K. W. Knox

The aggregation of human platelets by Lactobacillus species

The ability to aggregate human platelets was examined for five Lactobacillus rhamnosus strains and five Lactobacillus paracasei subsp. paracasei strains isolated from patients with infective endocarditis (IE), 25 laboratory isolates from the same two species, and 14 strains from five other oral species, namely Lactobacillus acidophilus, Lactobacillus fermentum, Lactobacillus oris, Lactobacillus plantarum and Lactobacillus salivarius. Amongst the L. rhamnosus strains, platelets were aggregated by all five IE strains and 8/16 laboratory strains. For the L. paracasei subsp. paracasei strains, the respective numbers were 2/5 and 2/9. Aggregation also occurred with 11/14 strains of the other five species; each species was represented. The optimal ratio of bacteria to platelets for aggregation was approximately 1:1, and there was considerable variation in the lag phase that preceded aggregation, depending on the source of the platelets. Overall, the lag phase varied between 0.25 +/- 0.1 and 20.4 +/- 3.2 min and the percentage aggregation ranged between 70 +/- 2.6 and 104 +/- 13.5%. Confirmation that aggregation was being observed came from studies with five strains on the inhibitory effects of EDTA, dipyridamole, apyrase, imipramine, acetylsalicylic acid and quinacrine. Inhibition of aggregation by L. rhamnosus strains by the peptide arginine-glycine-aspartic acid-serine (RGDS) further indicated a role for fibronectin and/or fibrinogen. Pronase treatment of cells for 1 h and extraction of bacterial surface components with 0.1 M-Tris/HCl (pH 8.5) at 37 degrees C for 1 h stopped aggregation in 8/9 IE strains. Extracted surface proteins (200 micrograms) completely inhibited platelet aggregation by 8/9 of the homologous strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptococcus australis sp. nov., a novel oral streptococcus.

Strains of streptococci were isolated from the mouths of children attending the United Dental Hospital, Sydney, Australia. These strains were analysed biochemically using the Rapid ID32 Strep microsystem, were subjected to DNA-DNA hybridization with other members of the oral streptococci and had their 165 rRNA analysed. On the basis of DNA-DNA hybridization, their nearest relative was Streptococcus parasanguinis, whereas, on the basis of 16S rRNA analysis, it was Streptococcus infantis. The name Streptococcus australis sp. nov. is proposed for the new species. The type strain is AI-1T (= ATCC 700641T = NCTC 13166T).

A new species of oral Streptococcus isolated from Sprague-Dawley rats, Streptococcus orisratti sp. nov.

Taxonomic studies were performed on an unusual oral Streptococcus strain isolated from Sprague-Dawley rats. The isolates were alpha-haemolytic, bile-tolerant, aesculin-hydrolytic and unable to grow in 6.5% NaCl. They fermented lactose, sucrose and trehalose. They were distinguished from other recognized species of oral and viridans streptococci by several biochemical characteristics and by Lancefields group antigen, as well as by unique DNA-DNA hybridization characteristics. 16S rDNA sequence studies confirmed the genealogical distinctiveness of the species. The results of the study demonstrated that the isolates represented a new species of the oral and viridans streptococci. The name Streptococcus orisratti sp. nov. is proposed for the new species. The type strain is A63T (= ATCC 700640T).

Biochemical properties of Streptococcus sobrinus reisolates from the gastrointestinal tract of a gnotobiotic rat

Streptococcus sobrinus strain 6715-13-201 was inoculated into the oral cavity of a gnotobiotic rat and then reisolated from different portions of the gastrointestinal tract. Fourteen isolates, selected on the basis of their colonial morphology, were then screened for their ability to adhere to saliva-coated hydroxyapatite (SHA) in vitro, and their ability to produce extracellular polysaccharide from sucrose, and low pH in glucose broth. Certain isolates were also tested for their cariogenic potential as monoinfectants in gnotobiotic rats. All isolates differed in their abilities to adhere to SHA, with most showing an increased level of adhesion in the presence of sucrose, but this did not correlate with their ability to be aggregated by dextran. Most isolates were capable of producing glucosyltransferases (with only one exception) and dextranases (also one exception). There was more variability in the production of dextranase inhibitor. No isolate was capable of producing dextranase inhibitor in the absence of dextranase production. There were no correlations between the ability of isolates to adhere in vitro or produce/utilize polysaccharides and their ability to produce caries in vivo. Due to the differences between strains in their abilities to adhere, produce polysaccharides, utilize polysaccharides or produce a low pH and the lack of correlation between any of these parameters and cariogenicity, the results suggest that the ability of strains to colonize and produce caries depends on a number of different characteristics, no one of which is essential.