ZaidKhalid MBBS220
Gram Positive Bacteria of Medical Importance
Intro on Gram Positive Bacteria
1. Has thick, multilayered cell wall composed of peptidoglycan
2. Peptidoglycan is important for
a. Maintaining the structure of cell
b. Replication
c. Survival of bacteria at hostile environments
3. Other components of cell wall
a. Techoic acid
i. Water soluble
ii. Covalently linked to peptidoglycan
iii. Essential for cell viability
iv. Important factors in virulence
b. Lipotechoic acid
i. Have fatty acid
ii. Anchored to the plasma membrane
iii. Common surface antigens to distinguish bacterial serotypes
iv. Promote attachment to other bacteria or mammalian cell receptors
c. Complex polysaccharides
i. Also called as C polysaccharides
ZaidKhalid MBBS220
COCCUS
2. Chains
a. Streptococcus
These two type can be differentiated thru CATALASE TEST
1. POSITIVE=STAPHYLOCOCCUS
2. NEGATIVE=STREPTOCOCCUS
Aerobes/Facultative Anaerobes
Categorized based on the arrangement
1. Cluster
a. Staphylococcus aureus
b. Staphylococcus epidermidis
c. Staphylococcus saprophyticus
b. Negative = need to be followed by Novobiocin test
2. Novobiocin test
a. Sensitive =staphylococcus epidemidis
b. Resistant=staphylococcus saprophyticus
Staphylococcus (arranged in clusters)
Identification of staphylococcus
1. Coagulase test
a. Positive = staphylococcus aureus
Name of bacteria
Staphylococcus
aurieus
1. Normal flora
a. Skin
b. Mucosal
layer
2. Presence at
anterior nares
(50-75% of
healthy
individuals)
Lab Characteristics
Virulence factors
Clinical diseases
Treatment
1. Produces golden
colony
a. Orange to
white
2. Positive in both
a. Catalase test
b. Coagulase test
3. Selective media
a. 7.5% NaCl
b. Mannitol salt
agar
1. Capsule
a. Inhibits
i. Chemotaxis
ii. Phagocytosis
2. Peptidoglycan
a. Provides osmotic stability
b. Stimulates the production
of endogenous
pyrogen/causing fever (like
endotoxin)
3. Protein A
a. Inhibit antibody mediated
clearance
b. Binds to IgG Fc receptor
4. Toxins
a. Exfoliative toxins
i. Splits IC bridges at SG of
epidermis
b. Enterotoxins
i. Superantigens, promotes
Toxic mediated diseases
1. Staphylococcus scalded skin
syndrome (Ritter’s disease)
a. Due to exfoliative toxins
2. Bullous(blister) impertigo (with pus)
a. Localised form of SSSS
b. Due to specific strains of toxin
producing S.aurieus (phage
type 71)
3. Staphylococcus food poisoning
a. Intoxification by enterotoxin in
foods
4. Toxic shock syndrome
a. Initiated with the localised
growth of toxin producing
strains at
i. Vagina
ii. Wound
b. Followed by the release of
TSST-1 into the bloodstream
1. Antibiotic of
choice
a. Cloxacillin
2. MRSA (Methicillin
Resistant
Staphylococcus
Aureus)
a. Vancomycin
b. Teicoplanin
c. Fusidic acid
ZaidKhalid MBBS220
Name of bacteria Lab Characteristics
Staphylococcus
Epidermidis
1. Present as
normal flora
1. Negative in
coagulase test
2. Sensitive to
Novobiocin test
proliferation of T cell,
release cytokines
c. Toxic Shock Syndrome
Toxin-1
i. Superantigen
1. Causes the leakage
of endothelial cells
5. Enzymes
a. Coagulase
i. Converts fibrinogen to
fibrin
b. Catalase
i. Catalyzes the removal of
hydrogen peroxide
c. Hyaluronidase
i. Hydrolyses hyaluronic
acid in connective tissue
d. Fibrinolysin
i. Dissolves fibrin clot
e. B-lactamase
i. Hydrolyses B-lactam
antibiotic
Suppurative/Pyogenic infection
1. Impetigo
2. Folliculitis
3. Furunculosis
4. Carbuncles
5. Wound infection
Virulence factors
Clinical diseases
Treatment
Much lower pathogenicity and
rarely causes disease in healthy
individuals
Slime is the virulence factor
