Pavithra. G. Palan.
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Staphylococci are gram positive cocci,
Occur in grape like clusters,
In Greek; staphyle - Bunch of grapes
Kokkus - Berry
CLASSIFICATION:
A) Based on coagulase production:
1. Coagulase positive: Eg- S. aureus
2. Coagulase negative: Eg- S. epidermidis
S. saprophyticus
B) Based on pathogenicity:
1. Common pathogen: Eg- S. aureus
2. Opportunistic pathogens: Eg- S. epidermidis
S. saprophyticus
3. Non pathogen: Eg- S. homonis
STAPHYLOCOCCUS AUREUS
MORPHOLOGY:
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These are spherical
cocci.
Approximately 1μm in
diameter.
Arranged
characteristically in
grape like clusters.
They are non motile
and non sporing.
A few strains possess
capsules.
CULTURE:
Media used :i) Non selective media: Nutrient agar,
Blood agar,
MacConkey’s agar.
ii) Selective media: Salt-milk agar,
Ludlam’s medium
Cultural Characteristics:
i) On nutrient agar- The colonies are large, circular,
convex, smooth, shiny, opaque and easily
emulsifiable. Most strains produce golden yellow
pigments.
ii) On MacConkey’s agar- The colonies are small
& pink in colour.
iii) On blood agar- Most strains produce βhaemolytic colonies.
Biochemical reactions:
1) Catalase test- Positive.
2) Coagulase testi) Slide coagulase test- Positive.
ii) Tube coagulase test- Positive.
SLIDE COAGULASE TEST
TUBE COAGULASE TEST
3) Reduces nitrate to nitrite.
4) Ferments mannitol anaerobically with acid only.
5) Urea hydrolysis test- Positive.
6) Gelatin liquefaction test- Positive.
7) Produces Lipase.
8) Produces Phosphatase.
9) Produces Thermostable nuclease.
PATHOGENICITY:
Source of infection:
A) Exogenous: patients or carriers
B) Endogenous: From colonized site
Mode of transmission:
A) Contact: direct or indirect( through fomites)
B) Inhalation of air borne droplets
Virulence factors:
These include
A) Cell associated factors
B) Extracellular factors
A) CELL ASSOCIATED FACTORS:
a) Cell associated polymers
b) Cell surface proteins
a) CELL ASSOCIATED POLYMERS
1. Cell wall polysaccharide
2. Teichoic acid
3. Capsular polysaccharide
b) CELL SURFACE PROTEINS:
1. Protein A
2. Clumping factor (bound coagulase)
Structure of Staphylococcal cell wall
B) EXTRACELLULAR FACTORS
a) Enzymes
b) Toxins
a) Enzymes:
1. Free coagulase
2. Catalase
3. Lipase
4. Hyaluronidase
5. DNAase
6. Thermonuclease
7. Staphylokinase (Fibrinolysin)
8. Phosphatase
b) Toxins:
1. Cytolytic toxins
i) Haemolysins
Alpha haemolysin
Beta haemolysin
Gamma haemolysin
Delta haemolysin
ii) Leucocidin (Panton-Valentine toxin)
2. Enterotoxin
3. Toxic shock syndrome toxin (TSST)
4. Exfoliative (epidermolytic toxin)
.
Disease:
Diseases produced by Staphylococcus aureus
is studied under 2 groups:
A) Infections
B) Intoxications
A) INFECTIONS:
Mechanism of pathogenesis:
Cocci gain access to damaged skin, mucosal or
tissue site
Colonize by adhering to cells or extracellular matrix
Evade the host defense mechanisms and multiply
Cause tissue damage
Common Staphylococcal infections are:
1) Skin and soft tissue: Folliculitis, furuncle (boil),
carbuncle, styes, abscess, wound infections,
impetigo, paronychia and less often cellulitis.
Folliculitis
Folliculitis
Furuncle (boil)
Carbuncle
Styes
Abscess
Impetigo
Wound infection
Paronychia
Cellulitis
2) Musculoskeletal: Osteomyelitis, arthritis, bursitis,
pyomyositis.
osteomyelitis
3) Respiratory: Tonsillitis, pharyngitis, sinusitis,
otitis, bronchopneumonia, lung abscess, empyema,
rarely pneumonia.
4) Central nervous system: Abscess, meningitis, intracranial
thrombophlebitis.
5) Endovascular: Bacteremia, septicemia, pyemia,
endocarditis.
Endocarditis
6) Urinary: Urinary tract infection.
B) INTOXICATIOINS:
The disease is caused by the bacterial exotoxins,
which are produced either in the infected host
or preformed in vitro.
There are 3 types1.
2.
3.
Food poisoning
Toxic shock syndrome
Staphylococcal scalded skin syndrome
1) Food poisoning:
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Enterotoxin is responsible for manifestations of
staphylococcal food poisoning.
