Download Bacteriology lecture no 5 2nd class *The Neisseriae

Bacteriology lecture no 5
2nd class
*The Neisseriae*
1-The Neisseriae are gram –negative cocci that usually
occur in pairs .
2-It includes two species Neisseriae gonorrhoeae
(gonococci)and Neisseria meningitidis (meningococci),both
are pathogenic for human.
3-Both typically are found associated with or inside
polymorphonuclear cells.
4-Some Neisseriae are normal inhabitant of the human
respiratory tract rarely if ever cause disease ,and occur
extracellulary .
5-Gonococci and Meningococci are closely related ,with
70%DNA homology, and are differentiated by a few
laboratory tests and specific characteristic .
6-Meningococci have polysaccharide capsules ,whereas
gonococci do. Most importantly ,the two species
differentiated by the usual clinical presentation of the
disease they cause.
7-Meningococci typically are found in the upper
respiratory tract and cause meningitis ,while gonococci
cause genital infections.
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Bacteriology lecture no 5
2nd class
*Morphology and identification .
A-Typically organisms
-Typically Neisseriae is a gram-negative ,nonmotile
diplococci.
-Individual cocci are kidney –shaped ,when organisms
occur in pairs ,the flat or concave sides are adjacent.
B-Culture :
-In 48 hours on enriched media e.g. modified –Thayer
Martin –Lewis and New-York city.
-Gonococci and meningococci form convex ,glistening
elevated ,mucoid colonies 1-5 mm in diameter .
-Colonies are transparent or opaque ,nonpigmented and
nonhemolytic.
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Bacteriology lecture no 5
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C-Growth characteristic .
-The Neisseriae grow best under aerobic condition ,but
some will grow in an anaerobic environment .
-They have complex growth requirements.
-Most Neisseriae oxidize CHO, producing acid but not gas
,and their CHO pattern are a mean of distinguishing them.
-Neisseriae produce oxidase and give positive oxidase
reaction ,the oxidase test are a key test for identifying
them.
-Meningococci and gonococci grow best on media
containing complex organic substance such as heated
blood ,hemin and animals protein and in an atmosphere
containing 5% CO2 e.g., candle jar.
-The organisms are rapidly killed by drying ,sunlight
,moist heat and many disinfectants.
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Bacteriology lecture no 5
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-They produce autolytic enzymes that result in rapid
swelling and lysis in vitro at 25Ċ and an alkaline Ph.
NEISSERIA GONORRHOEAE
-Antigenic structure.
N.gonorrhoeae is antigenically heterogeneous and
capable of changing its surface structure in vitro –and
presumably in vivo ,to avoid host defenses .Surface
structure include the following .
A-Pilli(Fimbriae)
It is the hair like appendages that extend up to several
micrometer from the gonococcal surface .They enhance
attachment to host cells and resistance to phagocytosis.
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Bacteriology lecture no 5
2nd class
B-Por.por protein extend through the gonococcal cell
membrane ,it occur in trimers to form pores in the surface
through which some nutrient enter the cells .Por protein
may impact intracellular killing of gonococci within
neutrophil by preventing phagosome lysozyme fusion.
C-Opa protein :These proteins function in adhesion of
gonococci within colonies and in attachment of gonococci
to host cell receptors, such as heparin –related
compounds and CD66 or carcinoembryonic antigenrelated cells adhesion molecules.
D-RMP(protein 3)
This protein is antigenically conserved in all gonococci. It
is a reduction –modifiable protein (RMP)and changes its
apparent molecular weight when in reduced state .It
associate with Por in the formation of pores in the cell
surface .
E-Lipooligosaccharide.Toxicity in gonococcal infection is
largely due to the endotoxic effect of LOS.
The gonococcal LOS and the human glycosphingolipid of
the same structural class react with the same monoclonal
antibody ,The presence on the gonococcal surface of the
same surface of the same surface structures as human
cells helps gonococci evade immune recognition.
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Bacteriology lecture no 5
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F-Others protein such as:
1-Lip(H8)is a surface exposed protein that is heat –
modifiable like Opa
2-Fbp(Ferric-binding protein)similar in molecular weight to
pors is expressed when the available iron supply is limited
e.g.in human infection.
3-IgA1 protease that splits and inactivates IgA1,a major
mucosal immunoglobulin of humans ,and this protein also
elaborates by Haemophilus influenzae and streptococcus
pneumonia.
