In vitro susceptibility of Streptococcus mutans to chlorhexidine and six other antimicrobial agents.

The susceptibility of Streptococcus mutans to chlorhexidine and to six commonly used, systemic antibacterial agents (amoxicillin, cefuroxime, penicillin, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin) was studied for 424 clinical isolates from 116 children and students. The MIC of chlorhexidine for all isolates was < or = 1 micrograms/ml. No resistance to the other antimicrobial agents was detected. Although widely exposed to various antimicrobial agents, S. mutans has remained susceptible to common antimicrobial agents, most importantly to chlorhexidine.     

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。     

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 susceptibility of Haemophilus influenzae to eight antibiotics

Freshly isolated strains of Haemophilus influenzae type B were studied for their in vitro susceptibility to eight antibiotics with a low concentration inoculum. No organisms were identified as being resistant to ampicillin, but minimal inhibiting concentrations for that antibiotic were somewhat higher than reported previously for a similar method. Carbenicillin and ticarcillin resembled ampicillin in activity, and the three agents were more effective on a weight basis than the other agents tested.     

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 Pythium insidiosum to macrolides and tetracycline antibiotics

We describe the in vitro activity of macrolides and tetracycline antibiotics against Pythium insidiosum. The MICs were determined according to CLSI procedures (visual MIC) and by a colorimetric method [3-(4,5-dimethyl-2-thiazyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT)]. The lowest geometric mean (GM) MIC (MICs in μg/ml) (0.39 and 0.7 by visual reading and colorimetric method, respectively) and MIC ranges (0.125 to 2.0) were obtained for minocycline, while the highest MICs were shown for erythromycin (GM of 7.58 and 12.25 by visual reading and colorimetric method, respectively, and MIC ranged from 2 to 32). This significant in vitro activity makes these classes of antibiotics good candidates for experimental treatment of pythiosis.     

In vitro susceptibility of Pythium insidiosum isolates to aminoglycoside antibiotics and tigecycline

This study evaluated the in vitro activity of aminoglycoside antibiotics and tigecycline against Pythium insidiosum. The susceptibility tests were carried out using the broth microdilution method in accordance with the CLSI document M38-A2. MIC values for gentamicin, neomycin, paromomycin, and streptomycin ranged from 32 to 64 mg/liter, and the minimal fungicidal concentration (MFC) ranged from 32 to 128 mg/liter, which are incompatible with safe concentrations of these drugs in plasma in vivo. Tigecycline showed the lowest MIC (0.25 to 2 mg/liter) and MFC (1 to 8 mg/liter) range values. The in vitro susceptibility observed to tigecycline makes this drug a good option in future tests in vitro and in vivo for the management of pythiosis.     

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 susceptibility of Clostridium difficile to new beta-lactam and quinolone antibiotics.

The in vitro susceptibilities of 34 to 73 clinical isolates of Clostridium difficile to 24 antimicrobial agents, including 18 beta-lactams, 4 fluoroquinolones, clindamycin, and metronidazole were examined. Metronidazole was the most active (MIC for 90% of the isolates [MIC90], 0.5 microgram/ml), followed by the carbapenems (Sch 34343, 4 micrograms/ml; imipenem, 8 micrograms/ml) and the antipseudomonas penicillins (piperacillin, 8 micrograms/ml; ticarcillin, 32 micrograms/ml; carbenicillin, 32 micrograms/ml). A monobactam (aztreonam) and most cephalosporins were either highly inactive (cefoxitin, cefuroxime, cefotiam, cefsulodin, ceftizoxime, cefbuperazone, and cefotaxime), with an MIC90 of greater than or equal to 128 micrograms/ml, or moderately inactive (ceftriaxone, cefmenoxime, cefoperazone, ceftazidime, and moxalactam), with an MIC90 of greater than or equal to 32 micrograms/ml. Clindamycin (MIC90, 32 micrograms/ml) and the fluoroquinolones (ciprofloxacin, 8 micrograms/ml; A-56619, 8 micrograms/ml; A-56620, 8 micrograms/ml; norfloxacin, 32 micrograms/ml) were only variably active. These in vitro data per se may not necessarily predict the relative risks for C. difficile-associated diarrhea or colitis during therapy with these agents. However, these data, in concert with knowledge of drug bioavailability in feces and the broad-spectrum antimicrobial activity on the resident bowel flora, may provide additional insight into the mechanisms and predictability of this complication with these agents. Careful monitoring for the emergence of C. difficile and fecal cytotoxin and for diarrhea during therapy with these agents is clearly indicated.     

