Epidemiology of penicillin resistant Neisseria

Objective-To study the epidemiology of Neisseria gonorrhoeae that exhibit both chromosomal and plasmid-mediated resistance to penicillin. Materials and methods-A total of 1589 strains of N gonorrhoeae isolated from patients attending St Mary's Hospital, London were tested for both their susceptibility to penicillin and for their auxotype and serotype. Results-Of the 940 non-penicillinase producing Ngonorrhoeae, 840 were considered penicillin sensitive (MIC <0 5 mg/l) and 100 were chromosomally-mediated resistant N gonorrhoeae (CMRNG), (MIC .1-0 mg/l). Of the 649 penicillinase producing Ngonorrhoeae (PPNG), 429 carried the 4.4 megadalton (MDa) penicillinase encoding plasmid and 220 carried the 3-2MDa plasmid. CMRNG were predominantly serogroup IB (90%). PPNG with 3.2 MDa plasmid were the only group more often serogroup IA (58%) than IB (42%). Serovar IA112 and requirement for arginine, hypoxanthine and uracil (AHU) were associated with increased susceptibility to penicillin whereas serovar IB-517 was associated with decreased susceptibility in nonPPNG. There was a significant difference in the distribution of the IA and IB serovars betweenPPNG carrying either the 4.4 MDa or 3.2 MDa plasmid. AHU and PAOU requiring strains were not foundamong PPNG and were uncommon among CMRNG. Conclusion-Some clear associations have been found but the pattern among PPNG appears more complex and in most instances could be related to clusters of a single strain over a short time span. Introduction Resistance to penicillin in N gonorrhoeae can be either chromosomally or plasmid mediated.' Chromosomal resistance is the result of low-level increases at multiple loci. Such resistance was first described in 19582 but could be overcome by increased therapeutic dosage. Plasmid-mediated resistance results from the presence of a TEM-1 type penicillinase and was first described in 1976'3 encoded on plasmids of 3-2 MDa and 4-4 (MDa)7 in N gonorrhoeae. Penicillinase-producing N gonorrhoeae (PPNG) are now common and their high level of resistance often results in failure to penicillin therapy. Other penicillinase encoding plasmids have been reported but are neither common nor widespread. In more recent years infections caused by chromosomally-resistant N gonorrhoeae (CMRNG) have increased89 and begun to present therapeutic