*Antigenic Heterogeneity.
-Gonococci have evolved mechanisms for frequently
switching from one antigenic form (pilin ,opa or LPS)to
another antigenic form of the same molecules.
-since pilin ,opa and LPS are surface exposed antigen on
gonococci ,they are important in the immune response to
infection ;the molecules rapid switching from one
antigenic form to another helps the gonococci elude the
host immune system.
*Pathogenesis and clinical finding :
-Gonococci exhibit several morphological types of colonies
,but only piliated bacteria appear to be virulent .
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Bacteriology lecture no 5
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-Gonococci that form opaque colonies are isolated from
men with symptomatic urethritis and from uterine cervical
culture ,while those that form transparent colonies are
isolated from those that are a symptomatic urethral
infection ;and from invasive form of gonorrhea including
salpingitis and disseminated infection .
-Gonococci attack mucous membranes of the
genitourinary tract ,eye ,rectum, and throat ,producing
acute suppuration that may lead to tissue invasion ,this is
followed by chronic inflammation and fibrosis.
-In males :There is usually urethritis ,with yellow creamy
pus and painful urination .This process may extend to the
epididymis.
-In females: The primary infection is in the endocervix and
extend to the urethra and vagina ,giving rise to
mucopurulent discharge ,this may extend to the uterine
tubes causing salpingitis ,fibrosis ,so infertility occur in 20%
of women with gonococcal infection .
-Gonococcal bacteremia leads to skin lesion especially
hemorrhagic papules and pustules on the hands ,forearm
,feet and leg and also cause suppurative arthritis ,usually
of knee ,ankles and wrists.
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-Gonococci can be cultured from blood or joint fluid of
only 30% of patient with gonococcal arthritis .
-Gonococcal ophthalmia neonatarum an infection of the
eye of the newborn is required during passage through an
infected birth canal .The initial conjunctivitis rapidly
progresses and if untreated result in blindness.
-To prevent gonococcal ophthalmia neonatarum
,instillation of tetracycline erythromycin ,or silver nitrate
into the conjunctival sac of the newborn is compulsory in
the U.S
.
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-Immunity: Repeated gonococcal infection are common
,protective immunity to reinfection does not appear to
develop as part of the disease process ,because of the
antigenic variety of gonococci.
Neisseria meningitidis
*Antigenic structure :at least 13 serogroup of
meningococci have been identified by immunological
specifity of capsular polysaccharide
-The most important serogroup associated with disease in
humans are A,B,C,X,and W-135.
-Meningococcal antigens are found in blood and CSF of
patients with active disease .
-The outer membrane proteins of meningococci have been
divided into classes on the basis of molecular weight .All
strain have either class1,class2,or class3 proteins these are
analogous to the por protein of gonococci and are
responsible for the serotypes specificity of meningococci.
-This protein help form pores in the meningococcal cell
wall, meningococci are piliated ,but unlike gonococci ,they
don’t form distinctive colony types indicating piliated
bacteria
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-Meningococcal LPS is responsible for many of the toxic
effect found in meningococcal disease .
*Pathogenesis and clinical finding.
-Human are the only natural hosts for whom meningococci
are pathogenic.
-The nasopharynx is the portal of entry ,there the
organism attach to epithelial cells with the aid of Pilli, they
may form part of the transient flora without producing
symptoms.
-From the nasopharynx ,organisms may reach the blood
stream producing bacteremia ,the symptoms may be like
those of an upper respiratory tract infection.
-Fulminant meningococcemia is more severe ,with high
fever and hemorrhagic rash ,there may be disseminated
intravascular coagulation and circulatory collapse.
-Meningitis is the most common complication of
meningococcemia ,it usually begins with intense headache
,vomiting ,and stiff neck and progresses to coma within a
few hours.
-Neisseria bacteremia is favored by the absence of
bactericidal antibodies (IgM,and IgG)inhibition of serum
bactericidal action by a blocking IgA antibodies ,or a
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complement deficiency (C5,C6,C7,or C8).
*Immunity.
-Immunity to meningococcal infection is associated with
the presence of specific ,complement-dependent
,bactericidal antibodies in the serum
*Other Neisseriae such as Neisseria luctimica,Neisseria
sicca,Neisseria subflara,Neisseria cinerea,Neisseria mucosa
are also numbers of normal flora of the respiratory tract
,particularly nasopharynx.
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