An outbreak of penicillin resistant Streptococcus pneumoniae investigated by a polymerase chain reaction based genotyping method.

AIMS: To characterise the genotypes of penicillin resistant Streptococcus 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 had been admitted to a care of the elderly ward where an outbreak had occurred. Penicillin resistant S pneumoniae were also obtained from a series of surveillance throat swabs taken from patients in the same ward. In addition, all penicillin resistant S pneumoniae isolated from specimens submitted for culture at the time of the outbreak were included. Four sensitive strains isolated from a routine microbiology laboratory were included as controls. A simple polymerase chain reaction (PCR) based genotyping method for the penicillin binding protein (PBP) genes 1a, 2x, and 2b was used to characterise the genotypes.

RESULTS

Nine patients were infected with serotype 9 S pneumoniae. Four of these patients died; two deaths were directly attributable to the infection. Tested 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 outbreak strain had altered PBP 1a, 2b, and 2x genes, a pattern clearly distinguishable from other penicillin resistant strains isolated at the same time.

CONCLUSIONS

This method is simple to perform and would enable many laboratories to characterise the genotype of penicillin resistant S pneumoniae and investigate transmission in their hospitals.