Minimum Inhibitory Concentration Measurements Research Articles

What Is the 'Minimum Inhibitory Concentration' (MIC) of Pexiganan Acting on Escherichia coli?-A Cautionary Case Study.

We measured the minimum inhibitory concentration (MIC) of the antimicrobial peptide pexiganan acting on Escherichia coli , and found an intrinsic variability in such measurements. These results led to a detailed study of the effect of pexiganan on the growth curve of E. coli, using a plate reader and manual plating (i.e. time-kill curves). The measured growth curves, together with single-cell observations and peptide depletion assays, suggested that addition of a sub-MIC concentration of pexiganan to a population of this bacterium killed a fraction of the cells, reducing peptide activity during the process, while leaving the remaining cells unaffected. This pharmacodynamic hypothesis suggests a considerable inoculum effect, which we quantified. Our results cast doubt on the use of the MIC as 'a measure of the concentration needed for peptide action' and show how 'coarse-grained' studies at the population level give vital information for the correct planning and interpretation of MIC measurements.

009.1 Standardised, quality assured time-kill curve analysis and pharmacodynamic functions of different antibiotics forin vitroevaluation of treatment regimens forneisseria gonorrhoeae

Introduction Neisseria gonorrhoeae shows increasing resistance to first line empirical treatment, which demonstrates the need for robust methods to evaluate antibiotic treatment regimens. Antibiotic efficacy is traditionally determined in vitro by measuring minimum inhibitory concentrations (MICs). Time-kill curve assays for N. gonorrhoeae have been difficult to standardise. We developed a new time-kill curve assay and used pharmacodynamics functions to analyse the relationship between antibiotic concentration and bacterial net growth rate. Methods We used a defined medium (Graver-Wade medium) and grew bacteria in 96-well microtiter plates. To measure colony forming units over a time course of six hours, we used a previously described drop plate method and spotted 10 µl droplets on chocolate agar with a multichannel pipette. The assay was validated using 16 reference strains, representing diffent clades of the N. gonorrhoeae phylogenetic tree. We then studied a highly sensitive strain isolated in 1954 in Denmark in detail. Penicillin G, spectinomycin, gentamicin, tetracyline, chloramphenicol, ciprofloxacin, azithromycin, cefixime and ceftriaxone were examined in concentrations from 0.016× to 16×MIC. A pharmacodynamic function was fitted to the net bacterial growth rates at each concentration, resulting in four parameters that describe the pharmacodynamic properties of each antibiotic. Results Our time-kill curve assay was reproducible for all the N. gonorrhoeae strains tested. Ciprofloxacin and spectinomycin induced the strongest bactericidal effect during the first six hours. Tetracycline and chloramphenicol were the only antibiotics that showed a purely bacteriostatic effect. Differences in the shape of the pharmacodynamic functions illustrate the time and concentration dependent properties of the antibiotics. Conclusion We developed a standardised, robust and quality-assured time-kill curve assay for N. gonorrhoeae . Pharmacodynamic functions allowed classification of nine antibiotics according to their antimicrobial properties. These methods can be used to investigate new antibiotic regimens and help to improve dosing strategies. Disclosure of interest statement This work was supported by SystemsX, Switzerland, Orebro County Council Research Committee and the Foundation for Medical Research at Orebro University Hospital, Sweden.

Evaluation of canine-specific minocycline and doxycycline susceptibility breakpoints for meticillin-resistant Staphylococcus pseudintermedius isolates from dogs.

Using the US Clinical and Laboratory Standards Institute (CLSI) human tetracycline breakpoints to predict minocycline and doxycycline susceptibility of Staphylococcus pseudintermedius (SP) isolates from dogs is not appropriate because they are too high to meet pharmacokinetic/pharmacodynamic data using a standard dose. New breakpoints have been approved for doxycycline and proposed for minocycline. Revised breakpoints are four dilutions lower than tetracycline breakpoints, providing a more conservative standard for classification of isolates. The objectives of this study were to measure minimum inhibitory concentrations (MICs) of minocycline and doxycycline of 100 canine meticillin-resistant SP clinical isolates, compare their susceptibilities to minocycline and doxycycline based on current and revised standards, and document their tetracycline resistance genes. E-test strips were used to determine MICs. PCR was used to identify tet genes. Using the human tetracycline breakpoint of MIC ≤ 4 μg/mL, 76 isolates were susceptible to minocycline and 36 isolates were susceptible to doxycycline. In contrast, using the proposed minocycline breakpoint (MIC ≤ 0.25 μg/mL) and approved doxycycline breakpoint (MIC ≤ 0.125 μg/mL), 31 isolates were susceptible to both minocycline and doxycycline. Thirty-one isolates carried no tet genes, two had tet(K) and 67 had tet(M). Use of the human tetracycline breakpoints misclassified 45 and five of the isolates as susceptible to minocycline and doxycycline, respectively. PCR analysis revealed that 43 and five of the isolates classified as susceptible to minocycline and doxycycline, respectively, possessed the tetracycline resistance gene, tet(M), known to confer resistance to both drugs. These results underscore the importance of utilizing the proposed minocycline and approved doxycycline canine breakpoints in place of human tetracycline breakpoints.

