AN OUTBREAK OF PENICILLIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE INVESTIGATED BY A POLYMERASE CHAIN-REACTION BASED GENOTYPING METHOD

Aims-To characterise the genotypes of penicillin resistant Streptococc us pneumoniae infecting patients in a care of the elderly ward and to study its transmission in a hospital environment. Methods-Isolates of S pneumoniae were cultured from specimens obtained from patients who h ad been admitted to a care of the elderly ward where an outbreak had o ccurred. Penicillin resistant S pneumoniae were also obtained from a s eries of surveillance throat swabs taken from patients in the same war d. In addition, all penicillin resistant S pneumoniae isolated from sp ecimens submitted for culture at the time of the outbreak were include d. Four sensitive strains isolated from a routine microbiology laborat ory were included as controls. A simple polymerase chain reaction (PCR ) based genotyping method for the penicillin binding protein (PBP) gen es 1a, 2x, and 2b was used to characterise the genotypes. Results-Nine patients were infected with serotype 9 S pneumoniae. Four of these pa tients died; two deaths were directly attributable to the infection. T ested against a battery of haemolytic streptococci and other organisms found in the respiratory tract, only two false positive reactions for PBP 2x were found among S mitis. The method demonstrated that the out break strain had altered PBP 1a, 2b, and 2x genes, a pattern clearly d istinguishable from other penicillin resistant strains isolated at the same time. Conclusions-This method is simple to perform and would ena ble many laboratories to characterise the genotype of penicillin resis tant S pneumoniae and investigate transmission in their hospitals.