Genetic studies of sulfadiazine-resistant and methionine-requiring Neisseria isolated from clinical material.

Deoxyribonucleate (DNA) preparations were extracted from Neisseria meningitidis (four isolates from spinal fluid and blood) and N. gonorrhoeae strains, all of which were resistant to sulfadiazine upon primary isolation. These DNA preparations, together with others from in vitro mutants of N. meningitidis and N. perflava, were examined in transformation tests by using as recipient a drug-susceptible strain of N. meningitidis (Ne 15 Sul-s Met(+)) which was able to grow in a methionine-free defined medium. The sulfadiazine resistance typical of each donor was introduced into the uniform constitution of this recipient. Production of p-aminobenzoic acid was not significantly altered thereby. Transformants elicited by DNA from the N. meningitidis clinical isolates were resistant to at least 200 mug of sulfadiazine/ml, and did not show a requirement for methionine (Sul-r Met(+)). DNA from six strains of N. gonorrhoeae, which were isolated during the period of therapeutic use of sulfonamides, conveyed lower degrees of resistance and, invariably, a concurrent methionine requirement (Sul-r/Met(-)). The requirement of these transformants, and that of in vitro mutants selected on sulfadiazine-agar, was satisfied by methionine, but not by vitamin B(12), homocysteine, cystathionine, homoserine, or cysteine. Sul-r Met(+) and Sul-r/Met(-) loci could coexist in the same genome, but were segregated during transformation. On the other hand, the dual Sul-r/Met(-) properties were not separated by recombination, but were eliminated together. DNA from various Sul-r/Met(-) clones tested against recipients having nonidentical Sul-r/Met(-) mutant sites yielded Sul-s Met(+) transformants. The met locus involved is genetically complex, and will be a valuable tool for studies of genetic fine structure of members of Neisseria, and of genetic homology between species.