Summary auto-generated
Researchers classified 16 Streptococcus mutans strains producing mutacins (bacteriocins) into four distinct groups (A-D) based on their inhibitory activity patterns and immunity characteristics. Group A strains (including mutacin I producer UA140) showed inhibition of other mutans streptococci but not Staphylococcus aureus or Enterococcus. Group B strains (including mutacin II producer UA96) inhibited Staph. aureus additionally and were pigmented. Group C strains inhibited both Staph. aureus and Enterococcus species. Group D strains (H7, H23) resembled group C but lacked immunity to their own bacteriocin products. Phylogenetic analysis using multilocus enzyme electrophoresis and phenotypic characteristics revealed that groups B and C were associated with distinct evolutionary lineages of S. mutans, suggesting the mutacin genes were chromosomally encoded and linked to core housekeeping genes rather than located on plasmids. Preliminary characterization confirmed at least four distinct mutacin types, with groups C and D representing previously undescribed bacteriocin activities in S. mutans.
Key findings
- Sixteen S. mutans mutacin-producing strains were classified into four distinct groups based on inhibitory activity patterns and immunity to their own bacteriocins
- Groups B and C strains were associated with specific evolutionary lineages of S. mutans, indicating mutacin genes are chromosomally located rather than plasmid-encoded
- Group C and D strains showed inhibitory activity against both Staphylococcus aureus and Enterococcus species, distinct from groups A and B
- Groups C and D represent two previously undescribed types of mutacin activity in S. mutans, expanding the known diversity of these oral bacteriocins
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Abstract
Bacteriocins produced by mutans streptococci are known as mutacins. In this study 16 broadly active mutacin-producing Streptococcus mutans strains from New Zealand, North America and Europe were classified into four groups (AD) on the basis of differences in their activity in deferred antagonism tests against either the homologous producer strain (to test for presence of self-immunity) or indicator strains Staphylococcus aureus 46 and Enterococcus faecium TE1. Two of the strains included in the study (UA140 and UA96) were representatives of the group I and II mutacin producer strains previously described by Caufield and co-workers. One of the New Zealand isolates of group A (S. mutans strain N) appeared to produce inhibitory activity similar to that of the group I prototype strain UA140. Four other New Zealand isolates of group B (S. mutans strains M19, M34, B34 and D14) had mutacin II-like activity. The group B mutacin producers differed from the group A mutacin producers in their additional activity against Staph. aureus 46. Seven S. mutans strains (M46, B46, B57, M12, M28, B28 and 13M) were distinguished from the group A and group B mutacin producers in that they inhibited E. faecium TE1. These were called group C mutacin producers. Strains H7 and H23 resembled the group C strains in their action on both indicator strains TE1 and 46. However, these two strains failed to exhibit immunity to their own inhibitory products in the deferred antagonism test and were separately classified as group D mutacin producers. Phylogenetic analysis of the strains by several genotypic and phenotypic characteristics revealed that the mutacin groups were associated with distinct evolutionary lineages of S. mutans.