aureus and Coagulase-Negative Staphylococci
cocci typicallyarranged in irregular and often grape-like clusters.
- Facultative anaerobes (def).
- Staphylococcus aureus is
the most pathogenic species and is implicated in a variety of infections.
- Clinically common species of staphylococci
other than S. aureus are often referred to as coagulase-negative staphylococci.
These staphylococci are normal flora of the skin and, as such, frequently
act as opportunistic pathogens, especially in the compromised host.
- Normal flora of human skin and
- Approximately 30% of adults and
most children are healthy nasal carriers of S. aureus. In the majority
of S. aureus infections the source of the organism is either the healthy
nasal carrier or contact with an abscess from an infected individual.
The portal of entry is usually the skin.
- Coagulase-negative staphylococci
are normal flora of the skin.
- Staphylococcus aureus causes
pus-filled inflammatory lesions known as abscesses. Depending on the location
and extent of tissue involvement, the infection is referred to as impetigo
(thin walled-vesicles on the skin that become pustular and encrusted), folliculitis
(an infected hair follicle), furuncules or boils (inflammation of the
subcutaneous layers of the skin), or carbuncles (multiple infection sites
with inflammation involving the skin and deeper connective tissue). It may
also spread through soft tissues and cause cellulitis. S. aureus frequently
causes infections of accidental wounds and postoperative wounds, although
it can also infect healthy intact skin.
- Less commonly, S. aureus
may escape from the local lesion and spread through the blood to other body
areas, causing a variety of systemic infections that may involve every system
and organ. Such systemic infections include septicemia (def),
septic arthritis (def),
and osteomyelitis (def),
as well as abscesses in the lungs, spleen, liver, and kidneys.
- S. aureus pneumonia
may also be a secondary respiratory complication of viral infections such
as measles and influenza.
- S. aureus is frequently
introduced into food by way of abscesses or the nasal cavity of food handlers.
If it is allowed to grow and produces an enterotoxin (def),
it can cause staphylococcal food poisoning.
- Some strains also produce TSST-1
(toxic shock syndrome toxin-1) and cause toxic shock syndrome (def),
usually associated with tampon use or wounds.
- Some strains also produce exfoliatin,
an exotoxin that causes scalded skin syndrome (def),
an infection usually seen in infants and young children.
- Coagulase-negative S.
saprophyticus is a relatively common cause of urinary tract infections,
especially in young, sexually active women, but is seldom isolated from other
- The great majority of infections
caused by other coagulase-negative staphylococci, including S. epidermidis,
S. haemolyticus, and S. hominis, are associated with intravascular devices
(prosthetic heart valves and intra-arterial or intravenous lines) and
shunts. Also quite common are infections of prosthetic joints, wound infections,
associated with foreign bodies, and endocarditis (def).
Infection , by Thomas Herchline, MD, Associate Professor, Department of
Internal Medicine, Division of Infectious Disease, Wright State University.
by Elizabeth P. Baorto, MD, MPH, Director, Division of Pediatric Infectious
Diseases, Atlantic Health System; and David
Baorto, MD, PhD, Medical Knowledge Engineer, Department of Medical Informatics,
Columbia University Medical Center.
Kaiser's Microbiology Home Page
Copyright © Gary E. Kaiser
All Rights Reserved
Updated: Feb. 15, 2005
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