Super Bug

Super Bug: Looking at the Evolution of MRSA: 

Tali Goldojarb Bio 7 Fall 2011 December 1, 2011 Super Bug: Looking at the Evolution of MRSA

What is MRSA?: 

What is MRSA? MRSA is methicillin -resistant Staphylococcus aureus . Most antibiotics do not affect it. What is methicillin ? Methicillin was an antibiotic used when penicillin was ineffective. Methicillin is no longer used

Why is it a Problem?: 

Why is it a Problem? MRSA is a problem because it cannot be cured It is a growing problem in hospitals and nursing homes ( ie sterile places) It is now becoming of concern on a community level Our ambitions to be increasingly sterile is a catalyst

Evolution of MRSA: 

Evolution of MRSA There is no clear, definite origin of MRSA Several sources cited different times and locations for the initial discovery There are several different magnitudes of MRSA as well as strains This will focus on a paper by Enright et al. that used sequence typing (ST) and an algorithm called BURST which looked at the allelic profiles of 912 MRSA variations and made a denrdogram based on that. These samples varied in their magnitudes as well as geographic location A dendrogram is kind of like a phylogenetic tree that shows relationships and ancestry.

Evolution of MRSA: 

Evolution of MRSA These are the current classifications of the various MRSA magnitudes MSSA: methicillin -sensitive S. aureus MRSA: methicillin -resistant S. aureus EMRSA: epidemic methicillin -resistant S. aureus GISA: glycidopeptide -intermediate S. aureus From these there are various strains based on genotype It is hypothesized that a successful strain of MSSA gave rise to MRSA when it inherited the mecA gene which controls the resistance. This then gave rise to the two other forms.

Results: 

Results It was found that the strains were all distantly related. One specific strain, ST8, appeared to give rise to others ST250. It seems as though ST8 is from the earlier generations though not the original MRSA itself. It identified a subgroup of significance due to the fact that almost all MRSA isolates from it could be traced back to the same time period, subgroup, and ancestor ( Enright et al. 7691). Other dendrograms that were made, although from more localized samples geogrphically , showed similar patterns

Conclusion: 

Conclusion It is still unclear as to the origin of MRSA Inferences are made based on allelic profiles There have been some findings supporting common ancestry between groups, but not as a whole MRSA is categorized based on their genetic markers that control the mecA gene, the resistance gene. MRSA is becoming a growing problem, especially in nursing homes and hospitals There is no cure for MRSA but there has been success in containing outbreaks

References: 

References Asada, K., Inaba , Y., Tateda -Suzuki, I., Kuwahara -Arai, K., Ito, T., And Hiramatsu , K. (1995). Evolution and resistance expression of MRSA. Evaluation of beta- lactam antibiotics against a set of isogenic strains with different types of phentypic expression. Acta Biochimica Polonica , 42, 517-524. http://www.ncbi.nlm.nih.gov/pubmed/8852342 Crisostomo , M.I., Wseth , H., Tomasz, A., Chung, M., Oliveira, D.C., de Lencastre , H. (2001) The evolution of methicillin resistance Staphylococcus aureus : similarity of genetic backgrounds in historically early methicillin susceptible and –resistant isolates and contemporary epidemic clones. PNAS , 98, 9865-9870. Doi:www.pnas.orgycgiydoiy10.1073ypnas.161272898 Enright , M.C., Robinson, D.A., Randle, G., Fell, E.J., Grundmann , H., Spratt, B. (2002) The evolutionary history of methicillin -resistant Staphylococcus aureus (MRSA). PNAS , 99, 7687-7692. www.pnas.org_cgi_doi_10.1073_pnas.122108599 Nubel , U., Dordel , J., Kurt, K., Strommenger , B., Westh , H., Shukla , S.K., Zemlickova , H., Lebiois , R., Wirth, T., Jombart , T., Balloux , F., Witte, W. (2010) A timescale for evolution, population expansion, and spatial spread of an emerging clone of methicillin -resistant Staphylococcus aureus . Plos Pathogens , 6, 1-12. http://www.plospathogens.org/article/info%3Adoi/10.1371/journal.ppat.1000855 Robinson, D.A., Enright , M.C. (2004) Multilocus sequence typing and the evolution of methicillin -resistant Staphylococcus aureus . Clinical Microbiology and Infection , 10, 92-97. http://www.ncbi.nlm.nih.gov/pubmed/14759234