Microbio Lec 6 - Neisseria

MICROBIOLOGY LECTURE 6 – Genus Neisseria Notes from Lecture USTMED ’07 Sec C – AsM 1. 2. 3.

4. 5.

Gram negative cocci that usually occurs in pairs Some are normal inhabitants of the human respiratory tract Some are pathogenic for humans and found associated with or inside the polymorphonuclears a. Neisseria meningitidis(meningococci) b. Neisseria gonorrheae(gonococci) Gonococci and meningococci are closely related with 70% homology Differences between gonococci and meningococci a. meningococci have polysaccharide capsules; gonococci do not. b. meningococci rarely have plasmids; most gonococci do

c. 6.

7.

meningococci typically are found in the upper respiratory tract and cause meningitis; gonococci cause genital infection

Neisseria meningitides a. has a prominent polysaccharide capsule that enhances virulence by its antiphagocytic action and induces protective antibodies b. divided into at least 13 serologic groups on the basis of the antigenicity of their capsular polysaccharides Neisseria gonorrheae(gonococcus) a. has no polysaccharide capsule but has multiple serotypes based on the antigenicity of its pilus protein b. marked antigenic variation in the gonococcal pili as a result of chromosomal rearrangement; more than 100 serotypes are known

c.

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have three outer membrane proteins (proteins I,II,and III) d. Protein II plays a role in attachment of the organism to cells and varies antigenically as well. Neisseria are gram negative bacteria and contain endotoxin in their outer membrane.

a. b.

NEISSERIA MENINGITIDIS

Pathogenesis 1. 2.

3.

Meningococcus – lipopolysaccharide (LPS) Gonococcus – lipooligosaccharide (LOS)

Both contain lipid A but LOS lacks the long repeating sugar side chains of LPS.

4.

9.

The growth of both organisms is inhibited by toxic metals and fatty acids found in certain culture media as in BAP. They are therefore cultured on “chocolate agar” containing blood heated to 80 C which inactivates the inhibitors. 10. Neisseriae are oxidase positive, ie, they possess the enzyme cytochrome c. – important laboratory diagnostic test wherein the colonies turn purple when exposed to phenylenediamine as a result of oxidation of the reagent by the enzyme

Humans are the only natural hosts for meningococci. They are transmitted by airborne droplets; they colonize the membranes of the nasopharynx and become part of the transient flora of the upper respiratory tract. From the nasopharynx, the organism can enter the blood-stream and spread to specific sites, such as the meninges or joints or be disseminated throughout the body (meningococcemia) Meningococci have three important virulence factors: a. Polysaccharide capsule – enables the organism to resist phagocytosis by polymorphonuclear leukocytes b. Endotoxin(LPS) – causes fever, shock, and other pathophysiologic changes

c.

Immunoglobulin A (IgA) protease- helps the bacteria attach to the membranes of the upper respiratory tract by cleaving secretory IgA

Clinical Findings 1.

Antigenic structure of Neisseria Gonorrhea 2.

Meningitis – symptoms are those of typical bacterial meningitis – fever, headache,vomiting, stiff neck and an increased level of PMN’s in spinal fluid Meningococcemia – clinical presentation is one of severe septicemia and shock

Waterhouse Frederichsen syndrome – the most severe form of meningococcemia characterized by high fever,shock, widespread purpura, disseminated intravascular coagulation and adrenal insufficiency. Meningococcal rash

1. 2. Neisseria gonorrhea virulence factors 3.

Initial rash – characterized by discrete, round,erythematous macules. Petechiae can be found in the skin, mucous membranes and conjunctivae; nailbeds are spared As the rash evolves, petechial and purpuric lesions are most pronounced on the trunk and lower extremities.

NEISSERIA GONORRHEAE

Pathogenesis

1. 2. 3. 4. 5. 6. 7.

8. 9.

Pili constitute one of the most important virulence factors, because they mediate attachment to mucosal cell surfaces and are antiphagocytic. Piliated gonococci are usually virulent, whereas nonpiliated strains are avirulent. Two virulence factors in the cell wall are: a. LOS (a modified form of endotoxin) b. outer membrane proteins The organism’s IgA protease can hydrolyze secretory IgA which could also block attachment to the mucosa. Gonococci have no capsules. The main host defenses against gonococci are antibodies (IgA and IgG, complement and neutrophils) Antibody mediated opsonization and killing within phagocytes occur, but repeated gonococcal infections are common primarily as a result of antigenic changes of pili and the outer membrane proteins. Gonococci infect primarily the mucosal surfaces eg. the urethra and vagina but dissemination occurs. The occurrence of dissemination is a function of the: a. strain of the gonococcus – important feature is the resistance to being killed by antibodies and complement b. effectiveness of the host i. Deficiency of the late acting complement components ii. Women during pregnancy and menses

eye, especially (keratitis).

Urethritis – characterized by thick, yellow purulent exudates containing bacteria and numerous neutrophils; frequent painful urination and possibly an erythematous meatus

2.