Killing of Streptococcus pneumoniae by azithromycin, clarithromycin, erythromycin, telithromycin and gemifloxacin using drug minimum inhibitory concentrations and mutant prevention concentrations

Streptococcus pneumoniae continues to be a significant respiratory pathogen, and increasing antimicrobial resistance compromises the use of β-lactam and macrolide antibiotics. Bacterial eradication impacts clinical outcome, and bacterial loads at the site of infection may fluctuate. Killing of two macrolide- and quinolone-susceptible clinical S. pneumoniae isolates by azithromycin, clarithromycin, erythromycin, telithromycin and gemifloxacin against varying bacterial densities was determined using the measured minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC). For kill experiments, 106–109 CFU/mL were exposed to the drug and were sampled at 0, 0.5, 1, 2, 3, 4, 6, 12 and 24h following drug exposure. The log10 reduction and percent reduction (kill) of viable cells was recorded. MICs and MPCs (mg/L) for azithromycin, clarithromycin, erythromycin, telithromycin and gemifloxacin were 0.063–0.125/0.5–1, 0.031–0.063/0.25–0.5, 0.063/0.25–0.5, 0.008/0.016 and 0.031/0.25, respectively. Killing 106–109 CFU/mL of bacteria by the drug MIC yielded incomplete killing, however log10 reductions occurred by 12h and 24h for all drugs. Exposure of 106–109 CFU/mL to MPC drug concentrations resulted in the following log10 reduction by 6h of drug exposure: azithromycin, 1.3–3.9; clarithromycin, 1.9–5.8; erythromycin, 0.8–4.7; telithromycin, 0.3–1.7; and gemifloxacin, 1.8–4.2. Bacterial loads at the site of infection may range from 106 to 109, and kill experiments utilising a higher bacterial inoculum provided a more accurate measure of antibiotic performance in high biomass situations. Killing was slower with telithromycin. Kill was greater and fastest with MPC versus MIC drug concentrations.

The Discrepancy of the Minimum Inhibitory Concentration Results for Methicillin-Resistant Staphylococcus aureus by Various Measurement Methods

Background: It has been postulated that there exists a discrepancy of methicillin-resistant Staphylococcus aureus (MRSA) minimum inhibitory concentration (MIC) results from various measurement methods. The association between higher MRSA MIC (MIC ≥ 2 μg/ml) and worse clinical outcome has been previously reported. Therefore, it is clinically essential to investigate whether such a discrepancy exists between the different MIC measurement methods. Methods: From November 2009 to March 2011, 55 MRSA isolates were prospectively obtained at two emergency departments in Japan. The MIC of the isolates were measured by Etest® and five broth microdilution (BMD) methods, namely Eiken®, MicroScan® prompt method, MicroScan® turbidity method, Phoenix® and Vitek2® system, respectively. The MIC results of vancomycin, teicoplanin, linezolid, daptomycin and quinupristin-dalfopristin (Q-D) were evaluated. Statistical analysis was performed using the Wilcoxon signed rank test and Bland-Altman’s analysis. Results: There was a tendency of constant and significant discrepancy of MIC results of anti-MRSA antibiotics between Etest® and the BMD methods for MRSA isolates. The averages of the vancomycin MIC were 1.86 μg/ ml in Etest® and 0.74 μg/ml in the Phoenix® method (p<0.01), respectively. For teicoplanin, they were 1.86 μg/ml and 0.60 μg/ml (p<0.01), and for linezolid they were 2.55 μg/ml and 1.18 μg/ml (p<0.01) with respect to Etest® and the Phoenix® method, respectively. Among the BMD methods, however, the MicroScan® prompt method and the MicroScan® turbidity method had less discrepancy from Etest® for vancomycin MIC measurement. Conclusion: The MIC measured by various BMD methods tended to show consistently lower results compared to those measured by Etest®. Among the BMD methods, however, the MicroScan® prompt method and the MicroScan® turbidity method had less discrepancy from Etest® for vancomycin MIC measurement.

