Pathogenic Role and Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Causing Severe Community-Acquired Pneumonia in Vietnamese Children

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Thank you for your submission.

Issue to be addressed

Line 58-59: data on antibiotic resistance of S. pneumoniae in preschool childrend... Please clarify how this relates to MRSA CAP in hospitalized children. How does resistance in Strep pneumo correlated to resistance in MRSA in children?

Line 78-82: subject methods. Did the study include children who were hospitalized twice that was beyond 14 days during the study period? This should be teased out in the study design for the reader. 

Line 112-114: The mechanism of identifying S. aureus and MRSA is listed here, but on LINE 308-309 the limitation stated that S. aureus was identified by the coagulase test alone? Please clarify the methodology of identifying MSSA and MRSA.

Line 216-217: I am unsure that you are trying to convey regarding vancomycin MIC decreasing 32 fold. Table 4 lists a single value under MIC90. No data regarding the distribution of MIC was given for the S. aureus. Did all 41 isolates have a MIC90 of 0.5? The same comment can be made with linezolid. Without a distribution of MIC values, table 4 is not much more useful than table 2. They both appear to convey the same message with the exception that Table 2 is more telling in that it includes data on intermediate susceptibility. 

I suggest that Table 4 be converted to MIC distribution or deleted. If deleted, you can still describe the MIC mode for vancomycin and linezolid in the text. 

Line 274-276: This sentence is awkward. It should read, MRSA strains identified in this study were found to be resistant to... and susceptible to...

Line 284: "Because rifampin is an anti-tuberculosis drug, it cannot treat clinical non-tuberculosis infections". Is this statement really true? What about as adjunct therapy for prosthetic infections? 

Line 285-287: Vancomycin and linezolid may be appropriate options for severe CAP caused by MRSA, rather than penicillin. When would you ever consider penicillin for MRSA? This sentence should be rewritten.

Line 290: Compared to HA-MRSA, CA-MRSA is [typically] less resistant to antibiotics. 

Line 299-302: Please clarify how susceptibility to vancomycin is a positive sign? The efficacy of vancomycin is tied to more than MIC breakpoints, but dosing and time to effective therapy. 

Line 304-305: Comparing your institution's susceptibility rate to that of Doudoulakakis and Ghahremani is not a fair comparison. First, there are in other parts of the world where antibiotic use is different. Second the study Doudoulakaks was in 2007-2014 and is likely much different now. Third the study by Ghahremani was in adults with an average age of 41.7 +/- 22.3. Both of these studies are not a true comparison. Please identify more recent studies in pediatric patients. If none are available, you should list the year of the study in your reference with the author's name. 

Line 310: relieved or believed???

Line 314-319: You need to expand your study limitations. If you included patients more than once, it needs to be specified here. It is not sufficient to list other limitations inherent to cross-sectional studies.You need to give us examples the limitations that are most pressing. I agree that a single institution (no "s") and small numbers are important. Because resistance rate are very dynamic you need to state something more and how this study can be used. Besides what is listed in the conclusion where vancomycin and linezolid should be the mainstay of therapy for MRSA.  

Other limitations include the fact that there are more antibiotic agents that can treat MRSA that were not included such as.... Also is there a reason why TMP/SMX is not tested. I think that would be an interesting topic for readers.  

Author Response

We are grateful for your relevant comments. Our manuscript has undergone English language editing by MDPI. Please find out the revised manuscript with the modifications marked up using the “Track Changes” function.

We would like to send our feedback to your comments point-by-point.

Please see the attachment below.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 2)

Thanks a lot for the invitation to re-review the resubmitted version of the manuscript.

In the revised manuscript, the authors amended the Introduction section with proper sections citing relevant literature. The Methods section improved by addition of relevant details regarding the study design and methods used.

Importantly, the limitations section was revised with addition of the potential caveats of the study.

Therefore, I consider that I my previous concerns were addressed properly by the authors.

Author Response

Dear Reviewer,

Thank you for your comments and acceptance.

Best regards.

Reviewer 3 Report (Previous Reviewer 1)

Dear authors,

all the corrections have been made and the paper improved

Author Response

Dear Reviewer,

Thank you for your comments and acceptance.

Best regards.

Round 2

Reviewer 1 Report (Previous Reviewer 3)

no further comments

Author Response

All authors thank you for your valuable comments and approval.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear authors,

I read your manuscript concerning the role of MRSA in CAP and epidemiology descriptions in Vietnam. The Manuscript, in its entirety, is easy to read, well structured and presents a real-life approach to the CAP in Vietnam. The study design is adequate, as well as the statistical analyses and the tables, essential in the paper. However, some points must be addressed and clarified.

1)      Line 18. “…causative agent of MRSA”. Is it not S. aureus the causative agent? Did you mean CAP?

2)      Line 27-26, you should report the methodic used for MIC

3)      Line 29-30, it is not clear if Bacterial strains are referred to S. aureus or all the isolated bacteria.

4)      Line 33. “Therefore, the antibiotic of choice for MRSA should be vancomycin or linezolid”, please be more careful and report “after antibiogram”. However, this strong affirmation is expressed throughout the text, which cannot be taken as an absolute criterion. As per guidelines and good clinical practice, the antibiotic choice must also consider the antibiogram. Furthermore, the introduction of new antibiotics into clinical practice, as widely described in the literature, determines the onset of drug resistance in a short time. If it is decided to use linezolid or vancomycin in treating CAP from MRSA, without an antibiogram, these would determine the expansion of drug resistance to these molecules. Moreover, we couldn’t plan proper antibiotic stewardship. Rewrite the sentence.

