Anti-biofilm Approach in Infective Endocarditis Exposes New Treatment Strategies for Improved Outcome

Infective endocarditis (IE) is a life-threatening infective disease with increasing incidence worldwide. From early on, in the antibiotic era, it was recognized that high-dose and long-term antibiotic therapy was correlated to improved outcome. In addition, for several of the common microbial IE etiologies, the use of combination antibiotic therapy further improves outcome. IE vegetations on affected heart valves from patients and experimental animal models resemble biofilm infections. Besides the recalcitrant nature of IE, the microorganisms often present in an aggregated form, and gradients of bacterial activity in the vegetations can be observed. Even after appropriate antibiotic therapy, such microbial formations can often be identified in surgically removed, infected heart valves. Therefore, persistent or recurrent cases of IE, after apparent initial infection control, can be related to biofilm formation in the heart valve vegetations. On this background, the present review will describe potentially novel non-antibiotic, antimicrobial approaches in IE, with special focus on anti-thrombotic strategies and hyperbaric oxygen therapy targeting the biofilm formation of the infected heart valves caused by Staphylococcus aureus. The format is translational from preclinical models to actual clinical treatment strategies.

Is hyperbaric oxygen or ozone effective in experimental endocarditis?

BACKGROUND

Infective endocarditis, a disease with high mortality and morbidity, is most commonly caused by Staphylococcus aureus; mortality and morbidity further increase in the presence of methicillin-resistant strains of S. aureus. Linezolid is the first of the oxazolidinones, a new antibiotic group that has been approved for the treatment of infections caused by gram-positive cocci. Linezolid reduces the quantity of microorganisms in vegetation to some extent; in addition, the use of hyperbaric oxygen (HBO) and ozone (O3) therapies is likely to improve targeted antibacterial effect.

MATERIALS AND METHODS

Fifty-six adult male Wistar rats weighing 300-350 g were used. The subjects were divided into groups as follows: Group 1 (n = 8): control group that was not inoculated with microorganisms and was untreated; Group 2 (n = 8): control group that was inoculated with microorganisms but was untreated; Group 3 (n = 8): linezolid treatment group; Group 4 (n = 8): O3 therapy group; Group 5 (n = 8): HBO therapy group; Group 6 (n = 8): linezolid + O3 therapy group; Group 7 (n = 8): linezolid + HBO therapy group.

RESULTS

In terms of reducing the number of colonies in the aortic valve, linezolid + HBO therapy was found to be the most effective treatment. Then, respectively linezolid + O3, linezolid, HBO, and O3 were found to be effective.

CONCLUSIONS

We found that linezolid significantly reduced the number of bacteria in the vegetation in the experimental endocarditis model, and HBO therapy increases the effectiveness of linezolid and makes this better than O3.

Low efficacy of tobramycin in experimental Staphylococcus aureus endocarditis

The empiric treatment of infective endocarditis (IE) varies widely and, in some places, a regimen of penicillin in combination with an aminoglycoside is administered. The increasing incidence of Staphylococcus aureus IE, poor tissue penetration by aminoglycosides and low frequency of penicillin-susceptible S. aureus may potentially lead to functional tobramycin monotherapy. Therefore, this study aimed to evaluate tobramycin monotherapy in an experimental S. aureus IE rat model. Catheter-induced IE at the aortic valves were established with S. aureus (NCTC 8325-4) and rats were randomised into untreated (n = 22) or tobramycin-treated (n = 13) groups. The treatment group received tobramycin once-daily. Animals were evaluated at 1 day post infection (DPI), 2 DPI or 3 DPI. Quantitative bacteriology and cytokine expression were measured for valves, myocardium and serum. A decrease of bacterial load was observed in valves and the spleens of the treated (n = 6) compared to the untreated group at 2 DPI (n = 8) (p ≤ 0.02 and p ≤ 0.01, respectively), but not at 3 DPI (n = 7). Quantitative bacteriology in the myocardium was not different between the groups. Keratinocyte-derived chemokine (KC) in the aortic valves was significantly reduced at 2 DPI in the tobramycin-treated group (p ≤ 0.03). However, the expression of interleukin (IL)-1b, IL-6 and granulocyte-colony stimulating factor (G-CSF) in the valves was not different between the two groups. In the myocardium, a significant reduction in IL-1b was observed at 2 DPI (p ≤ 0.001) but not at 3 DPI. Tobramycin as functional monotherapy only reduced bacterial load and inflammation transiently, and was insufficient in most cases of S. aureus IE.

Controlling hospital-acquired infection: focus on the role of the environment and new technologies for decontamination

There is increasing interest in the role of cleaning for managing hospital-acquired infections (HAI). Pathogens such as vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), multiresistant Gram-negative bacilli, norovirus, and Clostridium difficile persist in the health care environment for days. Both detergent- and disinfectant-based cleaning can help control these pathogens, although difficulties with measuring cleanliness have compromised the quality of published evidence. Traditional cleaning methods are notoriously inefficient for decontamination, and new approaches have been proposed, including disinfectants, steam, automated dispersal systems, and antimicrobial surfaces. These methods are difficult to evaluate for cost-effectiveness because environmental data are not usually modeled against patient outcome. Recent studies have reported the value of physically removing soil using detergent, compared with more expensive (and toxic) disinfectants. Simple cleaning methods should be evaluated against nonmanual disinfection using standardized sampling and surveillance. Given worldwide concern over escalating antimicrobial resistance, it is clear that more studies on health care decontamination are required. Cleaning schedules should be adapted to reflect clinical risk, location, type of site, and hand touch frequency and should be evaluated for cost versus benefit for both routine and outbreak situations. Forthcoming evidence on the role of antimicrobial surfaces could supplement infection prevention strategies for health care environments, including those targeting multidrug-resistant pathogens.

Towards diagnostic guidelines for biofilm-associated infections

Biofilms associated with the human body, particularly in typically sterile locations, are difficult to diagnose and treat effectively because of their recalcitrance to conventional antibiotic therapy and host immune responses. The study of biofilms in medicine today requires a translational approach, with examination of clinically relevant biofilms in the context of specific anatomic sites, host tissues, and diseases, focusing on what can be done to mitigate their pathologic consequences. This review, which grew out of a discussion session on clinical biofilms at the 5th ASM Biofilm Conference in Cancun, Mexico, is designed to give an overview of biofilm-associated infections (BAI) and to propose a platform for further discussion that includes clinicians, medical microbiologists, and biofilm researchers who are stakeholders in advancing the scientific pursuit of better diagnosis and treatment of BAI to mitigate their human and healthcare costs. It also highlights the need for better diagnostic markers, which exploit the difference between planktonic and biofilm cells.

Getting to the heart of the problem: serological and molecular techniques in the diagnosis of infective endocarditis

Infective endocarditis is diagnosed using the Duke criteria, which rely predominantly on cardiac imaging and recovery of a causative organism from the bloodstream. These criteria can be inconclusive, particularly when blood cultures remain sterile either due to the fastidious nature of the infecting organism or prior antibiotic therapy. Serology and, more recently, molecular techniques have been investigated as a solution to the problematic negative blood culture. The detection of elevated antibody levels has proved particularly useful in the diagnosis of those patients infected with organisms that cannot be cultured using standard laboratory methods, whilst molecular methods have been successfully used in the detection of both fastidious pathogens and those inhibited by prior antibiotic therapy. In view of recent and ongoing developments in the field of molecular diagnostics, these techniques will become increasingly important not only in the routine investigation of infectious disease, but specifically the diagnosis of endocarditis.