Lecture Notes on the
Staphylococci
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.:
- Staphylococcus
aureus
- 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
syndrome)
- 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
Staph.
- Many strains of Staphylococcus
aureus are
resistant to antibiotics. Methicillin resistant Staphylococcus aureus (MRSA) is
particularly threatening.
- Staphylococcus
aureus is
mannitol (+), coagulase (+), often beta-hemolytic and sensitive
to novobiocin.
- Staphylococcus
epidermidis
- Causes bacteremia, intravenous catheter
infections, CSF shunt infections, endocarditis, urinary tract
infections.
- Staphylococcus
epidermidis is
mannitol (-), coagulase (-) and novobiocin sensitive.
- Staphylococcus
saprophyticus
- Second most common cause of cystitis, after E.
coli, in young
women.
- Staphylococcus
saprophyticus is
mannitol (+ or -), coagulase (-) and novobiocin
resistant.
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
aureus on
MSA?
- What does the coagulase test measure?
- How might coagulase be important to Staphylococcus
aureus?
- What is serum? What is plasma? Which is used in
the coagulase test?