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PubMed2002

[Multicenter evaluation of a newly developed microdilution test, brothMIC NTM to determine minimum inhibitory concentrations of antimicrobial agents for nontuberculous mycobacteria].

We developed a new broth microdilution susceptibility test for nontuberculous mycobacteria to determine minimum inhibitory concentrations(MICs). The test method utilized air-dried microplates containing serially diluted antimicrobial agents and the modified Middlebrook 7H9 broth. The nine agents tested were rifampicin, isoniazid, ethambutol, streptomycin, kanamycin, levofloxacin, clarithromycin, ethionamide and amikacin. The test plates were reconstituted by inoculation of 0.1 ml of cell suspensions prepared in distilled water by a 1:100 dilution of the 0.5 McFarland suspension. After inoculation, the isolates resulted in incubation at 36 degrees C with clarithromycin at pH 7.4, and with the remaining agents at pH 6.6. The growth endpoints were visually read after 7-day and 10-day incubations for slowly growing nontuberculous mycobacteria, and after 3-day and 5-day incubations for rapidly growing mycobacteria, respectively. The reproducibility was evaluated with the five ATCC reference strains of nontuberculous mycobacteria. Of the 1,287 repeated tests of the four ATCC slowly growing strains(M. avium, M. intracellulare, M. kansasii and M. gordonae), 1,200(93.2%) of the MICs read after 7-day incubation fell within 3 log 2 dilutions. Also, a strain of rapidly growing mycobacteria, M. fortuitum, was repeatedly tested, and the reproducibility was estimated to be 93.3% after 3-day incubation. A total of 728 clinical isolates of nontuberculous mycobacteria comprising 14 species were tested against nine agents. The MICs against nontuberculous mycobacteria distributed in a wide range, and the activities of rifampicin, levofloxacin, clarithromycin were more potent. These results demonstrate this newly developed test method to be a practical, rapid, quantitative means to determine MICs for nontuberculous mycobacteria in clinical laboratories.

Anti-Bacterial Agents↗
PubMed2006

[Comparison of minimum inhibitory concentration and postantibiotic effect of eyedrops on isolates in National Surveillance of Infectious Keratitis in Japan].

PURPOSE: To determine the minimum inhibitory concentration (MIC) and postantibiotic effect (PAE) of antibiotic eyedrops against various isolates from infectious keratitis samples. METHOD: MIC and postantibiotic bactericidal effect (PABE)/postantibiotic fungicidal effect (PAFE) after 4 min of exposure to nine antibacterial eyedrops or four antifungals were examined using 100 clinical isolates collected by the National Surveillance of Infectious Keratitis in Japan in 2003. RESULT: The PABEs of tobramycin and micronomicin sulfate showed better results than other drugs, and the other drugs demonstrated various PABEs depending on the bacterial strains; in particular most drugs showed low PABE against Serratia marcescens. There were no significant differences between PABEs of methicillin-resistant and methicillin-susceptible Staphylococci. Also there was no statistical correlation between MIC and PABE of Staphylococci. All the antifungals demonstrated low PAFE against Candida spp. CONCLUSION: PABE/PAFEs vary among species of microorganisms, and since they have no relation with the usual MIC, various other factors, including species of isolates, actual clinical effects, and prevention of drug-resistance induction, should be considered in the selection of drugs.

Anti-Bacterial Agents↗
PubMed1996

Minimum inhibitory concentrations of intestinal Escherichia coli from broiler chickens after oral administration of apramycin.

This study describes the influence of apramycin on minimum inhibitory concentrations (MIC) of intestinal Escherichia coli in young broiler chickens, after oral administration of the antibiotic at a dosage equivalent to a prophylactic course of treatment for 10 d. The bacteria were isolated from cloacal swabs and caecal contents. MICs were determined by agar dilution procedures. MIC of apramycin for the investigated strains ranged from 1 microgram ml-1 to 16 micrograms ml-1. Strains obtained from undosed birds mainly had MIC values of 2 micrograms ml-1. MIC values of 8 micrograms ml-1 or more were recorded only among isolates obtained from chickens which had received apramycin. Administration of apramycin resulted in a slight but statistically significant increase in the average MIC. Statistically higher average MICs were recorded among isolates from cloacal swabs 10 d after withdrawal until the end of the experiment. For strains from caecal contents, this was demonstrated only on one sampling occasion, 15 d after withdrawal.