Time lapse investigation of antibiotic susceptibility using a microfluidic linear gradient 3D culture device.

This study reports a novel approach to quantitatively investigate the antibacterial effect of antibiotics on bacteria using a three-dimensional microfluidic culture device. In particular, our approach is suitable for studying the pharmacodynamics effects of antibiotics on bacterial cells temporally and with a continuous range of concentrations in a single experiment. The responses of bacterial cells to a linear concentration gradient of antibiotics were observed using time-lapse photography, by encapsulating bacterial cells in an agarose-based gel located in a commercially available microfluidics chamber. This approach generates dynamic information with high resolution, in a single operation, e.g., growth curves and antibiotic pharmacodynamics, in a well-controlled environment. No pre-labelling of the cells is needed and therefore any bacterial sample can be tested in this setup. It also provides static information comparable to that of standard techniques for measuring minimum inhibitory concentration (MIC). Five antibiotics with different mechanisms were analysed against wild-type Escherichia coli, Staphylococcus aureus and Salmonella Typhimurium. The entire process, including data analysis, took 2.5-4 h and from the same analysis, high-resolution growth curves were obtained. As a proof of principle, a pharmacodynamic model of streptomycin against Salmonella Typhimurium was built based on the maximal effect model, which agreed well with the experimental results. Our approach has the potential to be a simple and flexible solution to study responding behaviours of microbial cells under different selection pressures both temporally and in a range of concentrations.

Daptomycin Etest MICs for methicillin-resistant Staphylococcus aureus vary among different media

For optimum activity of daptomycin (DAP) in vitro, medium supplemented with calcium ions at physiological concentration (i.e., 50 mg/l) is required for determination of DAP minimum inhibitory concentration (MIC) in the Clinical and Laboratory Standards Institute (CLSI) broth microdilution (BMD) method. However, our literature review found that Mueller-Hinton agar (MHA) brands used for the DAP Etest had different calcium ion (Ca²⁺) concentrations among the reports. For 98 clinical methicillin-resistant Staphylococcus aureus isolates previously unexposed to DAP, MICs were assessed by use of the Etest with MHA plates with different media (MHA-A, MHA-B, and MHA-C) and compared with those from the CLSI reference BMD method. The instructions for the Etest recommend MHA with Ca²⁺ of 25-40 mg/l for DAP MIC testing; Ca²⁺ concentrations for each type of MHA were 20.4 mg/l in MHA-A, 45.2 mg/l in MHA-B, and 52.0 mg/l in MHA-C. When the MIC₅₀/MIC₉₀ of the clinical isolates were studied, the Etest MICs for MHA-A were 1-fold dilution higher than for the BMD value. In contrast, for MHA-B they were 1-fold dilution lower, and for MHA-C MIC₅₀ was 1.5-fold dilution lower and MIC₉₀ was 2-fold dilution lower. MICs measured in MHA with higher Ca²⁺ tended to be lower. Comparison of MICs between BMD and the Etest for each MHA showed they were significantly different (p < 0.0001). The correlation coefficient was 0.6258 (p < 0.0001) for MHA-A, 0.4224 (p < 0.0001) for MHA-B, and 0.2504 (p = 0.0129) for MHA-C. Our results suggest there are differences in DAP MICs between MIC testing methods and differences between Ca²⁺ concentrations in MHA. For more objective and accurate measurement of DAP MICs, there should be discussion about standardization of Ca²⁺ in MHA.

