Surveillance of antibiotic resistance in invasive isolates of Neisseria meningitidis in Australia 1994-1999

A total of 1434 strains of Neisseria meningitidis isolated from cases of in vasive meningococcal disease (IMD) in Australia between 1994 and 1999 were examined by standard methods for susceptibility to antibiotics used for tre atment and prophylaxis. The proportion of isolates fully susceptible to pen icillin decreased from 45% in 1994 to 26% in 1999 (P<0.001). All the other isolates were less sensitive to penicillin except for two meningococci with a penicillin MIC of 1 mg/l. The geometric mean penicillin MIC increased fr om 0.045 to 0.065 mg/l from 1994 to 1999. There was no significant differen ce in the geometric mean penicillin MICs of serogroup B and serogroup C men ingococci. Penicillin susceptibility was significantly associated with a po orer outcome. Isolates from survivors of IMD had a higher geometric mean pe nicillin MIC (0.06 mg/l) than those from fatal cases (0.048 mg/l) (P<0.001) . This suggests that factors other than the decrease in susceptibility to p enicillin observed were more relevant to outcome in IMD. All isolates were fully susceptible to ceftriaxone. Rifampicin resistance was infrequent (eig ht isolates in 6 years) and sporadic. A single isolate had decreased quinol one susceptibility. Despite the significant shift in susceptibility to peni cillin recorded, this group of antibiotics remains a suitable treatment for IMD in Australia.