The authors describe the identification of a strain of S. sciuri (even though the identification is unconvincing, see below) in an outbreak of exudative epidermitis (EE) in pigs. They go on to perform animal experiments which indicate that this strain can cause EE in an animal model of EE. My main problem with this paper is the poor identification of the outbreak-strain and the lack of proper controls in experiments throughout the paper. I therefore think that the conclusions the authors draw from their data are hardly justified.

I find the identification of this strain as S. sciuri unconvincing. This has been done on the basis of biochemical tests only. However, these tests can often produce misleading results. My doubts are further increased by the strange results of the ITS-PCR. Apparently, no controls on DNA of other Staphylococci were included in this experiment. It seems that the banding pattern (which is not very clear to begin with) was simply compared to previously published data. This is obviously wrong as ITS-PCR should have been performed by the authors themselves on several other, well-characterized Staphylococcus strains, esp. on S. sciuri and S. hyicus. This would control for any technical differences with the ITS-PCR technique between the laboratory of the authors and the original publication by Couto et al. Additionaly, other DNA-based methods should have been used to assign this strain to a Staphylococcus species (such as PFGE or ribotyping). Right now, it seems entirely possible to me that this strain is not S. sciuri at all, thereby negating most of the conclusions the authors make. It could even be the first “field-case” of S. chromogenes for all I know!

The authors show that feeding the isolated strain to piglets reproduces the clinical signs of EE. However, an important negative control was not carried out. I would want to see an experiment in which another strain (for example the type-strain or one of the exotoxin-negative S. sciuri strains described in the literature) of S. sciuri was fed to the piglets at the same (high) dose as described for the outbreak strains. This would show whether the strain isolated in this study is really “highly pathogenic” as claimed by the authors. This point is even more relevant for the mice studies: I would say it is hardly surprising that mice die when they are injected i.p. with any Staphylococcus strain at this high a dose.

I feel that the several lines on the role of S. sciuri in human disease are not correct. It is not a major human pathogen (see also other annotation on the Plos ONE website) and so the first and especially the last, way too speculative, line of the abstract are wrong.

There are several errors in English and/or typos in the text (for example: polymycin should be polymyxin and the first sentence of the abstract should read (even though I feel it is not scientifically justified; see above): Staphylococcus sciuri is an important human pathogen). Extensive proofreading should therefore be performed.