Comparative susceptibilities of penicillin-resistant pneumococci to co-trimoxazole, vancomycin, rifampicin and fourteen beta-lactam antibiotics

Eighty-four isolates of penicillin-resistant pneumococci were tested for susceptibility to vancomycin, rifampicin, cotrimoxazole, and 14 beta-lactam antibiotics by agar and microbroth dilution methods. Twenty-three were from adult patients with pneumococcal disease, 57 from nasopharingeal carriers (preschool children) and four were resistant South African isolates. For all isolates tested, imipenem (N-formimidoyl thienamycin), rifampicin, ceftriaxone and cefotaxime had the greatest activity ( MIC90 : 0 X 12, 0 X 25, 0 X 5 mg/l, respectively). Cefoxitin and latamoxef were the least active of the drugs studied. The remaining beta-lactams tested had less activity than that of penicillin. All strains were inhibited by 1 mg/l of vancomycin and all but one were resistant to cotrimoxazole. The excellent in-vitro activities of the newer beta-lactam agents (ceftriaxone, cefotaxime and, particularly, imipenem ) and vancomycin against penicillin-resistant pneumococci offer a considerable promise for their use in the treatment of pneumococcal meningitis caused by these strains.     

Activities of antimicrobial agents against intracellular pneumococci

Pneumococci can enter and survive inside human lung alveolar carcinoma cells. We examined the activity of azithromycin, gentamicin, levofloxacin, moxifloxacin, penicillin G, rifampin, telithromycin, and trovafloxacin against pneumococci inside and outside cells. We found that moxifloxacin, trovafloxacin, and telithromycin were the most active, but only telithromycin killed all intracellular organisms.     

In vitro susceptibilities of zygomycetes to combinations of antimicrobial agents

Combinations of antimicrobial agents were tested against 35 strains of zygomycetes. The interaction between amphotericin B and rifampin was synergistic or additive. Flucytosine alone was inactive and, upon combination with amphotericin B, synergy was not achieved. The combination of amphotericin B with terbinafine was synergistic for 20% of strains, and the interaction between terbinafine and voriconazole was synergistic for 44% of strains. Antagonism was not observed.     

Efficacy and pharmacodynamics of simulated human-like treatment with levofloxacin on experimental pneumonia induced with penicillin-resistant pneumococci with various susceptibilities to fluoroquinolones

Newer fluoroquinolones, such as levofloxacin, have shown an enhanced in vitro and in vivo activity against penicillin-resistant Streptococcus pneumoniae infections. The frequency of S. pneumoniae with reduced susceptibility to quinolones, although currently low, raises the question of the therapeutic efficacy of levofloxacin on infection due to such strains. We used an animal model of penicillin-resistant pneumococcal pneumonia using six strains with various levels of susceptibility to ciprofloxacin and levofloxacin in rabbits to induce pneumonia, and simulated a human-like treatment of 500 mg twice a day for 48 h. Strains' susceptibility profiles for ciprofloxacin and levofloxaxin were (ciprofloxacin/levofloxacin MIC, mg/L; genotype): 0.5/0.5 (Cip0.5), 2/1 (Cip2), 4/1.75 (Cip4), 8/1.75 (parC mutation) (Cip8), 10/2 (parC mutation) (Cip10), 64/16 (parC and gyrA mutations) (Cip64), respectively. All the strains induced a crude pneumonia in all rabbits. Significant bacterial reductions at the end of treatment in lung and spleen were observed for the four former strains (P < 0.05) but not for the latter two. An AUC/MIC ratio of at least 32 identified 95% of an at least bacteriostatic effect (P = 0.038) and 76% of a bactericidal effect (P = 0.09). Mutants were detected in treated animals infected with strains harbouring parC mutations (Cip8 and Cip10) and when the AUC/MIC ratio was between 13 and 31. We conclude that levofloxacin is effective against experimental pneumonia due to pneumococci with MIC < 1.5 mg/L, ineffective on experimental pneumonia due to pneumococci with MIC > or = 2 mg/L, and could be associated with the appearance of mutants when a parC mutation is pre-existing.     

Antibiotic susceptibilities of the Vibrionaceae to meropenem and other antimicrobial agents.

The in vitro activity of meropenem was compared with imipenem and other selected antimicrobial agents against 115 isolates from the family Vibrionaceae. No resistance was observed with meropenem or imipenem against these isolates. However, meropenem was generally four- to 16-fold more active than imipenem against the aeromonads and Vibrio cholerae. Meropenem showed excellent in vitro activity against the Vibrionaceae and may be useful for eradicating infections produced by these organisms.     

In vitro susceptibilities of Aeromonas hydrophila to 32 antimicrobial agents.

Minimal inhibitory concentrations of 32 antimicrobial agents for 20 strains fo Aeromonas hydrophila were determined by a microdilution method. Moxalactam was the most active drug tested. All strains were also susceptible to clinically achievable concentrations of mecillinam, cefamandole, cefuroxime, cefotaxime, aminoglycosides (except streptomycin), tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole.     