In vitro susceptibility of Coxiella burnetii to antibiotics, including several quinolones.

Antibiotic susceptibility testing of the rickettsial Q fever agent Coxiella burnetii was performed by using persistently infected L929 fibroblast cells. The efficacies of a variety of antibiotics with different metabolic targets were tested and compared. The most effective antibiotics in bringing about the elimination of the parasite from infected cells included several quinolone compounds and rifampin. Of the quinolone compounds tested, difloxacin (A-56619) was the most effective, followed by ciprofloxacin and oxolinic acid. These three quinolones were apparently rickettsiacidal. After 48 h of exposure to microgram amounts of the compounds (ranging from 2 micrograms of difloxacin per ml to 5 micrograms of the other two antibiotics per ml), the number of intracellular parasites markedly declined; after 10 days of treatment, very few intracellular rickettsiae were detected. Rifampin (1 microgram/ml) was also very effective in eliminating the parasites. Some of the 13 other antibiotics tested that were somewhat effective included chloramphenicol, doxycycline, and trimethoprim. The persistently infected L929 cells were found to provide a convenient system for the relatively rapid determination of the susceptibility of C. burnetii to antibiotics.     

In vitro development of resistance to six quinolones in Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus

Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus isolates were exposed to subinhibitory MICs of ciprofloxacin, sparfloxacin, gatifloxacin, moxifloxacin, clinafloxacin, and gemifloxacin during a 10-day period. Subculturing led to resistance development, regardless of the initial potencies of the quinolones. None of the quinolones was associated with a significantly slower rate of resistance development.     

In vitro susceptibility of Salmonella to ciprofloxacin and pefloxacin compared with three other antibiotics

The in vitro susceptibilities of 703 clinical isolates of Salmonella to ciprofloxacin (CIP) and pefloxacin (PEF) were compared with those to trimethoprim-sulfamethoxazole (TMP-SMZ), chloramphenicol (CO) and ampicillin (AP). All isolates were susceptible to CIP, while PEF inhibited 90.7% of the strains. In contrast, resistance rates of 40, 29.2 and 27% were detected for AP, TMP-SMZ and CO, respectively. PEF resistance was detected in S. panama (1), S. typhi (3) and S. typhimurium (17), the latter representing the most frequently serovar isolated in our country. None of the S. typhi isolates was resistant to CO. Combined resistance was most frequently found among S. typhimurium isolates, with the patterns PEF-TMP-SMZ-AP (10) and PEF-TMP-SMZ-CO-AP (5) predominating.     

In vitro susceptibility of recent antibiotic-resistant urinary pathogens to ertapenem and 12 other antibiotics

Background: The treatment of complicated urinary tract infections may require the use of a parenteral antibiotic with potent activity against the most common urinary pathogens. Ertapenem is a broad-spectrum 1beta-methyl carbapenem with a long plasma half-life that allows administration of a single daily dose. METHODS: The purpose of this work was to test the in vitro susceptibility to ertapenem, ampicillin, cefazolin, cefuroxime, cefotaxime, co-amoxiclav, piperacillin/tazobactam, imipenem, gentamicin, amikacin, fosfomycin, ciprofloxacin and co-trimoxazole of 482 strains of urinary pathogens of the family Enterobacteriaceae isolated from patients in the community of Madrid (40% from males). The distribution was as follows: Escherichia coli (n = 315), Proteus mirabilis (n = 42), Klebsiella spp. (n = 14) and AmpC-producing Enterobacteriaceae (n = 111). The strains studied were selected based on their resistance to quinolones and aminoglycosides, and their production of extended-spectrum beta-lactamases (ESBLs) or AmpC-type beta-lactamases. RESULTS: All the strains were susceptible to ertapenem, imipenem and amikacin. The MIC(90) of ertapenem ranged from a minimum of 0.03 mg/L for Proteus vulgaris and a maximum of 1 mg/L for Enterobacter spp. Ertapenem was the most active of all drugs tested in all cases. On comparing antibiotic resistance among ESBL-producing strains of E. coli (n = 35) and E. coli strains not producing ESBLs (n = 280), statistically significant differences were obtained for ciprofloxacin (P = 0.002) and gentamicin (P = 0.011). Regarding ertapenem, only a slight increase in MIC(50) was seen, the value being 0.015 mg/L for strains not producing ESBLs versus 0.03 mg/L for ESBL-producing strains. CONCLUSIONS: In view of its significant antibiotic potency against antibiotic-resistant Enterobacteriaceae, ertapenem may constitute a good therapeutic alternative in urinary infections caused by these pathogens.     

