Medical Microbiology I - Lecture10

MEDICAL MICROBIOLOGY I

Lesson 10Lesson 10

Neisseria and Diseases

Neisseria

2 species, Neisseria gonorrhoeae and

Neisseria meningitidis are strictly human

pathogens

The remaining 8 species are commonly The remaining 8 species are commonly

present on mucosal surfaces of the

oropharynx and nasopharynx, and

occasionally colonise the anogenital mucosal

membranes

Neisseria

Characteristics:

Aerobic

Gram negative cocci (diplococci) with adjacent sides

flattened together (resembling coffee beans)flattened together (resembling coffee beans)

Non-motile

Do not form endospore

Oxidase-positive

Most produce catalase (combine with the Gram

stain morphology allow for a rapid, presumptive

identification of a clinical isolate)

Neisseria

Neisseria gonorrhoeae


1. Physiology and Structure

N. gonorrhoeae is a fastidious organism, requiring complex media for growth and adversely affected by drying and fatty acids

Optimal growth temperature: 35 - 37C Optimal growth temperature: 35 - 37C

A humid atmosphere supplemented with carbon dioxide is either required or enhances growth of N. gonorrhoeae

Cell wall: thin peptidoglycan layer sandwiched between the inner cytoplasmic membrane and the outer membrane


The outer membrane is not covered with a

true carbohydrate capsule, as is found in N.

meningitidis

Cell surface-capsule like negative charge Cell surface-capsule like negative charge

Fresh clinical isolates have pili (virulence

factor)

The pili are composed of repeating protein

subunits (pilins), whose expression is

controlled by pil gene complex


Pili mediate attachment to non-ciliated

epithelial cells as well as provide resistance to

killing neutrophils

The Por proteins (formerly protein I) are porin The Por proteins (formerly protein I) are porin

proteins that form pores or channels in the

outer membrane

2 classes: PorA (resistant to serum killing and

thus are commonly associated with

disseminated disease) and PorB


Opa proteins (opacity proteins; formerly

protein II) are family of membrane proteins

that mediate binding to epithelial cells

Bacteria expressing the Opa proteins appear Bacteria expressing the Opa proteins appear

opaque when grown in culture

These proteins facilitate bacterial adherence to

each other and to eukaryotic cells


RMP proteins - highly conserved; reduction-

modifiable proteins; formerly protein III

These protein stimulate antibodies that block

serum bacterial activity against N. gonorrhoeaeserum bacterial activity against N. gonorrhoeae

Others: lipooligosaccharide (LOS), lipid A, -

lactamase which degrades penicillin


2. Pathogenesis and Immunity

Gonococci attach to mucosal cells, penetrate into the cells and multiply, and then pass through the cells into the sub-epithelial space, where infection is establishedspace, where infection is established

Pili - virulence; non-piliated - avirulent

After the initial attachment, Opa protein directs first a tighter association with the host cell surface and then the migration of bacteria into the epithelial cell


It was believed that the Por protein protects

the phagocytosed bacteria from intracellular

killing by inhibiting phagolysosome fusion

The gonococcal LOS stimulates the The gonococcal LOS stimulates the

inflammatory response and release of tumour

necrosis factor- (TNF-), which causes most

of the symptoms associated with gonococcal

disease


IgG3 is the predominant IgG antibody formed in

response to gonococcal infection

Antibodies to LOS can activate complement,

releasing complement component C5a, which has releasing complement component C5a, which has

a chemotactic effect on neutrophils

IgG and secretory IgA1 antibodies directed against

Rmp protein can block this bacteridal antibody

response

People with inherited complement deficiencies are

at considerably greater risk for systemic disease

Clinical Diseases

Genital infection in men is primarily restricted to the urethra

A purulent urethral discharge and dysuria develop after a 2-5 days incubation perioddevelop after a 2-5 days incubation period

Approximately 95% of all infected men have acute symptoms

Although complications are rare, epididymitis, prostatitis, and periurethral abscesses can occur

Clinical Diseases

Clinical Diseases

The primary site of infection in women is the cervix because the bacteria infect the endocervical columnar epithelial cells

The organism cannot infect the squamous epithelial cellsepithelial cells

Symptoms: vaginal discharge, dysuria, and abdominal pain

Ascending genital infection: salpingitis, tuboovarian abscesses, and pelvic inflammatory disease (10 - 20% women)

Clinical Diseases

Disseminated infections with septicaemia and infection of skin and joints occur in 1 - 3% of infected women and in a much lower percentage of infected men

Clinical manifestations of disseminated disease: Clinical manifestations of disseminated disease: fever, migratory arthralgias, suppurative arthritis in the wrists, knees and ankles, and a pustular rash on a erythematous base over the extremities but not on the head and trunk

