Lysozyme-mediated de-chaining of Streptococcus mutans and its antibacterial significance in an acidic environment

The ability of physiological amounts of lysozyme to de-chain two serotype c strains of Streptococcus mutans was determined. Both human and hen lysozymes were equally effective in chain breakage of S. mutans DPR and S. mutans DJR. De-chaining did not affect growth of cultures, but resulted in finely dispersed suspensions, at stationary phase, which were visibly different from untreated cultures. Less than 50 micrograms lysozyme per ml culture medium reduced chain length to virtually all diplococci and single cells, and this chain disruption increased total viable cell count. De-chaining required an active enzyme indicating that a degree of hydrolysis of the peptidoglycan occurred at the septae of the streptococci. De-chained S. mutans did not survive as well as streptococci of normal chain length when incubated under acidic conditions (pH 5.5), but gross cellular lysis was not apparent. The reduced aciduric property of the disrupted chains may have been due to a participation of autolysins or to a lethal triggered by the lysozyme-damaged peptidoglycan. De-chaining may be a mechanism by which lysozyme could regulate the levels of S. mutans in acidogenic plaque samples.