Endocarditis caused by Enterococcus faecalis with high-level resistance to aminoglycosides: failure of ampicillin and ceftriaxone combined therapy

V, Pal SK, Srivastava VK, Jyoti A, Kumar S, Kaushik S. Prospecting Potential Inhibitors of Sortase A from Enterococcus faecalis: A Multidrug Resistant Bacteria, through In-silico and In-vitro Approaches

Background:

Enterococcus faecalis (Ef) infections are becoming dreadfully common in hospital environments. Infections caused by Ef are difficult to treat because of its acquired resistance to different class of antibiotics, making it a multidrug resistant bacteria. Key pathogenic factor of Ef includes its ability to form biofilm on the surface of diagnostic and other medical devices. Sortase A (SrtA) is a cysteine transpeptidase which plays a pivotal role in the formation of biofilm in Ef, hence, it is considered as an important enzyme for the pathogenesis of Ef. Thus, inhibition of (SrtA) will affect biofilm formation, which will reduce its virulence and eventually Ef infection will be abridged.

Objective:

To find potential inhibitors of Enterococcus faecalis Sortase A (EfSrtA) through insilico and in-vitro methods.

Methods:

Gene coding for EfSrtA was cloned, expressed and purified. Three-dimensional model of EfSrtA was created using Swiss-Model workspace. In-silico docking studies using Autodock vina and molecular dynamics simulations of the modelled structures using Gromacs platform were performed to explore potential lead compounds against EfSrtA. In-vitro binding experiments using spectrofluorometric technique was carried out to confirm and validate the study.

Results:

In-silico docking and in-vitro binding experiments revealed that curcumin, berberine and myricetin bound to EfSrtA at nanomolar concentrations with high affinity.

Conclusion:

This is a first structural report of EfSrtA with curcumin, berberine and myricetin. Taking in account the herbal nature of these compounds, the use of these compounds as inhibitors will be advantageous. This study validated curcumin, berberine and myricetin as potential inhibitors of EfSrtA.

Combination of Ceftriaxone and Ampicillin for the Treatment of Enterococcal Endocarditis: A Qualitative Systematic Review

OBJECTIVE

The aim of this systematic review is to review all human trials assessing the efficacy and safety of ampicillin and ceftriaxone for enterococcal endocarditis and to discuss the clinical implications of the findings.

DATA SOURCES

MEDLINE (1946-), EMBASE (1974-), CENTRAL, Google Scholar, and the World Health Organization Clinical Trials Registry Platform were searched through January 2017 using the search terms ampicillin, penicillin, ceftriaxone, cephalosporin, enterococ*, and endocarditis. Unpublished studies were eligible for inclusion. Additional references were identified from literature citations.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials in humans that reported on clinical efficacy or adverse outcomes with ceftriaxone and ampicillin therapy in patients with enterococcal endocarditis were included. Case reports, nonhuman, and non-English studies were excluded.

DATA SYNTHESIS

Four observational clinical studies were identified. One examined the effects of ceftriaxone and ampicillin alone, and 3 compared the therapy to the current standard of care, ampicillin and gentamicin. The studies had small sample sizes and were not adequately designed or powered to establish noninferiority or equivalence to the current standard of care. Rates of clinical cure with ampicillin 2 g every 4 hours and ceftriaxone 2 g every 12 hours were similar to those of ampicillin and gentamicin. Ampicillin and ceftriaxone therapy was well tolerated with low rates of renal failure (0%-33%).

CONCLUSION

The evidence to support the use of ampicillin and ceftriaxone for enterococcal endocarditis is not definitive. In the absence of compelling evidence, clinicians may consider ampicillin and ceftriaxone in patients with Enterococcus faecalis infection at high risk for nephrotoxicity or those with aminoglycoside-resistant pathogens.

Efficacy of the Combination Ampicillin Plus Ceftriaxone in the Treatment of a Case of Enterococcal Endocarditis Due toEnterococcus faecalisHighly Resistant to Gentamicin: Efficacy of the “Ex Vivo” Synergism Method

The case of a patient with highly gentamicin-resistant Enterococcus faecalis endocarditis treated with an ampicillin + ceftriaxone combination is described. We have designed a method to evaluate synergism between the antibacterial activity of patient's serum taken during a given antibiotic regimen (ampicillin) to which another antibiotic (ceftriaxone) is added in vitro. In this patient the two-drug combination was able to stop the bacteremia and prevent the infection of the prosthetic valve.

In vitro Antimicrobial Activity of Ampicillin-Ceftriaxone and Ampicillin-Ertapenem Combinations Against Clinical Isolates of Enterococcus faecalis with High Levels of Aminoglycoside Resistance

This paper reports on the in vitro antimicrobial activity of ampicillin-ceftriaxone and ampicillin-ertapenem combinations against five strains of E. faecalis with high-level aminoglycoside resistance recovered from blood of septicemic patients. Double disk diffusion test and time killing curves were used. A bacteriostatic synergistic effect between ampicillin and ceftriaxone was detected using the disk diffusion assay for three of the five enterococcal strains studied. With the same three isolates enhanced bactericidal activity was also observed using time killing experiments. Overall, for these three strains, after 24 hr of contact, a decrease >/= 2 log(10) from the initial bacterial inoculum was registered with most ampicillin-ceftriaxone combinations, reaching with some of them a colony reduction >/= 3 log(10). This bactericidal interaction was negatively influenced increasing the bacterial inoculum. In all five isolates neither a bacteriostatic nor a bactericidal cooperation was observed for ampicillin combined with 2 mg/l of ertapenem.This investigation broadened the evidence of antimicrobial synergism in vitro between ampicillin and ceftriaxone in selected strains of Enterococcus faecalis with high-level aminoglycoside resistance.

