Susceptibility of Nocardia asteroides to 45 Antimicrobial Agents In Vitro

A method for preparing uniformly dispersed cultures of Nocardia asteroides for use in tests for susceptibility to antimicrobial agents is described. The minimal inhibiting concentration (MIC) of 45 agents for cultures thus prepared was determined with the use of a replica-inoculating apparatus. Minocycline at a concentration of 3.1 mug or less/ml inhibited 90% of the strains tested, and all were inhibited by 6.3 mug/ml. An erythromycin concentration of 0.8 mug or less/ml inhibited 40% of the strains, but the MIC for most of the others was > 100 mug/ml. The other agents were generally less active. Chemically related analogues varied in activity to different degrees. Also, the MIC of each antibiotic against different strains generally varied over a wide range. Sulfonamides and trimethoprim were not active against most strains in the method used. The size of the inoculum markedly affected the MIC of sulfonamides and had variable effects on other agents. Marked synergy of erythromycin with ampicillin was demonstrated for nearly all strains tested.     

In Vitro Antimicrobial Susceptibility Patterns of Blastocystis

Blastocystis is the most common human enteric protist with controversial clinical significance. Metronidazole is considered a first-line treatment for Blastocystis infection; however, there has been increasing evidence for the lack of efficacy of this treatment. Treatment failure has been reported in several clinical cases, and recent in vitro studies have suggested the occurrence of metronidazole-resistant strains. In this study, we tested 12 Blastocystis isolates from 4 common Blastocystis subtypes (ST1, ST3, ST4, and ST8) against 12 commonly used antimicrobials (metronidazole, paromomycin, ornidazole, albendazole, ivermectin, trimethoprim-sulfamethoxazole [TMP-SMX], furazolidone, nitazoxanide, secnidazole, fluconazole, nystatin, and itraconazole) at 10 different concentrations in vitro. It was found that each subtype showed little sensitivity to the commonly used metronidazole, paromomycin, and triple therapy (furazolidone, nitazoxanide, and secnidazole). This study highlights the efficacy of other potential drug treatments, including trimethoprim-sulfamethoxazole and ivermectin, and suggests that current treatment regimens be revised.     

Yersinia enterocolitica: In Vitro Antimicrobial Susceptibility

Using 21 antimicrobial agents, agar dilution susceptibility tests were carried out against 190 strains of Yersinia enterocolitica. Isolates from human, environmental, and animal sources had essentially equal susceptibility patterns.     

Susceptibilities of Gram-Negative Bacteria to Combinations of Antimicrobial Agents In Vitro

Combinations of either clindamycin or erythromycin with gentamicin, colimycin, or carbenicillin were studied for their antimicrobial effects on clinical isolates of Escherichia coli, Klebsiella sp., Proteus mirabilis, Serratia marcescens, Enterobacter aerogenes, and Pseudomonas aeruginosa. No antagonistic effects of the antibiotic combinations were observed. Synergistic effects of the antibiotic combinations were noted against most strains of E. coli tested, especially when either clindamycin or erythromycin was combined with gentamicin or colimycin. Of 16 other combinations of antibiotics examined with strains of E. coli as the test organisms, only the combination of penicillin G with either gentamicin or colimycin showed consistent synergy. The marked synergy of clindamycin combined with either gentamicin or colimycin was further demonstrated by following the kinetics of the bactericidal action of the antibiotic combinations and the effects on bacterial protein synthesis.     

Susceptibility of Streptococcus mutans to Antimicrobial Agents

Fifty strains of Streptococcus mutans, including defined strains and clinical isolates, were tested for susceptibility to 20 different antimicrobial agents. Minimal inhibitory concentrations were determined by a liquid microtiter procedure. Antibiotics that were most effective in concentrations below 0.1 μg/ml included penicillin, ampicillin, erythromycin, cephalothin, and methicillin. Antibiotics effective in concentrations between 0.1 μg and 10 μg/ml included rifampin, lincomycin, thiostrepton, spiromycin, vancomycin, streptolydigan, novobiocin, tetracycline, chloramphenicol, spectinomycin, and gentamicin. Antibiotics effective at higher concentrations ranging from 10 μg/ml to 400 μg/ml included the aminoglycosides kanamycin, neomycin, streptomycin, and kasugamycin. Although most antibiotics exhibited inhibitory effects in a narrow range of concentrations, antibiotics such as tetracycline, thiostrepton, and spiromycin had a 1,000-fold range from the lowest to highest concentrations required for growth inhibition.     

