In vitro activity of new quinolones against Clostridium difficile

We evaluated the in vitro activities of ofloxacin, levofloxacin, grepafloxacin, trovafloxacin and ciprofloxacin against Clostridium difficile. The MIC(90) was 128 mg/L for ofloxacin and levofloxacin, 64 mg/L for ciprofloxacin, 16 mg/L for grepafloxacin and 8 mg/L for trovafloxacin. Thirty per cent of isolates were resistant to trovafloxacin, and rates of resistance to ofloxacin, levofloxacin, grepafloxacin and ciprofloxacin were considerably higher. None of the antimicrobials studied would be a reliable therapeutic option against C. difficile. Whether some of the new fluoroquinolones can induce C. difficile-associated diarrhoea remains to be answered.     

In vitro susceptibility of 96 Capnocytophaga strains, including a beta-lactamase producer, to new beta-lactam antibiotics and six quinolones.

The in vitro activities of new beta-lactam antibiotics and new quinolones were studied against 96 Capnocytophaga strains, including a beta-lactamase-producing strain which was resistant to ampicillin, amoxicillin, carbenicillin, cephalothin, and cefamandole. All strains were susceptible to the combination of amoxicillin and clavulanic acid, ureidopenicillins, cefoxitin, broad-spectrum cephalosporins, and imipenem. Cephalothin and cefamandole did not show good activity against most strains. All Capnocytophaga spp. were uniformly susceptible to the five new quinolones tested.     

In vitro activities of new beta-lactam antibiotics against Acinetobacter spp

The in vitro activities of new beta-lactam antibiotics was studied and compared with those of other known agents against 51 clinical isolates of Acinetobacter calcoaceticus subsp. anitratus and 23 isolates of A. calcoaceticus subsp. lwoffi. Of the new beta-lactam antibiotics, imipemide (N-formimidoyl thienamycin), ceftazidime, ceftizoxime, ceftriaxone, and piperacillin demonstrated good activities. The minimal inhibitory concentrations for A. calcoaceticus subsp. lwoffi were lower than those obtained for A. calcoaceticus subsp. anitratus.     

In vitro activities of ramoplanin and four glycopeptide antibiotics against clinical isolates of Clostridium difficile.

Seventy strains of Clostridium difficile, all isolated from symptomatic patients, were found to be uniformly susceptible to ramoplanin, a new glycolipodepsipeptide antibiotic, and to four glycopeptides (vancomycin, teicoplanin, and two semisynthetic teicoplanin derivatives). Ramoplanin is recommended for further evaluation in the treatment of C. difficile-associated disease.     

In vitro synergy studies with Clostridium difficile.

Agar dilution anaerobic susceptibility studies using rifampin, vancomycin, metronidazole, and bacitracin individually and in combination were performed with Clostridium difficile. Fifty-five strains of C. difficile were studied. Eighty-five percent of strains tested (29 of 34) were synergistically inhibited by the combination of bacitracin and rifampin (fractional inhibitory concentration, less than or equal to 0.50).     

In vitro antagonism of beta-lactam antibiotics by cefoxitin.

We assessed the extent and mechanisms of antagonism of beta-lactam antibiotics by cefoxitin. In tests with 41 gram-negative isolates, cefoxitin antagonized cephalothin, cefamandole, cefsulodin, cefotaxime, moxalactam, ampicillin, carbenicillin, piperacillin, mezlocillin, and azlocillin, but not cephalexin, mecillinam, or N-formimidoyl thienamycin. The extent of antagonism varied with the beta-lactam and genus studied. However, antagonism occurred most often with strains possessing inducible cephalosporinases. Antagonism of cephalothin and cefamandole correlated closely with the induction of beta-lactamases capable of inactivating these drugs. Although antagonism of the remaining drugs occurred more often with strains possessing inducible beta-lactamases, these enzymes did not inactivate the drugs. Morphological studies revealed that cefoxitin inhibited filamentation and lysis produced by various beta-lactam drugs. Results of this investigation suggest that cefoxitin antagonizes beta-lactams via (i) induction of drug-inactivating beta-lactamases, and (ii) the induction of beta-lactamases that cannot inactivate the drug but serve as barriers against access to target proteins. This barrier appears most efficient for drugs that bind to penicillin-binding proteins 1 and 3.     

In vitro susceptibility of Brucella melitensis to antibiotics.