Complications of urethritis such as epididymitis and prostatitis in males and pelvic inflammatory disease in females; repeated infection may cause scarring with subsequent sterility in both sexes and may predispose females to ectopic pregnancy Rectal infections (prevalent in homosexual males) – characterized by painful defecation, discharge, constipation and proctitis Pharyngitis – characterized by purulent exudate; mild form mimics viral sore throat; severe form mimics streptococcal sore throat Disseminated infection (bloodstream invasion) – organisms initially localize in the skin, causing dermatitis (a single maculopapular, erythematous lesion), then spread to the joints, causing overt painful arthritis of the hands, wrists, elbows and ankles Infant eye infection (opthalmia neonatorum) – contracted during the passage through the birth canal; characterized by severe, bilateral purulent conjunctivitis that may lead to blindness

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Laboratory Diagnosis 1.

Microscopy

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Gram stain of Neisseria spp.Gram stained smear of a blood culture showing gram negative diplococci suggestive of Neisseria spp. The adjacent sides of the cell pairs look flattened and kidney bean shaped.

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Gram stain of Neisseria meningitides from a blood culture broth RBC and gram negative cocci in singles and pairs. The adjacent sides of the diplococci appear flattened.

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Gram stain of a urethral discharge Polymorphonuclears and gram negative intracellular diplococci is suggestive of Neisseria gonorrheae

2.

culture

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On physical examination, a mucopurulent urethral discharge is seen in 90% to 95% of men.

Neisseria gonorrheae on modified Thayer Martin(MTM) agar Colonies are small(0.5 to 1.0 mm. in diameter), gray, Glistening and opaque.

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Neisseria meningitidis on chocolate agar Colonies are more gray than yellow and nonhemolytic. In older cultures, a greenish cast appear beneath the Colonies in the area of heavy growth

3.

Oxidase test

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This test demonstrates that the organism is a member of the Neisseria family and is sufficient for presumptive diagnosisof Neisseria infection

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Tetramethyl-p-phenylene diamine hydrochloride is applied to colonies-----à purple color

It may appear spontaneously at the urethra without urethral manipulation(stripping)

Mucopurulent gonococcal cervicitis Mucopurulent gonococcal cervicitis Typical appearance of gonococcal infection in women – Cervical edema, erythema and mucopurulent discharge Gonococcal opthalmia with corneal opacification If untreated, it can rapidly progress to inflammation of other anatomical structures within the

Neisseria meningitidis on 5% sheep blood agar plate Colonies are round , smooth, opaque, glistening and 1-1.5 um in diameter and grayish in color but can appear Pink in color.

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Gonococcal urethritis with urethral discharge

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cornea

Pustular lesion of disseminated gonococcal infection on the heel

Clinical findings

1.

the

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Dimethyl compound(1%) may be used----à black color

4.

Identification of Neisseria spp. by carbohydrate utilization

- The standard method for identifying Neisseria spp. Is to determine acid in CTA(cystineTrypticase agar)medium, a Semisolid agar with 1% of each Of the carbohydrates glucose, Lactose, maltose and sucrose. Neisseria meningitidis – acid is Produced in both glucose and maltose

TREATMENT

1.

2.

Neisseria meningitides a. high doses of penicillin or ampicillin which may pass the blood brain barrier b. alternative antibiotics – chloramphenicol and the broad spectrum cephalosporins like cefotaxime and cextriaxone Neisseria gonorrhea a. Uncomplicated gonorrhea – initial therapy is ceftriaxone combined with tetracycline to manage dual infections with Chlamydia

b.

aqueous procaine penicillin G with oral probenecid

c.

if gonococci contain penicillinase, treat with spectinomycin

PREVENTION

1.

Neisseria meningitides a. Prophylactic treatment of persons who have significant exposure to disease patients. i. Minocycline and rifampin – used effectively for antibiotic mediated chemoprophylaxis ii. sulfonamide is recommended for persons exposed to sulfonamide susceptible strains with rifampin used for sulfonamide-resistant strains. b. enhancement of immunity to serogroups most commonly associated with disease i. Polyvalent vaccine – can be administered to children older than 2 yrs of age against groups A,C,Y and W135

Immunity to N. meningitidis group B must develop naturally after exposure to cross reacting antigens. Vaccination can be used to: a. Control an outbreak of disease with a serogroup present in the vaccine b. For travelers to hyperendemic areas c. For individuals at increased risk for disease (patients with complement deficiency)

2.

Neisseria gonorrhea a. avoiding multiple sexual partners. b. rapidly eradicating gonococci from infected individuals by means of early diagnosis and treatment c. finding cases and contacts through education and screening of populations at high risk d. mechanical prophylaxis(condoms) provides partial protection e. Chemoprophylaxis is of limited value because of the rise in antibiotic resistance of the gonococcus f. Gonococcal opthalmia neonatorum – local application of O.5 % erythromycin

opthalmic ointment or 1% tetracycline ointment to the conjunctiva of the newborn - fin [email protected] [email protected]