Staphylococci are common residents of the skin, but some species and strains can cause infections ranging from superficial pimples to serious disease. This lesson focuses on Staphylococcus aureus, less virulent staphylococci, infection patterns, resistance, and laboratory identification.
Staphylococcus epidermidis and S. hominis commonly inhabit healthy skin. S. aureus may also colonize healthy skin and the nose, but pathogenic strains can cause skin and systemic infections. Asymptomatic nasal carriers can transfer the bacteria from their noses to their hands, objects, and other people. Skin-to-skin contact and contaminated fomites contribute to its spread.
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What is MRSA?
MRSA is methicillin-resistant *Staphylococcus aureus*. It may be acquired in health-care settings or in the community and is resistant to certain antibiotics.
Why are many *S. aureus* infections purulent?
Some strains produce leukocidins that kill white blood cells. The resulting cellular debris and inflammatory material contribute to pus.
What distinguishes a carbuncle from a furuncle?
A furuncle is a deeper boil, while a carbuncle is a deeper lesion formed when multiple boils join together. Carbuncles are more likely to cause systemic symptoms.
What does coagulase testing help determine?
It helps distinguish coagulase-positive staphylococci, commonly *S. aureus*, from coagulase-negative species such as *S. epidermidis*.
How can *S. epidermidis* cause a serious infection?
It can be transferred to a catheter, prosthesis, or other medical device and enter internal tissues when the device bypasses the skin barrier.
Quiz questions
Which pigments can give some *Pseudomonas aeruginosa* wound drainage a blue-green color?Answer: Pyocyanin and pyoverdin
What can eyelid scarring from chronic trachoma cause?Answer: Inward turning of the eyelashes, called trichiasis
What treatment is generally required for necrotizing fasciitis?Answer: Urgent surgical debridement with intravenous antibiotics
Which bacterium causes gonococcal ophthalmia in newborns?Answer: *Neisseria gonorrhoeae*
What are biofilm persister cells?Answer: Dormant cells that can survive exposures lethal to actively growing cells
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.