The diversity of the opa gene in gonococcal isolates from men who have sex with men.
OBJECTIVE
To use a molecular typing method (opa-typing) to characterise gonococcal isolates obtained from men who have sex with men (MSM) attending a genitourinary medicine (GUM) clinic in Edinburgh during 2001. To compare the results of opa-typing with A/S (auxotype/serovar) phenotyping, and with epidemiological information obtained by contact tracing.


METHODS
Isolates were opa-typed by a PCR-RFLP method where the restriction fragments resulting from digestion with three separate restriction enzymes were resolved by polyacrylamide gel electrophoresis. Isolates were considered to have the same opa-type if the band patterns were identical or if they differed by one band between the three digestions.


RESULTS
40 opa-types were detected from a collection of 73 gonococcal isolates from 61 patients. 26 opa-types were unique, being found in one individual each, 14 different opa-types were found in more than one patient. Opa-typing was found to have a discrimination index (DI) of 0.96, compared to a DI of 0.87 for A/S phenotyping, indicating that opa-typing is better at discriminating between unrelated isolates. Opa-typing confirmed three epidemiological links established by contact tracing, and uncovered a further 13 clusters of isolates.


CONCLUSIONS
Opa-typing is a more discriminative method than A/S phenotyping when determining relatedness in gonococcal isolates. The ability of opa-typing to identify sexual networks not disclosed by contact tracing and conventional phenotyping make it a useful method for studying the spread of gonorrhoea with the potential to contribute to the control of this infection.
Scottish Neisseria gonorrhoeae Reference Laboratory, Department of Laboratory Medicine, Edinburgh Royal Infirmary, 51 Little France Crescent, Edinburgh EH16 4SA, Scotland, UK.
F
F
Howie
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H
Young
A
A
McMillan
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000302:isolation & purification; D015373:Bacterial Typing Techniques; D006069:Gonorrhea / Q000382:microbiology*; D018451:Homosexuality, Male; D006801:Humans; D008297:Male; D009344:Neisseria gonorrhoeae / Q000235:genetics*; D010641:Phenotype; D016133:Polymerase Chain Reaction / Q000379:methods; D012150:Polymorphism, Restriction Fragment Length
D001425:Bacterial Outer Membrane Proteins; C090348:Opa protein, Neisseria