Minimal inhibitory and minimal bactericidal concentrations were determined for eighteen methicillin-resistant Staphylococcus aureus isolates, the majority also resistant to gentamicin, obtained from the blood of bacteraemic patients. Fifty per cent of organisms had a greater than four-fold difference in M.I.C. and M.B.C. for vancomycin, 83% for rifampicin, and 89% for fusidic acid. In-vitro effects of two-drug combinations of vancomycin, rifampicin, and fusidic acid demonstrated neither synergy nor antagonism when measured by a checkerboard dilution technique. The relevance of these findings to choice of therapy of serious infection due to methicillin-gentamicin resistant Staph. aureus is yet to be determined.

No abstract

An Australia-wide survey of the prevalence of resistance to antimicrobial agents among Haemophilus influenzae was conducted on clinically significant isolates collected between July 1988 and September 1990. Laboratories from the capital cities of each Australian state and territory participated. Nine hundred and seventy clinical isolates were examined for beta-lactamase production and the MICs of ampicillin, coamoxiclav, chloramphenicol, cefaclor, ceftriaxone, cefotaxime, tetracycline, rifampicin, trimethoprim, sulphamethoxazole and co-trimoxazole were determined using the NCCLS agar dilution method with Haemophilus Test Medium. A smaller number of isolates were tested against penicillin V, penicillin G, ciprofloxacin, piperacillin and erythromycin in addition. The proportion of beta-lactamase producing strains was higher among invasive strains (21.6%) than non-invasive strains (14.2%) and varies considerably between states. The highest prevalence of ampicillin resistance was found in invasive strains from Canberra (40.8%), the lowest in non-invasive strains from Adelaide (5.1%). Paradoxically, in non-invasive strains, although beta-lactamase production was less common, resistance to other antimicrobials was commoner than in invasive strains and also varied between states.

The in vitro activity of 17 antimicrobial agents was tested against 25 clinical isolates of Gardnerella vaginalis. Minimum inhibitory concentrations were determined by agar dilution. The isolates were sensitive to penicillin, ampicillin, ticarcillin, piperacillin, cephalothin, cefoxitin, cefotaxime, cefoperazone, N-formimidoyl-thienamycin, chloramphenicol, clindamycin and erythromycin. MIC90 for the beta-lactam antibiotics ranged from 0.12 mg/l for penicillin to 2 mg/l for ticarcillin. Cefoperazone was the most active cephalosporin, inhibiting all isolates at 1.0 mg/l. N-formimidoylthienamycin was the most active of the newer beta-lactam compounds inhibiting all isolates with a concentration of 0.5 mg/l. Clindamycin and erythromycin were highly active, inhibiting all isolates at 0.6 mg/l. Susceptibility to tetracycline, gentamicin, metronidazole and tinidazole varied between strains. All isolates were resistant to rosoxacin. The hydroxy-metabolites of metronidazole and tinidazole were more active than the parent compounds, inhibiting all isolates.

No abstract