MRSA Staph Infection Pictures

MRSA and “Usual” Staph Aureus Pictures

It’s impossible to say from staph skin infection pictures, if the cause of infection is MRSA (Methicilin Resistant Staphylococcus Aureus) or an “usual” staph - MSSA (Methicillin Sensitive Staphylococcus Aureus). Even a staph carrier without any symptoms can have MRSA.  Folliculitis, which is usually a mild infection, may also be caused by MRSA or MSSA (folliculitis pictures).

Picture 1. A boil below the knee, caused by MRSA
(source: phil.cdc.gov)

 Pictures obtained by a light or electron microscope can’t help in distinguishing between MRSA and usual staph.

Picture 2. Staph aureus under the light microscope, magnified about 100x
source phil.cdc.gov

Picture 3. Cluster of MRSA bacteria as seen under the electron microscope
 (source phil.cdc.gov )

MRSA can be distinguished from MSSA by:

1. Antibiotic susceptibility test: an inhibitory zone (no bacteria growth) is seen around the methicillin (today oxacillin is used) disc put onto a staph colony, if a strain of staphylococci bacteria is methicillin sensitive. If bacteria are methicillin resistant, no inhibitory zone around the disc is seen (picture 4).

Picture 4. The growth of Staphylococcus aureus bacteria was inhibited by some antibiotics
, but not by Oxacillin (disc in upper right part)
, which is nowadays used to determine MRSA instead of methicillin
(source: gold.aecom.yu.edu )

Picture 5. Detail from picture 4.: oxacillin doesn’t suppress staphylococcal growth
(no inhibitory zone is seen around the disc) 

2. PCR (Polymerase Chain Reaction) (see lab tests for staph)

Picture of MRSA after PCR and chromatography