In vitro activity of telithromycin against Streptococcus pneumoniae resistant to other antibiotics, including cefotaxime

A total of 407 isolates of Streptococcus pneumoniae, most of which were resistant to one or more antibiotics, were tested for susceptibility to telithromycin and four other agents. Telithromycin was the most active agent tested, with 98% of isolates susceptible to < or = 1.0 mg/L. For strains resistant to the other antibiotics, susceptibility to telithromycin ranged from 98.6% for strains resistant to trimethoprim/sulfamethoxazole to 94.4% for strains resistant to cefotaxime.     

In vitro susceptibility of pathogenic Vibrio species to norfloxacin and six other antimicrobial agents.

The in vitro activity of norfloxacin and six other antimicrobial agents was tested against 93 vibrio strains representing the currently described pathogenic Vibrio species. Norfloxacin had excellent activity against all species, with the following MICs for 90% of the strains: 0.016 micrograms/ml for Vibrio cholerae (including tetracycline-resistant V. cholerae O1 strains), 0.25 micrograms/ml for V. parahaemolyticus, and 0.063 micrograms/ml for V. vulnificus.     

In vitro susceptibility of Sporothrix schenckii to six antifungal agents determined using three different methods

The in vitro susceptibility of Sporothrix schenckii to antifungal drugs has been determined with three different methods. Nineteen Peruvian clinical isolates of S. schenckii were tested against amphotericin B (AB), flucytosine (FC), fluconazole (FZ), itraconazole (IZ), voriconazole (VZ), and ketoconazole (KZ). Modified NCCLS M38-A, Sensititre YeastOne (SYO), and ATB Fungus 2 (ATBF2) methods were used to determine the MICs. ATCC isolates of Candida parapsilosis, Candida krusei, and Aspergillus flavus were used for quality control. Sporothrix inocula were prepared with the mycelial form growing on potato dextrose agar at 28 +/- 2 degrees C. MICs of AB, FC, FZ, and IZ were determined with all three methods, VZ with M38-A and SYO, and KZ with only SYO. The three methods showed high MICs of FZ and FC (MIC(90) of 0.5 microg/ml), being homogeneously lower than those of IZ and KZ. The M38-A method showed a variable MIC range of VZ (4.0 to 16 microg/ml); the geometric mean (GM) was 9.3 mug/ml. The MIC range of AB was wide (0.06 to 16 microg/ml), but the GM was 1.2 microg/ml, suggesting that the MIC is strain dependent. Agreement (two log(2) dilutions) between commercial techniques and the modified M38-A method was very high with FZ, IZ, and FC. In AB and VZ, the agreement was lower, being related to the antifungal concentrations of each method. The highest activity against S. schenckii was found with IZ and KZ. Lack of activity was observed with FZ, VZ, and FC. When AB is indicated for sporotrichosis, the susceptibility of the strain must be analyzed. Commercial quantitative antifungal methods have a limited usefulness in S. schenckii.     

In vitro susceptibility of enterococci strains isolated from urine samples to fosfomycin and other antibiotics

Enterococci are mostly isolated from urinary tract infections (UTIs). Increasing antibiotic resistance affects the success rate in empirical treatment, thus makes antibiotic susceptibility tests important. The aim of this study was to determine the species distribution and resistance patterns of Enterococcus strains isolated from urine samples to antibacterial agents including fosfomycin in a teaching hospital, Istanbul. The identification of 100 Enterococcus strains were determined by using conventional methods and API 20 Strep (bioMerieux France). The susceptibility testing was performed by disk diffusion and Etest. The majority of isolates were E. faecalis (67%), followed by E. faecium (33%). The ratio of E. faecalis to E. faecium was 2.03/1. E. faecalis and E. faecium strains were resistant to penicillin (38.8, 93.9%), ampicillin (4.8, 84.8%), vancomycin (1.5, 18.2%), teicoplanin (1.5, 18.2%), gentamicin (13.4, 58%), ciprofloxacin (34.3, 84.8%), levofloxacin (34.3, 87.9%), norfloxacin (38.8, 84.8%), tetracycline (89.6, 48.5%), nitrofurantoin (1.5, 39.4%), and fosfomycin (2.3, 0%) (p < 0.0001), respectively. Resistance to fosfomycin was observed in neither E. faecium strains, nor vancomycine-resistant enterococci strains. It was concluded that, enterococci are important pathogens for UTI; species identification and periodic evaluation of antibiotic susceptibility pattern would be guide for early empirical treatment and in uncomplicated UTI, fosfomycin could be an alternative option for therapy.