Streptococcus pneumoniae: how common is penicillin resistance in Australia?

Streptococcus pneumoniae in the past were uniformly susceptible to penicillin. Increasing levels of resistance are now seen worldwide. To define the prevalence of this resistance in Australia, a collaborative study was carried out on all pneumococcal isolates at 15 large metropolitan teaching hospitals. During 1989 details of results of penicillin testing using routine methods were recorded. Isolates found resistant to penicillin were forwarded to Woden Valley Hospital for determination of penicillin minimum inhibitory concentration (MIC). All invasive isolates from five of these hospitals were also forwarded during 1989 and 1990 for MIC testing. Of the 1822 isolates tested, 31 (1.7%) were recorded as penicillin resistant. However, only 16 of 22 resistant isolates forwarded for MIC testing had MICs of > or = 0.1 mg/L confirmed. After adjustment to account for discrepancies with different laboratory testing methods we calculated the likely penicillin resistance to be 1% of isolates. Two of 105 invasive strains tested were found to be penicillin resistant. We conclude that penicillin-resistant S. pneumoniae isolates, including isolates from invasive sites, are found in Australia. All of these isolates had an MIC between 0.1 and 1 mg/L and are thus regarded as 'intermediately' penicillin resistant isolates. No high level resistance (MIC > or = 2 mg/L) was observed. Ongoing surveillance is essential to detect changes in resistance patterns and prevalence, as this will have implications for the empiric treatment of serious disease caused by S. pneumoniae.