Critical Review of a scientific paper

Article Comparison of Two Chromogenic Media for Selective Isolation of Vancomycin Resistant Enterococci from Stool Specimens.  Journal of Clinical Microbiology, 47 4113-4116
Authors Heidrun Peltroche-Llacsahuanga, Janetta Top, Josefine Weber-Heynemann, Rudolf   Ltticken, and Gerhard Haase (2009).

Summary Overview
The purpose of the study is to compare the efficacy of two chromogenic media in on rapid detection of Vancomyin Resistant Enterecocci (VRE). The two chromogenic media under study are Chromoagar VRE (CHR) a formulation that originates from France and chomID VRE (C-ID), a formulation that originates from Germany. The introduction reveals the need to identify a medium that rapidly detects VRE. This justifies the study because serious clinical infections that are associated with VRE are on the rise (Peltroche-Llacsahuanga et al (2009 Sakka et al, 2008 Cheng, et al, 2004) yet rapid methods to detect these strains in patient samples are very costly. According to Peltroche-Llacsahuanga et al (2009) a study on the chromogenic media could provide a dependable yet affordable method in rapid detection of VRE strains and hence assist in the control of the spread of the clinical infections.  The chromogenic media performances are tested on selectivity, colony color stability and colony growth characteristics and the ability of VRE recovery from clinical stool samples. The materials used include all the June 2009 compliant species of Enterococcus which are 38 in number which are cultured on the two kinds of chromogenic media.  All these species are resistant to vancomycin at concentrations of 0.125 to 256 gml.  The National Reference Center for Streptococci acts as the data material that provides reference strains for the control experiment. Stool specimens from the gastrointestinal tracks of infected people are used as enriching media. Incubators, light microscope, digital cameras and stereomicroscope are the tools that assist in the detection process. Biochemical analysis and further identification is aided by xylose fermentation tests, Gram stain, furazolidone and mupirocin.

Confirmation of Enterococcus strains is performed by vancomycin, teicoplanin and multiplex PCR. The method entails collecting stool specimens from affected patients in intensive care unit, post surgical gastroenterology wards and oncology departments. Broth enrichment step is performed on the stool specimen overnight and reference strains Enterococcus faecium  (VREfm) and Enterococccus faecalis (VREfs) of different isotonic dilutions are streaked on both the mixed culture from patients samples and pure culture from the culture collection centers, then plated on the two chromogenic media. This is followed by a 48 hour incubatory period and observations are carried out at intervals of 24 hours. The results observed show that C-ID medium support prominent distinctive VRE colony growth as opposed to CHR after 24 hours of incubation in pure culture. In the mixed culture, a train that could not be detected with CHR was detected by C-ID and vice versa. Therefore both media had a high specificity of 98.2 percent. Individually, CHR showed a specificity of 96.5 percent while C-ID was at 97.5 percent. Color stability was also achieved after 48 hour incubation on CHR. C-ID assists distinction and early detection of colony characteristics after 24 hours but instability in colony color is observed after 48 hours. However, the study reveals that both CHR and C-ID are unable to perform rapid detection of Enterococcus. This is because of failure to detect most of the strains of Enterecocci in pure form, and only the growth of the reference strains on the media were detected. Miranda, et al (2005) highlights the efficacy of chromocult media, although the same problem of detection is observed. This is attributed to the high microbial load in the gut which led to a growth of most of gastrointestinal bacteria and yeast, an observation that has also been made by DAgata et al (2002).  Neither isotonic dilutions nor direct agar plating was able to assist in the pure selection of Enterococcus strain from the incubated cultures, although confirmation tests show that these strains were present. C-ID media presents a cost effective stool screening for detection of VRE but procedures for detection and confirmation slow down the process. Asir et al (2009) compares three chromogenic media-AES VRE agar, C-ID VRE agar which are synthetically designed for VRE detection and the traditional Oxoid VRE agar and the results show that all the media are useful in detection of VRE but it is easier with the VRE designed media. Khudaier et al (2007) use bile esculin azide chromogenic agar for VRE identification. A higher microbial load and spread of VRE occurs with patients on longer hospital stay (Donskey et al, 2001). However, selective decontamination of digestive tract suggested by some studies is not a valid method for suppressing VRE. Bonten (2006) reports that topical applications of antibiotics on affected admitted patients may not effectively eliminate VRE because of gene transfer within the strains, a study complying with that of Khudaier et al (2007) and DAgata et al (2002). Nahum et al (2002) recommend intravenous vancomycin prophylaxis but over a short period of time.  Peltroche-Llacsahuanga et al (2009) study does not point out to the possibility of gene transfer across the strains in the broth enrichment culture.  Any study done should consider caution to the workers especially those involved in collection of samples, and this is because of the high infection rate of clinical indications caused by VRE, as indicated through the study by Tokars et al (2001).