Dark Antimicrobial Mechanisms of Cationic Phenylene Ethynylene Polymers and Oligomers against Escherichia coli

The interactions of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) with E. coli cells are investigated to gain insights into the differences in the dark killing mechanisms between CPEs and OPEs. A laboratory strain of E. coli with antibiotic resistance is included in this work to study the influence of antibiotic resistance on the antimicrobial activity of the CPEs and OPEs. In agreement with our previous findings, these compounds can efficiently perturb the bacterial cell wall and cytoplasmic membrane, resulting in bacterial cell death. Electron microscopy imaging and cytoplasmic membrane permeability assays reveal that the oligomeric OPEs penetrate the bacterial outer membrane and interact efficiently with the bacterial cytoplasmic membrane. In contrast, the polymeric CPEs cause serious damage to the cell surface. In addition, the minimum inhibitory concentration (MIC) and hemolytic concentration (HC) of the CPEs and OPEs are also measured to compare their antimicrobial activities against two different strains of E. coli with the compounds’ toxicity levels against human red blood cells (RBC). MIC and HC measurements are in good agreement with our previous model membrane perturbation study, which reveals that the different membrane perturbation abilities of the CPEs and OPEs are in part responsible for their selectivity towards bacteria compared to mammalian cells. Our study gives insight to several structural features of the PPE-based CPEs and OPEs that modulate their antimicrobial properties and that these features can serve as a basis for further tuning their structures to optimize antimicrobial properties.

Comparison of Volatile Constituents, and Antioxidant and Antibacterial Activities of the Essential Oils of Thymus caucasicus, T. kotschyanus and T. vulgaris

A comparison of the chemical composition, and antioxidant and antibacterial activities of the essential oils obtained from the aerial parts of Thymus caucasicus, T. kotschyanus, and T vulgaris was carried out. The oils, obtained by hydrodistillation, were analyzed by GC and GC/MS. Twenty, 29 and 22 compounds representing 94.8%, 96.6% and 98.2% of the essential oils of T. caucasicus, T. kotschyanus and T. vulgaris, respectively, have been identified. The oil of T. caucasicus was characterized by 1,8-cineol (21.5%), thymol (12.6%), beta-fenchyl alcohol (8.7%), nerolidol (7.8%), terpinolene (7.2%), alpha-pinene (7.0%) and myrcene (6.8%). In the oil of T. kotschyanus, carvacrol (24.4%), beta-caryophyllene (14.5%), gamma-terpinene (12.4%), alpha-phellandrene (10.8%), p-cymene (9.8%) and thymol (6.8%) were the predominant compounds, whereas the main components of T. vulgaris oil were thymol (43.8%), p-cymene (15.2%), germacrene-D (11.7%), terpinolene (3.4%), carvacrol (3.2%), beta-caryophyllene (2.8%) and alpha-thujene (2.2%). In all three plants oil, hydrocarbon monoterpenes predominated over sesquiterpenes. Antioxidant activities were assessed by determining IC50 values in the DPPH radical scavenging assay. Antibacterial activity was determined by measuring minimum inhibitory concentration (MIC) using the broth dilution method. The essential oils of T. caucasicus, T. kotschyanus and T. vulgaris showed free radical scavenging and antibacterial activity.

Effect and Mechanism of Andrographolide on the Recovery of Pseudomonas aeruginosa Susceptibility to Several Antibiotics

Effectiveness and mechanism of action of andrographolide on the recovery of Pseudomonas aeruginosa susceptibility to antibiotics was investigated. In the presence of andrographolide, the Mueller-Hinton broth dilution method measured minimal inhibitory concentrations (MIC) of ceftazidine, cefpirome, chloramphenicol, L-ofloxacin, kanamycin, imipenem and meropenem. Real-time fluorescence quantitative polymerase chain reaction was used to determine mexB mRNA expressions in P. aeruginosa PAO1 strain and MexAB-OprM overexpressing strain. Relative mexB mRNA expression was detected in both strains incubated for 3 and 9 h. When andrographolide-treated groups were compared with controls, the MIC of ceftazidine, cefpirome, L-ofloxacin and meropenem for both strains decreased, and the relative mexB mRNA expression was significantly lower, although between andrographolide groups there were no significant differences. Compared with the inactivated quorum-sensing system, relative amounts of mexB mRNA in the PAO1 strain and MexAB-OprM overexpressing strain in the activated quorum-sensing system increased 10- and 30-fold, respectively. Andrographolide recovered P. aeruginosa susceptibility to antibiotics and reduced the MexAB-OprM efflux pump expression level.

