Epidemiological studies on Neisseria gonorrhoeae isolated in the United Kingdom

Seven hundred and seventy nine isolates of Neisseria gonorrhoeae from the County of Avon, United Kingdom, were examined by auxotyping and penicillin susceptibility testing. Prototrophic strains which were heterogeneous as judge by penicillin susceptibility were the most commonly isolated and increased in prevalence over the three year period. The group most generally susceptible to penicillin required ArgHypUra for growth and decreased in prevalence over the three year period. Ten strains failed to grow on the auxotyping medium. Serogrouping was undertaken on 408 isolates. All strains reacting with the WI reagents were ArgHypUra requiring. However auxotypically similar strains (ArgHypUra) reacted with WII/WIII reagents suggesting a distinct and separately evolved group. Twenty four strains did not type with the serogrouping reagents. Using contact pairs, W-class serology was found to be a stable marker during natural transmission. However auxotypes were found to be unstable in 22 of 104 contact pairs and of these 18 involved a single requirement for proline. This very high incidence of instability with respect to this marker means it is not possible to reliably differentiate between the prototrophic group and the group with a single requirement for proline.