No abstract

BO-1236, a new cephalosporin having an N-methyl-5,6-dihydroxyisoindolinium moiety on the 3-methylene of the cephem, showed potent activity against gram-negative organisms, including Pseudomonas aeruginosa. The in vitro activity of BO-1236 was superior or comparable to that of ceftazidime, cefotaxime, and cefoperazone in susceptibility tests with clinical isolates. BO-1236 was significantly more active than ceftazidime against P. aeruginosa strains susceptible or resistant to ceftazidime or gentamicin or both. MBCs were usually close to MICs, both of which were influenced by inoculum size to about the same degree as those of the other beta-lactams. BO-1236 was stable to all types of beta-lactamases except type I oxyiminocephalosporin-hydrolyzing enzyme, by which BO-1236 was slightly hydrolyzed. BO-1236 showed protective activity superior to that of ceftazidime and cefotaxime in experimental infections in mice caused by two strains of P. aeruginosa and showed activity comparable to that of ceftazidime and cefotaxime against other gram-negative bacterial infections.

BO-2727, a new 1-beta-methyl-carbapenem, was active at concentrations of 6.25 micrograms/ml or less against gram-positive and gram-negative bacteria, including some imipenem- and/or meropenem-resistant (MICs, > or = 12.5 micrograms/ml) Pseudomonas aeruginosa strains, against which it proved generally fourfold more active than imipenem and meropenem. BO-2727's antipseudomonal activity and its broad spectrum merit further investigation for clinical use by itself, since it was stable in the presence of renal dehydropeptidase I.

The porin expression of two clinical isolates of Serratia marcescens, which overproduced cephalosporinase and had decreased outer membrane permeability, were studied in comparison with those of reference strains. Separation of the porin proteins assessed by SDS-PAGE containing urea revealed that both clinical isolates overexpressed a single porin of 44 and 43 kilodalton (kDa), respectively. In contrast, the in-vitro porin deficient mutant, which was derived from the reference strain IFO3736 as latamoxef-resistant, showed decreased outer membrane permeability, but produced low levels of all three peptidoglycan associated porins of 45, 44 and 43 kDa, and overexpressed 39 kDa OmpA protein. These observations suggested that the clinical isolates had a different mechanism of latamoxef resistance compared with the mutant and overexpressed possible narrow transport channels of 44 or 43 kDa. The 45 kDa porin may facilitate a more effective channel than the other two proteins. Heterogeneity of porin profiles between biotypes was also suggested. The two isolates were also resistant to penicillins and cephalosporins tested, but imipenem was the most active agent and inhibited the isolates at 1.56 mg/L.

The in-vitro activity of imipenem combined with beta-lactam antibiotics was studied for 25 strains of methicillin and imipenem-resistant Staphylococcus aureus (MRSA) in comparison with that of fosfomycin combined with cefmetazole. Using the chequerboard agar dilution method, strong synergy was seen for all strains for imipenem with cefoperazone, cefotiam, cefpiramide or piperacillin. All fractional inhibitory concentration indices (FIC indices) of these combinations were less than or equal to 0.12. For the combination of imipenem with cefotiam the synergy was found to be bactericidal, but was not affected by the temperature of incubation, the concentration of sodium chloride in the medium or beta-lactamase production. However, for the combination of fosfomycin with cefmetazole only 44% of the strains with a mean FIC index of 0.55, showed synergy. The remaining 56% of strains showed either partial synergy (44%) or additive activity (12%). The combinations of imipenem with the beta-lactam antibiotics were more effective than that of fosfomycin with cefmetazole.