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Staphylococcal infections are caused by
species of the genus Staphylococcus.
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These gram-positive cocci colonize the
skin and anterior nasal vestibule of children and adults, and the
umbilicus, stool and perineum of neonates.
Three species are pathogenic in humans :
Staphylococcus aureus , Staphylococcus
epidermidis and Staphylococcus saprophyticus.
About 20% to 40% of adults are nasal
carriers of S. aureus, and many become carriers while in the hospital,
perhaps because medical personnel are more frequent carriers than the
general population.
Large numbers of staphylococci are
required for infection, and patients with more than 1000000 organisms
per milliliter of nasal fluid tend to infect themselves and spread the
staphylococci to others.
Most staphylococcal infections are
caused by S. aureus , which grows especially well on skin and mucous
membranes but can infect any part of the body.
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S. aureus causes a wide variety of
suppurative diseases, including among others
abscesses of the skin (impetigo, boils, styes,
carbuncles, breast abscesses, botryomycosis), abscesses of bone (osteomyelitis)
and other deep organs, infections of burns and surgical and other
wounds, infections of the upper and lower respiratory tracts (pharyngitis,
bronchopneumonia
, empyema), purulent arthritis, septicemia, acute
endocarditis and meningitis.
S. aureus
releases several exotoxins : enterotoxins, (enteritis and food
poisoning) ; exfoliative toxin (exfoliative skin disease); and
pyrogenic toxin (toxic shock syndrome).
S.
epidermidis causes only minor skin lesions, except in patients who
have surgically inserted prostheses or are immunodeficient.
S.
saprophyticus is responsible for bladder infections.
S. aureus, named for its golden-yellow
colonies on blood agar, produces coagulase (i.e., “coagulase-positive”).
S. epidermidis and S. saprophyticus,
which form white colonies on blood agar (hence the former name S.
albus), are coagulase-negative.
Staphylococci are spherical and about 1
micrometer in diameter, a size that usually requires an oil immersion
lens for identification in tissue sections.
In liquid culture medium as well in
tissue, staphylococci grow in characteristic clusters, because they
divide in successive perpendicular planes and daughter cells do not
separate.
These clusters distinguish
staphylococci from streptococci, which grow in chains.
Many strains of staphylococci have
developed resistance to penicillin and other antibiotics.
Penicillin resistance is caused by
plasmid-mediated production of penicillinase.
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INFECTION OF THE SKIN:
Staphylococcal infections cause a variety of cutaneous and systemic
infections, including impetigo, furuncle, subcutaneous abscess,
staphylococcal scalded skin syndrome , toxic shock syndrome and
neonatal toxic shock syndrome-like exanthematous disease, in
association with microbial virulence factors.
Carbuncles
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Furuncles (boils): click here
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Impetigo: click here ;
Toxic Shock Syndrome: click here .
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Skin infections- (Histopathological
patterns)
Staphylococcal
scalded skin syndrome:
The exfoliative toxin of S.
aureus causes the
“scalded skin
syndrome”, which
usually occurs in neonates, infants, and young children, typically in
the aftermath of conjunctivitis or minor staphylococcal
infection. A painful, brick-red rash begins on the face, neck, axilla,
and groin, and then becomes generalized. The rash leads to blisters or
bullae, and the upper dermis is shed in large sheets.
Breast abscesses
usually arise within a few weeks after
delivery, when staphylococci are transmitted from an infant with
neonatal sepsis to the skin glands in the breasts of the nursing
mother. The disease may be precipitated by the stasis of milk after
weaning or missed feeding.
Botryomycosis
(a
misnomer) is a chronic bacterial infection that may be caused by
staphylococci (as well as by
Streptococci
), E. coli, and other common bacteria).
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Botryomycosis patients as an indurated
fibrotic mass with draining sinuses and grains in a purulent exudates
and in tissue sections.
Microscopically, these grains cannot be
distinguished from those of
actinomycosis
or a
mycetoma
. Microcolonies of staphylococci in clusters within the grain are
surrounded by an amorphous eosinophilic coating (“Splendore-Hoeppli
phenomenon”).