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Eight types of enterotoxin are currently known, named
A, B, C1-3, D, E, and H.
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It usually occurs when preformed toxin is ingested with
contaminated food.
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The toxin acts directly on the autonomic nervous
system to cause the illness, rather than gut mucosa.
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The common food items responsible are - milk and
milk products, meat, fish and ice cream.
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Source of infection- food handler who is a carrier.
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Incubation period- 2 to 6 hours.
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Clinical symptoms- nausea, vomiting and
diarrhoea.
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The illness is usually self limited, with recovery in
a day or so.
2) Staphylococcal Toxic shock syndrome (STSS):
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STSS is associated with infection of mucosal or
sequestered sites by TSST( formerly known as
enterotoxin type F) producing S.aureus.
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It is fatal multisystem disease presenting with
fever, hypotension, myalgia, vomiting, diarrhoea,
mucosal hyperemia and erythematous rash which
desquamates subsequently.
2 types of STSS known:
i) Menstrual associated STSS: Here colonization of
S.aureus occurs in the vagina of menstruating
woman who uses highly absorbent vaginal
tampons.
ii) Non menstrual associated STSS: Here
colonization of S.aureus occurs in other sites like
surgical wound.
3) Staphylococcal scalded skin syndrome
(SSSS):
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Exfoliative toxin produced by S.aureus is
responsible for this.
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It is a skin disease in which outer layer of
epidermis gets separated from the underlying
tissues.
Types of SSSS:
Severe form
In new born
Milder form
- Ritter’s disease - Pemphigus
neonatorum
In older patients - Toxic epidermal - Bullous
necrolysis
impetigo
Ritter’s disease
Pemphigus neonatorum
Toxic epidermal necrolysis
Bullous impetigo
LAB DIAGNOSIS:
Specimens collected: Depends on the type of infection.
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Suppurative lesion- Pus,
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Respiratory infection- Sputum,
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Bacteremia & septicemia- Blood,
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Food poisoning- Feces, vomit & the remains of suspected
food,
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For the detection of carriers- Nasal swab.
Methods of examination:
I) Direct microscopy:
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Direct microscopy
with Gram stained
smear is useful in case
of pus, where cocci in
clusters are seen.
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This is of no value for
specimen like sputum
where mixed flora are
normally present.
II) Culture:
a) Media used:
b) Cultural Characteristics:
c) Gram staining:
Smears are examined
from the culture plate
and reveals Gram
positive cocci(1μm in
diameter) arranged in
grape like clusters.
d) Biochemical reactions:
III) Antibiotic sensitivity tests done as a guide to
treatment.
IV) Bacteriophage typing is done for
epidemiological purposes.
V) Serological tests are not useful.
TREATMENT:
 Drug resistance is common.
 Benzyl penicillin is the most effective antibiotic,
if the strain is sensitive.
 Cloxacillin or Methicillin is used against
beta-lactamase producing strains.
 Methicillin Resistant Staphylococcus aureus
(MRSA) strains have become common.
 Vancomycin is used in treatment of infections
with MRSA strains.
EPIDEMIOLOGY:
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Staphylococci are primary parasites of human
beings and animals.
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Hospital infections caused by staphylococci
deserve special attention because of their
frequency & they are caused by strains resistant to
various antibiotics.
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Staphylococci are the common cause of
postoperative wound infection and other hospital
cross infections.
PREVENTION:
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Isolation & treatment of MRSA patients.
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Detection of carriers among hospital staff, their
isolation & treatment.
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Avoid indiscriminate usage of antibiotics.
Coagulase Negative Staphylococci( CoNS ):
Two species of coagulase negative
Staphylococci can cause human infections-
1. Staphylococcus epidermidis
2. Staphylococcus saprophyticus
S. Epidermidis:
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It is a common cause of stitch abscesses.
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It has predilection for growth on implanted foreign bodies
such as artificial valves, shunts, intravascular catheters
and prosthetic appliances leading to bacteraemia.
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In persons with structural abnormalities of urinary tract, it
can cause cystitis.
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Endocarditis may be caused, particularly in drug addicts.
S.saprophyticus:
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It causes urinary tract infections, mostly in
sexually active young women.
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The infection is symptomatic and may involve the
upper urinary tract also.
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Men are infected much less often.
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It is one of the few frequently isolated CoNS that
is resistant to Novobiocin.
Distinguishing features of the major species of
staphylococcus
Characters
S.aureus
S.epidermididis
S.saprophyticus
Coagulase
+
-
-
Novobiocin
sensitivity
Sensitive
Sensitive
Resistant
Acid from
mannitol
fermentation
anaerobically
+
-
-
Phosphatase
+
+
-
Novobiocin sensitivity test
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