Penicillin and cephalosporin resistance in gonococci

Non-penicillinase producing Neisseria gonorrhoeae isolated at St Mary's Hospital, London were examined for the prevalence of resistance to penicillin and for decreased susceptibility to cefuroxime. Of the 941 non-PPNG tested 100 (10.6%) were resistant to penicillin (minimum inhibitory concentration, MIC, greater than or equal to 1 mg/l) and were considered to be chromosomally-resistant N gonorrhoeae (CMRNG). Decreased susceptibility to cefuroxime (MIC, greater than or equal to 0.5 mg/l) was detected in 79% of the CMRNG. The CMRNG were also more often prototrophic and of serogroup IB than the remaining non-PPNG. The correlation coefficient for resistance to penicillin and cefuroxime was high, 0.79. Transformation experiments with both genetically-defined strains and transformants obtained using DNA from clinical isolates, showed that increased resistance to cephalosporins was acquired in three steps in close association with penicillin. We think this suggests that the loci controlling resistance to the cephalosporins are identical or closely linked to those controlling penicillin resistance.