No Detection of Methicillin-Resistant Staphylococcus aureus in Dairy Goats
Round 1
Reviewer 1 Report
Rif.: Dairy-993936
Dear Authors,
Even if no MRSA were detected, the study adds information about the epidemiology of MRSA in goats in Europe, where different prevalence depending on the Country is observed.
Nevertheless, the manuscript needs some minor modifications:
Line 96: Please, describe the PCR protocol used to detect mecA and mecC genes or provide a reference
Lines 133-134: The meaning of this sentence is not very clear; I think that the Authors means that the occurrence of MRSA is not known because only selective media was used without typing assays on identified strains after their detection. Please, re-written this sentence and better clarify the meaning.
Line 140: Please, change 3 340 in 3,340
Conclusion section: Lines 150-151: Considering that I) as reported in the discussion section, the investigation has been carried out on a limited number of goat herds in respect to the total number estimated in Sweden II) although the investigation has been carried out from north to south of Sweden, the most of goat herds considered in this study were prevalently from some more restricted area of the Country as reported in figure 1; in my opinion, the conclusion section must be reformulated accordingly, writing for example “No samples were found to be positive to MRSA probably due to good management and biosecurity measures adopted in Sweden but considering I) and II) further investigations may be planned…”
Author Response
Dear reviewer,
Thanks for your clarifying revision. We have tried to modify the manuscript according to your comments. Please see below our step-by-step-response.
Line 96: Please, describe the PCR protocol used to detect mecA and mecC genes or provide a reference
A reference has been added, new reference [16].
Lines 133-134: The meaning of this sentence is not very clear; I think that the Authors means that the occurrence of MRSA is not known because only selective media was used without typing assays on identified strains after their detection. Please, re-written this sentence and better clarify the meaning.
This has now been clarified in the text
Line 140: Please, change 3 340 in 3,340
Done
Conclusion section: Lines 150-151: Considering that I) as reported in the discussion section, the investigation has been carried out on a limited number of goat herds in respect to the total number estimated in Sweden II) although the investigation has been carried out from north to south of Sweden, the most of goat herds considered in this study were prevalently from some more restricted area of the Country as reported in figure 1; in my opinion, the conclusion section must be reformulated accordingly, writing for example “No samples were found to be positive to MRSA probably due to good management and biosecurity measures adopted in Sweden but considering I) and II) further investigations may be planned…”
We disagree with this statement as it would be repetitive of the discussions part of the article, and to a large part be speculative and not a true conclusion. Moreover, most goat herds are in the western/northern parts of Sweden. Hence more herds from this region. This has been added in the Discussion.
Reviewer 2 Report
line 54: the form is not clear: potential a link ?
line 82: i have serious doubts n the attendibility of the sampling if they were not taken by experienced people...farmer are not clinicians
line 97: results and discussion should be separated in two different paragraphs
Author Response
Dear reviewer,
Thanks for your clarifying revision. We have tried to modify the manuscript according to your comments. Please see below our step-by-step-response.
line 54: the form is not clear: potential a link ?
This sentence has now been clarified
line 82: i have serious doubts n the attendibility of the sampling if they were not taken by experienced people...farmer are not clinicians
Swedish goat dairy farmers are often used to collect samples since it is expensive for them to call a vet. At SVA, we almost exclusively rely upon farmers collecting the material. Bot for studies, but also for routine sampling and during disease outbreaks.
line 97: results and discussion should be separated in two different paragraphs
I leave this to the editor to decide. For short communications it was ok according to the style of the journal.
Reviewer 3 Report
The spread of MRSA in livestock and the potential for contamination of food (especially unpasteurised dairy products) is of some interest. This short communication outlines that MRSA cannot be detected in dairy goats in Sweden, investigating its prevalence in a small population.
Introduction
Line 29 – I think that MRSA can no longer be described as an ‘emerging’ pathogen, considering its appearance in the 1960s and being epidemic in many healthcare settings since the 1990s.