In vitro susceptibilities of Pseudomonas pseudomallei to 27 antimicrobial agents.

Clinical isolates of Pseudomonas pseudomallei isolated in Thailand from 1981 to 1989 were tested for their in vitro susceptibilities to 27 antimicrobial agents, including older and newer quinolones, broad-spectrum cephems, carbapenems, monobactams, penicillins, tetracyclines, chloramphenicol, rifamycin, sulfamethoxazole, trimethoprim, and fosfomycin. Tosufloxacin, meropenem, CS-533, and minocycline were active against P. pseudomallei at levels comparable to or even greater than those of antimicrobial agents tested in previous studies, such as ciprofloxacin, ceftazidime, imipenem, carumonam, and piperacillin. Drug-resistant P. pseudomallei was found in only 1% of the isolates. The drug-resistant P. pseudomallei isolates displayed a unique pattern of susceptibility to the above-listed drugs.     

In vitro susceptibilities of Campylobacter-like organisms to twenty antimicrobial agents.

We determined MICs of 20 antimicrobial agents for 50 representative strains of four subgroups of Campylobacter-like organisms (CLOs) by agar dilution. Ampicillin, gentamicin, doxycycline, tetracycline, ceftriaxone, rifampin, spectinomycin, nalidixic acid, and chloramphenicol were active against all strains of CLOs. Most CLO strains (83%) were inhibited by 4 micrograms of sulfamethoxazole per ml and by 8 micrograms of trimethoprim-sulfamethoxazole per ml. Of type 1 strains, 28% were resistant to 8 micrograms of erythromycin per ml. In addition, cross resistance between erythromycin and clindamycin was always present. Type 1 strains exhibited a broad distribution of MICs of metronidazole and streptomycin, whereas all type 2 strains were uniformly susceptible to metronidazole and resistant to streptomycin. Unlike type 1 and 3 strains, type 2 CLOs were susceptible to cephalothin and penicillin G and highly resistant to streptomycin. The type 3 strain was uniquely resistant to cefazolin. The majority of strains were not inhibited by cefoperazone; and all were resistant to trimethoprim. In contrast to Campylobacter jejuni and Campylobacter fetus subsp. fetus, all CLOs tested were susceptible to 0.5 microgram of rifampin per ml.     

In vitro susceptibilities of Mycobacterium tuberculosis to 10 antimicrobial agents.

After preliminary in vitro screening of 10 antimicrobial agents against Mycobacterium tuberculosis, the MICs of the 6 most promising agents against 27 clinical isolates were determined by agar dilution. The two quinolone compounds tested (difloxacin and A-56620) were the most active, each inhibiting 50% of the strains at concentrations of 4 micrograms/ml. M. tuberculosis strains previously shown to be resistant to isoniazid, streptomycin, rifampin, or ethambutol were as susceptible to these quinolone compounds as susceptible strains.     

In vitro susceptibilities of Nocardia species to newer antimicrobial agents.

The in vitro activities of various quinolones, two newer cephalosporins, and imipenem against 23 strains of Nocardia asteroides, 4 strains of Nocardia brasiliensis, and 4 strains of Nocardia caviae were determined by an agar dilution method. PD-117558, a newer carboxyquinolone, and imipenem were the most active agents tested, inhibiting 90% of N. asteroides isolates at an MIC of 2 micrograms/ml. Of the 23 strains of N. asteroides, 15 were susceptible to cefpirome and 10 were susceptible to ciprofloxacin. The N. brasiliensis and N. caviae strains were very susceptible to PD-117558 (MIC, less than or equal to 1 microgram/ml), moderately susceptible to ciprofloxacin, and resistant to most of the other tested drugs.     

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.     

Antibiotic susceptibilities of 94 isolates of Yersinia pestis to 24 antimicrobial agents

Ninety-four isolates of Yersinia pestis collected by the French army between 1964 and 1988 were evaluated for their susceptibilities to 24 antibiotics by the agar dilution method. All the isolates were susceptible to beta-lactam antibiotics including imipenem, to fluoroquinolones, aminoglycosides and to doxycycline. The most active compounds were fluoroquinolone antibiotics, third-generation cephalosporins and aminoglycosides.     

In vitro susceptibilities of rapidly growing mycobacteria to newer antimicrobial agents.

The in vitro antimicrobial susceptibilities of 42 isolates of rapidly growing mycobacteria (Mycobacterium fortuitum, M. chelonae, and Mycobacterium species [other than M. fortuitum and M. chelonae]) to nine quinolones, including newer agents, two new aminoglycosides, and an aminocyclitol (trospectomycin) were determined by a broth microdilution method. The new quinolones, PD 117596, PD 127391, and PD 117558, showed excellent in vitro activities against M. fortuitum (MICs for 90% of isolates [MIC90s], 0.06, 0.06, and 0.12 microgram/ml, respectively). The MIC90 of ciprofloxacin for M. fortuitum was 0.5 microgram/ml. Only 14 to 28% of isolates of M. chelonae were susceptible to various quinolones. Most isolates of all three species were susceptible to the new aminoglycosides SCH 21420 and SCH 22591. The MIC90s of trospectomycin were 8 micrograms/ml for M. chelonae, 32 micrograms/ml for Mycobacterium species, and > 64 micrograms/ml for M. fortuitum.     