Critical Review
Generally, studies concerning evaluation of chromogenic agar in screening of VRE in stool samples are many and this is as a result of the high prevalence rates of clinical infections caused by VRE. In these terms, I would say that this is not a novel study but one that builds on other studies in the collective effort to find quicker methods to control VRE infections. Broth enrichment, PCR, and agar plating methods used for this study are widely used in microbiology studies, and several studies have compared various chromogenic agars (Asir et al, 2009). However, this is the first time that CHR and C-ID are compared on their performance in selectivity and stability of VRE strains.  This study is very important to medical microbiology. Detection of gastrointestinal flora requires rapid and accurate methodologies where pathogenecity is concerned, and therefore methods that can quickly identify disease causative agents need to be proposed. However, the method does not provide the solution to the problem and further studies need to be carried out in identifying a quicker method for VRE strains. At the moment Enterococcus detection on C-ID at 24 hours incubation seems a beneficial method although considerable delays occur in exact species identification. In hospitals the prevalence in clinical infections rates increase with the length of the hospital stay and hence early detection of VRE will aid in controlling this phenomenon. This article is well summarized with all important procedures noted in a short length. However, there is still need for further summarizing in discussion section. The mention and explanation of Pediococcus species and yeast occurrences seems to divert the attention from the purpose of the study and should have been handled as a separate study. Worth noting is that the authors have correctly used and written the bacterial names and have respected the biological nomenclature of writing scientific names. Generally, the article is concisely written but the use too many commercial abbreviations and referrals bring complexity and reduce the flow of the reading. The exclusion of titles within the study complicates the article further and jeopardizes the form organization, because it is hard to draw end of one section and the beginning of the next, except of the abstract which is bold and appears at the beginning of the document. This article is therefore written for microbiologists and an audience that is familiar with microbiological procedures.

The title of the article is of a clear and appropriate length and reflects the content of the paper. This makes it easier for the reader to grasp the purpose of the study.

For any scientific paper, the abstract is the core section because it provides the whole research in a nutshell. In my view, the authors have not achieved the purpose of total inclusive informative with this abstract. The abstract fully indicates the methodology, results and conclusions but it does not out line the aim of the study.

The introduction reveals the research question and enables the reader to understand the importance of the study. Understandably, non-infected patients but whose guts are colonized with VRE strains are potential source of the spread of clinical infections and studies are done find a control measure through rapid detection procedures. However, there is limited literature that relates this study to others. Most of the literatures quoted are in regard to the standard procedures used. The authors should have provided more literature to enable an easy understanding on why the two chromogenic agars were preferred in solving the research question.

Materials and methods
The materials and methods used are relevant for the research question. Any microbiological analysis procedure entails isotonic dilutions of culture, culture enrichment steps, incubation and streaking on selective media. Microscopes are important instruments in observing colony characteristics.  Bacteria identification methods like gram stains, E-tests and PCR are common in similar studies, and the methodology is replicable for several other microbiology studies. The article also mentions and refers to well known procedures rather than detailing them, for instance the gram stain method and multiplex PCR are common methods that have been mention rather than  being explained. Worth noting is that references have been provided for all the methods and even a mention of the kind of study on which the method applies has been explained in some instances. The article has highlighted a clear and well explained methodology.

The results presented are mostly from the authors work and there is a lack of comparison to other works.  The presentation of results in both word and graphic makes the article very comprehensive. A supplemental article is also availed to further enhance the understanding of the results. Studying colony characteristics in microbiology is best observed through photos taken. The article should have emphasized more on graphic presentations rather than explaining the colors and growth characteristics of colonies through text. Most of the results have been given in both text and figures.

Tables and figures
There is proper use of tables and figures which are well labeled but the legends are inadequately used, for instance on table 2. The tables in the article cannot be understood at first glance and one has to constantly refer to the text. The figures are clear and of high quality and can be understood as soon as one understands the article. The quality and design of the tables and figures is fairly good because of proportionality and labeling. However figure 1 is less proportionate in form.

The authors have appropriately interpreted their results but lack of comparison to other studies makes it hard to determine the position of this study as far rapid detection chromogenic media is concerned. The authors have also not discussed the issue of contrast observation on the media between their own findings and the expectation of the manufacturer. There could be possibilities that errors in manufacture or instruction pamphlets alter the interpretation of the results. Anyway, following the methodology and discussion, it can be argued that the authors conclusion is acceptable to their findings.


Post a Comment