Absence of autolytic activity (peptidoglycan nicking) in penicillin-induced nonlytic death in a group A streptococcus

Abstract

The extent of sublytic autolysin activity (peptidoglycan [PG] nicking) after exposure of exponentially growing cultures of a group A streptococcus (GAS) to benzylpenicillin (PenG) was studied by determining changes in the glycan chain length of PG polymers. The average PG chain length in isolated cell walls was estimated by calculating the ratio of the total hexosamine content (Morgan-Elson-reactive material) to reducing-end group content established via quantitation of [3H]borohydride reduction products. Comparison of the average PG chain length obtained from untreated control cultures of GAS with those obtained after exposure to a saturating dose of PenG revealed no decrease over a time interval equivalent to four mass doublings of the control cultures. Exposure to this concentration of PenG for a time equivalent to only two mass doublings resulted in approximately 90% loss of viability. In contrast, exposure of the lytic bacterium, Streptococcus faecium ATCC 9790, to a 50% growth inhibitory dose of PenG produced a 20% reduction in the average PG chain length concomitant with only a 65% loss of viability. Preliminary characterization of the autolytic system of GAS indicated that this streptococcus has a hexosaminidase-type autolysin. The results presented indicate the lack of autolytic activity in PenG-induced nonlytic death.