In vitro susceptibilities of aerotolerant Campylobacter isolates to 22 antimicrobial agents.

We evaluated the in vitro activities of 22 antimicrobial agents against 78 human and animal isolates belonging to two aerotolerant Campylobacter species, C. cryaerophila and C. butzleri, using a broth microdilution technique. An additional 10 antimicrobial agents were included at concentrations found in selective Campylobacter media. Strains of C. cryaerophila belonged to two DNA hybridization groups: DNA hybridization group 1A, which includes the type strain of C. cryaerophila, and DNA hybridization group 1B. The aminoglycosides, fluoroquinolones, and one tetracycline (minocycline) demonstrated the most activity against all DNA hybridization groups (C. cryaerophila DNA groups 1A and 1B and C. butzleri). Most isolates were resistant to cephalosporin antibiotics, with the exception of cefotaxime, and were variably susceptible to trimethoprim-sulfamethoxazole. C. cryaerophila DNA hybridization group 1A isolates were generally susceptible to the tetracyclines, chloramphenicol, nalidixic acid, azithromycin, erythromycin, and roxithromycin and moderately susceptible to clindamycin, trimethoprim-sulfamethoxazole, ampicillin, and ampicillin-sulbactam. The MICs of tetracyclines were higher for C. butzleri and C. cryaerophila DNA hybridization group 1B isolates than for C. cryaerophila DNA hybridization group 1A isolates, but most strains were still susceptible to doxycycline and tetracycline; all isolates were susceptible to minocycline. C. butzleri and C. cryaerophila DNA hybridization group 1B isolates were generally resistant to the macrolide antibiotics (including erythromycin), chloramphenicol, clindamycin, nalidixic acid, ampicillin, and trimethoprim-sulfamethoxazole. Differences in antimicrobial susceptibility between aerotolerant Campylobacter species and more common Campylobacter species, e.g., C. jejuni, suggest that different treatment strategies may be necessary. Strains of all three DNA hybridization groups of aerotolerant Campylobacter isolates were susceptible to colistin, polymyxin B, and rifampin at concentrations commonly used in selective media. These results suggest that primary isolation methods for Campylobacter species may need to be modified to include aerotolerant Campylobacter strains.     

In vitro susceptibilities of five Leptospira strains to 16 antimicrobial agents.

The in vitro activities of 16 antibiotics against five serovar strains of the genus Leptospira were determined. Five of the antibiotics (ampicillin, cefmetazole, moxalactam, ceftizoxime, and cefotaxime) exhibited a lower minimal inhibitory concentration than did penicillin G. In tests for minimal bactericidal concentration, ceftizoxime and cefotaxime were found to be more effective than penicillin G, streptomycin, tetracycline, ampicillin, and cefmetazole.     

In-vitro activity of ten antimicrobial agents against penicillin-resistant Streptococcus pneumoniae.

The minimum inhibitory concentrations (MICs) of ten antibiotics were determined by the agar dilution method for 40 strains of penicillin-resistant Streptococcus pneumoniae, all of which were clinical isolates from this laboratory. The antibiotics tested were clarithromycin, erythromycin, teicoplanin, vancomycin, ceftriaxone, cefodizime, azithromycin, ramoplanin, ciprofloxacin and MDL 62873. Of these agents, clarithromycin, vancomycin, teicoplanin, ceftriaxone, ramoplanin and MDL 62873 were the most active. The role of these antibiotics as alternatives to penicillin for the treatment of infections caused by penicillin-resistant S. pneumoniae is discussed.     

72株沙门菌血清型分布及药敏试验结果分析

目的：了解广东东莞地区沙门菌血清型分布,腹泻患者沙门菌检出数量及药敏试验结果,为该省今后的疾病防控,药物治疗提供参考依据。方法收集东莞市人民医院2013年4—12月门诊及住院患者腹泻粪便标本1150份,用改良亚硒酸盐磺绿增菌肉汤和沙门菌显色平皿分离检测沙门菌;药敏试验采用法国生物梅里埃ATB微生物鉴定和药敏分析系统及其配套药敏试条。结果共检出沙门菌72株,检出率为6．3％,分出21个血清型,以鼠伤寒沙门菌检出数量最多,22株（30．5％）,肠炎沙门菌16株（22．2％）。年龄分布1周岁以下42株（58．3％）,3-10岁12株（16．7％）,20岁以上18株（25．0％）。药敏试验结果耐药率较高的药物有哌拉西林（50．0％）,替卡西林（48．6％）。结论本地区腹泻患者检出沙门菌属以鼠伤寒沙门菌检出率最高,肠炎沙门菌次之,年龄1周岁以下较多。临床医师应加强对腹泻患者沙门菌属监测,尤以婴幼儿为重点,早期发现早期治疗以减少并发症发生。