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Questions and Answers
What is the shape of Neisseria organisms when they occur in pairs?
What is the shape of Neisseria organisms when they occur in pairs?
Which media is required for optimal growth of Neisseria gonorrhoeae?
Which media is required for optimal growth of Neisseria gonorrhoeae?
What type of bacteria are Neisseria species generally classified as?
What type of bacteria are Neisseria species generally classified as?
Which of the following statements is true regarding the growth requirements of Neisseria?
Which of the following statements is true regarding the growth requirements of Neisseria?
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What test is key for identifying Neisseria species?
What test is key for identifying Neisseria species?
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Which of the following species of Neisseria is capable of oxidizing only glucose?
Which of the following species of Neisseria is capable of oxidizing only glucose?
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Which substance is NOT typically added to selective media for Neisseria growth to suppress other bacteria?
Which substance is NOT typically added to selective media for Neisseria growth to suppress other bacteria?
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Which Neisseria species is NOT considered catalase positive?
Which Neisseria species is NOT considered catalase positive?
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What is the sole carbohydrate utilized by N. gonorrhoeae for acid production?
What is the sole carbohydrate utilized by N. gonorrhoeae for acid production?
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Which serogroup is NOT associated with diseases in humans caused by Neisseria meningitidis?
Which serogroup is NOT associated with diseases in humans caused by Neisseria meningitidis?
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What allows Neisseria meningitidis to evade the host immune system?
What allows Neisseria meningitidis to evade the host immune system?
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What role do the pili of Neisseria meningitidis play in infection?
What role do the pili of Neisseria meningitidis play in infection?
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Which symptom is NOT typically associated with meningitis caused by Neisseria meningitidis?
Which symptom is NOT typically associated with meningitis caused by Neisseria meningitidis?
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Which statement accurately describes the progression of invasive meningococcal disease (IMD)?
Which statement accurately describes the progression of invasive meningococcal disease (IMD)?
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What structure of Neisseria meningitidis plays a critical role in binding to host cells?
What structure of Neisseria meningitidis plays a critical role in binding to host cells?
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What is the most common presentation of cases following meningococcal bacteremia?
What is the most common presentation of cases following meningococcal bacteremia?
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What is the primary function of pili (fimbriae) in Neisseria gonorrhoeae?
What is the primary function of pili (fimbriae) in Neisseria gonorrhoeae?
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What role do Por proteins play in Neisseria gonorrhoeae?
What role do Por proteins play in Neisseria gonorrhoeae?
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How does the reduction-modifiable protein (Rmp) change its apparent molecular weight?
How does the reduction-modifiable protein (Rmp) change its apparent molecular weight?
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Which of the following statements about lipooligosaccharide (LOS) in Neisseria gonorrhoeae is true?
Which of the following statements about lipooligosaccharide (LOS) in Neisseria gonorrhoeae is true?
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What is the recommended culture medium for Neisseria gonorrhoeae specimens?
What is the recommended culture medium for Neisseria gonorrhoeae specimens?
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Which specimen type is NOT typically collected for the diagnosis of Neisseria gonorrhoeae?
Which specimen type is NOT typically collected for the diagnosis of Neisseria gonorrhoeae?
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What do Gram-stained smears of urethral or endocervical exudates typically reveal for presumptive diagnosis?
What do Gram-stained smears of urethral or endocervical exudates typically reveal for presumptive diagnosis?
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What should be done if immediate culture incubation for Neisseria gonorrhoeae is not possible?
What should be done if immediate culture incubation for Neisseria gonorrhoeae is not possible?
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What severe condition may result from fulminant meningococcemia?
What severe condition may result from fulminant meningococcemia?
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What specimen is not typically used for the isolation of N. meningitidis?
What specimen is not typically used for the isolation of N. meningitidis?
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Which method is commonly used to identify N. meningitidis in CSF specimens?
Which method is commonly used to identify N. meningitidis in CSF specimens?
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What characteristic of N. meningitidis colonies can assist in their identification?
What characteristic of N. meningitidis colonies can assist in their identification?
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What is the main risk factor for developing meningococcal bacteremia from nasopharyngeal colonization?
What is the main risk factor for developing meningococcal bacteremia from nasopharyngeal colonization?
