to the new genera Prevotella and Porphyromonas,

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