Download sheet 15 hashem abosafi

14/11/2013
microbiology sheet #15 part one
Hashem Abosafi
in this lecture :
1. we’ll continue about diphtheria
2. Listeria monocytogenes
what is the toxoid?
 it is a toxin that is no longer poisonous, but able to cause anti body production by the body
 a toxoid is prepared from a toxin by treating it with formalin
 this method is used for vaccination
in the last lecture we said that diphtheria can be treated by vaccination, actually this is a part of the triple vaccine
that is given to babies.
this disease has some indications, a thick, gray-green fibrin membrane, the pseudomembrane, often forms over the
site(s) of infection as a result of the combined effects of bacterial growth, toxin production, necrosis of underlying
tissue and the host immune response.
Symptoms of pharyngeal diphtheria vary from mild pharyngitis to hypoxia due to airway obstruction by the
pseudomembrane.
in slide #46 → under the microscope the C.Dephtheria has a chineese litter appearance
not all C.Diphtheria are toxogenic but they can acquire this property, How?
this actually happens if they are infected by a bacteriophage that carries the toxin gene.
How can we tell if a certain strain of C.Diphtheria is toxogenic or not, supposing that we have isolated that strain?
we do Elek’s Test, It is a toxin/antitoxin reaction
Toxin production by C.diphtheriae can be demonstrated by a precipitation between exotoxin and diphtheria
antitoxin
Procedure: A strip of filter paper impregnated with diphtheria antitoxin is placed on the surface of serum agar
The organism is streaked at right angels to the filter paper
in slide #48 : Incubate the plate at 37C for 48 hrs, after 48 hrs incubation, the antitoxin diffusing from filter paper
strip and the toxigenic strains produce exotoxin, which diffuses and results in four precipitation lines radiating from
intersection of the strip and the growth of organism
Epidemiology:
this disease used to be one of the big problems in the old days but it’s not any more because of the vaccination
Immunity test: How can we tell if a person is immune or not to Diphtheria? it can be tested serologically, or we can
do a test called Schick test which is a skin test where we inject the toxin, if redness happened then the person is not
immune, if no reaction happened then he/she is immune
14/11/2013
microbiology sheet #15 part one
Hashem Abosafi
Listeria monocytogenes
all types of bacteria that we’ve studied so far are extra cellular bacteria that grow and reproduce outside
cells(staphylococci, streptococci). This type is not, it ‘s an intra cellular bacteria, this is actually a pathogenicity factor,
this will help the bacteria to survive by protecting it from antibody attack, since antibodies cannot enter cells.
the only way they can be killed is by the activation of those cells to produce hydrogen peroxide, free oxygen radicals,
nitrous oxide → eventually it will be killed
→usually when the bacteria is engulfed by macrophages they enter it inside a phagosome, then the phagosome
fuses with the lysosome to form a phagolysosome and there the H2O2, ROS, …etc, along with lysosomal enzymes are
present and supposed to kill the bacteria
Listeria monocytogenes escapes from the phagosome before it fuses with the lysosome, it can do that by means of
an enzyme (Listeriolysin) which can break the membrane of the phagosome so it doesn’t fuse with the lysosome → it
won’t be killed and that is the pathogenicity factor that helps it to survive intracellularly.
L. monocytogenes infection is acquired from food (vegetable or animal products).
Most cases occur in immunocompromised hosts; newborns, elderly, cancer patients and transplant recipients.
It may be transmitted congenitally (mild flue like in mother) and the fetus develops a serious illness.
Depending on the stage of gestation, the fetus is either stillborn (dead at birth) or born with signs of congenital
manifestations, a condition known as granulomatosis infantiseptica.
this bacteria can grow at temperature extremes (very high / very low)
Listeriosis is a serious disease of humans with a mortality of more than 25%.
There are two main clinical manifestations, sepsis and meningitis.
Meningitis is often complicated by encephalitis which is exceptional among bacterial infections.
Occasionally, pyogenic infections of various organs have been found.
Relapses may occur after apparent recovery.
Diagnosis is made by isolation of the organism.
Control is achieved by hygienic food processing and storage.
Treatment: most antibiotics except cephalosporins can be given (e.g.. ampicillin and aminoglycosides)
End of midterm material
GOOOOOOD LUCK