Comment on: Guidelines for the antibiotic treatment of endocarditis in adults: report of the Working Party of the British Society for Antimicrobial Chemotherapy

Sir, In these guidelines, the authors recommend that ‘A minimum inhibitory concentration (MIC) . . . should be established by a standardized laboratory method to ensure susceptibility.’ What evidence is available that MIC determination improves patient care and outcome or influences the treatment? I know of one presentation at the European Congress for Clinical Microbiology and Infectious Diseases by Walton et al. from University College London Hospitals who analysed 129 cases of endocarditis and concluded that ‘Antibiotic treatment in endocarditis can be safely chosen on the result of disc sensitivity testing and adjusted on clinical grounds without MIC.’ The same group recently published analysis of 125 patients admitted between 1981 and 1999 in whom the MIC had been measured. Their conclusion is inconclusive: ‘The measurement of MIC appears prognostically important in deciding the surgical management of endocarditis.’ Can the experts who formulated the guidelines provide some evidence for their recommendation, please?

Assessment of Antimicrobial Activity of Fourteen Essential Oils When Using Dilution and Diffusion Methods

The lack of solubility and the high degree of volatility of essential oils present significant problems to determining the biological effects of these oils. The activity of 10 essential oils and 4 essential oil blends against a Gram-positive bacterium, Staphylococcus aureus., and a yeast, Candida albicans., was compared using a dilution assay and two diffusion methods. The tube dilution assay, using a 0.2% agar solution to provide a stable homogeneous dispersion of oils, was used to measure minimum inhibitory concentrations (MICs). The relative merits of using p.-iodonitro tetrazolium dye (INT) or optical density (OD) in measuring MIC of essential oils also were evaluated. All 14 oils were active against both microorganisms. Thyme, mountain savory, and Turkish oregano were the most active oils against S. aureus. with MICs of 0.31–0.42 µl/ml. Thyme, Turkish oregano, and mountain savory also were the most active against C. albicans. with MICs of 0.31–0.42 µl/ml. The MIC values as determined by INT or OD methods are strongly correlated for both microorganisms, and both give an accurate estimation of MIC. In the disk diffusion assay, thyme, Turkish oregano, Melissa, mountain savory, and the Exodus II (E2) blend were most active against S. aureus.. In the hole-plate assay, the same oils were active against S. aureus. except for Melissa. For C. albicans., thyme, Melissa, mountain savory, Turkish oregano, rosewood, E2 blend, and the T1 blend were most active in the disk diffusion assay. The same oils were active against C. albicans. in the hole-plate diffusion assay except for the T1 blend. Of the methods tested, the tube dilution assay best addresses the solubility and volatility concerns of essential oils. We favor the determination of MIC using INT because of several eliminated steps. Although there were differences in the way in which some essential oils responded in the two diffusion methods, the correlations between the disk and hole-plate diffusion methods were high and yielded comparable results. However, results from the dilution assay were weakly correlated with agar diffusion results. Diffusion assays are useful as a qualitative assessment of biological activity of essential oils but are not appropriate in assessing quantitative effects.

Decrease in Skin Permeation and Antibacterial Effect of Parabens by a Polymeric Additive, Poly(2-methacryloyloxyethyl phosphorylcholine-co-butylmetacrylate)

The inhibitory effect of poly(2-methacryloyloxyethyl phosphorylcholine-co-butylmetacrylate) (PMB) on the in vitro skin permeation of p-hydroxybenzoic acid and its esters (parabens; methylparaben, ethylparaben, n-propylparaben and n-butylparaben) as model compounds was evaluated. Solubility of the parabens in distilled water was increased by addition of PMB, and the increasing ratio was dependent on the concentration of PMB. The increment of the ratio was more marked in lipophilic parabens than hydrophilic ones. Skin permeability of parabens from their aqueous suspensions was decreased by addition of PMB, and the decreasing ratio was dependent on the PMB concentration. Then, antibacterial effect of parabens of their aqueous solutions was determined with and without PMB by measuring minimum inhibitory concentration (MIC) against E. coli and S. aureus. As results, MIC and antibacterial effect were increased and decreased, respectively, by addition of PMB. The contribution of PMB was more marked in butylparaben than methylparaben. These decreases in skin permeation and antibacterial effect of parabens by PMB are probably due to a higher solubility in water and a lower partition to the skin and bacterial membranes of parabens by addition of PMB.

Is the MIC useful in deciding to treat endocarditis surgically?