Administration, Oral↗
PubMed1996

The minimum inhibitory concentration of seventeen antimicrobials for Salmonella isolates from septic patients.

Herein we are reporting, for the first time in Kuwait, the minimum inhibitory concentrations (MICs) of Salmonella blood culture isolates vs. 17 clinically relevant antimicrobial agents. The screening of blood culture specimens was performed with the most advanced Bactec 9240 (Becton Dickinson). From over 20,000 blood cultures, 112 Salmonella isolates were obtained from 67 patients. Their MICs were determined using the automated Vitek microdilution technique (Biomerieux Vitek Inc.). During the whole 1991-1995 study period, the MICs for cefotaxime, ceftazidime, aztreonam, amikacin, gentamicin, ciprofloxacin and imipenem were below their respective susceptibility breakpoints. Resistance to chloramphenicol, ampicillin and cotrimoxazole varied from year to year, from 18% to 50%, except in 1991 when it was nil (1991 was the first year after the Gulf War, with very few newcomers from the Indian subcontinent). All ampicillin-susceptible S. typhi isolates had extremely low MIC values (< or = 0.25 microgram/ml).

Adult↗
PubMedDate not supplied

Influence of sub-minimum inhibitory concentrations of cefodizime on the phagocytosis, intracellular killing and oxidative bursts of human polymorphonuclear leukocytes.

It is generally recognized that sub-minimum inhibitory concentrations (sub-MICs) of antibiotics are still capable of interfering with some bacterial virulence parameters, thus facilitating host neutrophilic defenses such as phagocytosis, killing and oxidative bursts. This study investigated the interaction of Escherichia coli with these neutrophilic functions after pretreatment with various sub-MICs of cefodizime. E. coli exposed to 1/2 to 1/8 MICs of cefodizime showed the extensive production of long and very long filaments that interfere with the precise measurement of phagocytic and killing parameters. Our analysis was consequently extended to the activity of 1/16 to 1/64 MICs. The interesting finding was that, although phagocytosis was unaffected, killing was significantly increased in one strain at 1/16 MIC and in another at 1/32 MIC while in the last strain it was unaffected. Oxidative bursts were not modified by any of the sub-MICs. The knowledge that these sub-MICs are still effective in increasing bacteria killing, correlated with the pharmacokinetic curve of a common single dose of cefodizime 1 g i.m., showed that the killing effects of sub-MICs may last for as long as 12 h after the activity of the MIC value. This integrated information extends our knowledge of the ultimate efficacy of an antibiotic and provides further information for optimizing scheduling.

Adult↗
PubMed1994

Evaluation of 80% inhibition standards for the determination of fluconazole minimum inhibitory concentrations in three laboratories.

The purpose of this study was to evaluate 1:5 growth control dilutions (80% inhibition standards) to determine fluconazole minimum inhibitory concentration (MIC) end points in three laboratories. We tested 39 selected Candida species (in vitro susceptible: fluconazole MIC of < or = 1 microgram/ml, and resistant: fluconazole MIC of > or = 8 micrograms/ml) and Cryptococcus neoformans isolates by broth macro- and microdilution procedures following the National Committee for Clinical Laboratory Standards proposed reference method for yeasts (M27-P). Macrodilution MIC80% were the lowest drug concentrations with turbidity (growth) less than or equal to that of specific 1:5 dilutions of the growth control. Microdilution MICs-2 were the lowest drug concentrations in which there was prominent decrease of growth. A total of 1608 MICs were evaluated. C. krusei, C. parapsilosis, and C. tropicalis strains had reproducible fluconazole MICs by both tests (24 and 48 h). Fluconazole MIC80% and MIC-2 end points were consistent at 24 h (with C. albicans) and more variable at 48 h. MICs of C. neoformans were more reproducible at 72 h than at 48 h by both tests. This study suggests that the determination of fluconazole MICs is dependent on the length of incubation and the yeast being tested, and that antifungal testing of the yeasts may be performed by either test.

