Gram Negative Bacteria
NEISSERIA
General Characteristics:
Neisseria Species
Aerobic, gram-negative diplococci
Nonmotile
Oxidase positive
Catalase positive
Fastidious, capnophilic
Neisseria Species
Habitat
– Upper respiratory tract
– Genitourinary tract
– Alimentary(Digestive) tract
Primary pathogens:
– N. meningitidis
– N. gonorrhoeae
Neisseria meningitidis
Pathogenesis:
Humans are the only natural hosts
The organisms are transmitted by airborne
droplets
Colonize the nasopharynx and become
transient flora of the upper respiratory tract.
From the nasopharynx, the organism can enter
the bloodstream and spread to meninges or
cause meningococcemia.
High-risk groups are:
1) Infants aged 6 months to 2 years
2) Army recruits.
N. meningitidis is classified into serogroups
based on different capsular polysaccharides,
which are antigenic (stimulate a human
antibody response). There are 9 serotypes of
meningococcus (designated A, B, C, D, X, Y, Z,
W135, and 29E). Meningitis is caused by
groups A, B, and C.
It has three important virulence factors:
1. Polysaccharide capsule. It is antiphagocytic
in nature.
2. Endotoxin. It induces septic shock by
causing release of cytokines.
3. IgA protease. It cleaves the IgA antibodies
present in respiratory mucosa
Clinical Findings:
1. Meningitis
2. Meningococcemia
1.Meningitis. The symptoms are fever, headache,
stiff neck, and an increased level of Neutrophils
in spinal fluid.
2.Meningococcemia.
It occurs due to multiplication of bacteria in the
blood stream.
The severe form of it is life-threatening
Waterhouse-Friderichsen syndrome.
It is the septic shock induced by meningococcus
Also called Fulminant meningococcemia.
Feature include high fever, shock, widespread
purpura, disseminated intravascular coagulation,
thrombocytopenia, and adrenal insufficiency due
to bilateral adrenal hemorrhages.
Neck rigidity
Laboratory Diagnosis:
A. Specimens include.
1. Blood for culture and smears
2. Spinal fluid for smear, culture, chemical
analysis.
B. Blood smears on gram staining show gram
negative bean shaped diplococci.
C. Culture. The organism grows best on
chocolate agar incubated at 37°C in a 5% CO2
atmosphere. Colonies are transparent or
opaque.
D. Oxidase test. Positive
E. Maltose fermentation. The difference between
N. meningitidis and N. gonorrhoeae is made on
the
basis
of
maltose
fermentation.
Meningococci ferment maltose, whereas
gonococci do not.
F. Latex agglutination test, which detects
capsular polysaccharide in the spinal fluid.
 The classic medium for culturing Neisseria
is called the Thayer-Martin VCN media. This is
chocolate agar with antibiotics, which are
included to kill competing bacteria.
V stands for vancomycin, which kills grampositive organisms.
C stands for colistin (polymyxin) which kills all
gram-negative organisms (except Neisseria).
N stands for nystatin, which eliminates fungi.
Prevention:
Chemoprophylaxis and immunization both used
for prevention.
Rifampin or ciprofloxacin used for prophylaxis in
people who had close contact with the patient
There are two forms of the meningococcal
vaccine, each contains the capsular
polysaccharide of groups A, C, Y, and W-135
as antigens (Tetravalent vaccine)
1. Unconjugated
2. Conjugated
Neisseria gonorrhoeae:
(Gonococcus).
Non motile.
Humans are only reservoir, not part of normal
flora
Causes disease only in humans.
Killed by drying that’s why transmitted sexually.
Pathogencity:
The virulence factors are.
1.
Pili. Most important virulence factors.
Piliated gonococci are usually virulent, whereas non
piliated strains are avirulent.
2.
Two virulence factors in the cell wall
a. Lipooligosaccharride (LOS) (a modified form of
endotoxin). Endotoxin of gonococci is weaker than
that of meningococci.
b. Outer membrane proteins.(OMP).
OMP cause attachment of bacteria to epithelial cells
of the urethra, rectum, cervix, pharynx, or conjunctiva,
like pilli.
3. IgA protease.
The main host defenses against gonococci are
antibodies (IgA and IgG), complement, and
neutrophils.
IgA protease degrades one of these antibodies.
Virulence Factors
PILLI
Clinical Findings:
Transmitted sexually both in males and females.
Cause pyogenic infections.
Females are usually asymptomatic.
N. gonorrhea causes following infections.
1. Genitourinary tract infections ( Gonorrhea)
2. Disseminated infection via spread through blood
stream.
3. Rectal infections.
4. Pharyngitis
5. Ophthalmia neonatorum
1. Genitourinary tract infections :
Gonorrhea in men has features of urethritis
accompanied by dysuria and a purulent
discharge. Epididymitis can occur.
In women, infection is initially in the endocervix
(cervicitis), causing a purulent vaginal
discharge and intermenstrual bleeding.
The most frequent complication is ascending
infection to the uterine tubes (salpingitis) which
can lead to sterility or ectopic pregnancy
2. Disseminated gonococcal infection(DGI):
Commonly manifest as arthritis, synovitis, or
skin pustules.
Disseminated infection is the most common
cause of septic arthritis in sexually active
adults.
3.Rectal infections:
Prevalent in male homosexuals, are
characterized by constipation, painful
defecation, and purulent discharge.
4.Pharyngitis is contracted by oral-genital contact.
The condition may mimic a mild viral or a
streptococcal sore throat.
5.Ophthalmia neonatorum is an infection of the
conjunctiva acquired by a newborn during
passage through the birth canal of an infected
mother .
If untreated, acute conjunctivitis may lead to
blindness.
Lab diagnosis:
1.In the male, the finding of numerous neutrophils
containing gram negative diplococci in a smear
of urethral exudate provides a diagnosis of
gonococcal infection.
2.In the female a positive culture is also needed.
3.Culture:
N. gonorrhoeae grows best under aerobic
conditions, and most strains require CO2 also.
Gonococci are very sensitive to heating or
drying. Cultures must be plated rapidly.
N. gonorrhoeae grows rapidly producing small,
raised, grey or translucent colonies after
overnight incubation.
4. Oxidase test. Positive.
Laboratory Diagnosis:
Neisseria gonorrhoeae
Media Selection
Chocolate agar
– Subject to overgrowth of normal flora
Thayer-Martin agar is chocolate agar with
vancomycin, colistin, and nystatin
MTM contains the above plus trimethoprin
Specimen MUST be plated on warmed
media ASAP
Incubation
Inoculated culture media
must be incubated at 350 C
in 3% to 5% CO2 or candle
jar
Candle jar must use white
wax candles
Laboratory Diagnosis:
Neisseria gonorrhoeae
Colony morphology on
modified Thayer-Martin
(MTM) agar
– Small, beige- gray
– Translucent, smooth
Fresh growth must be
used for testing,
because N.
gonorrhoeae produces
autolytic enzymes
Laboratory Diagnosis:
Neisseria gonorrhoeae
– Oxidase Test
Test on filter paper or directly on plate
Oxidase reagent =Dimethyl or tetramethyl oxidase
reagent
Violet-purple color indicates a positive result
Laboratory Diagnosis:
Neisseria gonorrhoeae
Carbohydrate utilization
Cystine trypticase agar
(CTA)
– Contain 1% of a single
carbohydrate
Glucose, maltose,
lactose, sucrose
– Phenol red is pH
indicator
Read in 24-72 hours
Prevention
The prevention of gonorrhea involves the use of
safety measures and the immediate treatment
of symptomatic patients and their contacts.