1. Enables the bacteria to adhere
to medical instrument
especially
a. Urinary catheter
b. Prosthetic heart valve
1. Catheter-associated infection
2. Prosthetic heart valve endocarditis
3. Infection of orthopaedic prosthesis
(implant)
3. Antibiotic of
choice
a. Cloxacillin
4. MRSE (MultiResistant
Staphylococcus
Epidermidis)
a. Vancomycin
b. Fusidic acid
Systemic infection
1. Pneumonia
2. Pyemia
3. Septic arthritis
4. Osteomyelitis
5. Endocarditis
ZaidKhalid MBBS220
Streptococcus (arranged in chains)
1. Most are facultative anaerobes
2. Some only grow in atmosphere enhanced with CO2 (capnophillic growth)
Biochem classification
Serologic classification
Streptococcus pyogenes
A
Streptococcus agalactiae
B
Streptococcus dysgalatiae
C,G
Streptococcus bovis
D
Viridians group streptococci
Non-groupable
Streptococcus pneumonia
Non-groupable
Name of bacteria Lab Characteristics
Streptococcus
pyogenes
1. Chains
a. Short chains at
medical
specimens
b. Long chain in
liquid media
2. Enriched media of
blood agar
a. Optimal
growth
b. Large zone of
beta
haemolysis
3. Catalase negative
4. Sensitive to
bacitracin
Haemolysis pattern
Beta (B)
Beta (B), occasionally non-haemolytic
Beta
Alpha (A), non-haemolytic, occasionally Beta
Alpha (A) or non-haemolytic
Alpha (A)
Virulence factors
Clinical diseases
Treatment
1. Capsule
a. Anti-phagocytosis
2. Lipothecoic acid
a. Binds to epithelial cells
3. M protein
a. Adhesin
b. Antiphagocytic
4. Pyrogenic exotoxins
a. Acts as superantigen
b. Types
i. Spe A
ii. Spe B
iii. Spe C
5. Streptolysin S
a. Lyses
i. Leukocytes
ii. Platelets
iii. Erythrocytes
Suppurative/pyogenic streptococcal
diseases
1. Pharyngitis
a. Sore throat
2. Scarlet fever
a. Complication of pharyngitis
occurs when infecting strain is
lysogenized by temperate
bacteriophage
i. Stimulates the release of
pyrogenic exotoxin
3. Impetigo
a. Confined purulent happens
only on exposed areas
i. Arms
ii. Face
iii. Legs
b. Vesicles develop and turn to
pustules; rupture to produce
1. Penicillin
2. Pts with penicillin
allergic
a. Erythromycin
b. Cephalosporin
ZaidKhalid MBBS220
b. Stimulates release of
lysosomal enzyme
i. Non-immunologic
6. Streptolysin O
a. Lyses
i. Leukocytes
ii. Platelets
iii. Erythrocytes
b. Stimulates release of
lysosomal enzyme
i. Immunologic
7. Streptokinase
a. Lyses blood clot
b. Facilitate spread of bacteria
in tissue
8. DNAase
a. Depolymerizes cell-free
DNA in purulent material
crust
c. Primarily seen in young
children
4. Erysipelas (acute cellulitis)
a. Acute infection of the skin
b. Local pain
c. Inflammation
d. Lymph node enlargement
e. systemic signs
i. chills
ii. fever
iii. leukocytosis
5. Cellulitis
a. Involves the skin and deeper
subcutaneous tissues
6. Necrotizing fasciitis
a. Infection occurs deep in
subcutaneous layer
b. Spreads along the fascial plane
c. Characterized by extensive
destruction of muscle and fat
7. Streptococcal toxic shock syndrome
a. Involves multiple organs;
kidneys, lungs, heart and liver
Non-suppurative streptococcal diseases
1. Rheumatic fever
a. Inflammatory of heart, joints,
blood vessels and SC tissues
2. Acute glomerular nephritis
a. Inflammation of renal glomeruli
with oedema, HPT, hematuria
and proteinuria
ZaidKhalid MBBS220
Name of bacteria
Streptococcus
agalactiae
1. Colonizes
a. GIT
b. GUT
2. Transient
vaginal
carriage found
in 10-30% of
pregnant
women
Lab Characteristics
1. The only species
that has B antigen
2. Produces a narrow
zone of Betahaemolysis
Virulence factors
1. B antigen
2. Type-specific capsular
polysaccharides
a. Ia
b. Ib
