Friday, April 18, 2008

Evolution of MRSA

ResearchBlogging.orgStudent post submitted by Trevor Clark.

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


Marla April 18, 2008 at 10:33 PM  

Great article - great diagrams I have not seen before.
Although MRSA has become a nationwide problem, it seems that Fresno, CA is the only city in the entire nation to react by having medical benefits increased for themselves. No doubt that is due to the massive discharging of raw sewage taking place, behind felony altering of the city's sewer and water lines. A 45+ yr operation now being tied into the main line - it appears our water is being diverted as the public is told of a "water shortage." A trail of illness, infections, asthma, etc. is being disregarded - no safety precautions or warnings. This is why there are no older records of Fresno and why the city does not stand behind the ones they do have - felony alterations include property lines. Instead of permits or inspections, plat/parcel maps are altered to make it appear that things have always been this way. In other words, Fresno and the nearby cities can expect for MRSA to continue to increase - massive cover-up.

Steven Miller April 19, 2008 at 9:49 PM  

I'm not really sure what you are talking about. 'A trail of illness, infection, asthma, etc,' I'm pretty sure that infection and asthma falls under the category of illness. 'No doubt this is due to the massive discharging,' 'Water shortage,' '45+ year operation,' I do actually have doubt to what you are saying, I have never been effected by any supposed water shortage, and you've been around for 45 years to see this sewage dumping that has continuously occurred? What are the cross streets? I'll go check it out. Also, I'm going to take a wild guess you have not studied the epidemiology of etiology of MRSA-related infections because if you had, I don't believe you would be mentioning anything about your conspiracy theory related to sewage dumping because I have worked in a hospital here and a hospital in the bay area and I have personally observed MRSA infections at both sites. MRSA infections are commonly contracted post-operatively, with numerous factors involved, including contraction history, # of antibiotics used in the past, individual immune response, race, gender, etc......... I am also guessing that surgeons aren't using tap water derived from 'supposedly' contaminated water supplies to wash wound sites during surgery. I don't know if you've taken chemistry 170 but if you have, you would know that the FDA (are they a part of the 'cover-up'?) requires that municipal water supplies undergo more extensive testing than some water-bottle companies. Although I have not personally seen data on whatever it is that you are talking about, I would likely bet large sums of money that it has minimal to do with what Trevor is discussing.

Marla April 20, 2008 at 12:04 AM  

I have read several articles stating that MRSA breeds in raw sewage.
I have read that deadly bacteria, including pathogens from MRSA are airborne as well as waterborne.
I have read that MRSA has colonized in 25-33% of our nasal cavities, the result of breathing.
I have read that a portion of the 25-33% of the above, are infected with MRSA and can spread it by sneezing/coughing.
There is an ongoing discharging of raw sewage that follows the felony altering of water/sewer lines in Fresno, CA. The accompanying illness and infections are being disregarded / covered up. If I am incorrect about this mode of contracting or transmitting MRSA, then I apologize. But from what I have personally witnessed and read about, we have a problem in Fresno that appears to be contributing to the outbreak.

Steven Miller April 20, 2008 at 4:13 PM  

The articles I am concerned about seeing are the ones regarding this supposed discharge into Fresno sewers. Even if you have personally witnessed workers dumping radioactive waste into the sewers, I probably wouldn't believe you, nothing personal, I simply require proof. So please, show me a valid source regarding the dumping into sewage, and I might not be so quick to dismiss anything you say.

Marla April 20, 2008 at 10:28 PM  

Come see my web page (MySpace requires free registration)
Check out my first blog with diagrams, dated 2/5/08.

Anonymous April 21, 2008 at 10:37 AM  

People are crazy!!! Steven Miller will put you in your place!

Marla April 21, 2008 at 11:59 AM  

Who knows ..... Steven Miller may finally be the one who is capable of seeing beyond the smokescreen.

Trevor April 21, 2008 at 1:11 PM  

Please provide some of your so called resources that you say backs up what you are saying.

Marla April 22, 2008 at 12:30 PM  

I knew (even employed on 2 occasions) the ringleader for 25 yrs. (He is a former employee of the City of Fresno - his current insurance clients include water agencies.) He gave me hints about his "water project" but I did not "get it" until being targeted. I saw what he and his entourage did (inc city risk analyst.) I even saw the unauthorized group altering the utility pole to line back up to the illegally altered structures - PG&E has no record of this, yet there are witnesses to this. With all the lines/cables on the ground, I was ordered NOT to contact PG&E, which resulted in an additonal $900 to my bill that month. City records verify what is taking place - including the altered records in an attempt to cover it up. Had I not seen the same pattern done to countless others, or known of his ongoing obsession with development at Friant, or talk of diverting our water, I would have never figured it out. 45+ yrs has been put into this - but it is so beautifully covered up, no one sees or suspects anything.

Steven Miller April 23, 2008 at 12:03 AM  

My advice to Trevor and anyone else in the class, although there will be temptation from a subsequent posting from 'Marla,' my advice is do not respond to this or any other thread where this user posts.

Anonymous April 24, 2008 at 1:37 AM  

That's right kids - take heed in today's lesson: Hide from reality by burying your head in the sand.
(Pssst .... wouldn't it have looked a little better if you simply deleted the posts?)


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