Culture Harder: Use more specimen to increase MRSA culture yield relative to PCR
This article has been Reviewed by the following groups
Listed in
This article is not in any list yet, why not save it to one of your lists.Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) causes considerable morbidity and mortality in both community acquired and healthcare associated infections, but detecting colonization with MRSA has been shown to improve patient outcomes in certain clinical settings. MRSA colonization detection has been carried out in a variety of ways with molecular assays having superior sensitivity in most studies relative to culture, but culture is disadvantaged in some comparisons by utilization of low specimen volumes. We compared a commercial molecular assay to both low volume (10 µL) and high volume (650 µL) culture and found that increasing the volume utilized for culture led to detection of 25% more cases than low volume culture.
Article activity feed
-
The reviewers have highlighted major concerns with the work presented. Please ensure that you address their comments.
-
Comments to Author
This study demonstrates that using more clinical specimen may increase MRSA detection relative to PCR. The study shows that increasing the culture volume from 10 µL to 650 µL led to the detection of 25% more MRSA cases. However, in comparison, the study shows that molecular detection using PCR is far more sensitive than culture-based assays, even when using a higher inoculation volume. Thus, the overall study does not hold much potential in my opinion. Areas where the study can be potentially improved are listed below. Methodological rigor, reproducibility and availability of underlying data There are multiple areas where the study can be improved in terms of methodological rigor and reproducibility. 1. The article does not state why 650 µL has been used as the higher culture volume. The authors should …
Comments to Author
This study demonstrates that using more clinical specimen may increase MRSA detection relative to PCR. The study shows that increasing the culture volume from 10 µL to 650 µL led to the detection of 25% more MRSA cases. However, in comparison, the study shows that molecular detection using PCR is far more sensitive than culture-based assays, even when using a higher inoculation volume. Thus, the overall study does not hold much potential in my opinion. Areas where the study can be potentially improved are listed below. Methodological rigor, reproducibility and availability of underlying data There are multiple areas where the study can be improved in terms of methodological rigor and reproducibility. 1. The article does not state why 650 µL has been used as the higher culture volume. The authors should try testing an inoculum volume similar to that used in PCR or do a dose response with different inoculation volumes, if not done already. 650 µL is quite a high culture volume to be used on CHROMagar plates, which are usually designed for only streaking of clinical samples. Also, sparing 650 µL of clinical sample for an otherwise low-sensitive detection method does not sound practical. 2. There is no description of any replication of the testing done, especially of those that were culture positive but PCR negative. If authors ran out of samples, that highlights a major drawback in using more culture for detection. 3. Correlation of antibiotics with culture positivity needs to be described better. Results suggest that a Student's T-test was run to determine statistical significance. How many replicates (technical/biological?) were run for each group? 4. The main methods can be better summarized as a workflow/flowchart. A bit more detailed description of sub-methods (using MALDI-TOF, cefoxitin disk diffusion etc.) is necessary. 5. Underlying data is available as a supplementary file, which helps in understanding the results section. 6. Authors have not described patient sample collection in detail. Presentation of results 1. Table 1 can be better represented as a Venn diagram, with the %sensitivity written down in a table alongside. 2. The table legend does not have enough description of all abbreviations used (LRT Cx, sens%?). 3. There should be a separate table or figure showing the trend of antibiotic usage with culture positivity. 4. Supplementary data Excel file shows 414 negative cases, and a total of 94 positive cases. But results show 93 positive cases, does that mean 93 unique positives? Style and organization of paper Overall, the paper is concise and captures the information in an organized manner. But there are some key aspects that can be better explained with a bit more detail. For example, the paper lacks any figure. Replacing numbers in text with figures/tables might be helpful to understand things better. Some portions in the Introduction (lines 47-54) can be reframed to articulate thoughts in a better way. Line 26 sounds vague/superlative, please reframe. Literature analysis or discussion Please include relevant references for lines 30-35 and 39-41. The discussion section lacks proper explanation of the original study aim in the beginning: does more culture increase MRSA detection sensitivity by culture-based methods? Overall, it will be too ambitious to suggest that 25% more cases were detected by using more culture inoculum, since the actual difference was in only 13 samples, with some samples only showing a few mauve colonies with higher inoculum. So, confirming MRSA with only a culture-based assay with higher inoculum can lead to false-positive results if not confirmed by a secondary test like a PCR or MALDI-TOF. Minor comments 1. Line 11- Staphylococcus aureus should be in italics. 2. Line 51- mecA should be in italics. 3. Line 71- O in MALDI-ToF should be in uppercase (MALDI-TOF). Please check the usage in other places too. 4. Please define abbreviations as and when used. I have already mentioned it for table 1 but there are other abbreviations in text (such as BAL) that have not been described.
Please rate the manuscript for methodological rigour
Poor
Please rate the quality of the presentation and structure of the manuscript
Poor
To what extent are the conclusions supported by the data?
Partially support
Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?
No
Is there a potential financial or other conflict of interest between yourself and the author(s)?
No
If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?
Yes
-
Comments to Author
I liked the article. I only have minor comments; - "There are an almost infinite number of ways in which evaluation of MRSA colonization can be carried out": I agree there numerous ways to evaluate MRSA colonization (various sites/combinations of sites, various swabs, PCR/culture, various PCR tests, various culture media, with/without preceding enrichment culture) but "almost infinite" is an exaggeration. I suggest modifying the text. - Can you clarify whether both nares were swabed? - It is interesting that 3 of 12 cases that were positive in sputum/BAL were not detected by either PCR/culture. Does this contradict IDSA recommendations to guide empirical treatment/de-escalation in pneumonia? - Table 1; Add explanation of abbreviations below the table - Table 1; Please rephrase the "Group" names. It …
Comments to Author
I liked the article. I only have minor comments; - "There are an almost infinite number of ways in which evaluation of MRSA colonization can be carried out": I agree there numerous ways to evaluate MRSA colonization (various sites/combinations of sites, various swabs, PCR/culture, various PCR tests, various culture media, with/without preceding enrichment culture) but "almost infinite" is an exaggeration. I suggest modifying the text. - Can you clarify whether both nares were swabed? - It is interesting that 3 of 12 cases that were positive in sputum/BAL were not detected by either PCR/culture. Does this contradict IDSA recommendations to guide empirical treatment/de-escalation in pneumonia? - Table 1; Add explanation of abbreviations below the table - Table 1; Please rephrase the "Group" names. It is hard to understand what "No LRT Cx resulted" means. Also explain LRT and Cx abbreviations in the Table legend.
Please rate the manuscript for methodological rigour
Very good
Please rate the quality of the presentation and structure of the manuscript
Very good
To what extent are the conclusions supported by the data?
Strongly support
Do you have any concerns of possible image manipulation, plagiarism or any other unethical practices?
No
Is there a potential financial or other conflict of interest between yourself and the author(s)?
No
If this manuscript involves human and/or animal work, have the subjects been treated in an ethical manner and the authors complied with the appropriate guidelines?
Yes
-