The infecting pathogen and its susceptibility to antibiotics is used to suggest prognosis in endocarditis. A case study was performed in a tertiary referral cardiology centre to assess the contribution of the measurement of minimum inhibitory concentration (MIC) to the decision to treat endocarditis surgically. The records were examined of 125 patients admitted between 1981 and 1999 in whom the minimum inhibitory concentration for the pathogen had been measured. The measures of outcome were mortality at time of hospital discharge and at 6 months, surgical referral and cure by medical treatment. Endocarditis caused by Staphylococcus aureus with a raised MIC of flucloxacillin (methicillin) was associated with higher mortality even if glycopeptides were used in treatment (MIC≤0.25 mg/l 0/7 versus MIC 1–2 mg/l 4/13, P=0.01). Elevated MICs of flucloxacillin in S. aureus infection or of gentamicin in streptococcal disease were associated with surgical intervention. There were no significant differences between bacterial pathogens in mortality, surgical referral or cure by medical treatment. The measurement of MIC appears prognostically important in deciding the surgical management of endocarditis.

Prevalence and characterization of metallo-β-lactamases in clinical isolates of pseudomonas aeruginosa☆

The prevalence and the type(s) of metallo-β-lactamases (MBLs) produced by isolates of Pseudomonas aeruginosa were investigated. During 2001, 506 nonduplicate isolates were obtained from hospitalized patients. Eighty-two strains were selected because of resistance to carbapenems and/or ceftazidime. Screening for MBL production was performed in the latter isolates by the Etest MBL strips (AB Biodisk, Solna, Sweden) and by a broth microdilution method measuring minimum inhibitory concentrations (MICs) of imipenem alone and in the presence of metal-chelating agents (EDTA and o-phenanthroline). Specific DNA probes were used to investigate the presence of genes coding for IMP- or VIM-type enzymes. Overall, four isolates of P. aeruginosa (obtained from independent patients) were found to carry a bla VIM gene. Polymerase chain reaction (PCR) experiments and DNA sequencing revealed that the VIM-2 determinant was present in three cases, whereas VIM-1 was detected in one isolate. Surveillance programs should be adopted to avoid the spread of these worrisome resistance genes.

Antimicrobial susceptibilities of Escherichia coli strains from a turkey operation.

To measure minimum inhibitory concentrations (MIC) of 17 antimicrobials for Escherichia coli isolates from a turkey operation and assess whether small samples provide precise estimates of geometric mean MIC. Prospective study. 105 clinical isolates from birds and 1,104 fecal isolates from 20 flocks (poults and finisher hens). A Mueller-Hinton broth dilution panel was used to measure MIC, and MIC of fecal and clinical isolates were compared. We drew random samples of 5,10, 15, 20, 25, 30, 35, 40, and 45 isolates from each finisher flock and between 100 and 105 isolates from 5, 7, 10, and 20 flocks. Antimicrobial usage was determined for enrolled flocks. Six of 12 poult and 18 of 20 finisher flocks had been treated with antimicrobials, often for respiratory illnesses consistent with colibacillosis. All birds received gentamicin at the hatchery. More fecal than clinical isolates were resistant to ampicillin; however, more clinical isolates were resistant to ciprofloxacin, gentamicin, and sulfamethoxazole. Precise estimates of geometric mean MIC for flocks were obtained when > or = 15 fecal isolates were obtained per flock and, for the operation, when 105 isolates were obtained from > or = 7 flocks. Antimicrobial usage was common and may have contributed to the resistance patterns of isolates. With a modest allocation of laboratory resources, producers can monitor antimicrobial susceptibilities of clinical and fecal E coli to manage risks of antimicrobial usage and resistance.

