Neisseria Species and Gonorrhea: Characteristics, Virulence Factors, and Pathogenicity

PHT313 Lecture 1 2ndTerm 1436-1437 Dr. Hesham Radwan

Objectives By the end of this lecture the student must be: A) Identify the genus Nesseria B) describe the chemical tests for this genus C) Differentiate between different sps. D) List and match the symptoms, diagnosis and treatment for different sps.

1. Neisseria species 1. Primary pathogens: a. N. gonorrhoeae (Gonococcus) ALWAYS pathogenic b. N. meningitidis (Meningococcus) May be carried as commensal in nasopharynx flora (10-25% carrier) Grow on chocolate agar at 370C under 5-10% CO2 2. Non-pathogenic (Commensals) Example N. lactamica Grow on ordinary medium at room temperature Habitat of non-pathogenic Upper respiratory, Genitourinary andAlimentary tract 3

Pathogenic Neisseria General characteristics Gram-negative diplococci with adjacent sides flattened (like coffee beans) Non motile Oxidase and Catalase positive Aerobic, capnophilic (5% CO2) and oxidative Requires complex media pre-warmed to 370C Susceptible to cool temperatures, drying and fatty acids Soluble starch added to neutralize fatty acid toxicity Intracellular human-specific pathogen 4

a. Neisseria gonorrhoeae Virulence factors 1. Fimbrae (pili) To adhere to host cells and to each other >100 serotypes known according to pilus protein Has not polysaccharide Capsule 2. Outer membrane proteins (formerly Proteins I, II, & III) Involved in adherence to host cells 3. IgA protease- cleaves IgA on mucosal surfaces IgA blocks the ability of bacteria to adhere IgA protease involved in successful colonization 4. Lipopolysaccharide Prevents phagocytosis 5

Pathogenicity Pyogenic infection of columnar and transitional epithelial cells Urethral, endocervix, anal canal, pharynx, conjunctiva 1. Venereal (Sexual Transmitted Disease (STD)) A. Genital infections Gonorrhea B. Extragenital infections Pharyngitis and Anorectal infections 2. Non-venereal Ophthalmia neonatorum Vaginitis in small girls Contaminated toilet seats and contaminated towels 6

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Gonorrhea Gonorrhea transmitted by sexual intercourse Gonorrhea is the second most common venereal disease Incubation period: 2 to 7 days Females Males 50% risk of infection after single exposure 20% risk of infection after single exposure Symptomatic infections frequently diagnosed Most initially symptomatic (95% acute) Major reservoir is asymptomatic carriage Major reservoir is asymptomatic carriage Genital infection primary site is cervix (cervicitis), but vagina, urethra, rectum can be colonized Genital infection generally restricted to urethra (urethritis) with purulent discharge and dysuria Ascending infections in 10-20% including salpingitis (Fallopian tubes), tubo-ovarian abscesses, PID, chronic infections can lead to sterility Rare complications may include epididymitis, prostatitis, and periurethral abscesses Disseminated infections more common, including septicemia, infection of skin and joints (1-3%) Bacteremia and Gonococcal arthritis occurs as a result of disseminated gonococcal bacteremia Disseminated infections are very rare Can infect infant at delivery (opthalmia neonatorum) 8

Ophthalmia Neonatorum Contamination of infant s eye during labour through the birth canal of mother In infancy, an eye infection (ophthalmia neonatorum) may occur during vaginal delivery Conjunctivitis with mucopurulent discharge May cause blindness if not treated Infection is preventable with the application of erythromycin eye drops at birth (chlamydia & Neisseria) 9

Laboratory Diagnosis 1. Clinical specimens Gonnorhea Female Cervical discharge in acute and chronic Cervical swab may give positive results Male Acute: Urethral purulent discharge after urinating Chronic: The morning drop or prostatic massage Ophthalmia neonatorum Mucopurulent discharge 2. Direct microscopy (Gram stain) Small, gram-negative diplococci in presence of (WBCs) 10

Laboratory Diagnosis 3. Culture Inoculate specimen on non selective (chocolate agar) or selective media [Thayer-Martin] Incubated at 350 C in 5% CO2 The suspected colonies are Gram-negative diplococci with adjacent sides flattened (like coffee beans) 4. Biochemical tests Oxidase + & produce acid from glucose only Fresh growth must be used for testing, because N. gonorrhoeae produces autolytic enzymes 11

Prevention and control Penicillin no longer drug of choice due to: Continuing rise in the MIC Beta-lactamase production (some strains) Ceftriaxone, cefixime or fluoroquinolone combined with doxycycline or azithromycin for dual infections with Chlamydia Chemoprophylaxis against gonorrhea is of little value Chemoprophylaxis against ophthalmia neonatorum with 1% silver nitrate 1% tetracycline or 0.5% erythromycin eye ointment Measures to limit epidemic include education, detection, and follow-up screening of sexual partners, use of condoms No vaccine is available 12

b. Neisseria meningitidis (Meningcoccus) Encapsulated small, gram-negative diplococci Similar to Neisseria gonorrhoeae The main differences are N. gonorrhea Genital tract N. meningitidis Respiratory tract Present None Positive Available Portal of entry Polysaccharide capsule Absent Beta-lactamase Acid from maltose Vaccine Some Negative Not available 13

Pathogenicity: Pili-mediated receptor-specific colonization of cells of nasopharynx Antiphagocytic polysaccharide capsule Allows systemic spread in absence of specific immunity 13 serogroups six of which (A, B, C, W135, X, Y) can cause epidemics Serogroups A, B, C, Y, W135 account for 90% of all infections Serotypes A, B and C are the most common worldwide Serotype A is common in epidemics in Africa Toxic effects mediated by hyperproduction of LPS (endotoxin) Other virulence factors as in N. gonnorhea 14

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Clinical Infections 1. Meningitis (30-50%) 2. Meningitis with meningococcemia (40%), or 3. Meningococcemia without obvious meningitis (7-10%) Second most common cause of community-acquired meningitis Person-to-person transmission by respiratory droplets Commonly colonize nasopharynx of healthy individuals; highest oral and nasopharyngeal carriage rates in school-age children, young adults and lower socioeconomic groups Requires close contact with infectious person in crowded conditions (e.g. military barracks, prisons, Hajj and other) Requires lack of specific antibody (susceptibility) Incubation period is 2-10 days Symptoms: Fever, headache, stiff neck, nausea, vomiting and purulent meningitis with increased WBCs 16

Laboratory Diagnosis: Specimens CSF appears turbid (meningitis) Blood (meningecoocemia) Nasopharyngeal swabs (carrier) Large numbers (e.g. >107cells/ml) of encapsulated, small, gram-negative diplococci and PMN s can be seen microscopically in CSF Extracellular and intracellular Culture Transparent, non-pigmented nonhemolytic colonies on chocolate, TM agar with enhanced growth in 5% CO2 Biochemical and Immunologic tests Oxidase-positive Acid production from glucose and maltose Immunologic methods are available for sero-grouping 17

Prevention and control Prophylaxis 1. 2. 3. 1. Antibiotic prophylaxis is recommended for certain close contacts Avoid crowdedness Vaccination Several vaccines are available to control the disease They are designed to prevent serogroups A, C, Y, and W-135 They are lacking serogroup B antigen Tetravalent Meningococcal Polysaccharide vaccine (MPSV4) Available since 1981 and used for people >55 years 2. Meningococcal Conjugate Vaccine (MCV) When polysaccharides are conjugated to carrier proteins, the polysaccharide antigens become immunogenic in infants and prime for memory anticapsular antibody responses 18