No abstract

Streptococcus pyogenes, in addition to causing fulminant disease, can be carried asymptomatically and may survive in the host without causing disease. Long-term stationary-phase cultures were used to characterize the metabolism of cultures surviving after glucose depletion. Survival of stationary-phase cultures in glucosedepleted rich medium was truncated by switching the cells to phosphate-buffered saline or by the addition of antibiotics, suggesting that survival depended on the presence of nutrients and metabolic activity. The metabolites of the pyruvate-to-acetate (PA) pathway (acetate and formate) and amino acid catabolic pathways (ammonia) accumulated throughout long-term stationary phase (12 weeks). Acid and ammonia production was balanced so that the culture pH was maintained above pH 5.6. Strains isolated from long-term stationaryphase cultures accumulated mutations that resulted in unique exponential-phase metabolisms, with some strains expressing the PA pathway, some strains producing ammonia, and some strains expressing both in the presence of glucose. Strains expressing high levels of PA pathway activity during exponential growth were unable to survive when regrown in pure culture due to the production of excess acid. These data suggest that S. pyogenes diversifies during survival in stationary phase into distinct strains with different metabolisms and that complementary metabolism is required to control the pH in stationary-phase cultures. One of three survivor strains isolated from tonsillar discard material from patients expressed high levels of the PA pathway during exponential growth. Sequencing of multiple group A streptococcus regulators revealed two different mutations in two different strains, suggesting that random mutation occurs during survival.The human pathogen Streptococcus pyogenes (group A streptococcus [GAS]) is the causative agent of mild infections (e.g., impetigo and pharyngitis), severe disease (e.g., toxic shock syndrome and necrotizing fasciitis), and secondary sequelae (e.g., rheumatic fever and glomerulonephritis) (reviewed in references 17 and 32). Asymptomatic carriage and antibiotic treatment failure suggest that S. pyogenes may be able to persist in the host after the initial infection (5, 7). S. pyogenes asymptomatic carriage rates of 2.5% to 32% have been observed with large cohorts of school-age children worldwide (2,16,23,46,56,57,63,64). Carriage in adults is less frequent (1.3% to 4.9%) but has been observed with adult health care workers and military recruits (9, 34). Although not all cases of recurrent tonsillitis are clonal, carriage of S. pyogenes has been implicated as one of the causes of recurrent tonsillitis (5,7,8,46,52,53,56,59). In addition to recurrent tonsillitis, carriers have been associated with outbreaks of invasive disease (9, 15).Since the carried bacteria do not cause fulminant infection during carriage, it is likely that they survive in an altered growth state. Survival of bacteria has been characterized for both gram-negative and gram-positiv...