Download Gram Positive Bacteria

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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
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
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.
Streptococcal Diseases
Streptococcus pyogenes
Streptococcus pyogenes
Pyogenes means pus producing
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One of the most important pathogens
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Gram positive cocci in chains
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Lancefield Serological Group A
Beta Hemolytic on blood agar
Gram Stain of S. pyogenes
Hemolysis on Blood Agar Plates
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Alpha hemolysis-organism excretes hemolysins
which partially break down rbc (incomplete
hemolysis) thus a greenish zone appears around
colony. S. pneumoniae
Beta hemolysis-organisms excretes potent hemoysins
which completely lyse rbc (complete hemolysis) thus
a clear zone appears around colony. S. pyogenes
S.pyogenes
S. pneumonia
Beta hemolysis
Alpha hemolysis
Diseases caused by S. pyogenes
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Strep throat
Impetigo
Erysipelas
Cellulitis
Invasive Strep A infections
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Necrotizing fasciitis
Myositis
Toxic shock-like syndrome
Erysipelas
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Acute infection and imflammation of the
dermal layer of skin.
Painful red patches which enlarge and thicken
Treatment -penicillin or erythromycin
Erysipelas
Strep Throat
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Most common of all Strep diseases
Spread by saliva or nasal secretions
Incubation period 2-4 days
Sore throat, slight fever (101)
Important to treat immediately to avoid post
strep diseases
Diagnosis and treatment of Strep Throat
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Tell tale symptoms are slight fever associated
with sore throat and visual of pus in back of
throat
Quick diagnostic tests (Molecular) available
but must be confirmed by throat swab and
growth on blood agar (beta hemolysis)
Diagnosis and treatment of Strep Throat
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If the strain of S. pyogenes is lysogenic for a
particular phage which expresses an
erythrogenic toxin the result is Scarlet fever
Rash appears and characteristic is the
strawberry colored tongue
Strawberry Tongue
Treatment of Strep
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Penicillin G or Erythromycin are drugs of
choice
Although the disease is self-limiting it is
important to treat immediately to avoid post
strep complications
Poststreptococcal diseases
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Rheumatic Fever-autoimmune disease
involving heart valves,joints, nervous system.
Follows a strep throat
Acute glomerulonehritis or Bright’s Diseaseinflamatory disease of renal glomeruli and
structures involved in blood filter of kidney.
Due to deposition of Ag/Ab complexes
Rheumatic Fever
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Most common cause of permanent heart valve
damage in children
Exact cause not yet known but there appears to
be some antibody cross reactivity between the
cell wall of S. pyogenes and heart muscle
Rheumatic Fever
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Diagnosis is based on symptoms and is
difficult
Occurs most frequently between ages of 6 and
15
US it is about 0.05% of pop having strep
infections
100x more frequent in tropical countries
Rheumatic Fever
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Treatment is via salicylates (aspirin
derivatives) and corticosteroids to decrease
inflammation and fever.
Glomerular Nephritis
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Diagnosis based on history of Strep throat and
clinical findings.
Symptoms include fever, malaise,edema,
hypertension and blood or protein in urine
Occurs in 0.5% of those having strep throat.
Glomerular Nephritis
Treatment and Recovery
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Penicillin or erythromycin to eradicate and
residual strep infection
80-90% of cases recover with bed rest lasting
for months
Kidney damage in the remainder is often
permanent resulting in chronic glomerular
nephritis
Streptococcus Pneumonia
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Caused by infection with Streptococcus
pneumoniae (Pneumococci)
Gram positive, alpha hemolytic, not of
lancefield serotype A
Often part of normal flora of respiratory track
and becomes infective once hosts resistance is
lowered. Classified as an endogenous
infection.
Strep Pneumonia
Strep Pneumonia
S. pneumoniae
Alpha hemolysis
Strep pneumonia
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Predisposing factors: upper respiratory viral
infection, diabetes, alcoholism
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60-80% of all pneumonias
Strep Pneumonia
Cause of strep pneumonia
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Primary virulence factor is the capsular
polysaccharide which protects the organism
against phagocytosis
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Pathogenesis is due to rapid growth of bacteria
in alveolar spaces
Symptoms of Strep Pneumonia
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Onset abrupt
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Chest pains
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Chills
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Labored breathing
Diagnosis of Strep pneumonia
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Chest Xray
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Culture and staining
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Biochemical tests of isolated organism
Treatment of Strep Pneumonia
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Typically treated with Penicillin G cefotaxime,
oflaxacin or for those allergic to penicillins can
be treated with erythromycin or tetracycline
Pneumococcal vaccine (Pneumovax 23 or Pnuimmune 23) is available for the elderly
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