Comparison of Two Chromogenic Media for Selective Isolation of Vancomycin-Resistant Enterococci for Stool Specimens

 Bacteria are widely known agents of diseases not just in humans, but almost in all organisms. The study of bacteria, known as microbiology, has already found an antidote to the common bacteria known to infect and infest different organisms. The genus of bacteria Enterococci are organisms found on intestines of humans and female genital parts. They are innate organisms in the environment that cause several infections that must be prevented because of their threatening effects. Vancomycin is the drug that is use to treat infections caused by Enterococci. However, through time, some strains of the Enterococci have been resistant to Vancomycin that caused a more alarming threat. This is why the isolation of these bacteria is important in the field of medicine. If isolation is done properly, the bacteria can now be observed and studied and maybe another drug can be invented as a cure to these infectious bacteria (Centers for Disease Control and Prevention 2008, n.pag.).

Two Chromogenic mediums are used in this study. ChromID VRE and ChromAgar VRE are used to screen Vancomycin resistant species of Enterococcus namely, E. faecium and E. faecalis. These two organisms can resist various drugs that cause the high prevalence of infections, especially in hospitals ( 2010).

Although there are many drugs invented to treat bacterial infections, scientists are still on research finding a cure for those bacteria who are resistant to drugs. Little is known on the types of bacteria that have the ability to resist drugs such as Vancomycin. The occurrence of antibiotic-resistant bacteria is now increasing in prevalence therefore it is important to detect these types of bacteria and isolate them in order to conduct a separate study that involves the examination of these resistant bacteria and know their weakness to detect the type of antibiotic that will eliminate them. The study Comparison of Two Chromogenic Media for Selective Isolation of Vancomycin-Resistant Enerococci for Stool Specimens, the scientists attempted to isolate the different Vancomycin resistant Enterococci by using two Chromogenic Media C-ID (Chrom-ID VRE) and CHR (Chrom Agar VRE). The VRE used were isolated from non infected patients but are gut-colonized.

The study aims to compare the two media in terms of efficiency and effectiveness to survey the presence of VRE. There are criteria considered in the comparison of the two selectivity, stability of colony color and growth characteristics and the ability of to sustain VRE from clinical stool specimens (Peltroche-Llacsahuanga, et al. 2009, 4113-4116).

After the series of experiments using the two media, the researchers have found out that C-ID and CHR are not effective in isolating the Vancomycin-resistant Enterococci, since the two did not meet the expectations in terms of fast detection of the organisms especially when the specimens were plated immediately from the stool sample. It was then assessed that plating from the stool sample direct to the medium is also not effective method in isolation of VRE because of the very rapid growth of different bacteria and yeasts on the media. Also, the color that is expected is overthrown by the different colors eluded again by the different organisms, bacteria and yeasts. The study also confirmed the importance of pre cultivation of the organism from the stool sample a night before plating it on to the media needed in order to have a preliminary elimination of unwanted organisms and to have a successful isolation of the selected organism (Peltroche-Llacsahuanga, et al. 2009, 4113-4116).

In terms of specificity, the two media showed good performance in eliminating all types of growth of Enterococcus strains other than its VRE strains. It was observed in this study that in terms of color, CHR medium showed more clarity in the differentiation of VREfs from VREfm than the C-ID medium. An unstable color indication of growth was observed in C-ID medium as there are many shades of colors that appeared on the medium. This caused the difficult assessment of the organism to be isolated. Also, there was an uneven coloration in the purple color of VREfm even after 24h-incubation. The researchers concluded that a proper sampling and pre cultivation is needed to achieve pure culture of VRE organisms. However, it was shown in table 1 that there are other types of organisms detected to be present in the media side from the VRE that are supposed to be the only organism present in the culture. This suggests that the isolation of the organism was not successful and that the results are still for confirmation. There were many errors detected during the experiment (Peltroche-Llacsahuanga, et al. 2009, 4113-4116).

Article Critique
For the General critique, I have searched the internet and found out that this study is not unique. The study has been done although the comparison of the two media is unique in this study. However, there are already numerous studies that pertain to the ability and effectiveness of CHR and C-ID media. A study by Delmas et., al. (2007) entitled Evaluation of a New Chromogenic Medium, chromID VRE, for Detection of Vancomycin-Resistant Enterococci in Stool Samples and Rectal Swabs shows that .there are similarities in this study with that of Peltroche-Llacsahuangaet., al. The use for example of stool samples and C-ID medium, it was already stated in the earlier study of Delmas et al. al. that stool samples are not good source of isolates. This study was done before the similar study done by Peltroche-Llacsahuanga. They should have read first related literature before proceeding to their research in order to eliminate previous mistakes done by other scientists (Delmas, et al. 2007, 2731-2733).

The title completely stands for the whole study since the whole research is abut the two media and their comparison whether which medium is better in terms of isolating VRE. The content does match with the title. However, the abstract is very incomplete. It jumped already to the results without even giving a brief and concise introduction of the objectives and methods of their study. The conclusion was also not clear on which media was better. Also, the statement in the abstract is contradicting the statement in the text since was stated there that the two media did not meet the expectations in isolating the organisms based on the different factors namely selectivity, stability of colony color and growth characteristics and the ability of to sustain VRE from clinical stool specimens. This statement is in contrast to the statement in the abstract since it says there that the two media performed equally well. Also, the word equally is not supported by facts from the results since I have read that C-ID is a better media than CHR because CHR media can also support Staphylococcus species (Jones, et al. n.d., n.pag.).

The researchers gave a very short introduction stating only that VRE can give serious infections. However, it did not give any concrete facts on the prevalence rate and mortality rate caused by infections from VRE. This lack of facts can decline the relevance of the study and people will tend to not take the infections caused by VRE seriously. It is important to lay down the facts to threaten the people if necessary in order to relay the significance of this study. Also, for readers that have no knowledge on microbiology, the paper seems very hard to understand because they did not define the scientific terms used in the paper.

Since the paper is not unique, the researchers should have included papers of other scientists that are similar to their study. A review of related literature is important also to point out the significance of your study. It is needed to detect which discovery is unique in your study. Together with this, the results should be tested again as a confirmatory to be sure that there were no contaminants during the experiment that added to the sources of error. The presentation of data is easy to analyze and the use of texts and tables were used as necessary.

Overall, the paper was not exactly that good because of the various mistakes in the procedures. There were several negative results in the study that should be the reason why this study should be repeated and confirmed. Also, the group should have a good background on other related or similar studies in order to know the better procedure to follow in isolating VRE specimens. The results presented are not that acceptable. Examine in table 1 that there are many organisms aside from VRE that have shown growth on the media. This proves that the isolation was not pure. The errors may be from a contaminated media or the isolation method itself of the VRE from the stool sample is not effective. These results showing a mixture of specimens in the medium shows that the goal of the study is not achieved which is the isolation of the VRE organisms from a stool sample. The comparison was then only based on the ability of the medium to be selective. In this case, both media were not considered as highly selective because of the presence of yeasts and other bacteria in the media.

Furthermore, the researchers should elicit a trial experiment to test the procedure of the experiment and eliminate all possible sources of error. The medium used should be sterilized properly using autoclave or other sterilizing process to make sure that there are no contaminants on the medium. This will enable the researchers to detect more easily the source of contamination of the media. The stool sampling method should also be checked to again prevent the growth of unwanted organisms on the media. After successfully isolating the organism from the source can the scientists have a comparison on the growth of VRE on the two media Having shown in the results that there are other organisms that can survive on the two media, it can now be concluded that the medium is not selective to VRE.


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