Neisserial strains which exhibited characteristics of both N. gonorrhoeae and N. meningitidis were isolated from the eyes of patients with conjunctivitis in rural Egypt. Strains of this species have been isolated from men with urethritis in Alexandria, Egypt (unpublished data).
The "Egyptian" isolates exhibit characteristics of both N. gonorrhoeae and N. meningitidis (Table 1).
|Characteristic||Similarity to N. gonorrhoeae or N. meningitidis.|
|Colony Morphology||Produces large, pigmented colonies (similar to N. meningitidis).|
|Acid Production||Produces acid from glucose but not maltose (similar to N. gonorrhoeae).|
|Enzyme Substrate Test||Produces prolylaminopeptidase (similar to N. gonorrhoeae); does not produce gamma-glutamylaminopeptidase as does N. meningitidis.|
|Reaction in temperature-sensitive transformation test for N. gonorrhoeae||Gave positive reaction but at a lower frequency than for N. gonorrhoeae (similar to N. gonorrhoeae).|
|Reaction with N. gonorrhoeae-specific monoclonal antibodies||No reaction|
|Reaction with N. meningitidis-specific serotyping reagents||No reaction|
|Requirement for cystine/cysteine for growth on chemically defined (auxotyping) medium||Require cystine/cysteine (similar to N. gonorrhoeae).|
Note: N. meningitidis strains do not require cystine/cysteine to grow on auxotyping medium
The "Egyptian" strains have been identified as N. gonorrhoeae subsp. kochii; they are thought to have been the organism described by Koch in 1883 . This subspecies has not been documented in the United States; clinical isolates of this subspecies would be identified as N. gonorrhoeae by biochemical tests but probably would not be identified as N. gonorrhoeae if serological tests were used as the sole diagnostic test.
Acid produced only from Glucose
|Enzyme Substrate Test||Hydroxyprolylaminopeptidase-positive|
|Nitrate Reduction Test||Nitrate -ve|
Although strains of some organisms do not grow on medium on which polysaccharide is detected, polysaccharide may be detected in the growth inoculated onto the plate. N. gonorrhoeae subspecies kochii does not produce polysaccharide from sucrose.
(Reaction with 30% hydrogen peroxide)
Strains produce a strong (4+) reaction similar to N. gonorrhoeae.
(Reaction with 3% hydrogen peroxide)
If acid production or enzyme substrate tests are used to identify strains of "N. kochii," these strains will be identified as N. gonorrhoeae. Since strains of this group are classified as N. gonorrhoeae, this is an accurate identification. However, experienced laboratorians will be puzzled by the fact that the colony morphology of these strains is similar to N. meningitidis and, because of this similarity, may be inclined to identify them as maltose-negative strains of N. meningitidis. However, unlike N. meningitidis strains which produce gamma-glutamylaminopeptidase, strains of N. gonorrhoeae subsp. kochii produce hydroxyprolylaminopeptidase.
Depending on the identification test used, several strains of Neisseria and related species may be misidentified as N. gonorrhoeae subsp. kochii; the biochemical characteristics of these species are shown in Table 3.
Table 3. Differential characteristics of Neisseria spp. which produce acid only from glucose.
|-||-||-||Weak (1+) to|
|(M. catarrhalis)||-||-||-||-||-||GND||No reaction||+||-||+||Strong (3+ to 4+)|
Abbreviations: GND, Gram-negative diplococcus; GNR, Gram-negative rod; +, most strains positive; -, most strains negative; R, strains grow well on selective medium for N. gonorrhoeae and/or show no inhibition around a colistin disk (10 micrograms); (R), most strains susceptible, some strains known to be resistant.
Although enzyme substrate tests are intended to be used only for the identification of Neisseria spp. isolated on selective media for N. gonorrhoeae, these tests do provide additional information that may aid in accurately identifying an isolate. These tests should, however, not be used as the primary identification test for strains isolated on nonselective media.
Although enzyme substrate tests are intended to be used only for the identification of Neisseria spp. isolated on selective media for N. gonorrhoeae, isolates of other Neisseria spp. give the same reaction (hydroxyprolylaminopeptidase-positive) in this test as do isolates of N. gonorrhoeae. Thus, additional tests must be performed to differentiate between these species.
Table 4. Supplemental tests which permit differentiation among Neisseria and related species that produce hydroxyprolylaminopeptidase in enzyme substrate tests.
|Species that Produce|
|"N. kochii"*||Diplococci||+||-||-||-||-||-||-||Strong (4+)|
|N. gonorrhoeae||Diplococci||+||-||-||-||-||-||-||Strong (4+)|
|K. denitrificans||Rod filaments||+||-||-||-||-||+||-||-||R|
|(N. cinerea)||Diplococci||-||-||-||-||-||-||-||Weak (2+)|
|N. sicca||Diplococci||+||+||+||+||-||-||+||Weak (2+)|
|N. mucosa||Diplococci||+||+||+||+||-||+||+||Weak (2+)|
|(N. flavescens)||Diplococci||-||-||-||-||-||-||+||Weak (2+)|
Abbreviations: +, most strains positive; -, most strains negative; R, strains grow well on selective medium for N. gonorrhoeae and/or show no inhibition around a colistin disk (10 micrograms); (R), most strains susceptible, some strains known to be resistant; S, strains susceptible, no strains known to be resistant.
*Strains of N. gonorrhoeae subsp. kochii have colonies that resemble N. meningitidis but do not type with meningococcal serotyping tests.
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