The article, Evolution and pathogenesis of Staphylococcus aureus: lessons learned from genotyping and comparative genomics, is well written and also well diagramed. The article is looking to obtain an understanding of what the exact biologic role of methicillin resistant S. aureus (MRSA) is. The authors want to understand the existence and the mechanism of evolution for the genesis of C-MRSA. The paper gives a clear background of MRSA but it does not go into depth about the history of how it has evolved to what it is now. It is clearly stated by the authors that, not much is known about how MRSA is able to evolve as quickly as it does to medications.
The body of the paper dives right into the evolution of the core genome of MRSA. My focus is more towards how MRSA has evolved in the hospital and medial setting and the effects that it has had on humans. The research conducted for the paper was vital for them to understand the clonal structure so they could compare it to the strains that common today. They were able to obtain an understanding of what genes it had by running it through a multilocus sequence typing (MLST). “MLST is currently the most popular typing method through the sequencing of seven housekeeping genes (arcC, aroE, glpF, gmk, pta, tpi, and yqiL). For each gene, the different sequences are assigned as alleles and the alleles at the seven loci provide an allelic profile, which unambiguously define the sequence type (ST) of each isolate.” From the data collected from the MLST they were able to analyze and conclude that point mutations have given rise to new alleles more frequently than recombination. Their data shown in figure 1 is good, but I still do not have a clear understanding on how their calculations came about. I would have liked to see a side-by-side comparison of the genes from each individual strains that they were able to sequence successfully. Anyone can talk about what they have found, but I need to see proof through more data.
Fig. 1. Protein homology between nine sequenced Staphylococcus aureus genomes. In each box is the number of orthologues shared by the corresponding strains and median nucleotide divergence that reflects divergence between the two strains. The orthologue was constructed by the orthomcl program (Li et al., 2003). Nucleotide divergence is defined as the number of mismatch bases divided by the number of comparable bases. The color intensity in each box is in inverse proportion to the nucleotide divergence. The accession numbers of the S. aureus genomes are: NC_002745 (N315), NC_002758 (Mu50), NC_003923 (MW2), NC_002953 (MSSA476), NC_002951 (COL), NC_007795 (NCTC8325), NC_007793 (USA300), NC_002952 (MRSA252), NC_007622 (RF122).
The second half of the paper was geared more towards what I was interested in. They talked about how MRSA enters a host and clearly explained the life cycle of MRSA on what they gathered from their studies. Community-acquired MRSA (C-MRSA) has become a problem and is considered to be a super bug since doctors and scientist have not yet found a cure or a drug to fight it. The evolution of MRSA to become what it has become today has interested the medical community and also has sparked an interest in me. This paper does a good job in bringing some light towards possible ways to fight MRSA; “staphylococcal species are one of the most important topics in the research of the evolution and pathogenesis of S. aureus”.
Fig. 4. Illustration of the hypothetical Staphylococcus aureus evolutionary history. The whole S. aureus species can be divided into two putative subspecies (Robinson et al., 2005a). The circles with different colors represent different agr groups, and the circles with numbers inside represent the corresponding clonal complexes. The arrows on the right side indicate the important phases during the S. aureus evolution.
The table and figures that were used were well done overall. They were clearly explained and could be understood. The way the paper was written and put together made is so those who have taken an entry-level genetic course would be able to understand and follow what was being said.
Feng, Y., Chen, C., Su, L., Hu, S., Yu, J., Chiu, C. (2007). Evolution and pathogenesis of Staphylococcus aureus: lessons learned from genotyping and comparative genomics. FEMS Microbiology Reviews DOI: 10.1111/j.1574-6976.2007.00086.x
Robinson, D.A. (2005). Evolutionary Genetics of the Accessory Gene Regulator (agr) Locus in Staphylococcus aureus. Journal of Bacteriology, 187(24), 8312-8321. DOI: 10.1128/JB.187.24.8312-8321.2005