Dextranase enhances antibiotic efficacy in experimental viridans streptococcal endocarditis

Abstract

In endocarditis, exopolysaccharide production by viridans streptococci has been associated with delayed antimicrobial efficacy in cardiac vegetations. We compared the eflicacies of temafloxacin alone and in combination with dextranase, an enzyme capable of hydrolyzing 20 to 90%o of the bacterial glycocalyx, in a rabbit model of endocarditis. In in vivo experiments, rabbits were infected intravenously with 108 Streptococcus sanguis organisms and were treated 6 days later with temafloxacin (50 mg/kg of body weight intramuscularly twice a day) alone or combined with dextranase (1,000 U per rabbit per day intravenously). After 4 days of treatment (day 11), the animals were sacrificed and vegetations were quantitatively cultured. For ex vivo experiments, rabbits were infected as stated above and, on day 11, vegetations were excised aseptically and incubated in vitro in rabbit serum alone (control) or with temafloxacin or temafloxacin plus dextranase at concentrations similar to peak levels in plasma. In vitro, dextranase alone had no antimicrobial effect. In vivo and ex vivo, temafloxacin combined with dextranase was more elfective than temafloxacin alone (P < 0.05). Our results suggest that dextranase is able to increase the effects of temafloxacin by reducing the amount of bacterial glycocalyx in infected vegetations, as confirmed in vitro by electron microscopy showing a markedly reduced amount of glycocalyx and a more clearly visible fibrin matrix.Previous studies have suggested that the difficulty in curing endocarditis could be due to heterogeneous diffusion of some antibiotics into fibrin vegetations (5) or to the reduced metabolic activity of organisms inside vegetations, especially the older ones (11,12,14). However, other factors may account for the difficulty in curing endocarditis, among them the secretion of exopolysaccharide by some organisms inside vegetations.Viridans streptococci still represent a major cause of native valve endocarditis. These streptococci are known to produce an exopolysaccharide (glycocalyx) composed predominantly of dextran in the human mouth and have been shown to produce dextran in experimental cardiac vegetations (18). This production is strain dependent and can be quantified by histochemical techniques (18) or tryptophan quantitative assay (9). Glycocalyx-producing strains form larger vegetations (18). Also, the presence of glycocalyx surrounding viridans streptococci within cardiac vegetations adversely affects penicillin efficacy (8,20). Experimental vegetations infected by exopolysaccharide-producing strains of viridans streptococci are more difficult to sterilize than those infected by exopolysaccharide-deficient strains (20). Moreover, combining penicillin with dextranase, an enzyme capable of hydrolyzing 20 to 90% of the bacterial glycocalyx, has been shown to facilitate sterilization of experimental vegetations infected with a glycocalyx-producing strain of Streptococcus sanguis (8).Glycocalyx could alter the efficacy of penicillin by increasing the size of the vegetat...

Lack ofin vitrobiofilm formation does not attenuate the virulence ofStreptococcus gordoniiin experimental endocarditis

“…Likewise, the influence of pretreatment duration of infection on the efficacy of antibiotic treatment may be related to the lower metabolic activity of bacteria growing in the vegetation (Cremieux et al, 1993;Entenza et al, 1994). Furthermore, Mghir et al (1994) confirmed the presence of biofilm-compatible structures in the vegetations of rabbits infected with streptococci. The biofilm-like structure was related to dextran production and treatment of the animals with dextranase decreased the infection severity and facilitated antibiotic-induced bacterial eradication.…”

Microbial Dextran-Hydrolyzing Enzymes: Fundamentals and Applications

“…Enzymatic digestion of the glycocalyx by dextranase has been shown to enhance the antibiotic activity of penicillin and temafloxacin (33,128).…”

Cloning, characterization, and heterologous expression of a dextranase gene from Penicillium pinophilum SMCU3-14

“…Moreover, dextranase has been used in degrading dextran to an appropriate smaller size range suitable for use as a synthetic blood volume expander in patients suffering from hypovolaemic shock 11 . The use of dextranase has also been proposed as a method to increase antibiotic efficacy in infective endocarditis and a universal targeting method for therapeutic agents 12 . Sources of dextranases are widespread: the enzyme has been found in mammalian tissues and in various microorganisms, such as fungi, yeasts, bacteria, and Actinomyces 13,14 .…”