DETERMINATION OF PENICILLIN SUSCEPTIBILITY OF STREPTOCOCCUS-PNEUMONIAE USING THE POLYMERASE CHAIN-REACTION

Aim-To develop a polymerase chain reaction (PCR) based method to detec t penicillin susceptibility in isolates of Streptococcus pneumoniae (S P). Methods-PCR primers were designed to amplify differential nucleoti de sequences of the penicillin-binding protein (PBP) genes 2b, 2x, and 1a in penicillin susceptible and resistant strains of SP Primers deri ved from the PBP 2x and 2b genes were designed to amplify products fro m penicillin susceptible S pneumoniae (PSSP), whereas primers derived from the PBP 1a gene were designed to amplify gene sequences of penici llin resistant S pneumoniae (PRSP). Results-Two hundred and thirty cli nical isolates of SP from the USA, UK, Kenya, Romania, and the Kingdom of Saudi Arabia were tested. Of the isolates, 116 were penicillin sus ceptible, 65 were intermediately resistant, and 49 were highly resista nt. PCR identified 108 (93%) of 116 of PSSP isolates, 55 (85%) of 65 i ntermediately resistant isolates, and all of the 49 highly resistant i solates of SP The susceptibility of 16 (7%) isolates could not be dete rmined using PCR. All of these 16 isolates had a minimum inhibitory co ncentration (MIC) of penicillin less than or equal to 1 mg/l. None of the highly resistant isolates was identified as penicillin susceptible by PCR, although two of the isolates with intermediate resistance (MI C = 0.125 mg/l) were. Conclusion-Using primers that differentially ide ntify the genotypes of susceptible and resistant strains of SP, PCR pr ovides a rapid method for determining the penicillin susceptibility of SP isolates and could potentially be used for testing clinical sample s.