Upper respiratory tract infection:
Streptococcus pyogenes.
Neisseriae meningitidis.
Haemophilus influenzae, and H parainfluenzae.
Bordetella pertussis
Corynebacterium diphtherium
Streptococcus pyogenes infection:
Microscopy:
Gram positive cocci in
chains, capsulated and
non-motile.
Cultural characteristics:
Facultative anaerobic bacterium
, beta-hemolytic on blood agar,
and bacitracin sensitive.
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Virulence factors and clinical picture:
Streptococcus pyogenes has several virulence factors :
1- capsule and M protein: anti-phagocytic activity.
2- Streptolysin-O exotoxin: the Beta-hemolysin.
3- Streptolysin-S exotoxin: a cardiotoxic exotoxin with betahemolytic activity.
Clinical picture:
Transmission: aspiration of airsoles (inhalation).
Primary infection: tonsillitis, pharyngitis, and follicular tonsillitis.
Secondary infection: Scarlet fever and septic shock.
( toxigenic strains in blood stream).
Long term Streptococcus pyogenes infection:
It could be complicated with Rheumatic fever and postinfectious
glomerulonephritis.
Clinical picture of Streptococcus pyogenes:
Scarlet fever is characterized by:
1-Sore throat
2-Fever
3-Bright red tongue with a
"strawberry" appearance
4-Characteristic skin rash.
Neisseriae meningitidis infection:
Microscopy:
Gram negative cocci 0.8 µm in
diameter, Kidney-shaped, occur in
pairs. In clinical specimens:
present in neutrophils
(intracellular).
Cultural characteristics:
All species grow best on chocolate
agar or Thayer-Martin medium at
A microaerophilic conditions
of 5-10 % CO2.
It is a fastidious bacterium
Show an optimum growth at 37C.
Virulence factors and clinical picture:
Neisseriae meningitidis virulence factors include:
1- The outer membrane lipo-oligosaccharide.
2- The polysaccharide capsule.
3- The adhesion pili.
Clinical picture:
Transmission: inhalation of airsoles.
Primary infection: upper respiratory: pharyngitis, epiglottitis,
Secondary: bacteremia, and septicemia.
Meningococcemia (cause disseminated intravascular coagulation (DIC), a
condition where blood starts to clot throughout the body) causing ischemic tissue
damage.
Meningoencephalitis.
The characteristic skin rash (purpura) (DIC) of meningococcal septicemia,
caused by Neisseria meningitidis
A
Haemophilus influenzae, and H. parainfluenzae :
Haemophilus influenzae:
Microscopy:
Gram’s negative coccobacilli, rod-shaped pleomorphic bacteria.
Some strains are capsulated. Non-motile, and non-spore forming.
Cultural characteristics:
Aerobic or facultative anaerobic bacteria that isolated on chocolate
agar, which supplies special growth factors namely, factor X
(haemin) and factor V (NAD). They can grow on blood agar around
Staph aureus (satellitism phenomenon).
H. parainfluenzae requires factor V only.
Haemophilus influenzae and H.parainfluenzae:
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Clinical picture:
Transmission: inhalation of droplets.
Primary infection: upper respiratory epiglottitis.
sinusitis in children.
Secondary:
bacteremia, could cause septicemia (toxigenic strains).
The infection is extended to cause meningoencephalitis.
Haemophilus influenzae is associated also with a specific
bacterial pneumonia, if aspirated into lower respiratory
tracts.
Clinical picture:
a
Bordetella pertussis:
Microscopy and culture:
Gram’s-negative non-motile, non-sporing capsulated
short bacilli.
Bordetella pertussis is the most important pathogenic
strain that causes whooping cough.
They are strict aerobe and growth best on selective and
enrichment media such as charcoal cephalexin blood agar
for 4-6 days, colonies are shiny small and pearly grey
(mercury drop).
Cultural characteristics and clinical picture:
A child complaining
of whooping cough.
Shiny small pearly grey (mercury
drop) colonies of Bordetella
pertussis on Charcoal Cephalexin
blood agar.