Susceptibility of Anaerobic Bacteria to 23 Antimicrobial Agents

The antimicrobial susceptibility of 492 anaerobic bacteria, the majority of which were recent clinical isolates, was determined by the agar dilution technique. Penicillin G was active against most of the strains tested at 32 U or less/ml, but only 72% of Bacteroides fragilis strains were susceptible at this level and 9% required 256 U or more/ml. Ampicillin was effective against most of the strains except B. fragilis at 16 μg or less/ml. Amoxicillin was active against only 31% of B. fragilis, 76% of other Bacteroides species, and 67% of Fusobacterium species at 8 μg/ml. Two new penicillins, mezlocillin and azlocillin, were similar to ampicillin in their activity. Carbenicillin and ticarcillin inhibited all but a few strains at 128 μg or less/ml. BLP 1654 was somewhat more active than penicillin G against B. fragilis but had similar activity against other anaerobes. Cephalothin was inactive against B. fragilis, and only 65% of other Bacteroides species were inhibited by 32 μg or less/ml. It was effective against all other anaerobes at that level. Cefamandole showed somewhat greater activity than cephalothin against B. fragilis but generally less activity against gram-positive organisms. Cefazaflur (SKF 59962) was comparable to cephalothin against B. fragilis. Cefoxitin was distinctly more active than cephalothin against B. fragilis. These latter two agents were less active than cephalothin against the gram-positive anaerobes. Chloramphenicol remains active against anaerobic bacteria at 16 μg or less/ml, with rare exceptions. Thiamphenicol was similar to chloramphenicol in its activity. Clindamycin was very active against most of the anaerobes at 8 μg or less/ml. Erythromycin and josamycin were also tested, with josamycin showing greater activity against B. fragilis than either erythromycin or clindamycin. A new oligosaccharide, everninomicin B, was less active than clindamycin against B. fragilis but more active against clostridia and some of the other strains tested. Most of the groups of bacteria tested demonstrated a trend toward resistance to tetracycline. Doxycycline and minocycline were somewhat more active than was tetracycline. Metronidazole was active against the majority of the anaerobes tested; resistance ws demonstrated by some of the gram-positive cocci and gram-positive, non-sporeforming bacilli.     

Susceptibility of Anaerobic Bacteria to Ten Antimicrobial Agents

The susceptibility pattern of 265 anaerobic bacteria from clinical isolates to 10 antimicrobial agents was investigated by the agar dilution technique. Penicillin G, in a concentration of 16 μg/ml, was active against most organisms, important exceptions being 12% of Bacteroides melaninogenicus and 24% of B. fragilis strains. The susceptibility of strains to ampicillin was similar to their susceptibility to penicillin G. Carbenicillin, at ≤128 μg/ml, inhibited all but a few strains. Cefamandole was less active than the penicillins; 82% of B. melaninogenicus, 32% of B. fragilis, and 75% of Fusobacterium strains were inhibited by ≤16 μg/ml. A trend towards tetracycline resistance was seen in many bacterial groups, especially Bacteroides, Fusobacterium, and Clostridium. All organisms were susceptible to chloramphenicol and clindamycin in concentrations of ≤16 μg/ml and ≤4 μg/ml, respectively. Erythromycin was less active than clindamycin against all strains tested. Metronidazole and tinidazole were active against most anaerobes, but resistance of a few strains in each group was encountered. The increased resistance of B. melaninogenicus strains to penicillin, and emergence of anaerobes resistant to >16 μg of imidazole per ml may have therapeutic implications.     

In Vitro Activity of 39 Antimicrobial Agents Against Treponema hyodysenteriae

The in vitro activities of 39 antimicrobial agents against 23 isolates of Treponema hyodysenteriae, the majority of which were field isolates, were determined by the agar dilution technique. Quinoxalines, pleuromutilin, nitroimidazoles, and nitrofuran were the most active. Their activities ranged from /=100 mug/ml. Macrolides showed varying degrees of activity depending upon isolates.     

Susceptibility of Clostridium septicum to 23 Antimicrobial Agents

The in vitro susceptibility of Clostridium septicum was studied with a microtiter broth dilution method. Several antimicrobial agents demonstrated consistently good activity against the organism.     