Candida↗
PubMed1980

Comparison of sensititre dried microtitration trays with a standard agar method for determination of minimum inhibitory concentrations of antimicrobial agents.

A total of 222 clinical isolates were used to test the accuracy of Sensititre dried microtitration trays for determining minimum inhibitory concentrations (MICs) of antimicrobial agents. In comparison with an agar dilution technique, 89.5% of all the pairs of results were within one doubling dilution. The 2,420 pairs of MIC results with finite values gave a corresponding figure of 86.8%. Exclusion of sulfisoxazole results, which demonstrated a significant interlaboratory variation in accuracy, raised this value to 89.1%. Very good differentiation of beta-lactamase-producing strains of Staphylococcus aureus (24 of 24 giving an MIC greater than or equal to 0.25 micrograms/ml) and Haemophilus influenzae (3 of 3 giving an MIC greater than or equal to 32 micrograms/ml) was obtained with the Sensititre system. This method also clearly distinguished erythromycin-resistant S. aureus strains (7 of 7 giving an MIC greater than 32 micrograms/ml) from the susceptible strains (26 of 28 giving an MIC less than or equal to 0.5 microgram/ml plus 1 strain at 1.0 microgram/ml and 1 at 2.0 micrograms/ml). Sensititre offers an accurate and convenient method of determining MICs comparable to those obtained with the agar dilution procedure, with the advantage of an extended shelf life when stored at room temperature.

Aminoglycosides↗
PubMed2003

Factor analysis of minimum-inhibitory concentrations for Escherichia coli isolated from feedlot cattle to model relationships among antimicrobial-resistance outcomes.

Factor analysis was used to assess relationships in the minimum-inhibitory concentration among 17 antimicrobials tested on isolates of Escherichia coli isolated from 360 faecal samples obtained from feedlot cattle. Six factors were extracted using maximum-likelihood factor analysis. The factors were interpretable antimicrobial groupings based on class of antimicrobial and previously described associations. New-generation cephalosporins, older-generation beta-lactams, fluoroquinolones and aminoglycosides grouped separately as classes of antimicrobials on four of the six factors. One of the remaining factors was a grouping of antimicrobials that had been identified as being related in previous feedlot studies. The last factor was a grouping of three of the five antimicrobials that comprise the antimicrobials found in penta-resistant strains of Salmonella Typhimurium. The factor analysis described patterns in the MIC data that would not have been apparent if only antimicrobial-resistance data categorized as susceptible-resistance had been analysed.

Animals↗
PubMed1981

Correlation of penicillin minimum inhibitory concentrations and penicillin zone edge appearance with staphylococcal beta-lactamase production.

Production of staphylococcal beta-lactamase was shown to be correlated with penicillin G minimum inhibitory concentrations (MICs) of greater than 0.05 microgram/ml for 97% of the Staphylococcus aureus and 99% of the Staphylococcus epidermidis strains tested. However, it is important to note that of the isolates for which MICs were equal to or less than 0.05 micro/ml, a significant percentage (16% of S. aureus and 5% of S. epidermidis) were beta-lactamase producers. Thus, lack of beta-lactamase production, which implies susceptibility to penicillin, cannot be presumed solely on the basis of low MICs. Beta-lactamase production can be easily predicted from disk diffusion susceptibility tests by observing the appearance of the penicillin inhibition zone edge. A sharply demarcated edge was correlated with beta-lactamase production for 100% of the S. aureus and 93% of the S. epidermidis strains tested. The presence of this type of zone edge when a penicillin zone measures in the intermediate or susceptible range indicates that the isolate should be checked for beta-lactamase production.

Microbial Sensitivity Tests↗
PubMed1995

[Consecutive annual changes in minimum inhibitory concentration in clinically isolated Neisseria gonorrhoeae strains].

Between 1983 and 1991, 465 gonococcal strains isolated in the urological department of Japanese Red Cross Medical Center. The minimum inhibitory concentration (MIC) of these isolates to 22 kinds of antibiotics including penicillins (PC), cephems, tetracyclins (TC) and new quinolons (NQ) were determined and the annual difference of MIC was studied. The annual incidence of penicillinase producing neisseria gonorrhoeae (PPNG) of these 9 years were distributed in 3 to 17% and increasing tendency was not observed. As for Penicillin G, the MIC 90 of PPNG was seven fold higher than that of non-PPNG. No remarked difference was observed between MIC 90 of Cephems, TC and NQ of PPNG and non-PPNG. No annual difference was observed in MIC of PC, Cephems and SPCM. However the rising tendency of MIC was observed in NQ.

