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

Differential in vitro susceptibility to ampicillin/ceftriaxone combination therapy among Enterococcus faecalis infective endocarditis clinical isolates

OBJECTIVES

To investigate the genomic diversity and β-lactam susceptibilities of Enterococcus faecalis collected from patients with infective endocarditis (IE).

METHODS

We collected 60 contemporary E. faecalis isolates from definite or probable IE cases identified between 2018 and 2021 at the University of Pittsburgh Medical Center. We used whole-genome sequencing to study bacterial genomic diversity and employed antibiotic checkerboard assays and a one-compartment pharmacokinetic-pharmacodynamic (PK/PD) model to investigate bacterial susceptibility to ampicillin and ceftriaxone both alone and in combination.

RESULTS

Genetically diverse E. faecalis were collected, however, isolates belonging to two STs, ST6 and ST179, were collected from 21/60 (35%) IE patients. All ST6 isolates encoded a previously described mutation upstream of penicillin-binding protein 4 (pbp4) that is associated with pbp4 overexpression. ST6 isolates had higher ceftriaxone MICs and higher fractional inhibitory concentration index values for ampicillin and ceftriaxone (AC) compared to other isolates, suggesting diminished in vitro AC synergy against this lineage. Introduction of the pbp4 upstream mutation found among ST6 isolates caused increased ceftriaxone resistance in a laboratory E. faecalis isolate. PK/PD testing showed that a representative ST6 isolate exhibited attenuated efficacy of AC combination therapy at humanized antibiotic exposures.

CONCLUSIONS

We find evidence for diminished in vitro AC activity among a subset of E. faecalis IE isolates with increased pbp4 expression. These findings suggest that alternate antibiotic combinations against diverse contemporary E. faecalis IE isolates should be evaluated.

Ampicillin-Ceftriaxone vs Ampicillin-Gentamicin for Definitive Therapy of Enterococcus faecalis Infective Endocarditis: A Propensity Score-Matched, Retrospective Cohort Analysis

Background

Ampicillin-ceftriaxone (AC) has emerged as an alternative antibiotic regimen for enterococcal infective endocarditis (EIE) with reduced toxicity compared with ampicillin-gentamicin (AG), but evidence regarding its success in reducing EIE-associated death in the United States is limited.

Methods

We conducted a retrospective, propensity score–matched cohort analysis of EIE patients treated with AC or AG between 2010 and 2017 at 3 hospitals in Pittsburgh, Pennsylvania. We assessed all-cause 90-day mortality as the primary outcome and in-hospital mortality, length of hospital stay, hospital readmissions, adverse events, and relapse of bacteremia as the secondary outcomes.

Results

A total of 190 patients with EIE (100 treated with AC and 90 with AG) were included. Ninety-day mortality was significantly higher with AC than AG (21% vs 8%; P = .02). After propensity score matching, 56 patients in each group remained for the outcomes analysis. Documented aminoglycoside resistance, presence of annular or aortic abscess, and complete pacemaker removal were the significantly different variables between the 2 matched cohorts. We observed no statistically significant difference in 90-day mortality between the 2 treatment groups (11% vs 7%; P = .55). Adverse events were more common in patients treated with AG (25 vs 39; P = .0091), and more patients in the propensity score–matched AG cohort switched antibiotic regimens than in the AC group (10% vs 49%; P < .0001).

Conclusions

Patients treated with AC demonstrate no significant differences in mortality, treatment failure, or bacteremia relapse compared with AG in a propensity score–matched EIE cohort.

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.

In vitro trials of some antimicrobial combinations against Staphylococcus aureus and Pseudomonas aeruginosa

Staphylococcus aureus and Pseudomonas aeruginosa are rapidly increasing as multidrug resistant strains worldwide. In nosocomial settings because of heavy exposure of different antimicrobials, resistance in these pathogens turned into a grave issue in both developed and developing countries. The aim of this study was to investigate in vitro antibiotic synergism of combinations of β-lactam-β-lactam and β-lactam-aminoglycoside against clinical isolates of S. aureus and P. aeruginosa. Synergy was determined by checkerboard double dilution method. The combination of amoxicillin and cefadroxil was found to be synergistic against 47 S. aureus isolates, in the FICI range of 0.14-0.50 (81.03%) followed by the combination of streptomycin and cefadroxil synergistic against 44 S. aureus isolates in the FICI range of 0.03-0.50 (75.86%). The combination of streptomycin and cefadroxil was observed to be synergistic against 39 P. aeruginosa isolates in the FICI range of 0.16-0.50 (81.28%). Further actions are needed to characterize the possible interaction mechanism between these antibiotics. Moreover, the combination of streptomycin and cefadroxil may lead to the development of a new and vital antimicrobial against simultaneous infections of S. aureus and P. aeruginosa.

Intrinsic and acquired resistance mechanisms in enterococcus

Enterococci have the potential for resistance to virtually all clinically useful antibiotics. Their emergence as important nosocomial pathogens has coincided with increased expression of antimicrobial resistance by members of the genus. The mechanisms underlying antibiotic resistance in enterococci may be intrinsic to the species or acquired through mutation of intrinsic genes or horizontal exchange of genetic material encoding resistance determinants. This paper reviews the antibiotic resistance mechanisms in Enterococcus faecium and Enterococcus faecalis and discusses treatment options.

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.