Genetic Studies of Sulfadiazine-resistant and Methionine-requiringNeisseriaIsolated From Clinical Material

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Abstract
Deoxyribonucleate (DNA) preparations were extracted fromNeisseria meningitidis(four isolates from spinal fluid and blood) andN. gonorrhoeaestrains, all of which were resistant to sulfadiazine upon primary isolation. These DNA preparations, together with others from in vitro mutants ofN. meningitidisandN. perflava, were examined in transformation tests by using as recipient a drug-susceptible strain ofN. 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 ofp-aminobenzoic acid was not significantly altered thereby. Transformants elicited by DNA from theN. meningitidisclinical isolates were resistant to at least 200 μg of sulfadiazine/ml, and did not show a requirement for methionine (Sul-r Met+). DNA from six strains ofN. 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 B12, 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. Themetlocus involved is genetically complex, and will be a valuable tool for studies of genetic fine structure of members ofNeisseria, and of genetic homology between species.