Streptococcus species, inhibition

A jS-D-galactosidase has been isolated from culture filtrates of a Streptococcus species by affinity chromatography on agarose derivatized with either oxamic acid or l-thio-jS-D-galactopyranose. The substrate specificity of the enzyme is similar to that of the jS-D-galactosidase from E. coli the enzyme was inhibited by H4edta and was activated by Mn +, Ca +, and Mg + ions. 

Antibacterial Spectrum. Hawley reported that various species and strains of the genera Staphylococcus, Streptococcus, Neisseria, Bacillus, Clostridium, and Corynebacterium are inhibited by nisin (Hawley 1957A, B). Mattick and Hirsch (1947) added actinomycetes, pneumococci, mycobacteria, and Erysipelothrix to this list. The nisin concentration required for complete inhibition is organism specific and ranges from 0.25 to 500 units per milliliter. Inhibition of L. casei by antibiotics from S. lactis and S. cremoris was observed by Baribo and Foster (1951). Inhibition of Propionibacterium by nisin but not of coliform bacteria was reported by Galesloot (1957). 

Many bacteria are much more sensitive than E. coli to crystal violet. Thus Streptococcus pyogenes is inhibited by a dilution of 1 in 320000 (though not by 1 in 640000) and Staphylococcus aureus is killed by 1 in 2000000. Although these differences may be partly due to differences in sites of loss, there are different values for different species and (in the hosts) for different tissues in the one species. This affords a basis for the selective action of cationic drugs. 

Chlorhexidine initially was used as a general disinfectant because of its broad antibacterial action (9). It was later shown to inhibit dental caries and reduce the formation of dental plaque (10). In vitro inhibition studies have shown chlorhexidine to be effective against species found in infected root canals such as Enterococcus faecalis (11) and Streptococcus mutans (12), and because of this, it was introduced as an endodontic irrigant in the early 1960 s (10). Chlorhexidine is increasingly being incorporated into endodontic materials due to its ability to increase antimicrobial properties and improve prognosis. 

Nisin belong to a group of polypeptide antibiotics (called bacteriocins) produced by Streptococcus lactis which have inhibitory properties directed toward other LAB (Radler, 1990a, 1990b). Yeasts, by comparison, are unaffected. The concentration needed for inhibition varied with species. Leu-conostoc oenos and Pediococcus sp. were controlled at relatively low treatment levels, whereas lactobacilli required much higher doses for inhibition (Radler, 1990a). 

Bactericidal activity Lactobacilli ferment lactose to lactic acid, thereby reducing the pH to a level that harmful bacteria cannot tolerate. Hydrogen peroxide is also produced, which inhibits the growth of Gram-negative bacteria, ft has also been reported that lactic acid producing bacteria of the Streptococcus and Lactobacillus species produce antibiotics. 

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