Lecture 6: Neisseria - Warith Al-Anbiyaa University

Lecture 6 :Neisseria Warith Al-Anbiyaa University College of Medicine Department Microbiology Dr Nisreen Jawad  Learning objectives After reading this lesson, you will be able to: 1. explain the characteristics of Neisseria species...

Lecture 6 :Neisseria Warith Al-Anbiyaa University College of Medicine Department Microbiology Dr Nisreen Jawad  Learning objectives After reading this lesson, you will be able to: 1. explain the characteristics of Neisseria species 2.discuss the diagnosis of disease caused by Neisseria species  The Neisseria Gram-negative cocci, usually occur in pairs to form (diplococci) The two medically important species are 1. Neisseria gonorrhoeae (gonococci) 2. Neisseria meningitidis (meningococci) Some other species are members of normal human respiratory tract microbiota, and either rarely or never cause disease  The typical Neisseria A Gram-negative, non motile kidney shaped diplococcus, The bacterial cells are about 0.8 µm in diameter. Culture features On enriched media (e.g. chocolate agar) , after 48 hours of incubation, the organisms can form convex, glistening, elevated, mucoid colonies – Their size can be 1–5 mm in diameter. – non pigmented and can be transparent or opaque, – non hemolytic. Growth Characteristics The Organisms grow best under aerobic conditions Oxidize carbohydrates, producing acid but not gas Meningococci and gonococci are fastidious, growing on media that containing complex organic substances such as heated blood, hemin, and animal proteins It requires an atmosphere containing 5% CO2. They are sensitive to the desiccation, moist heat, sunlight, and many different disinfectants Kovac’s oxidase test The oxidase test is a key test for identifying them. It determines the presence of cytochrome oxidase. When bacteria are treated with Kovac’s reagent (tetramethylparaphenylene diamine hydrochloride) the Neisseria rapidly turn into dark purple  1. Pili : The hair-like appendages extends from the gonococcal cell surface They enhance attachment to host cells and resistance to phagocytosis 2. Outer membrane proteins A- Por proteins o extends through the gonococcal cell membrane o Affect the intracellular killing of gonococci within neutrophils by preventing phagosome–lysosome fusion. o Confers resistance of gonococci to the bactericidal activity of normal human serum via binding to C3b and C4b proteins of human complement system.  B. Opa proteins : mediate adhesion of gonococci to host cell receptors. C. Rmp (Protein iii) This protein associates with Por in the formation of pores in the cell surface. 3. IgA1 protease : inactivates IgA1 antibodies, which are the main mucosal antibody of humans. 4. Lipooligosaccharide (endotoxin) It differs from lipopolysaccharide (LPS) of other Gramnegative bacteria as it lack the long O-antigen side chains and so called lipooligosaccharide (LOS). Their endotoxic effects are responsible for the toxicity in gonococcal infection Pathogenesis Transmission : 1. Sexual contact 2. Birth (infection of newborns during passage through an infected birth canal) Diseases 1– Gonococci can attack the mucous membranes of different sites of the body including : the genitourinary tract, eye, rectum, and throat, – resulting in acute suppuration that may lead to tissue invasion; followed by chronic inflammation and fibrosis. – Men usually have urethritis, with yellow, creamy pus and painful urination. – Urethral infection in men can be asymptomatic In women: The primary infection is in the endocervix which then extends to the urethra and vagina, leading to mucopurulent discharge. It may then progress to the uterine tubes, causing salpingitis, fibrosis, and obliteration of the tubes. Infertility occurs in 20% of women with gonococcal salpingitis. Chronic gonococcal cervicitis and proctitis are often asymptomatic. 2- Gonococcal bacteremia leads to skin lesions on the hands, forearms, feet, and legs 3- Gonococcal ophthalmia neonatorum It is an infection of the eye in newborns, acquired during passage through an infected birth canal. The progress of the initial infection is very rapid and can result in blindness if untreated  Diagnosis A. Specimens – Pus and secretions are taken from the urethra, cervix, rectum, conjunctiva, throat, or synovial fluid for culture and smear. – Blood culture is necessary in systemic illness B. Smears – Gram-stained smears of urethral or endocervical exudates reveal many diplococci within pus cells C. Culture – pus or mucus specimens can be streaked immediately after collection on enriched or selective medium (eg, Chocolate agar, Thayer-Martin and modified Thayer-Martin medium [MTM]) – and incubated at 37°C in 5% CO2 ,. – After 48 hours of incubation , the growing organisms can be identified by Gram-stained smear; by oxidase test; by coagglutination, immunofluorescence staining and any further laboratory tests.  