In Vitro Activity of Antimicrobial Agents on Legionnaires Disease Bacterium

Six isolates of Legionnaires disease bacteria were tested for their susceptibility to 22 antimicrobial agents. The most active agent was rifampin (minimal inhibitory concentration, 相似文献   

In Vitro Activity of Retapamulin against Staphylococcus aureus Resistant to Various Antimicrobial Agents

Retapamulin and six other antimicrobial agents were evaluated against 155 methicillin-resistant Staphylococcus aureus (MRSA) isolates, including strains resistant to vancomycin, linezolid, daptomycin, and mupirocin by microdilution tests. Time-kill assays were performed against representative MRSA, vancomycin-intermediate S. aureus (VISA), and vancomycin-resistant S. aureus (VRSA) isolates. Retapamulin and mupirocin demonstrated MIC₉₀s of 0.12 μg/ml and 8 μg/ml, respectively, with resistance seen in 2.6% and 10% of isolates, respectively. Retapamulin maintained good activity against 94% (15/16) of mupirocin-resistant isolates.     

In Vitro Antimicrobial Susceptibility of Anaerobic Bacteria Isolated from Clinical Specimens

The minimal inhibitory concentrations of 601 clinical isolates of anaerobic bacteria to 10 different antimicrobial agents were determined by an agar-dilution technique. Nearly all strains were resistant to kanamycin and gentamicin, although moderate activity to both drugs was noted with Fusobacterium sp., anaerobic cocci, some strains of Bacteroides melaninogenicus, and nonsporeforming gram-positive bacilli. Chloramphenicol at 12.5 mug/ml inhibited all but three of the strains tested. Tetracycline at 6.25 mug/ml had high activity against all groups tested, with the exception that only 39% of strains of Bacteroides fragilis were inhibited at this concentration. Excluding certain species of Bacteroides, the majority of anaerobes were inhibited by penicillin at 3.1 mug/ml or less and by cephalothin at 12.5 mug/ml or less. Lincomycin at 6.2 mug/ml or less was active against nearly all strains. Erythromycin at a concentration of 3.1 mug/ml was active against B. fragilis; however, erythromycin was less active against the other groups. Most of the minimal inhibitory concentrations of lincomycin exceeded those of clindamycin by fourfold. Rifampin inhibited virtually all strains at 3.1 mug/ml.     

In Vitro Susceptibility of Pathogenic Naegleria and Acanthamoeba Species to a Variety of Therapeutic Agents

Six pathogenic strains of Naegleria fowleri, two of Acanthamoeba castellanii, and three of Acanthamoeba polyphaga were tested in vitro for susceptibility to a variety of potentially useful therapeutic agents. Minimal motility inhibitory concentrations and minimal inhibitory concentrations were determined by a technique of subculturing pure clones of amoebae in plastic tissue culture chamber slides containing liquid axenic media and serially diluted drug, incubating at 30°C for Acanthamoeba and at 37°C for Naegleria, and observing on an inverted microscope at 6 h for inhibition of motility and at 24 and 48 h for inhibition of growth. Drug concentrations were selected on the basis of fluid levels achievable in humans. Amphotericin B, clotrimazole, and miconazole were the most effective drugs against Naegleria, whereas polymyxin B sulfate and pentamidine isethionate were somewhat effective against pathogenic Acanthamoeba. Our results suggest that amphotericin B is the most effective agent against Naegleria, but few agents are effective against Acanthamoeba.     

Standardized Antimicrobial Disc Susceptibility Testing of Anaerobic Bacteria: In Vitro Susceptibility of Clostridium perfringens to Nine Antibiotics

The in vitro susceptibility of 43 strains of Clostridium perfringens to nine antibiotics was determined by a standardized test for rapid-growing anaerobes. Good correlation was established between the agar dilution susceptibility and the disc diffusion susceptibility results. The inhibition zone diameters around the antibiotic discs, however, were generally much smaller than those of gram-negative anaerobes previously studied. All of the strains tested were susceptible in vitro to chloramphenicol, clindamycin, doxycycline, minocycline, penicillin, and vancomycin. Erythromycin showed poor in vitro activity against this organism, with only 7% of the strains susceptible, 72% intermediate in susceptibility, and 21% resistant. In tests of the 43 strains against lincomycin, 58% were susceptible, 32.5% were intermediate in susceptibility, and 9.5% were resistant. Against tetracycline, 37% of the strains were intermediate in susceptibility and the rest were susceptible.     

In vitro susceptibilities of Mycoplasma hyopneumoniae field isolates

The in vitro susceptibilities of 21 Mycoplasma hyopneumoniae field isolates were determined using a broth microdilution technique. One isolate showed acquired resistance to lincomycin, tilmicosin, and tylosin, while five isolates were resistant to flumequine and enrofloxacin. Acquired resistance against these antimicrobials in M. hyopneumoniae field isolates was not reported previously.     

