Transcript NEISSERIA
NEISSERIA The genus Neisseria contains two important pathogens: 1. Neisseria meningitidis 2. Neisseria gonorrhoeae. N. meningitidis causes meningitis and meningococcemia. N. gonorrhoeae causes gonorrhea,neonatal conjunctivitis (ophthalmia neonatorum) and pelvic inflammatory disease (PID). Properties: Neisseriae are gram-negative diplococci ( Bean shaped). Oxidase-positive; i.e., they possess the enzyme cytochrome c and produce oxidase. They are cultured on "chocolate" agar N.meningitidis is maltose fermenter N. gonorrhoeae is maltose non fermenter N.meningititidis produces no beta lactamases. Some of N. gonorrhoeae produce beta lactamases. Meningococcus has at least 13 serogroups on the basis of capsular polysaccharides. Important ones are A,B,C,Y and W-135. The endotoxin of N. meningitidis is a lipopolysaccharide (LPS) but the endotoxin of N. gonorrhoeae is a lipooligosaccharide (LOS). N.meningitidis is encapsulated while N.gonorrhoea has no capsule PILLI 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. N. meningitidis is the most common cause of meningitis in persons between the ages of 2 and 18 years. Outbreaks of meningitis are most common in winter and early spring, and favored by close contact between individuals. It has three important virulence factors: 1. Polysaccharride 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. 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. Manitol fermentation. The difference between N. meningitidis and N. gonorrhoeae is made on the basis of manitol fermentation. Meningococci ferment maltose, whereas gonococci do not F. Latex agglutination test, which detects capsular polysaccharide in the spinal fluid. 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: (Goonococcus). Non motile. Humans are only reservoir, not part of normal flora Causes disease only in humans. Killed by drying that’s why transmitted sexually. Pathogenecity: 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). 3. OMP cause attachment of bacteria to epithelial cells of the urethra, rectum, cervix, pharynx, or conjunctiva, like pilli. IgA protease. The main host defenses against gonococci are antibodies (IgA and IgG), complement, and neutrophils. IgA protease degrades one of these antibodies. Certain strains of gonococci cause disseminated infections. These gonococci resist killing by bacteria due to protein Porin A (OMP). It inactivates the C3b component of complement. 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. Prevention The prevention of gonorrhea involves the use of safety measures and the immediate treatment of symptomatic patients and their contacts.