Botryomycosis resists antibiotic
therapy, probably because the fibrosis and compactness of the grains
prevents adequate levels of drug from reaching the bacteria. The
lesion should be totally excised.
ABSCESSES OF BONE (OSTEOMYELITIS):
Acute staphylococcal osteomyelitis most
commonly afflicts boys between 3 to 10 years of age, most of whom have
a history of infection or trauma. The bones of the legs are involved
in most patients. Many patients have an underlying bacteremia (S.
aureus) with systemic symptoms. Osteomyelitis may become chronic if
not properly treated.
Adults after 50 years of age are more
frequently afflicted with osteomyelitis of the vertebra. The onset of
localized back pain is usually abrupt, but may follow staphylococcal
infection of the skin or urinary tract, prostatic surgery, infected
abortion, puerperal infection, or a surgical procedure such as pinning
a fracture.
INFECTIONS OF
BURNS AND SURGICAL WOUNDS:
Burns and surgical wounds may become
infected with S. aureus from the patient’s own nasal carriage or from
medical personnel. The appearance of visible pus in the wound depends
on the interaction of bacteria, host factors, and foreign bodies.
Neonates, the elderly, the malnourished, and the obese all have
increased susceptibility.
INFECTIONS OF THE UPPER AND LOWER
RESPIRATORY TRACT (PHARYNGITIS
BRONCHOPNEUMONIA AND EMPYEMA)
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Bronchopneumonia
Staphylococcal infections of the
respiratory tract most commonly occurs in infants less than 2 years of
age, and especially in those under 2 months.
They usually occur in winter, when
viral respiratory diseases are prevalent.
The child often has an underlying
staphylococcal skin infection. Infection of the respiratory tract is
mild at first, but suddenly worsens.
Characteristic features include fever
and spasms of dry coughing, followed by marked tachypnea with
expiratory grunting, sternal retraction, cyanosis, progressive
lethargy, and shock.
There are ulcers of the upper airway
and scattered foci of pneumonia.
Other common complications are pleural
effusion, empyema, and pneumothorax.
Radiological examination of the chest
show patchy infiltrates, which progress rapidly. Gram-positive cocci
are seen in aspirated tracheal or pleural fluid, which is often
bloody.
In adults, staphylococcal pneumonia may
follow viral influenza, a disease that destroyed the ciliated surface
epithelium and leaves the bronchial surface vulnerable to secondary
infections.
Patients with chronic lung disease and
chronic heart disease (especially rheumatic valve disease) are also at
increased risk for staphylococcal pneumonia.
ACUTE AND CHRONIC BACTERIAL ARTHRITIS:
S. aureus is the causative
organism in half of all cases of septic arthritis. Most of those who
have the disease are adults, 50 to 70 years old, and usually only a
single joint is involved.
Rheumatoid arthritis and steroid
therapy are common predisposing conditions.
The acute onset of staphylococcal
arthritis is marked by severe, throbbing pain, often worse at night,
which is accompanied by shaking chills and fever.
Acute staphylococcal arthritis may be
confused with an acute episode of rheumatoid arthritis.
SEPTICEMIA:
Septicemia with S. aureus
occurs in patients with lowered resistance who are in the hospital for
other diseases or conditions.
Some having underlying staphylococcal
infections (for example, osteomyelitis or septic arthritis), some have
had surgery (especially transurethral resection of the prostate), and
some have infections from an indwelling intravenous catheter.
Staphylococcal septicemia is associated
with the common symptoms of bacteremia, such as shaking chills and
fever.
Miliary abscesses and staphylococcal
endocarditis are serious complications.
BACTERIAL
ENDOCARDITIS:
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Infective Endocarditis
Acute and subacute bacterial
endocarditis are complications of septicemia caused by S. aureus (as
well as by S. epidermidis).
Endocarditis may develop spontaneously
on normal valves or on valves damaged by rheumatic fever.