解脲支原体和人型支原体的药敏分析

【目的】了解解脲支原体(Uu)和人型支原体(Mh)的耐药状况,指导临床合理用药。【方法】应用支原体培养鉴定药敏试剂盒进行检测。【结果】512例门诊患者,251例支原体培养阳性,阳性率49.02%;Uu单项感染164例(32.03%)显著高于Mh感染(17例3.32%)和Uu Mh混合感染(70例13.67%)(P<0.01);药敏结果显示,以交沙霉素和强力霉素敏感性最强(90.04%,89.24%),其次为司帕沙星和克拉霉素(70.92%,69.32%),而对环丙沙星、可乐必妥和红霉素敏感性较差。【结论】选择敏感有效的抗生素对于控制支原体的传播和蔓延尤为重要。     

Microdilution Transfer Plate Technique for Determining In Vitro Synergy of Antimicrobial Agents

A microdilution transfer plate technique for determining in vitro synergy of antimicrobial agents is described. Combinations of gentamicin-nalidixic acid against Proteus mirabilis and rifampin-amphotericin B against Candida albicans are used as examples to demonstrate the technique. Results correlate with published data obtained by conventional methods. The technique is effective for evaluating the in vitro effects of antimicrobial agent combinations against both bacteria and fungi. The technique enables one to produce a checkerboard gradient in a fast, convenient, and reproducible way; results are easily visualized.     

In Vitro Activity of Oral Antimicrobial Agents Against Clinical Isolates of Pasteurella multocida

Pasteurella multocida causes a wide variety of infections and is the most common localized soft tissue infection after animal bite injuries. Penicillin or amoxicillin has been considered agent of choice for therapy. Reported β-lactamase production by some isolates, the therapeutic dilemma of the penicillin allergic patient, and the polymicrobial nature of some infections led to this study of alternate antimicrobial agents. The in vitro activity of ampicillin, amoxicillin/clavulanate, cefprozil, cefuroxime, erythromycin, clarithromycin, trimethoprim/sulfamethoxazole, ciprofloxacin, and tetracycline were compared to penicillin against 73 geographically diverse isolates of P. multocida from human infections collected since 1991. MIC₉₀ (μg/mL) were as follows: penicillin ≤0.06; ampicillin ≤0.5; amoxicillin/clavulanate ≤0.5; cefaclor 1.0; cefprozil 1.0; cefpodoxime 0.06; cephalothin 2.5; cefuroxime ≤0.25; erythromycin 2.0; azithromycin 1.0; clarithromycin 4.0; trimethoprim/sulfamethoxazole ≤0.5/9.5; ciprofloxacin ≤0.25; tetracycline ≤2.0. No β-lactamase producing isolates were found in this study. This in vitro study has identified alternate oral agents to penicillins that may be appropriate for therapy of P. multocida infections.     

Susceptibility of Three Groups of Staphylococcus aureus to Newer Antimicrobial Agents

Because of the need for non-beta-lactam antimicrobics with antistaphylococcal activity, 14 antimicrobics (3 penicillinase-resistant penicillins, 7 aminocyclitols [5 new], 2 macrolides [1 new], clindamycin, and a new polysaccharide, everninomicin) were tested in vitro for activity against 22 penicillin-susceptible, 51 penicillin-resistant, and 47 methicillin-resistant strains of Staphylococcus aureus. Gentamicin, tobramycin, sisomicin, and verdamicin inhibited almost all strains at concentrations less than 1 mug/ml. The methicillin-resistant strains were as susceptible as other strains to the aminocyclitols and everninomicin. In contrast, many of the methicillin-resistant strains were also resistant to erythromycin, rosamicin, and clindamycin at attainable serum concentrations. The use of the bacterial synthetic amino acid medium, in comparison with Mueller-Hinton broth, resulted in an increase in the observed resistance of methicillin-resistant strains to the penicillinase-resistant semisynthetic penicillins.     

Susceptibility of Campylobacter fetus subsp. jejuni to Twenty Antimicrobial Agents

One hundred recent clinical isolates of Campylobacter fetus subsp. jejuni were tested by an agar dilution technique for susceptibility to each of 20 antimicrobial agents. Doxycycline and gentamicin were the most active of the drugs examined, inhibiting all strains at concentrations achievable in serum. Although the median minimal inhibitory concentration of erythromycin was low, 8% of the isolates were highly resistant. All isolates of Campylobacter fetus subsp. jejuni were relatively resistant to the beta-lactam antibiotics. Some strains were highly resistant to metronidazole and tinidazole.