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What is the function of MTM agar in the laboratory?
What is the function of MTM agar in the laboratory?
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Which test is considered presumptive for identifying N. meningitidis?
Which test is considered presumptive for identifying N. meningitidis?
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What is a major risk associated with fulminant meningococcemia?
What is a major risk associated with fulminant meningococcemia?
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Study Notes
Neisseria
- Gram-negative cocci that occur in pairs (diplococci)
- Neisseria gonorrhoeae (gonococci) and Neisseria meningitidis (meningococci) are exclusively pathogenic for humans
- Typically found associated with or inside polymorphonuclear cells (PMNs)
Morphology and Identification
- Aerobic, Gram-negative, nonmotile diplococcus, approximately 0.8 µm in diameter
- Individual cocci are kidney bean shaped
- When in pairs, the flat or concave sides are adjacent
- Grow on sheep blood agar, chocolate agar, and selective agar media (eg, modified Thayer-Martin agar, Martin-Lewis agar and New York City medium)
- N. meningitidis grows on sheep blood agar as well as selective media
- N. gonorrhoeae requires enriched chocolate agar and/or selective media for optimal growth
- Selective media contain vancomycin (suppression of Gram-positive bacteria), colistin (suppression of Gram-negative bacteria), and other inhibitory substances to suppress the growth of many of the commensal microorganisms from these clinical sites.
- N. gonorrhoeae, N. meningitides, and N. lactamica are colistin-resistant, and are therefore able to grow on these selective media
- Grow best under aerobic conditions; however, some Neisseria species (eg, N. gonorrhoeae) are capable of growing under anaerobic conditions.
- Produce acid but not gas by oxidation of various carbohydrates; the oxidase test is hence a key test for identifying neisseriae
- All Neisseria species, with the exception of N. elongata, are catalase positive
- Grow best on media containing complex organic substances, such as heated blood, hemin, and animal proteins, and in an atmosphere containing 5% CO
2 - Rapidly killed by drying, prolonged exposure to sunlight, moist heat, and many disinfectants
- Produce autolytic enzymes that result in rapid swelling and lysis in vitro at 25°C and at an alkaline pH.
Neisseria gonorrhoeae
- Oxidize only glucose and differ antigenically from the other neisseriae.
Antigenic Structure
- N. gonorrhoeae is antigenically heterogeneous and capable of changing its surface structures in vitro---and presumably in vivo---to avoid host defenses.
- Surface structures include the following:
- Pili (Fimbriae): Enhance attachment to host cells and resistance to phagocytosis. Made up of stacked pilin proteins.
- Por: Extends through the gonococcal cell membrane. Forms pores in the surface through which some nutrients enter the cell. Por proteins may impact intracellular killing of gonococci within neutrophils by preventing phagosome-- lysosome fusion.
- Opa Proteins: Adhesion of gonococci within colonies and in attachment of gonococci to host cell receptors.
- Rmp (Protein III): A reduction-modifiable protein (Rmp) and changes its apparent MW when in a reduced state. Associates with Por in the formation of pores in the cell surface.
- Lipooligosaccharide: In contrast to the enteric Gram-negative rods, gonococcal lipopolysaccharide (LPS) does not have long O-antigen side chains and is called a lipooligosaccharide (LOS). Toxicity in gonococcal infections is largely attributable to the endotoxic effects of LOS.
- Other Proteins: Lip (H8) is a surface exposed protein that is heat modifiable like Opa. The Fbp (ferric-binding protein).
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.
Smears
- Gram-stained smears of urethral or endocervical exudates typically reveal many diplococci within PMNs, therefore providing a presumptive diagnosis.
Culture
- Immediately after collection, pus or mucus is streaked on enriched selective medium (eg, modified Thayer-Martin medium [MTM]) and incubated in an atmosphere containing 5% CO
2at 37°C. - To avoid overgrowth by contaminants, selective media contain antimicrobial drugs (eg, vancomycin, colistin, nystatin, and trimethoprim).
- If immediate incubation is not possible, the specimen should be placed in a CO
2- containing transport-culture system. - Forty-eight hours after culture, presumptive identification can be achieved by the organisms' appearance on a Gram-stained smear and by a positive oxidase test.