It may also follow insertion of
prosthetic valves or other intracardiac surgery.
Those with intravenous heroin addiction
also have an increased risk of endocarditis from infection with S.
aureus.
In addition to the symptoms of
septicemia, a heart murmur is usual, with or without evidence of
embolization to other organs.
MENINGITIS:
Staphylococcal meningitis is a
complication of surgical procedures on the central nervous system.
Infections of shunts in the brain may be caused by S. aureus or S.
epidermidis. Although staphylococcal meningitis is often not
clinically evident, it may be found at autopsy in patients with
septicemia or endocarditis.
STAPHYLOCOCCAL
FOOD POISONING:
Staphylococcal food poisoning
is caused by the ingestion of preformed staphyloccal enterotoxin
in prepared food.
This commonly involves food eaten in a restaurant (not
industrially processed food), especially unrefrigerated meats, milk,
or custard and other milk products.
The food (not the patient’s excreta) must be tested for
staphylococci. Food that contains more than 100000000 staphylococci
per gram contains enough enterotoxin to cause food poisoning. S.
aureus has caused more than half of the food poisoning epidemics in
which causative agent has been identified.
Thus, the incidence is much higher than that of
epidemics caused by
Salmonella
,
Clostridium Perfringens
,
Shigella
or Streptococcus.
At least six enterotoxins are produced by some of the
coagulase-positive strains of S. aureus, and enterotoxins are also
produced by by a few coagulase-negative strains. Enterotoxins are
resistant to heat and withstand cooking for 20 to 60 minutes.
Usually, nausea and vomiting begin within a few hours
of ingesting the toxin.
In some cases, however, diarrhea and abdominal
discomfort are the only symptoms.
Patients with more severe food poisoning have bloody
mucus in the vomitus and stools, as well as muscle cramps, headache,
and sweating.
The acute phase commonly lasts 4 to 6 hours, and
recovery is complete within 1 or 2 days.
STAPHYLOCOCCAL GASTROENTERITIS:
Acute
gastroenteritis is characterized by histologic changes in both stamach
and small intestine.
Within 2 hours of
the introduction of enterotoxin, there is a neutrophilic exudates in
the stomach.
By 6 hours the
gastric mucosal cells are depleted of mucus, and the mucosa is covered
by a mucopurulent exudates.
The inflammatory
reaction in the stomach subsides within 24 hours.
In the small
intestine, by 4 hours there is focal degeneration of the epithelium of
the villi, elongation of crypts, and infiltration of neutrophils in
the lamina propria.
After 12 hours
regression begins, and by 48 to 72 hours the mucosa appears normal.
INFECTIONS WITH S.
EPIDERMIDIS:
S. epidermidis, an opportunistic
pathogen, causes only minor skin lesions, except in patients
undergoing surgery for insertion of prosthetic devices and patients
with impaired immune systems.
In healthy persons, the organism
usually resides on the skin of the axilla, head, nose, and limbs.
Infections with S. epidermidis are
often associated with foreign bodies, such as prosthetic valves,
shunts for cerebrospinal fluid, joint prostheses.
Prosthetic valvular endocarditis, for
example, may be caused by contaminated coronary suction lines during
the insertion of prosthetic valves, with subsequent infection of
repaired areas of the heart and prosthetic valve.
Deep sternal wound infections may
result, often in the first few weeks after the operation.
S. epidermidis can be the direct cause
(without foreign body) of bladder infections, endocarditis, and other
infections.
Strains of S. epidermidis are
frequently resistant to penicillin and other
antimicrobial
agents, and infected prostheses and grafted vessels are often need to
be replaced.
INFECTIONS WITH S. SAPROPHYTICUS
S.
saprophyticus resembles S. epidermidis, but biochemical assays and the
pattern of drug resistance distinguish the two. For reasons unknown,
S. saprophyticus causes bladder infections, primarily in young women.
Strains of S. saprophyticus are sensitive to many antibiotics.
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