HIGH-LEVEL TETRACYCLINE-RESISTANT NEISSERIA-GONORRHOEAE IN ONTARIO, CANADA - INVESTIGATION OF A CLUSTER OF ISOLATES, SHOWING CHROMOSOMALLY MEDIATED RESISTANCE TO PENICILLIN COMBINED WITH PLASMID-MEDIATED RESISTANCE TO TETRACYCLINE

Between 1991 and 1994, plasmid-mediated, tetracycline-resistant Neisse ria gonorrhoeae (TRNG) increased from 61.8% to 85.96% of all resistant isolates in Ontario, Canada, Ninety-nine isolates with tetracycline M ICs > 32 mg/L were characterized by auxotype/serovar (A/S) class, plas mid profile, hybridization with eight tetracycline-resistant probes, a nd pulsed-field gel electrophoresis (PFGE) of genomic DNA after digest ion with NheI and SpeI restriction endonucleases. A cluster of 82 isol ates with penicillin MICs of 2-4 mg/L and tetracycline MICs of 128 mg/ L (chromosomally mediated resistance) belonged to A/S class NR/IB-1 an d had identical or closely related PFGE profiles, Seventeen isolates, TRNG (10) and penicillinase-producing TRNG (7), with tetracycline MICs of 64-256 mg/L, belonged to eight A/S classes and displayed 12 differ ent PFGE profiles, The 99 isolates hybridized only with the TetM probe , Phenotypic and molecular characterization indicated a diverse popula tion throughout the Province of Ontario.