Lecture Notes on the
The Staphylococci are gram
(+) cocci which appear to be arranged in clusters. These organisms
are salt tolerant and catalase positive.
Three species are important in humans as part of the
normal flora and as pathogens.:
- causes boils, carbuncles, impetigo, abcesses,
postsurgical wounds, pneumonia and osteomyelitis.
- There are several toxin associated pathologies
associated with this organism including:
- toxic epidermal necrosis (scalded skin
- toxic shock syndrome
- food poisoning
- Many of these toxins are Super-Antigens which
can cause the host's T-cells to over-produce interleukin-2
(IL-2) and other cytokines. This overproduction of immune
cytokines is responsible for some of the profound pathology
associated with these staphylococcal toxins
- This organism also has Protein A, a substance
which binds to the Fc part of the antibody molecule.
- Remember that in order for antibodies to be
effective against microorganisms, the antibody must bind to
the organism via the antibody binding site or Fab. This type
of binding allows the Fc region to interact with complement
or macrophages which then work to destroy the microorganism.
Because it binds to antibody the other away around, protein
A sabotages the host's antibody defenses against
- Many strains of Staphylococcus
resistant to antibiotics. Methicillin resistant Staphylococcus aureus (MRSA) is
mannitol (+), coagulase (+), often beta-hemolytic and sensitive
- Causes bacteremia, intravenous catheter
infections, CSF shunt infections, endocarditis, urinary tract
mannitol (-), coagulase (-) and novobiocin sensitive.
- Second most common cause of cystitis, after E.
coli, in young
mannitol (+ or -), coagulase (-) and novobiocin
Questions for Thought..........
- Why is Mannitol Salt Agar considered to be both a
selective and a differential medium?
- What is the biochemistry of the color change that
occurs with Staphylococcus
- What does the coagulase test measure?
- How might coagulase be important to Staphylococcus
- What is serum? What is plasma? Which is used in
the coagulase test?