Line 38 – ‘a goat herds’ I believe this should be plural? (No ‘a’)
Line 47 – Could a more specific reference to the increasing trend in mecC-MRSA in Denmark be given here?
Line 52 – This study regarding wild hares appears to discuss mecA (but I can only access the abstract).
General – A lot of discussion is made re: mecC-MRSA prevalence but this study appears to be more generally about MRSA and so maybe a more ‘general’ MRSA overview can be given?
General – The word ‘occurrence’ is used in many places where I believe ‘prevalence’ may be more appropriate.
Methods
Line 91 – Was turbidity of the broth noted to give some indication that sampling had been adequate? Were broths plated onto any non-selective agar to confirm the presence of methicillin-susceptible S. aureus or other staphylococcal species for confirmation of sampling adequacy?
Line 95 – This reference describes the use of MALDI-TOF for non-aureus staphylococcal infections, but the study is detecting MRSA.
Line 96 – Please reference the PCR methods used.
Results/Discussion
General – Please indicate if there was any non-mecA/C growth on the Brilliance agar, or rather that there was no growth from any sample. Was there any growth not indicative of S. aureus (e.g. pink / white colonies)?
Line 118-123 – The description of MRSA prevalence here reads more like an introduction, but further expansion on how sampling methods can result in varying prevalence described, and how the sampling methods used in this paper compare to others that detected higher prevalence, would be valuable.
Line 133 – Were any colonies of any type detected? Did broth become turbid? If no bacteria were detected at all, especially from goat swabs, does this represent a sampling issue?
Line 136/140 – Please put this reference into the reference list
Line 142 – Considering the limitations described in the preceding sentence re: small sampling numbers, and the next sentence which shows that mecC-MRSA has been described in Swedish goats, can the authors justify that these results indicate ‘no emerging spread’ of MRSA, or just that it is at lower prevalence than was detectable in the study?
Conclusions
This section appears to duplicate without adding any extra clarity to this short communication.
Author Response
Dear reviewer,
Thanks for your clarifying revision. We have tried to modify the manuscript according to your comments. Please see below our step-by-step-response.
Line 29 – I think that MRSA can no longer be described as an ‘emerging’ pathogen, considering its appearance in the 1960s and being epidemic in many healthcare settings since the 1990s.
The definition of emerging diseases is quite broad, and although already identified in 60s and might be epidemic in healthcare settings in many countries’ MRSA is still emerging in other settings and countries and increasing in numbers. You also have the detection and emergence of new variants of MRSA such as mecC-MRSA mentioned in the current manuscript.
You will also see several papers on MRSA in for example Emerging Infectious Diseases, meaning that it is per definition emerging. We believe that it is fair to call it an emerging pathogen, so we have kept the sentence as it is, but this is not a big issues for us, so the emerging can be deleted if required. Emerging has been deleted in the Discussion.
Line 38 – ‘a goat herds’ I believe this should be plural? (No ‘a’)
Correct. “a” has now been deleted
Line 47 – Could a more specific reference to the increasing trend in mecC-MRSA in Denmark be given here?
A specific reference has now been added as new reference [9]. Subsequent references have consequently been renumbered
Line 52 – This study regarding wild hares appears to discuss mecA (but I can only access the abstract).
This is correct this was a mistake by the authors the correct reference has been added, we also choose to use the broader term lagomorphs in the text instead of hares.
General – A lot of discussion is made re: mecC-MRSA prevalence but this study appears to be more generally about MRSA and so maybe a more ‘general’ MRSA overview can be given?
We disagree, the reason for the focus on mecC-MRSA in the introduction was the previous findings of this specific variant in Swedish goat herds which was a unexpected finding due to the general low occurrence of MRSA in animals in Sweden. This was also the reason for the current study, and a potential connection between goats and mecC-MRSA was also suggested by the Australian screening study. So, the focus of mecC-MRSA is in our opinion warranted as it is the basis for the study. However, as a response to the comment we have reformulated the last paragraph of the introduction to highlight this.
