European Journal of Clinical Microbiology最新文献

When testing Pseudomonas aeruginosa against netilmicin, MICs were markedly affected by the concentration of cations added to the test medium. A susceptible disk test result (zone greater than or equal to 15 mm) corresponded to MIC less than or equal to 4.0 micrograms/ml in unsupplemented broth, less than or equal to 12 micrograms/ml in broth with half the usual amount of cations and less than or equal to 32 micrograms/ml in broth with the recommended concentration of cations. Tests with 30 micrograms netilmicin disks best predicted susceptibility as determined by MICs in broth without added cations. When the MICs were determined in cation supplemented broth, the number of interpretive discrepancies increased to an unacceptably high level.

In 1984 the European Study Group on Antibiotic Resistance (ESGAR), which is made up of 29 laboratories in 12 European countries, consecutively collected gram-negative bacilli and staphylococci isolates from blood and using the microdilution method performed susceptibility testing with 11 beta-lactam antibiotics. A total of 2,578 isolates were collected; 68% were gram-negatives and 32% staphylococci. Pseudomonas spp. accounted for 12% of the strains, Enterobacter spp. 7%, Serratia spp. 3%, indole-positive Proteus spp. 1%, Citrobacter spp. and Morganella spp. 0.9% each. Strains with inducible beta-lactamases were detected by the cefoxitin disc diffusion method in 11% of all gram-negatives and in 67% of the relevant species. The production of inducible beta-lactamase was confirmed by elevated MICs to and decreased killing by piperacillin, cefotaxime and ceftazidime after induction of enzyme production with low concentrations of cefoxitin. This phenomenon was not observed with mecillinam or the new penem Sch 34343.

The in vitro activity of RO 23-6240 was compared with that of norfloxacin, ofloxacin and ciprofloxacin as well as four other antimicrobial agents against 345 recent clinical isolates. The MICs of RO 23-6240 against Enterobacteriaceae and Acinetobacter anitratum was less than or equal to 0.5 mg/l. At the same concentration of the compound 90% of staphylococci were inhibited. Against Enterococcus faecalis and Pseudomonas aeruginosa RO 23-6240 proved less active, having MIC90 values of 4.0 mg/l and 8.0 mg/l, respectively. Enterobacteriaceae and staphylococci strains that were resistant to piperacillin, cefotaxime or tobramycin were susceptible to the compound. In general the activity of RO 23-6240 was comparable to those of norfloxacin and ofloxacin, but less than that of ciprofloxacin.

Most strains of enterobacteria and Pseudomonas aeruginosa produce chromosomally-determined Class I beta-lactamases. When synthesized copiously these enzymes cause resistance to almost all beta-lactams, except imipenem and, sometimes, carbenicillin and tenocillin. Elevated beta-lactamase production arises transiently, via induction, in Pseudomonas aeruginosa and Enterobacter, Citrobacter, Morganella, indole-positive Proteus and Serratia spp. when these organisms are exposed to beta-lactams. Permanent high-level enzyme production arises via mutation, in the stably-derepressed mutants of these species. These mutants arise spontaneously at high frequency (10(-5) -10(-8). Most early penicillins and first-generation cephalosporins are strong inducers of Class I enzymes at sub-inhibitory concentrations, as are cefoxitin and imipenem. Consequently their MICs reflect what lability these antibiotics have to inducibly-expressed beta-lactamase. Except with imipenem this lability usually is so great that the inducible enzyme causes clinical resistance. Although most other newer cephalosporins and ureidopenicillins are labile to the Class I enzymes they induce poorly below the MIC, and their lability is not reflected in resistance unless secondary inducers (e.g. cefoxitin or imipenem) are present. Although the weak inducer activity of these agents helps to maintain their activity against the inducible cells it renders the drugs highly selective for the pre-existing stably-derepressed mutants. Many cases have been reported where stably-derepressed mutants have overrun inducible populations of bacteria in patients undergoing therapy with beta-lactamase-labile weak inducers such as ureidopenicillin and third-generation cephalosporins.

A case of hepatopulmonary hydatid disease in a Cypriot who presented with pyogenic infection with Streptococcus milleri is described. Although hydatid disease and pyogenic liver abscess are both rare in the UK, an underlying echinococcal pathology should be suspected in any patient from an area endemic for hydatid who presents with a pyogenic hepatic or hepatopulmonary abscess.

The antispirochetal activity in vitro and in vivo of several antibiotics against ten isolates of Borrelia burgdorferi from human spinal fluids and skin biopsies was determined. Borrelia burgdorferi was most susceptible in vitro to erythromycin, ceftriaxone and cefotaxime (MIC90: 0.06, 0.06, 0.12 mcg/ml respectively). Less activity was observed with tetracycline, amoxycillin and lincomycin (MIC90: 0.50 mcg/ml), imipenem and augmentin (MIC90: 0.25 mcg/ml), oxacillin (MIC90: 1 mcg/ml), ciprofloxacin (MIC90: 2 mcg/ml) and ofloxacin (MIC90: 4 mcg/ml). Penicillin G, normally regarded as appropriate treatment for Lyme disease, had an MIC90 of only 4 mcg/ml. With the exception of erythromycin, activity in vitro corresponded to the activity in vivo. Erythromycin, however, was less active in vivo, and penicillin G showed poor activity both in vitro and in vivo.