Efficacy of tigecycline alone and in combination with gentamicin in the treatment of experimental endocarditis due to linezolid-resistant Enterococcus faecium

Tigecycline and Gentamicin-Combined Treatment Enhances Renal Damage: Oxidative Stress, Inflammatory Reaction, and Apoptosis Interplay

Although the combination of antibiotics is generally well-tolerated, they may have nephrotoxic effects. This study investigated whether tigecycline (TG) and gentamicin (GM) co-administration could accelerate renal damage. Male Wistar rats were randomly divided into six experimental groups: the control, TG7 (tigecycline, 7 mg/kg), TG14 (tigecycline, 14 mg/kg), GM (gentamicin, 80 mg/kg), TG7+GM, and TG14+GM groups. The combination of TG and GM evoked renal damage seen by the disruption of kidney function tests. The perturbation of renal tissue was mainly confounded to the TG and GM-induced oxidative damage, which was exhibited by marked increases in renal MDA (malondialdehyde) along with a drastic reduction in GSH (reduced-glutathione) content and CAT (catalase) activity compared to their individual treatments. More obvious apoptotic events and inflammation were also revealed by elevating the annexin-V and interleukin-6 (IL-6) levels, aside from the upregulation of renal PCNA (proliferating cell nuclear antigen) expression in the TG and GM concurrent treatment. The principal component analysis indicated that creatinine, urea, annexin-V, IL-6, and MDA all played a role in discriminating the TG and GM combined toxicity. Oxidative stress, inflammatory response, and apoptosis were the key mechanisms involved in this potentiated toxicity.

Global priority pathogens: virulence, antimicrobial resistance and prospective treatment options

Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp. and Salmonella spp. are part of a group of pathogens that pose a major threat to human health due to the emergence of multidrug-resistant strains. Moreover, these bacteria have several virulence factors that allow them to successfully colonize their hosts, such as toxins and the ability to produce biofilms, resulting in an urgent need to develop new strategies to fight these pathogens. In this review, we compile the most up-to-date information on the epidemiology, virulence and resistance of these clinically important microorganisms. Additionally, we address new therapeutic alternatives, with a focus on molecules with antivirulence activity, which are considered promising to combat multidrug-resistant bacteria.

Combatting resistant enterococcal infections: a pharmacotherapy review

INTRODUCTION

The role of enterococci in infectious diseases has evolved from a gut and urinary commensal to a major pathogen of concern. Few options exist for resistant enterococci, and appropriate use of the available agents is crucial.

AREAS COVERED

Herein, the authors discuss antibiotics with clinically useful activity against Enterococcus faecalis and E. faecium. The article specifically discusses: antibiotics active against enterococci and their mechanism of resistance, pharmacokinetic and pharmacodynamic principles, in vitro combinations, and clinical studies which focus on urinary tract, intra-abdominal, central nervous system, and bloodstream infections due to enterococci.

EXPERT OPINION

Aminopenicillins are preferred over all other agents when enterococci are susceptible and patients can tolerate them. Daptomycin and linezolid have demonstrated clinical efficacy against vancomycin-resistant enterococci (VRE). Synergistic combinations are often warranted in complex infections of high inoculum and biofilms while monotherapies are generally appropriate for uncomplicated infections. Although active against resistant enterococci, the pharmacokinetics, efficacy and safety of tigecycline and quinupristin/dalfopristin can problematical for severe infections. For cystitis, amoxicillin, nitrofurantoin, or fosfomycin are ideal. Recently, approved agents such as tedizolid and oritavancin have good in vitro activity against VRE but clinical studies against other resistant enterococci are lacking.

Resistance mechanisms and clinical characteristics of linezolid-resistant Enterococcus faecium isolates: A single-centre study in South Korea

OBJECTIVES

This study aimed to determine the prevalence of linezolid-resistant (LR) vancomycin-resistant enterococci and to investigate the mechanisms of linezolid resistance with clinical and microbiological characterisation.

METHODS

All vancomycin-resistant Enterococcus faecium (VREF) isolated from blood and rectal swab cultures during 2012-2015 were tested for linezolid resistance. LR-VREF isolates were tested for antimicrobial susceptibility, glycopeptide resistance genes and virulence genes. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed. Isolates were tested for known mechanisms of linezolid resistance.

RESULTS

Among 389 VREF isolates, 7 (1.8%) were found to be resistant to linezolid. All LR-VREF isolates carried the vanA gene. Five isolates had both hyl and esp genes. The isolates were susceptible to tigecycline, daptomycin and quinupristin/dalfopristin, except for one isolate with daptomycin resistance. Two LR-VREF isolates recovered from patients with previous linezolid exposure contained the G2576T mutation in 23S rRNA and exhibited high-level resistance to linezolid (MIC>64mg/L). The other five isolates recovered from linezolid-naïve patients revealed no known linezolid resistance mechanism and exhibited low-level resistance to linezolid (MICs=8-16mg/L). Plasmid-mediated genes encoding cfr or optrA were not detected. LR-VREF isolates were represented by six different sequence types, belonging to hospital lineages, and were assigned to seven PFGE types.