c. II
d. VII
Clinical diseases
Most infections in newborns are
acquired from mother;
pregnancy/delivery
Neonates at high risk
1. Premature ruptures of membrane
2. Long labours
3. Preterm delivery
4. Disseminate maternal group B
streptococcal disease
5. Mother without type-specific
antibody/low compliment levels
Early onset neonatal disease
1. Younger than 7 days of age
2. Characterized by
a. Bacteremia
b. Pneumonia
c. Meningitis
Late onset neonatal disease
1. 1week-3 months of life
2. Exogenous source
a. Mother
b. Other infant
3. Bacteremia with meningitis
Other group B streptococcus infections
1. Urinary tract infection
2. Wound infection
3. Bacteremia
Treatment
1. Penicillin alone
2. Penicillin plus
aminoglycosides
for serious
infection
ZaidKhalid MBBS220
Name of bacteria
Streptococcus
pneumonia
1. Commonly
known as
pneumococcus
2. Encapsulated
coccus
arranged in
pairs or short
chains
Lab Characteristics
1. Appear alphahaemolytic on
blood agar
a. Production of
pneumolysin,
degrades
haemoglobin
2. Can be
differentiated
from S. Viridans
a. Sensitive to
Optochin
b. Soluble in bile
solubility test
c. Quellung
reaction
i. Polyvalent
anticapsular
antibodies
will show
swelling of
the
capsule
Virulence factors
1. Capsule
a. Antiphagocytic
2. Secretory Ig A protease
a. Disrupts secretory IgAmediated clearance
3. Pneumolysin
a. Able to destroy ciliated
epithelial cells
b. Activates classic
complement pathway
4. Teichoic acid
a. Activates alternative
compliment pathway
Clinical diseases
1. Pneumonia
a. Most common causes of
community acquired disease
2. Sinusitis and otitis media
a. Most common causes
infections at sinuses and ear
b. Preceded by viral infection of
upper respiratory tract
3. Meningitis
a. Most common at any age
except neonate
4. Bacteraemia
a. Pneumonia
i. 25-30% of pts
b. Meningitis
i. More than 80% of pts
Treatment
1. Penicillin is the
DOC
2. Penicillin allergic
pts
a. Cephalospori
n
b. Vancomycin
c. Erythromycin
3. Immunization with
23-valent
pneumococcal
vaccine can
prevent the
infection
ZaidKhalid MBBS220
Name of bacteria
Viridan
streptococci
Colonizes :
1. Oropharynx
2. GIT
3. GUT
Most isolates do
not possess a
group specific
carbohydrate
Name of bacteria
Enterococcus sp
Colonizes GIT
Most common to
be isolated are
1. Enterococcus
faecium
2. Enterococcus
faecalis
Lab Characteristics
Virulence factors
Collection of
1. Alpha-haemolytic
2. Non-haemolytic
Clinical diseases
1. Dental carries
2. Infective endocarditis
3. Intra-abdominal infections
Treatment
Ampicillin
Resistance to
Optochin
Some strains are
nutritionally deficient,
needing presence of
exogenous pyridoxal
vitB6
Lab Characteristics
Arranged in pairs or
short chains
Often confused with
pneumococcal
Virulence factors
1. Most infections originate from
normal flora
2. Pts who at risk
a. Prolonged hospitalization
b. Use of broad-spectrum of
antibiotic
i. Cephalosporin,
resistant to this drug
Clinical diseases
1. Urinary tract infection
2. Wounds infection
a. Intra-abdominal, usually
polymicrobial
3. Bacteraemia
4. Endocarditis
Treatment
Ampicillin
ZaidKhalid MBBS220
BACILLUS
Aerobes/facultative anaerobes
1. Categorized based on ability to form spore
a. Spore forming
i. Bacillus
Bacillus spp
1. Spore forming gram-positive bacilli
2. Clinically important species
Name of bacteria
Bacillus
anthracis
1. Spore forming
2. Causative
agent of
anthrax
Considered to be
one of the most
feared biological
warfare
Bacillus cereus
1. Ubiquitous
(found
everywhere)
2. Non-fastidious
3. Spore forming
bacteria
b.
i.
ii.
iii.
a.
b.