충치균 (Streptococcus mutans)에 대한 다시마 추출물의 항균활성

우리 나라 연안에서 채취한 해조류 27종의 <TEX>$80\%$</TEX> ethanol 추출물이 Streptococcus mutans KCTC 3300의 증식에 미치는 영향을 검색하고, 다시마의 추출용매별 항균성과, <TEX>$80\%$</TEX> ethanol 추출물을 용매분획하였을 때 획분별 MIC를 측정하였다. S. mutans KCTC 3300에 대한 해조류 추출물의 항균활성은 다시마가 가장 강하였고, 갈파래, 청각, 감태, 곰피 및 미역도 비교적 높은 활성을 나타내었으며 홍조류보다 갈조류와 녹조류에 속하는 종이 대체적으로 강하였다 다시마의 항균활성은 추출용매에 따라 차이가 있었으나 용매별 가용성 획분의 량과 항균성간에는 뚜렷한 관련이 나타나지 않았다. 5. mutans KCTC 3300과 S. sobrinus KCTC 3307에 대한 해조류의 <TEX>$80\%$</TEX> ethanol 추출물의 MIC는 해조류의 종뿐만 아니라 동일한 해조류 추출물의 경우에도 균종에 따라 차이가 있었다. 다시마의 <TEX>$80\%$</TEX> ethanol 추출물을 유기용매를 사용하여 순차 분획하였을 때 항균활성 물질의 대부분은 ether 획 분에 이행하여 이 획분의 MIC는 105<TEX>$\mu$</TEX>g/mL이었고, 수용성 획분은 약 5,500<TEX>$\mu$</TEX>g/mL의 농도에서도 균의 증식을 저지하지 못하였다. In previous reports the authors have screened the inhibition effects of marine algae extracts on halitosis, and demonstrated that a brown algae, Eisenia bicyclis (' Daehwang') possess not only strong deodorant effect bug also considerable anticariogenic activities. In this study, we screened antibacterial effects of various marine algae, and measured minimum inhibitory concentration (MIC) value of them against mutans streptococci in vitro. Among the 27 species of marine algae, <TEX>$80\%$</TEX> ethanol extract of dried sea-mustard, Laminaria japonica ('Dasima') showed the strongest inhibition activity against Streptococcus mutans KCTC 3300. The extracts of Ulva lactuca ('Galparae'), Codium fragile ('Cheonggak'), Ecklonia cava ('Gamtae'), E. stolonifera ('Gompi') and Undalia Pinnatifida ('Miyeok') showed slightly weaker inhibitory potency than L. japonica. Differences of MIC values in <TEX>$80\%$</TEX> ethanol extract of some species of marine algae were observed depending on test bacterial species, i.e., S. mutans KCTC 3300 or S. sobrinus KCTC 3307. Eighty percent ethanol extract of dried L japonica was fractionated with diethyl ether, chloroform, ethyl acetate, n-buthanol and water successively, The ether-soluble fraction had inhibitory effect on S. mutans KCTC 3300, however the inhibitory effects were not found in the other fractions. The MIC values of <TEX>$80\%$</TEX> ethanol extract and ether fraction were 180 and 105 <TEX>$\mu$</TEX>g/mL respectively, while no significant inhibition activity of water-soluble fraction was found even when the fraction was added up to 5,500 <TEX>$\mu$</TEX>g/mL.

Handwashing: Are Experimental Models a Substitute for Clinical Trials? Two Viewpoints

CLINICAL RELEVANCE OF EXPERIMENTAL MODELS FOR TESTING EFFICACY OF TOPICAL ANTIMICROBIAL PRODUCTS Elaine Larson, PhD, RN, FAAN, CIC The need for standardized test methodologies for the evaluation of topical antimicrobial products has been formally recognized in the United States by the Food and Drug Administration (FDA), by a Committee for Standardization of Disinfectants in Europe and, subsequently, the Council of Europe. Brief histories of their activities are summarized by Bruch and Larson1 and by Ayliffe.2 Most test programs include in vitro evaluation to measure minimum inhibitory concentrations (MIC) of the active ingredient against a battery of standard test organisms as a screening mechanism to demonstrate antimicrobial activity. However, a myriad of variations exist with regard to other aspects of testing. Some of the variations in test methodology can be explained on the basis of why products are being tested. Indications for use of a product, the frequency and intensity of its use and the desired effect(s) are criteria an investigator considers in

Handwashing: Are Experimental Models a Substitute for Clinical Trials? Two Viewpoints

CLINICAL RELEVANCE OF EXPERIMENTAL MODELS FOR TESTING EFFICACY OF TOPICAL ANTIMICROBIAL PRODUCTS Elaine Larson, PhD, RN, FAAN, CIC The need for standardized test methodologies for the evaluation of topical antimicrobial products has been formally recognized in the United States by the Food and Drug Administration (FDA), by a Committee for Standardization of Disinfectants in Europe and, subsequently, the Council of Europe. Brief histories of their activities are summarized by Bruch and Larson1 and by Ayliffe.2 Most test programs include in vitro evaluation to measure minimum inhibitory concentrations (MIC) of the active ingredient against a battery of standard test organisms as a screening mechanism to demonstrate antimicrobial activity. However, a myriad of variations exist with regard to other aspects of testing. Some of the variations in test methodology can be explained on the basis of why products are being tested. Indications for use of a product, the frequency and intensity of its use and the desired effect(s) are criteria an investigator considers in