Determination of minimum inhibitory concentrations
01 Jul 2001-Journal of Antimicrobial Chemotherapy (Oxford University Press)-Vol. 48, Iss: 6, pp 5-16
TL;DR: Standardized methods for determining minimum inhibitory concentrations and MBCs are described and like all standardized procedures, the method must be adhered to and may not be adapted by the user.
Abstract: Minimum inhibitory concentrations (MICs) are defined as the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation, and minimum bactericidal concentrations (MBCs) as the lowest concentration of antimicrobial that will prevent the growth of an organism after subculture on to antibiotic-free media. MICs are used by diagnostic laboratories mainly to confirm resistance, but most often as a research tool to determine the in vitro activity of new antimicrobials, and data from such studies have been used to determine MIC breakpoints. MBC determinations are undertaken less frequently and their major use has been reserved for isolates from the blood of patients with endocarditis. Standardized methods for determining MICs and MBCs are described in this paper. Like all standardized procedures, the method must be adhered to and may not be adapted by the user. The method gives information on the storage of standard antibiotic powder, preparation of stock antibiotic solutions, media, preparation of inocula, incubation conditions, and reading and interpretation of results. Tables giving expected MIC ranges for control NCTC and ATCC strains are also supplied.
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TL;DR: The aim of broth and agar dilution methods is to determine the lowest concentration of the assayed antimicrobial agent (minimal inhibitory concentration, MIC) that, under defined test conditions, inhibits the visible growth of the bacterium being investigated.
Abstract: The aim of broth and agar dilution methods is to determine the lowest concentration of the assayed antimicrobial agent (minimal inhibitory concentration, MIC) that, under defined test conditions, inhibits the visible growth of the bacterium being investigated. MIC values are used to determine susceptibilities of bacteria to drugs and also to evaluate the activity of new antimicrobial agents. Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into a nutrient agar medium followed by the application of a standardized number of cells to the surface of the agar plate. For broth dilution, often determined in 96-well microtiter plate format, bacteria are inoculated into a liquid growth medium in the presence of different concentrations of an antimicrobial agent. Growth is assessed after incubation for a defined period of time (16-20 h) and the MIC value is read. This protocol applies only to aerobic bacteria and can be completed in 3 d.
4,223 citations
Cites methods from "Determination of minimum inhibitory..."
...A list of solvents for frequently used antibiotics is found in ref...
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TL;DR: This review aims to consolidate clinically relevant background information on the ESKAPE pathogens and provide a contemporary summary of bacterial resistance, alongside pertinent microbiological considerations necessary to face the mounting threat of antimicrobial resistance.
Abstract: In recent years, the Infectious Diseases Society of America has highlighted a faction of antibiotic-resistant bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) - acronymically dubbed 'the ESKAPE pathogens' - capable of 'escaping' the biocidal action of antibiotics and mutually representing new paradigms in pathogenesis, transmission and resistance. This review aims to consolidate clinically relevant background information on the ESKAPE pathogens and provide a contemporary summary of bacterial resistance, alongside pertinent microbiological considerations necessary to face the mounting threat of antimicrobial resistance.
1,039 citations
TL;DR: It is found that antibiotic-resistant phenotypic variants of P. aeruginosa with enhanced ability to form biofilms arise at high frequency both in vitro and in the lungs of CF patients.
Abstract: Colonization of the lungs of cystic fibrosis (CF) patients by the opportunistic bacterial pathogen Pseudomonas aeruginosa is the principal cause of mortality in CF populations1,2. Pseudomonas aeruginosa infections generally persist despite the use of long-term antibiotic therapy1,3. This has been explained by postulating that P. aeruginosa forms an antibiotic-resistant biofilm4,5 consisting of bacterial communities embedded in an exopolysaccharide matrix. Alternatively, it has been proposed that resistant P. aeruginosa variants may be selected in the CF respiratory tract by antimicrobial therapy itself1,6. Here we report that both explanations are correct, and are interrelated. We found that antibiotic-resistant phenotypic variants of P. aeruginosa with enhanced ability to form biofilms arise at high frequency both in vitro and in the lungs of CF patients. We also identified a regulatory protein (PvrR) that controls the conversion between antibiotic-resistant and antibiotic-susceptible forms. Compounds that affect PvrR function could have an important role in the treatment of CF infections.
969 citations
TL;DR: The overall study emphasizes the potential of plant-derived molecules as a green and sustainable source of new broad spectrum antimicrobial products.
Abstract: The increased resistance of pathogenic microorganisms is frequently attributed to the extreme and inadequate use of antibiotics and transmission of resistance within and between individuals. To counter the emergence of resistant microorganisms, considerable resources have been invested in the search for new antimicrobials. Plants synthesize a diverse array of secondary metabolites (phytochemicals) known to be involved in defense mechanisms, and in the last few years it is recognized that some of these molecules have health beneficial effects, including antimicrobial properties. In this study, the mechanism of action of gallic (GA) and ferulic (FA) acids, a hydroxybenzoic acid and a hydroxycinnamic acid, was assessed on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Listeria monocytogenes. The targets of antimicrobial action were studied using different bacterial physiological indices: minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), membrane ...