- The definitive species level of the sub-cultured bacteria may be determined by their ability to produce acid from certain carbohydrates by oxidation; the only carbohydrate used by N. gonorrhoeae is glucose.
Neisseria meningitidis
- The six most important serogroups associated with disease in humans, worldwide, are A, B, C, X, Y, and W-135.
- Incorporation of human sialic acid derivatives such as NANA into the meningococcal capsules allows the organism to be overlooked by the host immune system
- The outer membrane of N. meningitidis consists of proteins and LPS that play major roles in organism virulence.
- There are two porin proteins (Por A and Por B), interact with host cells.
- The opacity proteins (Opa) are comparable to Opa of the gonococci and play a role in attachment.
- Meningococci are piliated and these structures initiate binding to nasopharyngeal epithelial cells and other host cells such as endothelium and erythrocytes.
- The lipid A disaccharide of meningococcal LPS is responsible for many of the toxic effects found in meningococcal disease.
- The highest levels of endotoxin.
Pathogenesis, Pathology, and Clinical Findings
- The nasopharynx is the portal of entry.
- Organisms attach to epithelial cells with the aid of pili; they may form part of the transient microbiota without producing symptoms and/or disease.
- Invasive meningococcal diasease (IMD) occurs in only a small number of individuals who acquired the organism and are transient carriers; infants and adolescents have the highest incidence of IMD in developed countries.
- From the nasopharynx, organisms may reach the bloodstream, producing meningococcal bacteremia.
- The initial symptoms during this stage of the actual infection may be similar to those of an upper respiratory tract, "flu-like" infection, but IMD quickly ensues.
- IMD typically presents as meningitis, sepsis (ie, meningococcemia), or as a combination of both.
- Meningitis is the most common complication of meningococcal bacteremia.
- Usually begins suddenly with an intense headache, vomiting, photophobia, confusion, and stiff neck; it may progress to coma within a few hours.
- Fulminant meningococcemia is more severe, presenting with a high fever and a hemorrhagic rash; the patient may also develop disseminated intravascular coagulation and ultimate circulatory collapse with bilateral hemorrhagic necrosis of the adrenal glands with subsequent adrenal failure (Waterhouse-Friderichsen syndrome).
- In meningitis, the meninges are acutely inflamed, with thrombosis of blood vessels and exudation of polymorphonuclear leukocytes, so that the surface of the brain is covered with a thick purulent exudate.
- The exact mechanisms that transform an asymptomatic colonization of the nasopharynx into meningococcal bacteremia, subsequently leading to meningococcemia and meningitis, are not very well understood.
Diagnostic Laboratory Tests
- The typical specimens for isolation of N. meningitides include blood for culture and cerebrospinal fluid (CSF) for smear and culture.
- Puncture material or biopsies from petechiae may be taken for smear and culture.
- Nasopharyngeal swab cultures are suitable for carrier surveys.
Smears
- Gram-stained smears of the sediment of centrifuged spinal fluid or of petechial aspirate often show typical neisseriae within polymorphonuclear leukocytes or extracellularly.
Culture
- Although neisseriae are inhibited by certain toxic factors present in media and polyanethole sulfonate (anticoagulant) present in commercial blood culture broths, this seems to be of a lesser problem for the ability to recover N. meningitidis from blood cultures, compared to N. gonorrhoeae.
- CSF specimens are plated on sheep blood agar and chocolate agar and then incubated at 37°C in an atmosphere of 5% CO
2. - A MTM agar favors the growth of neisseriae, inhibits many other bacteria, and is used for nasopharyngeal cultures.
- Colonies of N. meningitidis are gray, convex, and glistening, with entire edges; a positive oxidase test together with a Gram-stain showing Gram-negative diplococci provides presumptive organism identification.
- Spinal fluid and blood generally typically yield pure cultures that can be further identified by carbohydrate oxidative reactions and subsequent agglutination with type-specific or polyvalent serum.
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Description
Test your knowledge on the genus Neisseria, including the morphological characteristics, growth requirements, and pathogenicity of key species such as Neisseria gonorrhoeae and Neisseria meningitidis. This quiz will challenge your understanding of Gram-negative cocci and their identification methods.
