Antimicrobial activity of Streptococcus salivarius K12 on bacteria involved in oral malodour.

OBJECTIVE: To investigate the antimicrobial activity of the bacteriocin-producing strain Streptococcus salivarius K12 against several bacteria involved in halitosis. DESIGN: The inhibitory activity of S. salivarius K12 against Solobacterium moorei CCUG39336, four clinical S. moorei isolates, Atopobium parvulum ATCC33793 and Eubacterium sulci ATCC35585 was examined by a deferred antagonism test. Eubacterium saburreum ATCC33271 and Parvimonas micra ATCC33270, which have been tested in previous studies, served as positive controls, and the Gram-negative strain Bacteroides fragilis ZIB2800 served as a negative control. Additionally, the occurrence of resistance in S. moorei CCUG39336 to S. salivarius K12 was analysed by either direct plating or by passage of S. moorei CCUG39336 on chloroform-inactived S. salivarius K12-containing agar plates. RESULTS: S. salivarius K12 suppressed the growth of all Gram-positive bacteria tested, but the extent to which the bacteria were inhibited varied. E. sulci ATCC35585 was the most sensitive strain, while all five S. moorei isolates were inhibited to a lesser extent. Natural resistance seems to be very low in S. moorei CCUG39336, and there was only a slight decrease in sensitivity after exposure to S. salivarius K12 over 10 passages. CONCLUSION: Our studies demonstrate that S. salivarius K12 has antimicrobial activity against bacteria involved in halitosis. This strain might be an interesting and valuable candidate for the development of an antimicrobial therapy for halitosis.

Isolation of Desulfomicrobium orale sp. nov. and Desulfovibrio strain NY682, oral sulfate-reducing bacteria involved in human periodontal disease.

The species of sulfate-reducing bacteria that prevail in sites affected by periodontal disease may be different from those commonly occurring in the digestive tracts of healthy individuals. Ten strains of mesophilic sulfate-reducing bacteria (SRB) were isolated from subgingival plaque in periodontal lesions of ten patients with periodontitis. Characterization on the basis of morphological, physiological and phylogenetic properties demonstrated two distinct types of oral SRB. One strain was a curved rod with high motility. For dissimilatory sulfate reduction, lactate or pyruvate was oxidized incompletely to equimolar amounts of acetate. Desulfoviridin and cytochrome c3 were present in this mesophilic vibrio and the cellular lipid profile was similar to that from members of the genus Desulfovibrio. The 16S rDNA sequence was similar to that of the proposed 'Desulfovibrio fairfieldensis'. Cells of the nine other strains were straight, rod-shaped, exhibited a low growth rate and oxidized substrates incompletely to acetate. These SRB, like members of the genus Desulfomicrobium, lacked desulfoviridin. Analysis of the 16S rDNA sequences of seven of the nine isolates showed a high degree of similarity among these oral strains, forming a distinct lineage within the genus Desulfomicrobium. The cellular lipid profile of a representative oral strain, NY678T, was in accordance with that of other Desulfomicrobium species, but also showed dissimilar features. The phenotypic and phylogenetic analyses indicate that these rod-shaped SRB from the oral cavity could be regarded as a new species, for which the designation Desulfomicrobium orale sp. nov. is proposed.

Identification of archaeal rDNA from subgingival dental plaque by PCR amplification and sequence analysis.

A PCR assay for the amplification of small subunit ribosomal DNA (SSU rDNA) of Euryarchaea was developed and used to detect archaeal rDNA in 37 (77%) out of 48 pooled subgingival plaque samples from 48 patients suffering from periodontal disease. One major group of cloned periodontal sequences was identical to Methanobrevibacter oralis and a second minor group to Methanobrevibacter smithii. These two groups and a third novel group were found to be more than 98% similar to each other over an 0.65-kb segment of the 16S rRNA gene sequenced. M. oralis was found to be the predominant archaeon in the subgingival dental plaque. Phylogenetic analysis of partial SSU rDNA sequences revealed evidence for a distinct cluster for human and animal Methanobrevibacter sp. within the Methanobacteriaceae family.

Transduction of antibiotic resistance markers among Actinobacillus actinomycetemcomitans strains by temperate bacteriophages Aa phi 23.

Actinobacillus actinomycetemcomitans (Aa) strain ST1 carries the tetracycline (Tc) resistance transposon Tn916 and the Aa phi ST1 prophage, which is closely related to temperate bacteriophage Aa phi 23. High titre phage preparations were obtained from this strain by mitomycin C induction and were used to transduce the TcR determinant to the TcS recipient strains ZIB1001 and ZIB1015 (MIC 2 micrograms Tc/ml). TcR transductants (MIC > or = 32 micrograms Tc/ml) were detected at frequencies of 3 x 10(-6) to 5 x 10(-8) per pfu. All TcR transductants examined contained the entire Tn916 inserted at several different locations within the Aa genome. They appear to have resulted from generalized transduction. In addition both bacteriophages, Aa phi 23 and Aa phi ST1, were capable of transducing the chloramphenicol (Cm) resistance marker of plasmid pKT210 (transduction frequencies of 2 x 10(-5) to 3 x 10(-7) per pfu) to the recipient strain ZIB1001 (MIC 8 micrograms Cm/ml). Eleven CmR ZIB1001 transductants (MIC > or = 100 micrograms Cm/ml) studied carried a plasmid indistinguishable from pKT210 by restriction analyses. In view of the high prevalence of this phage family, and the increasing use of tetracycline in periodontitis therapy, these findings may have clinical importance.

Regulation of the activity of the type IC EcoR124I restriction enzyme.

Restriction-modification (R-M) systems must regulate the expression of their genes so that the chromosomal genome is modified at all times by the methyltransferase to protect the host cell from the potential lethal action of the cognate restriction endonuclease. Since type I R-M systems can be transferred to non-modified Escherichia coli cells by conjugation or transformation without killing the recipient, they must have some means to regulate their restriction activity upon entering a new host cell to avoid restriction of unprotected host DNA and cell death. This is especially true for EcoR124I, a type IC family member, which is coded for by a conjugative plasmid. Control of EcoR124I restriction activity is most likely at the post-translational level as the transfer of the EcoR124I system into a recipient cell that already expressed the HsdR subunit of this system was not a lethal event. Additionally, the kinetics of restriction activity upon transfer of the genes coding for the EcoR124I RM system to a recipient cell are the same, irrespective of the modification state of the recipient cell or the presence or absence of the EcoR124I HsdR subunit in the new host cells. The mechanism controlling the restriction activity of a type IC R-M system upon transfer to a new host cell is different from that controlling the chromosomally coded type IA and IB R-M systems. The previously discovered hsdC mutant, which affects the establishment of the type IA system EcoKI, was shown to affect the establishment of the type IB system EcoAI, but to have no influence on EcoR124I.