Non-sporing
Corynebacterium
Listeria
Nocardia
Bacillus anthracis
Bacillus cereus
Virulence factors
Clinical diseases
1. Capsule is present in
virulent strains
2. Virulent strains produce
3 exotoxins that
combine to form
a. Edema toxin
i. Protective antigen
+ edema factor
b. Lethal toxin
i. Protective antigen
+ lethal factor
3. Spores can survive in soil
for years
1. Cutaneous anthrax
a. Most common form
b. Starts with painless papules at site of inoculation
c. Rapid progress to an ulcer surrounded by
vesicles
d. Later become necrotic eschar
2. Inhalation anthrax
a. Most deadly form
b. Progress to shock and death within 3 days of
initial symptoms
3. Gastrointestinal anthrax
a. Rare case
b. Commonly fatal disease
i. Mortality of up to 100%
1. Gastroenteritis
a. Emetic forms
b. Diarrhoea forms
2. Ocular infection following trauma in the eye
3. Other opportunistic infection
a. IV catheter-related sepsis
1. Enterotoxins
a. Heat-stable
i. Causes emetic
b. Heat-labile
i. Causes diarrhoea
2. Cytotoxic enzymes
a. Cereolysin-potent
haemolysin
b. Phospholipase C
Treatment
1. DOC: ciprofloxacin
2. Alternative antibiotics
a. Penicillin
b. Chloramphenicol
c. Doxycycline
d. Erythromycin
3. Vaccination can control the
spread of the disease
4. Spores are difficult to destroy
ZaidKhalid MBBS220
Anaerobes Bacillus
4. Remarkable capacity of clostridia to cause disease is because
a. Capable to survive at adverse environment by forming spore
b. Rapidly grow at enriched nutrition, deprived oxygen
c. Production of numerous
i. Histolytic toxins
ii. Enterotoxins
iii. Neurotoxins
Clostridium sp
1. Spore forming
2. Ubiquitous
3. Recognized harmful pathogens
a. Clostridium perfringes
b. Clostridium tetani
c. Clostridium botulinum
d. Clostridium deficile
Name of bacteria
Lab Characteristics
Clostridium
perfringes
1. Large
rectangular
1. Forms spores
2. Produces double
zone haemolysis
on blood agar
a. Alpha toxins
b. Delta toxins
3. Nagler’s reaction
a. Opalescence is
seen when
toxins act with
egg yolk
medium
Virulence factors
Clinical diseases
Treatment
1. α toxins
a. Lethal toxin phospholipase C
b. Increase vascular
permeability
c. Haemolysin produces
necrotizing activity
2. β toxins
a. Lethal toxin-necrotizing
activity
3. θ toxins
a. heat and oxygen labile
haemolysin-cytolytic
4. Enterotoxins
a. Alter membrane permeability
i. Cytotoxic
ii. Enterotoxic
5. Neuramidase
a. Alters cell surface ganglioside
receptors
b. Promotes capillary
thrombosis
1. Soft tissue infections
a. Cellulitis
b. Suppurative myositis
c. Myonecrosis
d. Gas gangrene
2. Food poisoning
a. Short incubation period (824hrs)
b. Abdominal cramps
c. Watery diarrhoea
d. Nausea/emesis
e. No fever
f. Last less than 24 hrs
3. Necrotizing enteritis
a. Abdominal pain
b. Bloody diarrhoea
c. Shock
d. Peritonitis
c. Caused by β toxins C.perfringes
C
6. Septicaemia
1. Immediate
treatment is vital
for serious
infection
2. Systemic infection
requires surgical
procedure
3. High dose of
penicillin should
also be employed
ZaidKhalid MBBS220
Name of bacteria
Clostridium
tetani
1. Ubiquitous
2. Found in most
soil
3. GIT humans
and animals
4. Obligate
anaerobes
5. Spores shape
like a
drumstick
Clostridium
botulinum
1. Agent of
botulism
2. Spore forming,
fastidious
organism
3. 7 antigenically
distinct
botulinum
toxins
a. A to G
b. A,B, E and F
are
pathogenic
to human
Virulence factors
1. Spore formation
2. Production of enzymes
3. Production of toxins
a. Tetanolysin
i. Oxygen labile haemolysin