5)  Genes' name in italic style

6)      Line 99, L

7)      Add the standard deviation at the ages.

8)      Remove “Clearly” at the beginning of sentences in the discussion.

9)      Line 278-282, references reported are not adequate

10)   The conclusion must be improved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Thanks for the invitation to review the current manuscript.

In the current study, the authors aimed to identify the fraction of CA-pneumonia caused by MRSA among children admitted to a single site in Vietnam. Such an aim is relevant considering the previous evidence of an increasing prevalence of MRSA among such a study group.

The main result indicated the common occurrence of MRSA in CA-pneumonia among the study group. There are several issues that should be addressed by the authors as follows:

Major

1.      The authors should conduct a thorough literature review citing relevant references.

2.      The authors should inspect the manuscript carefully for typos and language errors.

3.      The methods need better clarification particularly for MIC determination approach.

Minor:

1.      Regarding the highlights of the study included prior to the Abstract section, please follow the journal guidelines as listed in: https://www.mdpi.com/journal/arm/instructions. These highlighted can be incorporated in the Abstract.

2.      In the Abstract and main text, please spell out the abbreviation upon the first encounter: E.g., CLSI in line 31.

3.      Reference 1 can be supplemented by recent reviews addressing the clinical significance of MRSA. E.g., https://doi.org/10.1016/j.cmi.2022.03.015; https://doi.org/10.1186/s13756-019-0673-5.

4.      Reference 2 can also be supplemented by additional references to support the observation of increasing MRSA relevance in CA-pneumonia in children: https://doi.org/10.1055/s-0040-1709992; https://doi.org/10.1186/s12879-014-0582-4.

5.      In line 44, please add a reference (CLSI or EUCAST) supporting the MIC for oxacillin among Staph aureus isolates. It is even better to mention the MIC for cefoxitin considering its higher utility as an indicator for oxacillin susceptibility.

6.      The mentioned genes in the main text should be italicized. E.g., line 44, mecA

7.      In the Introduction, the authors can benefit from adding a paragraph highlighting the prescription practices of antibiotics in Vietnam with a special focus on the antibiotic stewardship programs in the country and at the study site. Additionally, the authors are recommended to add a paragraph on the prevalence of antibiotic resistance trends in the country.

8.       Reference number 4 appears misplaced since the authors should cite a document from the WHO. The same applies for reference number 5.

9.      Age should be listed among the exclusion criteria as well.

10.   One of the limitations in the Methodology is the sole dependence on the slide coagulase test for Staph. aureus identification. This comes in relation to the possibility of other Staphylococci being slide coagulase positive (e.g., S lugdunensis and S schleiferi). Please consider this point in the limitations of the study.

11.   The approach for determining the MICs was not clear and should be mentioned by the authors. Automated system? Broth microdilution? E-test? Please specify.

12.   Line 175: highest should be replaced by oldest.

13.   In Table 1: It is better to compare MRSA and MSSA vs other groups rather than combining them. So, the column “Severe CAP (n=239)” should be replaced by “Severe CAP caused by other agents rather than Staphylococcus aureus (n=193)”. Analysis should be repeated accordingly.

14.   The authors should add a paragraph listing the potential limitations of the study.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Thank you for your submission.

Please minimize mixing decimal points of periods and commas. This seems to be more common towards the end of the paper. An example is line 218-219. "...severe CAP 41/234 (17,5%); in which, mainly 218 MRSA 32/41 (78.0%). "

Line 63, remove the hyphen before inclusion and exclusion criteria. Please create a sentence instead of bullet points. Remove hyphen on line 114 prior to "Antimicrobial" as well

I don't think the paragraph from line 94-97 that describes culture medium is necessary. 

Line 177-178 is awkward. "Boys were more susceptible than girls with a male/female ratio of 2.7/1. "  I think you are talking about incident rates.  The exact line is repeated again on line 229-230. Feel free to change it up. 

Table 1. You are missing IQR for median and SD for mean numbers

Line 189, Spell out MIC because it is the title.

Line 190-195. The paragraph discusses resistance rates but is excluding TMP/SMX, which is also excluded in Table 2. It is listed on line 116 as part of standard testing. Please do not delete it from line 116 but add results in the paragraph and Table 2 OR justify why it is not represented. 

Line 208 Table 4. I am not sure if this table is necessary

Line 218. instead of agent, I think organism would be more appropriate.

Line 233-234. "Compared to the overall number of severe CAP cases, this rate is lower (the rate of malnutrition in children with severe CAP is 45,8%). It means that malnutrition has not been recorded to affect the child's ability to get S. aureus."  I don't think you can make this statement in a cross-sectional study. You are only able to observe and report the rates. You cannot make causation statements. 

Line 280. For HA-MRSA, several studies..... hospital [22].  How can you make a statement about several studies when you only reference one study that was also a cross-sectional study of only 384 patients on another continent that isn't remotely associated with your institution's ecological flora.

You are missing a limitation section. Include why recent hospitalization with 14 days instead of 30 days was an exclusion criteria. This appears to mix community acquire pneumonia with possible health care acquired pneumonias. A better option would be to include whether patients received antibiotics recently. 

Other limitations to include are those inherent to cross-sectional studies, single institutions, effects of small numbers on statistical analysis (especially analysis on table 3)

Author Response

Please see the attachment.

Author Response File: Author Response.pdf