Question

The commonest organism causing cellulitis is:

• A. Streptococcus pyogenes
• B. Streptococcus faecalis
• C. Streptococcus viridans
• D. Microaerophilic streptococci

Hint:

Streptococcus pyogenes is the classic cause of non-purulent cellulitis.

Answer 1

The Correct Option is A

The question asks for the germ most often responsible for cellulitis, a spreading skin and soft tissue infection without a clear pus pocket.

1. Streptococcus pyogenes: This is group A streptococcus, well known for spreading fast through tissue planes because of the enzymes it produces. It is the organism most commonly blamed for typical cellulitis.
2. Streptococcus faecalis: Now classed as Enterococcus faecalis, this organism is more linked to urinary tract, biliary and intra-abdominal infections, not the usual cause of skin cellulitis.
3. Streptococcus viridans: This group lives normally in the mouth and is far better known for causing infective endocarditis and dental abscesses than skin cellulitis.
4. Microaerophilic streptococci: These organisms are typically part of mixed infections in low oxygen wounds, such as synergistic gangrene, rather than being the leading cause of straightforward cellulitis.

Among the four choices, only Streptococcus pyogenes fits the profile of the classic organism causing cellulitis.

Let's summarize:

• Cellulitis without abscess is most often caused by beta hemolytic streptococci.
• Streptococcus pyogenes, group A strep, is the single most common organism.
• The other three streptococcal species are linked to different infections, not typical cellulitis.

So the commonest organism causing cellulitis is Streptococcus pyogenes.