Epidemiological typing of Streptococcus pyogenes by pyrolysis mass spectrometry

Strains of Streptococcus pyogenes from an outbreak of infection on a burns unit (15), a collection of routine isolates from another hospital(12) and isolates from a national survey of throat infections in children in the community(4) were examined blind by pyrolysis-mass spectrometry (Py-MS). The outbreak strains (M22 T12) previously found to give identical typing results in conventional tests, formed a closely similar cluster and were distinct from other hospital and community strains. One hospital and one community strain were loosely associated with this cluster. Another cluster comprised six antibiotic-susceptible strains and two community strains. Six strains did not fall within the clusters; four were antibiotic-resistant strains isolated in hospital, one an antibiotic-resistant strain isolated in the community, and one a susceptible hospital strain. Results show that Py-MS is a potentially valuable method for rapid comparison of strains in studies of infection.