Adolescent↗
PubMed1981

Partition coefficients of some aromatic alcohols in an n-heptane/water system and their relationship to minimum inhibitory concentration against Pseudomonas aeruginosa and Staphylococcus aureus.

The partition coefficients of the homologous series of aromatic alcohols were determined in an n-heptane/water system. The minimum inhibitory concentrations of benzyl alcohol, 2-phenylethanol, 3-phenylpropanol, 4-phenylbutanol and 5-phenylpentanol were elucidated against Pseudomonas aeruginosa and Staphylococcus aureus. The linear relationship log1/C = a log P + b postulated by Hansch was found to apply.

Alcohols↗
PubMed2005

Disposition of orally administered cefpodoxime proxetil in foals and adult horses and minimum inhibitory concentration of the drug against common bacterial pathogens of horses.

OBJECTIVES: To determine the disposition of orally administered cefpodoxime proxetil in foals and adult horses and measure the minimum inhibitory concentrations (MICs) of the drug against common bacterial pathogens of horses. ANIMALS: 6 healthy adult horses and 6 healthy foals at 7 to 14 days of age and again at 3 to 4 months of age. PROCEDURE: A single dose of cefpodoxime proxetil oral suspension was administered (10 mg/kg) to each horse by use of a nasogastric tube. In 7- to 14-day-old foals, 5 additional doses were administered intragastrically at 12-hour intervals. The MIC of cefpodoxime for each of 173 bacterial isolates was determined by use of a commercially available test. RESULTS: In 7- to 14-day-old foals, mean +/- SD time to peak serum concentration (Tmax) was 1.7 +/- 0.7 hours, maximum serum concentration (Cmax) was 0.81 +/- 0.22 microg/mL, and elimination half-life (harmonic mean) was 7.2 hours. Disposition of cefpodoxime in 3- to 4-month-old foals was not significantly different from that of neonates. Adult horses had significantly higher Cmax and significantly lower Tmax, compared with values for foals. The MIC of cefpodoxime required to inhibit growth of 90% of isolates for Salmonella enterica, Escherichia coli, Pasteurella spp, Klebsiella spp, and beta-hemolytic streptococci was 0.38, 1.00, 0.16, 0.19, and 0.09 microg/mL, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration at a dosage of 10 mg/kg every 6 to 12 hours would appear appropriate for the treatment of equine neonates with bacterial infections.

Administration, Oral↗
PubMed2006

In-vitro susceptibility testing by agar dilution method to determine the minimum inhibitory concentrations of amphotericin B, fluconazole and ketoconazole against ocular fungal isolates.

PURPOSE: To standardize in-vitro antifungal susceptibility testing by agar dilution method to find out the minimum inhibitory concentration (MIC) of amphotericin B, fluconazole and ketoconazole on ocular fungal isolates. METHODS: A total of 180 ocular fungal isolates (130 filamentous fungi and 50 yeasts) were included. The antifungal drugs such as amphotericin B (0.0625-8 microg/mL), fluconazole (0.2-819.6 microg/mL) and ketoconazole (0.025-6.4 microg/mL) were incorporated in doubling dilutions in the yeast nitrogen base medium. The MIC was determined as the lowest concentration of the antifungal drug preventing growth of macroscopically visible colonies on drug containing plates when there was visible growth on the drug-free control plates. RESULTS: All 50 ocular isolates of yeast were susceptible to amphotericin B, while two (4%) and five (10%) strains were resistant to fluconazole and ketoconazole respectively. Of the 130 filamentous fungi tested, six (4.6%) were resistant to amphotericin B, 49 (37.7%) and 10 (7.6%) were resistant to fluconazole and ketoconazole respectively. Percentile 50 (MIC 50) and Percentile 90 (MIC 90) for all the three antifungal agents were calculated. Aspergillus niger, Aspergillus terreus and Candida krusei were found to be resistant to fluconazole and ketoconazole. CONCLUSION: This technique was found to be reliable, cost effective and easy to perform with consistent results.