ii. Plasmid encoded
b. Tetanospasmin
i. Heat labile neurotoxin
ii. Responsible for tetanus
iii. Block neurotransmitter for
inhibitory synapses, thus
excitatory synaptic activity is
unregulated (spastic paralysis)
1. Spore formation
2. Production of toxins
a. Botulinum toxins
i. Prevents the release of
neurotransmitter acetylcholine
b. Binary toxin
i. Disrupts vascular permeability
Clinical diseases
1. Tetanus
1. Food-borne botulism
a. Blurred vision with fixed dilated pupils
b. Dry mouth (anti cholinergic activity of
the toxins)
c. Constipation
d. Abdominal pain
e. Fever is absent
f. Flaccid paralysis
g. Death associated with respiratory
paralysis
2. Infant botulism
a. Caused by neurotoxin
3. Wound botulism
Treatment
1. Requires debridement
2. Antibiotic therapy
a. Penicillin
b. Metronidazole
3. Passive immunization
a. Antitoxin globulin
4. Vaccination
a. Tetanus toxoid
ZaidKhalid MBBS220
Name of bacteria
Clostridium
difficile
1. Ubiquitous
organism
2. Spore forming
3. Strict
anaerobes
4. Exposure to
antibiotic is
associated
with
overgrowth of
C. difficile thus
resulting in
subsequent
disease
(endogenous
infection)
Virulence factors
1. Spore formation
a. Permits organism to survive
months in the hospital
environment
2. Enterotoxin A
a. Produces chemotaxis
b. Induces cytokine
c. Produces hypersecretion of fluid
d. Produces haemorrhagic necrosis
3. Cytotoxin B
a. Induces depolymerisation of actin
with loss of cellular cytoskeleton
Clinical diseases
1. Antibiotic-associated diarrhoea
2. Pseudomembranous colitis
Treatment
1. Implicated antibiotic should
be discontinued
2. Severe disease
a. Vancomycin
b. Metronidazole
ZaidKhalid MBBS220
Aerobes Bacillus/ non-sporing
Name of bacteria
Corynebacteriu
m diptheriae
1. Pleomorphic
2. Causative
agent of
diphtheria
Lab Characteristics
Virulence factors
1. Albert satin
a. Metachromic
granules
within cell
may be visible
2. Potassium tellurite
agar
a. Black colonies
are seen
3. Elek test
a. Toxin and
antitoxin
combine to
form antigenantibody
complexes
b. Form
precipitation
on the agar in
the form of
visible lines
1. Exotoxin
a. Tox gene that codes for the
toxins is introduced by
lysogenic bacteriophage
b. Inhibits protein synthesis by
inactivating the elongation
factor 2
c. Can be detected thru Elek
test
Clinical diseases
1. Diphtheria
a. Onset is sudden
b. Malaise
c. Sore throat
d. Exudative pharyngitis
e. Low-grade fever
2. Exudates evolve into thich
pseudomembrane which
composed of
a. Bacteria
b. Lymphocytes
c. Plasma cells
d. Fibrin
e. Dead cells
Can extend from nasopharynx or
down to the larynx
Treatment
1. Early use of
antitoxin to
neutralize the
toxin
2. Erythromycin to
kill the
corynebacterium
thus preventing
excretion of
exotoxin
3. Admin of
diphtheria vaccine
and booster to
susceptible
population
ZaidKhalid MBBS220
Coccobacilus gram positive
Name of bacteria
Listeria
monocytogenes
1. Facultative
anaerobes
2. Motile at room
temperature
3. Isolated form
soil, veggie
and water
Lab Characteristics
1. Weak beta
haemolytic
2. Capable of
growing at 4oc
a. Increase
number when
contaminated
food is
refrigerated
Clinical diseases
1. Associate with consumption of contaminated food
a. Soft cheese
b. Milk
c. Raw veggie
2. Transplacental spread from mother to neonate
3. Neonatal infection
a. Bacteraemia
b. Meningitis
c. Meningoencephalitis
4. Adult infection
a. Mild-influenza like illness
b. Primary bacteraemia
c. Meningitis
Treatment
1. Severe infection
a. Ampicillin
b. Combine
with
gentamicin