N. gonorrhoeae is a leading cause of purulent arthritis in adult

Clinical Diseases

Clinical Diseases

Other diseases associated with N.

gonorrhoeae:

Perihepatitis (Fitz-Hugh-Curtis syndrome)

Purulent conjunctivitis, particularly in Purulent conjunctivitis, particularly in

newborns infected during vaginal delivery

(opthalmia neonatorum)

Anorectal gonorrhoea in homosexual men and

pharyngitis

Laboratory Diagnosis

Microscopy: Gram stain

Culture: Thayer-Martin medium, chocolate agar

Identification: oxidase-positive (acid produced Identification: oxidase-positive (acid produced oxidatively from glucose but not from other sugars), Gram negative diplococci that grow on chocolate agar

Genetic probes: sensitive, rapid (2 - 4 hrs)

Serology: gonococcal antigen-antibody detected; not recommended

Neisseria meningitidis

1. Physiology and Structure

The meningococci form transparent, non-pigmented colonies on chocolate agar, and their growth is enhanced in a moist atmosphere with 5% carbon dioxideatmosphere with 5% carbon dioxide

Isolates with large polysaccharide capsules appear as mucoid colonies

Meningococci are oxidase-positive and are differentiated from other Neisseria species by the production of acid from oxidation of glucose and maltose but not sucrose or lactose


N. meningitidis is subdivided into serogroups and serotypes

13 serogroups, with antigenic differences in their polysaccharide capsule, have been describeddescribed

A, B, C, X, Y and W135

The serotype classification of isolates is based on differences in the proteins in the outer membrane and in the oligosaccharide component of LOS


Serotype classification has proven useful for

epidemiologic classification and for the

characterisation of virulent strains

All group A meningococci have the same outer- All group A meningococci have the same outer-

membrane proteins and belong to a single

serotype, whereas the meningococci in group

B and C belong to multiple serotypes


2. Pathogenesis and Immunity

The outcome in a person exposed to N. meningitidis depends on the following 4 factors:

Whether the bacteria are able to colonise the nasopharynx (mediated by pili)nasopharynx (mediated by pili)

Whether specific group- and serotype-specific antibodies are present

Whether systemic spread occurs without antibody-mediated phagocytosis (protection afforded by polysaccharide capsule)

Whether toxic effects (mediated by the LOS endotoxin) are expressed


Experiments with nasopharyngeal tissue organ

cultures have shown that meningococci attach

selectively to specific receptors for

meningococcal pili on non-ciliated columnar meningococcal pili on non-ciliated columnar

cells of the nasopharynx

Meningococci without pili are less able to bind

these cells

Neisseria meningitidisMeningococcal disease occurs in the absence of

specific antibodies directed against the

polysaccharide capsule and other expressed

bacterial antigens

Infants are initially afforded protection by the

passive transfer of maternal antibodiespassive transfer of maternal antibodies

Immunity can be stimulated by colonisation with

N. meningitidis or other bacteria with cross-

reactive antigens (e.g. colonisation with N.

meningitidis sp; exposure to E. coli K1 antigen,

which cross-reacts with the group B capsular

polysaccharide)


Bactericidal activity also requires the existence

of complement

Patients with deficiencies in C5, C6, C7, or C8 of

the complement system are estimated to be at a the complement system are estimated to be at a

6000-fold greater risk for meningococcal disease

Meningococci are internalised into phagocytic

vacuoles and are able to avoid intracellular

death, replicate, and then migrate to the sub-

epithelial spaces

Protection: anti-phagocytic capsule


The vascular wall damage associated with meningococcal infection (e.g. endothelial damage, inflammation of vessel walls, thrombosis, disseminated intravascular coagulation) is largely attributed to the action coagulation) is largely attributed to the action of the LOS endotoxin present in the outer membrane

N. meningitidis produces excess membrane fragments that are released into the extracellular space


This continuous hyper production and release

of endotoxin may cause the severe endotoxic

reaction seen in patients with meningococcal

diseasedisease

Clinical Diseases

Meningitidis

The disease usually begins abruptly with headache, meningeal signs, and fever

Very young children may have only non- Very young children may have only non-specific signs, such as fever and vomiting

Mortality approaches 100% in untreated patients but is less than 10% in patients in whom appropriate antibiotic therapy is instituted promptly

