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Flashcards in Gram-Negative Cocci Deck (22)
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Describe the gram-staining characteristics of Neisseria spp.

Neisseria are gram-negative diplococci with adjacent sides flattened. They resemble coffee beans. In a direct smear, pathogenic Neisseria are intracellular.


How do the growth requirements of pathogenic and nonpathogenic Neisseria differ?

The pathogens require an enriched medium (chocolate agar) and increased carbon dioxide. The nonpathogens grow on blood agar without increased carbon dioxide.


Which specimens might yield pathogenic Neisseria?

CSF, blood, synovial fluid, and genital specimens. These specimens should not be refrigerated because pathogenic Neisseria are sensitive to low temperatures. When Neisseria is suspected, it is best to plate the specimens directly and to use a carbon dioxide generating transport device.


Which species of Neisseria is always considered a pathogen?

N. gonorrhoeae. Some individuals carry N. meningitidis in the nasopharynx.


Which Neisseria species are part of the normal flora?

N. lactamica, N. flavescens, N. sicca, N. subflava, and N. mucosa are normal in the upper respiratory tract. N. cinerea is normal flora of the oropharynx and genital tract.


Name several gonococcal selective media.

Modified Thayer Martin (MTM), Martin Lewis, and New York City medium (NYC).


Which specimens are plated on gonococcal selective media?

Specimens for GC screens from sites with normal flora such as genital specimens, throat swabs, and rectal swabs. Normal flora is inhibited.


What organisms besides N. gonorrhoeae may grow on gonococcal selective media?

N. meningitidis, N. lactamica, N. cinerea, Moraxella (Branhamella) catarrhalis, and Kingella denitrificans.


Which pathogenic Neisseria can grow on blood agar?

N. meningitidis. N. gonorrhoeae does not.


Name several ways in which N. gonorrhoeae and N. meningitidis are alike.

Both are gram-negative diplococci, oxidase-positive, catalase-positive, and positive for glucose utilization.


How can N. gonorrhoeae and N. meningitidis be differentiated?

By enzyme substrate tests, antigen detection tests, or tests of sugar utilization. N. meningitidis is positive for maltose and N. gonorrhoeae is negative.


Which Neisseria causes salpingitis adn opthalmia of the newborn?

N. gonorrhoeae.


What non-culture tests are available for detection of N. gonorrhoeae directly from clinical specimens?

Antigen detection tests, direct specimen nucleic acid probes, and nucleic acid amplification tests.


What constitutes a definitive diagnosis of N. gonorrhoeae?

Colonies with typical colonial morphology
Gram-negative diplococci
Confirmation by biochemical, enzymatic, serologic, or nucleic acid test


Which gram-negative diplococci are normal in the upper respiratory tract and cause otitis media and sinusitis in children?

Moraxella (Branhamella) catarrhalis.


Which rapid test can differentiate N. meningitidis from N. lactamica?

ONPG. N. lactamica is ONPG-positive; N. meningitidis is ONPG-negative.


What are the CTA sugar reactions for N. gonorrhoeae, N. meningitidis, N. lactamica, and Moraxella catarrhalis?

N. gonorrhoeae: glucose (+), maltose (-), lactose (-)
N. meningitidis: glucose (+), maltose (+), lactose (-)
N. lactamica: glucose (+), maltose (+), lactose (+ slow)
M. catarrhalis: glucose (-), maltose (-), lactose (-)


Which Neisseria produces rapid and inmediate bubbling with 30% hydrogen peroxide (superoxol test)>

N. gonorrhoeae. N. meningitidis adn N. lactamica produce weak delayed bubbling.


What is PPNG?

Penicillinase-producing Neisseria gonorrhoeae. These penicillin-resistant organisms can be identified by a positive B-lactamase test.


What organism might be mistaken for Neisseria on a Gram stain?

Moraxella catarrhalis, Kingella denitrificans, and Acinetobacter.


Which of the following is oxidase-negative: Neisseria, Moraxella, Kingella, or Acinetobacter?



A gram-negative coccobacillus isolated from cerebrospinal fluid on chocolate agar resembles either Moraxella or Neisseria. What is the single best test to differentiate these two organisms?

Moraxella and Neisseria appear similar on a Gram stain, both are oxidase-positive, and both grow on gonococcal selective media. They can be differentiated by sugar utilization tests. Moraxella is negative for all the carbohydrates in the sugar utilization test. Neisseria is positive for at least one, depending on the species.