Nucleic Acid Amplification Tests Provides direct detection of N gonorrhoeae in genitourinary specimens Advantages : better detection, more rapid results, and the ability to use urine as a specimen source. Treatment Because of the problems with antimicrobial resistance in N gonorrhoeae, Uncomplicated infections – ceftriaxone (250 mg) given intramuscularly as a single dose – Oral cefixime (400 mg ) as a single dose. Possible concomitant chlamydial infections – 1 g of azithromycin orally in a single dose or – 100 mg of doxycycline orally twice a day for 7 days  Prevention The infection rate can be reduced by – The early diagnosis and the treatment, which can eradicate the gonococcal infection rapidly – avoiding multiple Sexual partners, Mechanical prophylaxis (condoms) provides partial protection. Chemoprophylaxis : is with limited effects due to the increasing antibiotic resistance of the gonococci. Gonococcal ophthalmia neonatorum this infection can be prevented by local application of 0.5% erythromycin ophthalmic ointment or 1% tetracycline ointment to the conjunctiva of newborns  Neisseria meningitidis Differential features – Gram-negative diplococcucci – Obligate commensal to humans – The nasopharynx is the portal of entry – Grouped into 13 serogroups depending on the structure and immunogenicity of their capsular polysaccharides. – The serogroups that associated with disease in humans are A, B, C, X, Y, and W-135. – The bacteria utilize the maltose ( in contrast to gonococci)  Pathogenesis Transmission: bacteria can colonize around 5-10 % of healthy individual asymptomatically The bacteria transmit from one person to another via respiratory droplets, After colonizing the nasopharynx, it can reach the blood stream and then spread to the meninges A small rate of healthy carriers can develop diseases  Important virulence factors – Pili and outer membrane proteins (Opa and Opc) play the key role in colonization process as adhesins – Capsular polysaccharide: antiphagosytic confers resistance to serum bactericidal activity – IgA protease : inhibit IgA activity and promote – Lipooligosaccaride (endotoxine): Responsible for the endotoxin activity of the meningococcal infection causing fever, septic shock in the systemic infection  Diseases: The nasopharynx is the portal of entry. The bacteria colonize the healthy individual as a transient flora without causing disease (carriage state). In few cases , the bacteria can reach the bloodstream, disseminated and producing bacteremia Fulminant meningococcemia is severe, with a high fever and a hemorrhagic rash Waterhouse-Friderichsen syndrome, when the patient have disseminated intravascular coagulation and circulatory collapse Meningococcal meningitis is the most common complication of meningococcemia.  Diagnosis A. Specimens Specimens of blood are taken for culture Specimens of spinal fluid are taken for smear, culture, and chemical determinations. Nasopharyngeal swab cultures are suitable for carrier surveys. Puncture material from petechiae may be taken for smear and culture. B. Smears Gram-stained smears of the sediment of centrifuged spinal fluid or of petechial aspirate often show typical neisseriae within polymorphonuclear leukocytes or extracellularly. C. Culture Blood and Cerebrospinal fluid specimens are plated on agar culture media A modified MTM with antibiotics (selective media ) is used for nasopharyngeal cultures The grown colonies of neisseriae on solid media can be identified by Gram stain and the oxidase test Spinal fluid and blood generally yield pure cultures that can be further identified by carbohydrate oxidative reactions and agglutinatio D. Serology Antibodies against the capsular polysaccharides can be used as a detection test Their positivity can be detected by latex agglutination or hemagglutination tests or by their bactericidal activity. Polymerase Chain Reaction (PCR): using primers targeting specific meningococcal genes , providing rapid and sensitive detection  Treatment Penicillin G In persons who are allergic for penicillins chloramphenicol or a third generation cephalosporin (cefotaxime or ceftriaxone) can be used as alternatives  Prevention Vaccination – Capsular polysaccharides vaccines are available for groups A, C, Y, and W-135 – Tetravalent conjugate vaccines such as Menveo , contain capsular polysaccharides of group A, C, Y, W135 conjugated to diphtheria toxoid. – Bexero (protein based vaccine) provide protection against group B maningococci chemoprophylaxis – Rifampin or ciprofloxacin can be sued for decrease and eradicate the carrier rate and serve as chemoprophylaxis for people who are with close contact with the patients (such as household)