Clinical Diseases

The incidence of neurologic sequelae is low,

with hearing deficits and arthritis most

commonly

Clinical Diseases

Meningococcemia

Septicaemia with or without meningitis is a

life-threatening disease

Thrombosis of small blood vessels and multi- Thrombosis of small blood vessels and multi-

organ involvement are characteristic clinical

features

Clinical Diseases

Clinical Diseases

Small petechial skin lesions on the trunk and

lower extremities are common and may

coalesce to form larger haemorrhagic lesions

Overwhelming disseminated intravascular Overwhelming disseminated intravascular

coagulation with shock, together with the

bilateral destruction of the adrenal glands

(Waterhouse-Friderichsen syndrome), may

ensue

Clinical Diseases

A milder, chronic septicaemia has also been

observed

Bacteremia can persist for days or weeks, and

the only signs of infection are a low-grade the only signs of infection are a low-grade

fever, arthritis, and petechial skin lesions

The response to antibiotic therapy in patients

with this form of the disease is generally

excellent

Clinical Diseases

Other syndromes

Pneumonia, arthritis, and urethritis

Meningococcal pneumonia is usually preceded by a respiratory tract infection

Symptoms: cough, chest pain, rales, fever and Symptoms: cough, chest pain, rales, fever and chills

Evidence of pharyngitis is observed in most affected patients

Prognosis in patients with meningococcal pneumonia is good


Most useful specimens for the detection of

meningococci are blood and cerebrospinal

fluid (CSF)

Although the organism is present in the blood Although the organism is present in the blood

of most patients with systemic disease,

additives in blood culture broths can be toxic

for Neisseria and can therefore inhibit or delay

bacterial growth


Because the bacterial count in CSF is high, the Gram negative diplococci are readily seen within polymorphonuclear leukocytes on Gram stain

Counter-immunoelectrophoresis or the agglutination of latex particles used to detect soluble polysaccharide antigen

N. meningitidis is relatively non-immunogenic and does not react with the test antigens

Treatment, Prevention and Control

Antibiotic therapy and supportive management for the complications of meningococcal disease have significantly reduced the mortality associated with the diseasedisease

Sulfonamides - successful; however, widespread resistance to the agents has now negated their effectiveness

Penicillin - more common; resistancy also becoming common


Because penicillin therapy remains effective

against most of these isolates, the clinical

significance of low-level resistance is unknown

Resistance to chloramphenicol and rifampin Resistance to chloramphenicol and rifampin

has been observed, so isolates from patients

whose does not respond to empirical therapy

should be evaluated carefully for antibiotic

resistance


Eradication of the pool of healthy carriers of

N. meningitidis is unlikely

Therefore, efforts have been concentrated on

the prophylactic treatment of people exposed the prophylactic treatment of people exposed

to diseased patients and on the enhancement

of immunity to the serogroups most

commonly associated with the disease


Sulfonamides were used for prophylaxis, but now

they are no longer considered reliable

Penicillin is ineffective in eliminating the carrier

statestate

Minocycline and rifampin have been effectively for

antibiotic-mediated chemoprophylaxis because

these antibiotics are secreted into the mucus

However, toxic effects have been associated with

minocycline, and rifampin-resistant N. meningitidis

can arise during treatment


Prophylaxis with a sulfonamide is

recommended for people exposed to

susceptible strains, with rifampin used for

those with sulfonamide-resistant strainsthose with sulfonamide-resistant strains

Vaccines directed against the group-specific

capsular polysaccharides have been

developed for antibody-mediated

immunoprophylaxis


A polyvalent vaccine effective against

serogroups A, C, Y, and W135, which can be

administered to children older than 2 years,

has been developedhas been developed

The vaccine cannot be administered to

children in younger age groups because they

do not respond to polysaccharide antigens


The group B polysaccharide is a weak immunogen and cannot induce a protective antibody response

Thus, immunity to group B N. meningitidis must develop naturally after exposure to cross-develop naturally after exposure to cross-reacting antigens

Vaccination with a suspension containing serogroup A can be used for control of an outbreak of disease, for travelers to hyper-endemic areas, or for people at increased risk for disease

Other Neisseria Species

Neisseria species such as Neisseria sicca and

N. mucosa are commensal organisms in the

oropharynx

Implicated in isolated cases of meningitis, Implicated in isolated cases of meningitis,

osteomyelitis, and endocarditis as well as

bronchopulmonary infection, acute otitis

media, and acute sinusitis

Other Neisseria Species

The observation of many Gram negative

diplococci associated with inflammatory cells

in a well-collected respiratory specimen would

support the etiologic role of these organismssupport the etiologic role of these organisms

Most isolates of N. sicca and N. mucosa are

susceptible to penicillin, although low-level

resistance caused by altered penicillin-binding

protein has been observed

Medical Microbiology I - Lecture10

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