The in vitro susceptibilities of 86 recent clinical isolates of Brucella melitensis to minocycline, streptomycin, co-trimoxazole, rifampin, and six fluoroquinolones were determined. Minocycline exhibited the lowest MIC and was followed by rifampin and streptomycin. Among the quinolones, WIN 57273 and ciprofloxacin were the most active agents. No antibiotic combination of these agents exhibited synergy against 15 selected isolates. In killing rate experiments, streptomycin exhibited the most rapid kill (less than 12 h), while a complete kill with minocycline, rifampin, and ciprofloxacin was delayed up to 48 h. The combinations of streptomycin with each of minocycline, rifampin, or ciprofloxacin exhibited the fastest kills (within 2 h), while with the other combinations, a complete kill was delayed up to 96 h. These results demonstrate the discrepancy between the results of various in vitro methods in evaluating the antibiotic susceptibility of B. melitensis.     

In vitro susceptibility of Clostridium difficile isolates from patients with antibiotic-associated diarrhea or colitis.

In vitro susceptibility tests were performed on 84 strains of Clostridium difficile to 11 antimicrobial agents. All isolates were from the stools of patients with antibiotic-associated diarrhea or colitis in which there was a cytopathic toxin that was neutralized by Clostridium sordellii antitoxin. Over 95% of the strains were susceptible to vancomycin, penicillin G, ampicillin, and metronidazole at concentrations of 4 microgram/ml. Susceptibility to clindamycin was variable; 60% of the strains were susceptible at 1 microgram/ml, and 9% were resistant at 128 microgram/ml. Studies of individual isolates showed that a major portion of the strains were relatively susceptible to the antimicrobial agent implicated in causing the disease.     

In vitro susceptibility of Ehrlichia sennetsu to antibiotics.

Antibiotic efficacies were evaluated by Diff-Quik (Dade, Düdingen, Federal Republic of Germany) staining of Ehrlichia sennetsu in P388D1 murine macrophages grown in 96-well microtiter plates. Sennetsu disease is generally cured with tetracyclines. In vivo, E. sennetsu is susceptible to doxycycline and is resistant to erythromycin, penicillin, and chloramphenicol. Our study confirmed, in vitro, the efficacy of doxycycline, which had an MIC of 0.125 micrograms/ml. E. sennetsu was found to be resistant to erythromycin, chloramphenicol, penicillin, gentamicin, and co-trimoxazole, while it was very susceptible to ciprofloxacin (MIC, 0.125 micrograms/ml) and rifampin (MIC, 0.5 micrograms/ml).     

In vitro antimicrobial activity of eight new beta-lactam antibiotics against penicillin-resistant Neisseria gonorrhoeae.

Increasing numbers of cases of penicillin-resistant gonorrhea necessitate the evaluation of new antibiotics for treatment of this disease. We tested the susceptibility of 92 penicillinase-producing (PP) Neisseria gonorrhoeae isolates and 88 penicillin-susceptible (PS) isolates to eight new beta-lactam antibiotics. The minimal inhibitory concentrations of these antibiotics were determined by the agar plate method. PP and PS N. gonorrhoeae isolates were susceptible to clinically achievable levels of all antibiotics tested. There were, however, marked differences among the drugs with regard to the concentration required to inhibit growth. The PP N. gonorrhoeae isolates were extremely susceptible to ceftriaxone, ceftizoxime, and cefotaxime, highly susceptible to moxalactam and cefoperazone, and less susceptible to cefoxitin, ceforanide, and cefonicid (geometric mean minimal inhibitory concentrations were 0.002, 0.003, 0.007, 0.03, 0.07, 0.6, 2.4, and 3.1 micrograms/ml, respectively). Although this in vitro study showed PP N. gonorrhoeae isolates to be comparatively more susceptible to ceftriaxone, ceftizoxime, and cefotaxime than to the other antibiotics, these results may not correlate with clinical efficacy.     

In vitro susceptibility of cephalothin-resistant Enterobacteriaceae and Pseudomonas aeruginosa to Amikacin and selected new beta-lactam agents.

Amikacin was evaluated in vitro by agar dilution testing against 148 different clinical isolates of cephalothin-resistant Enterobacteriaceae and Pseudomonas aeruginosa in parallel with cephalothin, cefoxitin, moxalactam, N-formimidoyl thienamycin, ceftriaxone, and cefmenoxime. Cefsulodin was also evaluated against 39 isolates of P. aeruginosa. More than 80% of all isolates tested were also gentamicin resistant, as determined by disk testing. Moxalactam and amikacin had comparable high activities against Proteus species, Escherichia coli, Serratia species, and Providencia species, and both amikacin and N-formimidoyl thienamycin had comparably high activities against the Klebsiella-Enterobacter group. N-Formimidoyl thienamycin was the most active agent against P. aeruginosa, followed by cefsulodin and amikacin.     

