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      Methods for in vitro evaluating antimicrobial activity: A review

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          Abstract

          In recent years, there has been a growing interest in researching and developing new antimicrobial agents from various sources to combat microbial resistance. Therefore, a greater attention has been paid to antimicrobial activity screening and evaluating methods. Several bioassays such as disk-diffusion, well diffusion and broth or agar dilution are well known and commonly used, but others such as flow cytofluorometric and bioluminescent methods are not widely used because they require specified equipment and further evaluation for reproducibility and standardization, even if they can provide rapid results of the antimicrobial agent's effects and a better understanding of their impact on the viability and cell damage inflicted to the tested microorganism. In this review article, an exhaustive list of in vitro antimicrobial susceptibility testing methods and detailed information on their advantages and limitations are reported.

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          Antimicrobial susceptibility testing: a review of general principles and contemporary practices.

          An important task of the clinical microbiology laboratory is the performance of antimicrobial susceptibility testing of significant bacterial isolates. The goals of testing are to detect possible drug resistance in common pathogens and to assure susceptibility to drugs of choice for particular infections. The most widely used testing methods include broth microdilution or rapid automated instrument methods that use commercially marketed materials and devices. Manual methods that provide flexibility and possible cost savings include the disk diffusion and gradient diffusion methods. Each method has strengths and weaknesses, including organisms that may be accurately tested by the method. Some methods provide quantitative results (eg, minimum inhibitory concentration), and all provide qualitative assessments using the categories susceptible, intermediate, or resistant. In general, current testing methods provide accurate detection of common antimicrobial resistance mechanisms. However, newer or emerging mechanisms of resistance require constant vigilance regarding the ability of each test method to accurately detect resistance.
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            Surveillance for severe acute respiratory infections (SARI) in hospitals in the WHO European region - an exploratory analysis of risk factors for a severe outcome in influenza-positive SARI cases

            Background The 2009 H1N1 pandemic highlighted the need to routinely monitor severe influenza, which lead to the establishment of sentinel hospital-based surveillance of severe acute respiratory infections (SARI) in several countries in Europe. The objective of this study is to describe characteristics of SARI patients and to explore risk factors for a severe outcome in influenza-positive SARI patients. Methods Data on hospitalised patients meeting a syndromic SARI case definition between 2009 and 2012 from nine countries in Eastern Europe (Albania, Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, Romania, Russian Federation and Ukraine) were included in this study. An exploratory analysis was performed to assess the association between risk factors and a severe (ICU, fatal) outcome in influenza-positive SARI patients using a multivariate logistic regression analysis. Results Nine countries reported a total of 13,275 SARI patients. The majority of SARI patients reported in these countries were young children. A total of 12,673 SARI cases (95%) were tested for influenza virus and 3377 (27%) were laboratory confirmed. The majority of tested SARI cases were from Georgia, the Russian Federation and Ukraine and the least were from Kyrgyzstan. The proportion positive varied by country, season and age group, with a tendency to a higher proportion positive in the 15+ yrs age group in six of the countries. ICU admission and fatal outcome were most often recorded for influenza-positive SARI cases aged >15 yrs. An exploratory analysis using pooled data from influenza-positive SARI cases in three countries showed that age > 15 yrs, having lung, heart, kidney or liver disease, and being pregnant were independently associated with a fatal outcome. Conclusions Countries in Eastern Europe have been able to collect data through routine monitoring of severe influenza and results on risk factors for a severe outcome in influenza-positive SARI cases have identified several risk groups. This is especially relevant in the light of an overall low vaccination uptake and antiviral use in Eastern Europe, since information on risk factors will help in targeting and prioritising vulnerable populations. Electronic supplementary material The online version of this article (doi:10.1186/s12879-014-0722-x) contains supplementary material, which is available to authorized users.
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              Comparison of three different in vitro methods of detecting synergy: time-kill, checkerboard, and E test.

              An in vitro method of detecting synergy which is simple to perform, accurate, and reproducible and has the potential for clinical extrapolation is desirable. Time-kill and checkerboard methods are the most widely used techniques to assess synergy but are time-consuming and labor-intensive. The Epsilometer test (E test), a less technically demanding test, has not been well studied for synergy testing. We performed synergy testing of Escherichia coli ATCC 35218, Enterobacter cloacae ATCC 23355, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 29213 with various combinations of cefepime or ceftazidime with tobramycin or ciprofloxacin using time-kill, checkerboard, and E test techniques. Time-kill testing was performed against each organism alone and in combinations at one-fourth times the MIC (1/4 x MIC) and 2 x MIC. With checkerboard tests, the same combinations were studied at concentrations ranging from 1/32 x to 4 x MIC. Standard definitions for synergy, indifference, and antagonism were utilized. E test strips were crossed at a 90 degree angle so the scales met at the MIC of each drug alone, and the fractional inhibitory concentrations index was calculated on the basis of the resultant zone on inhibition. All antimicrobial combinations demonstrated some degree of synergy against the test organisms, and antagonism was infrequent. Agreement with time-kill testing ranged from 44 to 88% and 63 to 75% by the checkerboard and E test synergy methods, respectively. Despite each of these methods utilizing different conditions and endpoints, there was frequent agreement among the methods. Further comparisons of the E test synergy technique with the checkerboard and time-kill methods are warranted.
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                Author and article information

                Contributors
                Journal
                J Pharm Anal
                J Pharm Anal
                Journal of Pharmaceutical Analysis
                Xi'an Jiaotong University
                2095-1779
                2214-0883
                02 December 2015
                April 2016
                02 December 2015
                : 6
                : 2
                : 71-79
                Affiliations
                [0005]Laboratory of Microbial Biotechnology, Faculty of Sciences and Techniques, University Sidi Mohamed Ben Abdellah, B.P. 2202 Imouzzer Road, Fez, Morocco
                Author notes
                [* ]Corresponding author. b.mounyr@ 123456gmail.com
                Article
                S2095-1779(15)30015-0
                10.1016/j.jpha.2015.11.005
                5762448
                29403965
                fcd6e58f-e144-4963-9939-333b2ae38ced
                © 2015 Xi'an Jiaotong University

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

                History
                : 22 August 2015
                : 21 November 2015
                : 23 November 2015
                Categories
                Review Paper

                thin-layer chromatography (tlc)–bioautography,time-kill test,antimicrobial gradient method,agar diffusion method

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