General – The word ‘occurrence’ is used in many places where I believe ‘prevalence’ may be more appropriate.
We the authors disagree, as most of the studies are not true prevalence studies, but merely carried out to detect MRSA in a certain habitat. Therefore, we believe that occurrence (or potentially abundance in some cases) is a better term than prevalence.
Line 91 – Was turbidity of the broth noted to give some indication that sampling had been adequate? Were broths plated onto any non-selective agar to confirm the presence of methicillin-susceptible S. aureus or other staphylococcal species for confirmation of sampling adequacy?
…37+-overnight. “The overnight enrichments showed turbidity indicating bacterial growth.” Has now been added to the paragraph From each overnight enrichment…
This text has now been clarified.
Line 95 – This reference describes the use of MALDI-TOF for non-aureus staphylococcal infections, but the study is detecting MRSA.
Added:
Nonnemann, B., L. Svennesen, U. Lyhs, K.A. Kristensen, I.C. Klaas, K. Pedersen. Bovine mastitis bacteria resolved by matrix-assisted laser desorption/ionization time of flight mass spectrometry. J. Dairy Sci. 2019,102, 2515-2524. DOI: 10.3168/jds.2018-15424.
Line 96 – Please reference the PCR methods used.
Added: Pichon, B., Hill, R., Laurent, F., Larsen, A.R., Skov, R.L., Holmes, M., Edwards, G.F., Teale, C., Kearns, A.M., 2012. Development of a real-time quadruplex PCR assay for simultaneous detection of nuc, Panton-Valentine leucocidin (PVL), mecA and homologue mecALGA251. J. Antimicrob. Chemother. 67, 2338–2341.
General – Please indicate if there was any non-mecA/C growth on the Brilliance agar, or rather that there was no growth from any sample. Was there any growth not indicative of S. aureus (e.g. pink / white colonies)?
The description in the M&M section has been modified to explain this:
…manufacturer’s instructions. Growth of colour-less colonies was considered non-aureus and not further analysed. Dark-blue colonies were confirmed as S. aureus using Matrix…
Line 118-123 – The description of MRSA prevalence here reads more like an introduction, but further expansion on how sampling methods can result in varying prevalence described, and how the sampling methods used in this paper compare to others that detected higher prevalence, would be valuable.
The information included is of interest to put or negative results in perspective as this would not be the case in other countries and that other MRSA can be detected than mecC-MRSA.
We agree with the statement that methods and sampling is a relevant factor to considered when comparing occurrence between different settings and countries, that is why we included the following line “However, direct comparison of occurrence between studies should be done with care since different methods for sampling and detection are used in different studies.” Although since the focus of the current study was not methodological and that it is a short-communication we feel that an extended discussion on this subject is not warranted.
Line 133 – Were any colonies of any type detected? Did broth become turbid? If no bacteria were detected at all, especially from goat swabs, does this represent a sampling issue?
See above
Line 136/140 – Please put this reference into the reference list
Included
Line 142 – Considering the limitations described in the preceding sentence re: small sampling numbers, and the next sentence which shows that mecC-MRSA has been described in Swedish goats, can the authors justify that these results indicate ‘no emerging spread’ of MRSA, or just that it is at lower prevalence than was detectable in the study?
We understand your point and we still believe that these goats are quite representative for the Swedish dairy goat population. We have now deleted emerging but kept spread. We also think the word indicates show that we are not completely certain.
Conclusions
This section appears to duplicate without adding any extra clarity to this short communication.
We leave this to the editor to decide. We believe it helps the reader.
Round 2
Reviewer 3 Report
A well thought rebuttal to my review and useful amendments to the text.
Author Response
See attachment.
Author Response File: 
Author Response.docx
