TYPING BY SEROVAR, ANTIBIOGRAM, PLASMID CONTENT, RIBOPROBING, AND ISOENZYME TYPING TO DETERMINE WHETHER NEISSERIA-GONORRHOEAE ISOLATES REQUIRING PROLINE, CITRULLINE, AND URACIL FOR GROWTH ARE CLONAL

Neisseria gonorrhoeae isolates requiring proline, citrulline, and urac il for growth (PCU-) have homogeneous phenotypes; most are plasmid-fre e, belong to few serovars, and are significantly associated with inter mediate levels of susceptibility to penicillin, tetracycline, erythrom ycin, and cefoxitin. Because of their lack of variation by these crite ria, molecular typing methods, ribotyping (restriction fragment length polymorphism [RFLP] of rRNA genes), and multilocus enzyme electrophor esis were explored as tools for further distinguishing PCU- isolates. By ribotyping, selected PCU- isolates could be separated into four gro ups on the basis of the hybridization patterns (RFLPs) of SmaI- and Av aII-digested DNA with probes containing rRNA sequences. Most of the is olates (18 of 23 isolates) belonged to a single RFLP (group I). One is olate each was in groups II and IV, and three isolates were in group I II. All isolates except one, isolate NS791, had similar multilocus enz yme electrophoresis patterns. Strain NS791 was unusual in that it cont ained a variant cryptic plasmid with an insert in the 0.46-kb MspI-Hin fI fragment of the 4.2-kb plasmid, it was the only isolate belonging t o RFLP group IV, and it differed in its multilocus enzyme electrophore sis pattern, having different mobilities for glyceraldehyde phosphate dehydrogenase, phosphoglucose isomerase, 6-phosphogluconate dehydrogen ase, and glutamate dehydrogenase. Serovars of PCU- isolates appeared t o be more indicative of strain divergence than RFLP or isoenzyme typin g. Multilocus enzyme electrophoresis indicated that PCU- isolates are clonal.