For what I've seen so far, MRSA can be only resistant to meticillin but still be senible to other drugs, Linezolid and Vancomycin for instance (but also Gentamicyn and Clindamicyn). It is quite common in hospitalized patients or some other assistance residence/retirement home, here in north of Italy it reaches almost the 30% of the isolates with S.aureus. It is quite dangerous cause it can spread easely from colonization to infection if the patient gets compromised for some healty reasons, but is not as dangerous as a MDR one. It is far less common but if it occures is really hard to control. It can get resistance even to other drugs making the Vancomycin the only alternative, and in some cases in different countries it can be resistant even to vancomycin. At that point even if it's "rare" it is really dangerous. More pathogenic? Probably MDR is, yes, but as I said it's far less frequent. Also the pathogenicity is related to other things, like toxins production (PV and others)  which is not necessarily related with the resistances (fortunatly most of the time panton-valentine leukocidin positive S.aureus are all sensible strain) but still more dangerous for the invasiveness.

All this, of course, makes more sense if you relate it with the epidemiology of your place. Check on what drugs are usually used, with what frequence and if suitably or not. A bad antibiotic use is the first cause of MDR and MRSA occuring.

Hoping to be helpful.

Greetings,

Ramona.

http://www.ncbi.nlm.nih.gov/pubmed/17234914

As the name implies, the main difference between methicillin sensitive (MSSA) and methicillin resistant Staph aureus (MRSA) is its sensitivity to beta lactams. There is no such thing as multidrug resistant Staph aureus (as opposed to MDR gram negative infections, such as ESBL, CRE, etc). MSSA will have resistance patterns and can in fact be resistant to quite a number of antibiotics but as long as it is sensitive to methicillin it will still be called MSSA. 

Both organisms are highly pathogenic and consequences can be seen in bacteraemias (example, infective endocarditis and discovertebral osteomyelitis). Both organisms can produce toxins and make them more virulent (the main example that has been cited above is PVL).

As to which one is more pathogenic, it really depends on a number of factors, including the host and environmental factors. MRSA bacteraemias are generally associated with a higher mortality than MSSA bacteraemias and I am attaching an article from Clinical Infectious Diseases to this effect. However, one cannot ignore MSSA bacteraemias which also carries significant mortality. In Scotland, we have an algorithm of how to investigate and treat MSSA bacteraemias and I am attaching an article I co-authored which depicts this algorithm.

Hope this helps.

Ivan

Article Invasive Staphylococcus aureus infections in diabetes mellitus

Both organisms are highly pathogenic ,MRSA consider a problem in World wide and MRSA can be MultiDrug resistance to different Antibiotics.