Enterococcal endocarditis on native and prosthetic valves: a review of clinical and prognostic factors with emphasis on hospital-acquired infections as a major determinant of outcome

Enterococci are the third leading cause of infectious endocarditis, and despite advances in diagnosis and treatment, the mortality of enterococcal endocarditis has not changed in recent decades. Although variables such as advanced age, cardiac failure, and brain emboli have been recognized as risk factors for mortality, cooperative multi-institutional studies have not assessed the role of other variables, such as nosocomial acquisition of infection, the presence of comorbidities, or the changing antimicrobial susceptibility of enterococci, as factors determining prognosis.We conducted the current study to determine the risk factors for mortality in patients with enterococcal endocarditis in a single institution. We reviewed 47 consecutive episodes of enterococcal endocarditis in 44 patients diagnosed according to the modified Duke criteria from a retrospective cohort study of cases of infectious endocarditis. The main outcome measure was inhospital mortality. We applied stepwise logistic regression analysis to identify risk factors for mortality.Predisposing heart conditions were observed in 86.3% of patients, and 17 had prosthetic valve endocarditis. A portal of entry was suspected or determined in 38.2%; the genitourinary tract was the most common source of the infection (29.7%). Comorbidities were present in 52.2% of cases. Twelve episodes (25.5%) were acquired during hospitalization. Only 3 isolates of Enterococcus faecalis were highly resistant to gentamicin. Eighteen patients (40.9%) needed valve replacement due to cardiac failure or relapse. Comparing cases of native valve and prosthetic valve endocarditis, we found no differences regarding complications, the need for surgical treatment, or mortality. Eight of 44 (18%) episodes were fatal. Age over 70 years (p = 0.05), heart failure (odds ratio [OR], 1.61; 95% confidence interval [CI], 1.15-2.25; p = 0.001), presence of 1 or more comorbidities (OR, 3.2; 95% CI, 1.11-9.39; p = 0.02), and nosocomial acquisition (OR, 8.05; 95% CI, 1.50-43.2; p = 0.01) were associated with mortality. In the multivariate analysis, only nosocomial acquisition increased the risk of mortality. In patients with enterococcal endocarditis, nosocomial acquisition of infection is an important factor determining outcome. As the incidence of bacteremia and the population of elderly people at risk continue to grow, the hazard of acquiring nosocomial enterococcal endocarditis may increase; hence, major emphasis must be put on prevention.

Efficacy of ampicillin plus ceftriaxone in treatment of experimental endocarditis due to Enterococcus faecalis strains highly resistant to aminoglycosides

The purpose of this work was to evaluate the in vitro possibilities of ampicillin-ceftriaxone combinations for 10 Enterococcus faecalis strains with high-level resistance to aminoglycosides (HLRAg) and to assess the efficacy of ampicillin plus ceftriaxone, both administered with humanlike pharmacokinetics, for the treatment of experimental endocarditis due to HLRAg E. faecalis. A reduction of 1 to 4 dilutions in MICs of ampicillin was obtained when ampicillin was combined with a fixed subinhibitory ceftriaxone concentration of 4 micrograms/ml. This potentiating effect was also observed by the double disk method with all 10 strains. Time-kill studies performed with 1 and 2 micrograms of ampicillin alone per ml or in combination with 5, 10, 20, 40, and 60 micrograms of ceftriaxone per ml showed a > or = 2 log10 reduction in CFU per milliliter with respect to ampicillin alone and to the initial inoculum for all 10 E. faecalis strains studied. This effect was obtained for seven strains with the combination of 2 micrograms of ampicillin per ml plus 10 micrograms of ceftriaxone per ml and for six strains with 5 micrograms of ceftriaxone per ml. Animals with catheter-induced endocarditis were infected intravenously with 10(8) CFU of E. faecalis V48 or 10(5) CFU of E. faecalis V45 and were treated for 3 days with humanlike pharmacokinetics of 2 g of ampicillin every 4 h, alone or combined with 2 g of ceftriaxone every 12 h. The levels in serum and the pharmacokinetic parameters of the humanlike pharmacokinetics of ampicillin or ceftriaxone in rabbits were similar to those found in humans treated with 2 g of ampicillin or ceftriaxone intravenously. Results of the therapy for experimental endocarditis caused by E. faecalis V48 or V45 showed that the residual bacterial titers in aortic valve vegetations were significantly lower in the animals treated with the combinations of ampicillin plus ceftriaxone than in those treated with ampicillin alone (P < 0.001). The combination of ampicillin and ceftriaxone showed in vitro and in vivo synergism against HLRAg E. faecalis.