Citations

Ciprofloxacin or rifampin was significantly (P less than 0.05) more effective than vancomycin or the combination of vancomycin plus gentamicin for the treatment of Staphylococcus epidermidis experimental endocarditis. There were no significant differences in efficacy among any of the combinations of antimicrobial agents that included ciprofloxacin or rifampin. One animal treated with rifampin alone and one treated with the combination of vancomycin, rifampin, and gentamicin were found to be infected with rifampin-resistant strains of S. epidermidis during therapy. Resistant subpopulations of S. epidermidis were not detected during therapy with any other antimicrobial agent used alone or in combination. Ciprofloxacin alone or in combination with rifampin was effective therapy against S. epidermidis experimental endocarditis.

Padac test strips failed to detect the production of β-lactamase by 10 strains of penicillin-resistant staphylococci.

A comparison between direct and standardized disk diffusion tests was made on a total of 300 urine specimens containing ≥10 5 organisms/ml. Of these, 246 represented pure cultures and 54 represented mixed cultures. The number of major discrepancies per organism tested in pure culture was 18 (7.3%) and in mixed cultures it was 23 (42.6%). The percentage of major discrepancies per total number of antimicrobial drug comparisons made was 1.4%. Although this procedure may be of value in selected cases with pure cultures of organisms present in quantities ≥10 5 /ml, its use on a routine basis is not recommended.

This study examined (i) the activity of gentamicin added to agar in ratios of 1:100 and 1:1,000 to produce a final concentration of 1 μg/ml, (ii) the uniformity of distribution of gentamicin in agar in relation to the amount of mixing, and (iii) the effect of agar depth on the activity of gentamicin against Pseudomonas aeruginosa . Although the ratio of antibiotic solution to agar had no significant effects on activity of the antibiotic, the amount of mixing did. Agar depth had no significant effect on the activity of gentamicin.

Ampicillin resistance (minimal inhibitory concentration ≥10 μg/ml) in the absence of beta-lactamase activity by Haemophilus influenzae was noted in tests performed with Mueller-Hinton agar containing one lot of supplement C. All strains, except five with known resistance due to beta-lactamase activity, were inhibited by 0.6 μg or less of ampicillin per ml of chocolatized blood agar.

Checkerboard bactericidal studies were performed with two strains each of Streptococcus mitis, S. salivarius , and S. sanguis , and the results were analyzed by the use of isobolograms. Synergy between penicillin and streptomycin or gentamicin was demonstrated with four strains, representing two of S. salivarius , one of S. sanguis , and one of S. mitis ; the remainder were either too susceptible or too resistant to be analyzed. Clindamycin with streptomycin or gentamicin acted synergistically with three strains, representing two of S. sanguis and one of S. salivarius ; the remainder were either too susceptible or too resistant to be analyzed.

Data derived from testing the bactericidal activity of combinations of penicillin with gentamicin or streptomycin and of clindamycin with gentamicin on nine isolates of Streptococcus mutans were analyzed by preparing isobolograms to determine the presence of additive, synergistic, or antagonistic effects. Synergy with penicillin-aminoglycoside combinations was found in two strains; additive effects occurred in seven instances with penicillin-gentamicin combinations; and antagonism occurred in eight instances with clindamycin-gentamicin combinations.

The in vitro activities of verdamicin and gentamicin were studied in parallel against 1,049 bacterial isolates. Verdamicin demonstrated activity similar to that of gentamicin against members of the family Enterobacteriaceae and against Pseudomonas aeruginosa at 2 and 8 μg/ml, respectively. Proteus rettgeri and Providencia stuartii were notably more susceptible to verdamicin. The new aminoglycoside was also highly active against staphylococci but was not effective against group D streptococci.

Minimal inhibitory concentrations of clindamycin, minocycline, metronidazole, penicillin, and carbenicillin were determined by agar dilution against 150 recent clinical isolates of anaerobic bacteria. Ninety-nine percent of Bacteroides fragilis and all B. melaninogenicus, Clostridium perfringens , and Fusobacterium were inhibited by clindamycin at 3.1 μg/ml. Only 58% of other clostridial species were inhibited by this concentration of clindamycin. Minocycline at 3.1 μg/ml inhibited 72% of C. perfringens , 81% of other Clostridium species, and 66, 75, and 100% of B. fragilis, B. melaninogenicus , and Fusobacterium , respectively. Metronidazole at 12.5 μg/ml inhibited all bacteria tested. B. fragilis was resistant to both penicillin and carbenicillin at 6.2 μg/ml. Concentrations of 25 μg/ml for penicillin and 100 μg/ml for carbenicillin were needed to inhibit more than 90% of B. fragilis . Organisms other than B. fragilis were moderately or extremely susceptible to the penicillins.

Kanamycin, BB-K8, and gentamicin were tested in parallel against 1,037 bacterial strains isolated from clinical material. The activity of BB-K8 at 20 μg/ml was comparable to that of gentamicin at 8 μg/ml against Pseudomonas aeruginosa and against Enterobacteriaceae , with the exception of gentamicin-resistant strains of Proteus rettgeri and Providencia stuartii , in which case the activities of BB-K8 and kanamycin were the same. BB-K8 exhibited little or no activity against streptococci. The activity of BB-K8 was affected by pH and inoculum size. A regression graph for inhibition data with a 10-μg disk of BB-K8 was developed, and synergistic activity of penicillin and BB-K8 against Streptococcus faecalis was tested.