744 citations
Cites methods from "Determination of minimum inhibitory..."
...The MIC was determined as the lowest concentration of phenolic acids at which no growth was detected.(6,31,35,65) All tests were performed in triplicate with three repeats....
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...Minimum Inhibitory Concentration (MIC) of phenolic acids was determined by the microdilution method.(6,9,14,16,31,47,92) The MIC was determined as the lowest concentration of phenolic acids at which no growth was detected....
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TL;DR: Joint collaboration across the world with international bodies is needed to assist the developing countries to implement good surveillance of antibiotic use and antibiotic resistance, and strengthening of regulations that direct antibiotic manufacture, distribution, dispensing, and prescription is needed, hence fostering antibiotic stewardship.
Abstract: Due to the increased demand of animal protein in developing countries, intensive farming is instigated, which results in antibiotic residues in animal-derived products, and eventually, antibiotic resistance. Antibiotic resistance is of great public health concern because the antibiotic-resistant bacteria associated with the animals may be pathogenic to humans, easily transmitted to humans via food chains, and widely disseminated in the environment via animal wastes. These may cause complicated, untreatable, and prolonged infections in humans, leading to higher healthcare cost and sometimes death. In the said countries, antibiotic resistance is so complex and difficult, due to irrational use of antibiotics both in the clinical and agriculture settings, low socioeconomic status, poor sanitation and hygienic status, as well as that zoonotic bacterial pathogens are not regularly cultured, and their resistance to commonly used antibiotics are scarcely investigated (poor surveillance systems). The challenges that follow are of local, national, regional, and international dimensions, as there are no geographic boundaries to impede the spread of antibiotic resistance. In addition, the information assembled in this study through a thorough review of published findings, emphasized the presence of antibiotics in animal-derived products and the phenomenon of multidrug resistance in environmental samples. This therefore calls for strengthening of regulations that direct antibiotic manufacture, distribution, dispensing, and prescription, hence fostering antibiotic stewardship. Joint collaboration across the world with international bodies is needed to assist the developing countries to implement good surveillance of antibiotic use and antibiotic resistance.
670 citations
Cites background from "Determination of minimum inhibitory..."
...The MIC describes the lowest or least concentration of a drug that is required to inhibit visible bacterial growth after overnight incubation [114]....
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References
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TL;DR: Many members of the Academy of Pediatrics seem to be generally unaware of the fact that the Academy has participated for ten years in a very interesting and valuable organization, the National Committee for Clinical Laboratory Standards (NCCLS).
Abstract: Many members of the Academy of Pediatrics seem to be generally unaware of the fact that your Academy has participated for ten years in a very interesting and valuable organization, the National Committee for Clinical Laboratory Standards (NCCLS). The NCCLS has only three kinds of members: professional organizations, industrial (clinical laboratory instruments and supplies), and government agencies (CDC, FDA, NBS, NIH). Each member is represented by one delegate and one alternate. At present there are close to 110 members, of which 20 are professional societies.
13,750 citations
Journal Article•
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TL;DR: The data suggest that high inocula should be used to determine MICs of ampicillin for M. catarrhalis but that this precaution is unnecessary with the cephalosporins tested or with coamoxiclav.
Abstract: Summary The effect of inoculum size on the results of agar dilution MIC tests was assessed for 20 Moraxella catarrhalis isolates with BRO-1 enzyme, 20 with BRO-2 enzyme and 15 isolates that did not produce β-lactamase. The compounds tested were ampicillin, coamoxiclav, cefaclor, cefixime and cefetamet, and the inocula were 104, 105, 106 and 107 cfu/spot. The MICs of ampicillin for BRO-1 and BRO-2 producers were consistently higher than those for non-producers at inocula of 107 cfu/spot but overlapped with those for non-producers at lower inocula. A small β-lactamase-related inoculum effect was seen with coamoxiclav; small inoculum effects also occurred with cefaclor and cefixime but were not related to enzyme presence or type. MICs of cefetamet were the least affected by the inoculum size. For all the compounds, the degree of correlation between MICs and the inhibition zones observed in disk diffusion tests was independent of the inoculum used in the MIC tests. These data suggest that high inocula should be used to determine MICs of ampicillin for M. catarrhalis but that this precaution is unnecessary with the cephalosporins tested or with coamoxiclav.
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"Determination of minimum inhibitory..." refers background in this paper
...To prevent organisms such as Proteus species from swarming, media have been adapted by increasing the agar content or adding 50 mg/L p-nitrophenyl glycerol (PNPG) (BDH Merck, Lutterworth, Leicestershire, UK) or 350 mg/L Matexil (AstraZeneca, Cheshire, UK).(3) PNPG, Matexil and increased agar concentration can all alter MICs significantly with some agents....
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