CONCLUSIONS

The prevalence of LR-VREF in this centre was low. Both linezolid exposure and horizontal transmission appear to be responsible for acquisition of LR-VREF in hospitalised patients. Prudent use of linezolid and improved infection control strategies are needed to limit the spread of LR-VREF.

Role of Combination Antimicrobial Therapy for Vancomycin-Resistant Enterococcus faecium Infections: Review of the Current Evidence

Enterococcus species are the second most common cause of nosocomial infections in the United States and are particularly concerning in critically ill patients with preexisting comorbid conditions. Rising resistance to antimicrobials that were historically used as front-line agents for treatment of enterococcal infections, such as ampicillin, vancomycin, and aminoglycosides, further complicates the treatment of these infections. Of particular concern are Enterococcus faecium strains that are associated with the highest rate of vancomycin resistance. The introduction of antimicrobial agents with specific activity against vancomycin-resistant Enterococcus (VRE) faecium including daptomycin, linezolid, quinupristin-dalfopristin, and tigecycline did not completely resolve this clinical dilemma. In this review, the mechanisms of action and resistance to currently available anti-VRE antimicrobial agents including newer agents such as oritavancin and dalbavancin will be presented. In addition, novel combination therapies including β-lactams and fosfomycin, and the promising results from in vitro, animal studies, and clinical experience in the treatment of VRE faecium will be discussed.

Emergence of linezolid resistance in hepatobiliary infections caused by Enterococcus faecium

Enterococcal infections are common in liver transplantation and hepatopancreaticobiliary (HPB) surgery. Linezolid is frequently used to treat not only vancomycin-resistant Enterococcus (VRE), but also vancomycin-sensitive Enterococcus (VSE) infections, and resistance can develop. This study evaluated all the Liver Unit patients who developed infections with linezolid-resistant Enterococcus (LRE) in order to elicit the association with prior linezolid usage, to explore possible risk factors for infection, and to better understand the epidemiology of these isolates in this patient group. Between 2010 and 2015, infections with LRE developed in 10 patients (8 following liver transplantation and 2 following HPB surgery) after 22-108 days of treatment. Selected pulsed-field gel electrophoresis demonstrated that 2 out of 10 patients were cocolonized with different strains and indicated that cross-transmission may have occurred. In conclusion, in this group of patients with complex hepatobiliary infections, the optimal antibiotic strategies for the treatment of Enterococcus faecium infections are not clearly defined, and there is a significant risk of emergence of resistance to linezolid in E. faecium after exposure to this agent in patients, especially in the presence of a deep source of infection on a background of hepatic artery insufficiency. Caution is needed when using prolonged courses of linezolid in this setting, and further studies are necessary to determine the optimum treatment.

Combination antibiotic therapy for the treatment of infective endocarditis due to enterococci

INTRODUCTION

Enterococci are common causes of infective endocarditis (IE) in both health care and community-based setting. Enterococcal IE requires bactericidal therapy for an optimal outcome. For decades, cell-wall-active antimicrobial agents (penicillins or vancomycin) in combination with aminoglycosides were the cornerstone of the treatment; however, the emergence of antibiotic resistance has significantly reduced the efficacy of these regimens.

MATERIALS AND METHODS

Data for this review were identified by searches of MEDLINE and references from relevant articles on antibiotic combination regimens for the treatment of enterococcal IE. Abstracts presented in scientific conferences were not searched for.

CONCLUSION

New effective and safe combination treatments, including double-β-lactam and daptomycin/β-lactam combination, are proving useful for the management of IE due to enterococci.

Efficacy of tigecycline-colistin combination in the treatment of carbapenem-resistant Klebsiella pneumoniae endocarditis

Here we discuss the efficacy of colistin-tigecycline combination in the treatment of multidrug-resistant (MDR) Klebsiella pneumoniae infective endocarditis (IE). We report a case of a 67-year-old head-injured patient who developed a carbapenem-resistant K. pneumoniae IE. The patient was treated with colistin-tigecycline combination, with a favourable outcome. In conclusion, colistin-tigecycline combination may be a possible combination in the therapy of IE caused by MDR Enterobacteriaceae.

Enterococcal endocarditis revisited

The Enterococcus species is the third main cause of infective endocarditis (IE) worldwide, and it is gaining relevance, especially among healthcare-associated cases. Patients with enterococcal IE are older and have more comorbidities than other types of IE. Classical treatment options are limited due to the emergence of high-level aminoglycosides resistance (HLAR), vancomycin resistance and multidrug resistance in some cases. Besides, few new antimicrobial alternatives have shown real efficacy, despite some of them being recommended by major guidelines (including linezolid and daptomycin). Ampicillin plus ceftriaxone 2 g iv./12 h is a good option for Enterococcus faecalis IE caused by HLAR strains, but randomized clinical trials are essential to demonstrate its efficacy for non-HLAR EFIE and to compare it with ampicillin plus short-course gentamicin. The main mechanisms of resistance and treatment options are also reviewed for other enterococcal species.