Decreased susceptibility of penicillin-resistant pneumococci to twenty-four beta-lactam antibiotics.

The in-vitro activity of 24 beta-lactam antibiotics was compared using three groups of pneumococci and an agar dilution method comprising 100 penicillin-susceptible, 100 intermediately penicillin-resistant, and 100 highly penicillin-resistant pneumococcal strains. Our results show that intermediately penicillin-resistant and highly penicillin-resistant pneumococci had decreased sensitivity to other beta-lactam agents. According to their relative in-vitro activity, the antimicrobials were classified into three groups. The first group included drugs more active than penicillin (imipenem, meropenem, cefotaxime, ceftriaxone, and cefpirome), which could be useful for the treatment of infections due to penicillin-resistant strains. The second group showed slightly lesser activity than did penicillin, and included: ampicillin, cefdinir, cefuroxime, cefoperazone, azlocillin, mezlocillin, piperacillin, cephalothin, and cefamandole. The remaining antibiotics (oxacillin, cefixime, ceftizoxime, cefetamet, cefaclor, ceftazidime, cefoxitin, cefonicid, and latamoxef) showed poor activity against penicillin-resistant strains, precluding their use for empirical treatment in areas with a high prevalence of penicillin-resistant strains.     

In-vitro susceptibility of Pseudomonas aeruginosa to old and new beta-lactam antibiotics and aminoglycosides

In-vitro, activities of gentamicin, tobramycin, netilmicin, amikacin, cefsulodin, latamoxef (moxalactam), carbenicillin, ticarcillin and piperacillin were compared against 147 randomly selected strains of Pseudomonas aeruginosa. Tobramycin was the most active aminoglycoside (MIC 90:4 mg/l), complete cross resistance with gentamicin (MIC 90:8 mg/l) was observed. Amikacin was the best alternative aminoglycoside (MIC 90:12 mg/l) Netilmicin showed only moderate activity (MIC 90:16 mg/l). Cefsulodin was the most active beta-lactam antibiotic (MIC 90:8 mg/l) but significant cross-resistance was observed with ticarcillin (MIC 90:32 mg/l) and piperacillin (MIC 90:12 micrograms/ml). Carbenicillin was two dilutions less active than ticarcillin, latamoxef showed a good activity (MIC 90:64 mg/l). Having the highest ratio between serum achievable concentration and MIC 90, piperacillin could be the best alternative drug to the aminoglycosides, of the tested antibiotics.     

In vitro susceptibilities of Capnocytophaga isolates to beta-lactam antibiotics and beta-lactamase inhibitors

The susceptibilities of 43 pharyngeal isolates of Capnocytophaga to beta-lactam antibiotics, alone or in combination with beta-lactamase inhibitors, were tested by an agar dilution method. The 34 beta-lactamase-positive strains were highly resistant to beta-lactams, but the intrinsic activities of clavulanate, tazobactam, and sulbactam against Capnocytophaga, even beta-lactamase producers, indicates that these beta-lactamase inhibitors could be used for empirical treatment of neutropenic patients with oral sources of infection.     

巴尔通体对19种抗生素体外敏感性分析

目的 检测巴尔通体菌株对10类19种抗生素最低抑菌浓度（MICs）,分析药物敏感性及耐药性,为指导临床用药和耐药监测提供实验和数据参考。方法 采用E试验法,检测巴尔通体属11种、35株菌株对强力霉素、阿奇霉素、利福平等19种抗生素的MICs。将培养的巴尔通体菌制成McFarland（MCF）2.0浊度的菌悬液,均匀涂布于含5%去纤维羊血的胰酶大豆琼脂培养基上,置5% CO2的37℃培养箱培养。培养5~7 d后判读MICs。结果 35株巴尔通体菌在体外对强力霉素、阿奇霉素、红霉素、克拉仙霉素等13种抗生素敏感,MICs 0.016 mg/L;34株对利福平敏感,MICs 0.002 mg/L;对克林霉素、丁胺卡那霉素、万古霉素、多粘菌素和磺胺类5种抗生素不敏感,MICs较高。结论 绝大多数巴尔通体菌对强力霉素等14种抗生素敏感,但也对克林霉素等5种抗生素不敏感,在对巴尔通体病进行治疗时要注意选择敏感药物。