Abstract
BackgroundInfective endocarditis (IE) is associated with high rates of mortality. Prolonged treatments with high-dose intravenous antibiotics often fail to eradicate the infection, frequently leading to high-risk surgical intervention. By providing a mechanism of antibiotic tolerance, which escapes conventional antibiotic susceptibility profiling, microbial biofilm represents a key diagnostic and therapeutic challenge for clinicians. This study aims at assessing a rapid biofilm identification assay and a targeted antimicrobial susceptibility profile of biofilm-growing bacteria in patients with IE, which were unresponsive to antibiotic therapy.ResultsStaphylococcus aureus was the most common isolate (50%), followed by Enterococcus faecalis (25%) and Streptococcus gallolyticus (25%). All microbial isolates were found to be capable of producing large, structured biofilms in vitro. As expected, antibiotic treatment either administered on the basis of antibiogram or chosen empirically among those considered first-line antibiotics for IE, including ceftriaxone, daptomycin, tigecycline and vancomycin, was not effective at eradicating biofilm-growing bacteria. Conversely, antimicrobial susceptibility profile of biofilm-growing bacteria indicated that teicoplanin, oxacillin and fusidic acid were most effective against S. aureus biofilm, while ampicillin was the most active against S. gallolyticus and E. faecalis biofilm, respectively.ConclusionsThis study indicates that biofilm-producing bacteria, from surgically treated IE, display a high tolerance to antibiotics, which is undetected by conventional antibiograms. The rapid identification and antimicrobial tolerance profiling of biofilm-growing bacteria in IE can provide key information for both antimicrobial therapy and prevention strategies.
Highlights
Infective endocarditis (IE) is associated with high rates of mortality
The most frequent bacterial etiology was represented by S. aureus, which was isolated from 50% of the samples, followed by E. faecalis and S. gallolyticus, both isolated in 2 cases
Conventional antimicrobial susceptibility assessment showed that all the bacterial isolates were highly susceptible in vitro to most antibiotics, including those considered of choice for the treatment of IE
Summary
Infective endocarditis (IE) is associated with high rates of mortality. Prolonged treatments with highdose intravenous antibiotics often fail to eradicate the infection, frequently leading to high-risk surgical intervention. This study aims at assessing a rapid biofilm identification assay and a targeted antimicrobial susceptibility profile of biofilm-growing bacteria in patients with IE, which were unresponsive to antibiotic therapy. The rapid identification of the specific microbial etiology and targeted antimicrobial therapy are fundamental for. Di Domenico et al BMC Microbiology (2019) 19:228 prevalent microbial isolate, associated with approximately 30% of cases of IE, while coagulase-negative staphylococci account for more than 10% of cases [5, 11, 19]. Streptococcus gallolyticus appears as the major causative agent, accounting for 20–50% of streptococcal-related IE [5, 11, 19]. Gram-negative bacilli are rare, accounting for 5% of cases of IE, while Fungi have been only seldom described [11]
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