Amphotericin B↗
PubMed1998

Minimum inhibitory concentration of smoke wood extracts against spoilage and pathogenic micro-organisms associated with foods.

Antimicrobial activity of seven commercial smoke preparations (four liquid and three solid) was studied. The minimum inhibitory concentration (MIC) was determined against a selection of food spoilage and pathogenic micro-organisms. The main smoke components were identified and quantified by gas chromatography/mass spectrometry. The most effective condensate was S2. All strains except Salmonella enteritidis were inhibited by S2 with an MIC < 0.5-1.5%. Smoke extract L2 inhibited growth of Vibrio vulnificus, Yersinia enterocolitica, Bacillus subtilis, Staphylococcus aureus, Listeria monocytogenes, L. inocua, Brochothrix thermosphacta and Lactococcus lactis ssp lactis with an MIC of < 0.2-0.8%. The condensate L3 inhibited effectively V. vulnificus, B. subtilis, L. innocua and Staph. aureus. L1, L4, S1 and S3 had no inhibitory effects at levels tested against most micro-organisms. Vibrio vulnificus was the most susceptible micro-organism to test compounds. The antimicrobial activity of smoke preparations was related to the concentration of phenols.

Bacteria↗
PubMed1979

Comparison between agar and broth minimum inhibitory concentrations of cefamandole, Cefoxitin, and cefuroxime.

The in vitro susceptibility to cefamandole, cefoxitin, and cefuroxime of clinical isolates of Streptococcus faecalis, Klebsiella, and indole-positive Proteus was assayed using minimum inhibitory concentration (MIC) determinations in broth and on solid media. It could be demonstrated that the agar dilution MICs obtained when S. faecalis was tested against cefuroxime and when indole-positive Proteus strains were tested against cefamandole tended to be considerably lower than those obtained with the broth dilution technique. The Klebsiella strains tested did not show any major differences with regard to MICs in broth or on solid media. Using an animal experimental infection model it could be demonstrated that with indole-positive Proteus the higher broth MIC correlated better to the observed data than the lower agar MIC when a beta-lactamase-producing strain was tested. The data obtained indicated that the beta-lactamase of the indole-positive Proteus strain was inducible. The results of the study gave evidence for a risk of false susceptibility of some bacterial species against cefamandole when agar techniques, e.g. paper disk diffusion, are used. For cefuroxime, the same phenomenon can be expected with S. faecalis and to some extent with indole-positive Proteus. In this study, cefoxitin seemed considerably less affected by the technique used for susceptibility testing.

Bacteria↗
PubMedDate not supplied

Therapeutic effect of oral levofloxacin, ciprofloxacin, and ampicillin on experimental murine pneumonia caused by penicillin intermediate Streptococcus pneumoniae for which the minimum inhibitory concentrations of the quinolones are similar.

The therapeutic efficacy of oral treatment with levofloxacin, ciprofloxacin, and ampicillin on an experimental pneumonia caused by the penicillin-intermediate Streptococcus pneumoniae for which the minimum inhibitory concentrations (MICs) of the quinolones are similar was assessed in immunocompetent CBA/J mice. Levofloxacin exhibited a dose-dependent therapeutic effect, and achieved complete eradication of S. pneumoniae from the lungs at 120 mg/kg/day, whereas ciprofloxacin and ampicillin were hardly effective at all. A pharmacokinetic study in infected mice revealed good oral absorption and lung tissue penetration of levofloxacin (peak lung concentration: 5.95 microg/g of lung), low oral absorption of ciprofloxacin in spite of a good penetration into lung tissue (1.10 microg/g of lung), and low lung tissue penetration of ampicillin despite rather good oral absorption (1.71 microg/g of lung). In an in vitro time-kill study that simulated the peak concentration of drugs in the lungs of infected animals, the killing activity of levofloxacin was found to be greater than that of ciprofloxacin and ampicillin. These data suggest that the therapeutic efficacy of levofloxacin in this model is attributable to both its potent bactericidal activity and excellent pharmacokinetic profile.

Ampicillin↗