Evaluation of telavancin activity versus daptomycin and vancomycin against daptomycin-nonsusceptible Staphylococcus aureus in an in vitro pharmacokinetic/pharmacodynamic model

Functional and structural characterization of Hyp730, a highly conserved and dormancy-specific hypothetical membrane protein

Membrane proteins represent major drug targets, and the ability to determine their functions, structures, and conformational changes will significantly advance mechanistic approaches to both biotechnology and bioremediation, as well as the fight against pathogenic bacteria. A pertinent example is Mycobacterium tuberculosis (H37Rv), which contains ~4000 protein-coding genes, with almost a thousand having been categorized as 'membrane protein', and a few of which (~1%) have been functionally characterized and structurally modeled. However, the functions and structures of most membrane proteins that are sparsely, or only transiently, expressed, but essential in small phenotypic subpopulations or under stress conditions such as persistence or dormancy, remain unknown. Our deep quantitative proteomics profiles revealed that the hypothetical membrane protein 730 (Hyp730) WP_010079730 (protein ID Mlut_RS11895) from M. luteus is upregulated in dormancy despite a ~5-fold reduction in overall protein diversity. Its H37Rv paralog, Rv1234, showed a similar proteomic signature, but the function of Hyp730-like proteins has never been characterized. Here, we present an extensive proteomic and transcriptomic analysis of Hyp730 and have also characterized its in vitro recombinant expression, purification, refolding, and essentiality as well as its tertiary fold. Our biophysical studies, circular dichroism, and tryptophan fluorescence are in immediate agreement with in-depth in silico 3D-structure prediction, suggesting that Hyp730 is a double-pass membrane-spanning protein. Ablation of Hyp730-expression did not alter M. luteus growth, indicating that Hyp730 is not essential. Structural homology comparisons showed that Hyp730 is highly conserved and non-redundant in G+C rich Actinobacteria and might be involved, under stress conditions, in an energy-saving role in respiration during dormancy.

Evaluation of Telavancin Alone and Combined with Ceftaroline or Rifampin against Methicillin-Resistant Staphylococcus aureus in an In Vitro Biofilm Model

Infections caused by biofilm-producing methicillin-resistant Staphylococcus aureus (MRSA) bacteria are challenging due to increasing antibiotic resistance. Synergistic activities of lipopeptides and lipoglycopeptides with β-lactams have been demonstrated for MRSA, but little is known about biofilm-embedded organisms. Our objective was to evaluate two telavancin (TLV) dosage regimens (7.5 mg/kg of body weight and 10 mg/kg every 24 h [q24h]) alone and in combination with ceftaroline (CPT) (600 mg every 8 h [q8h]) or rifampin (RIF) (450 mg every 12 h [q12h]) against two biofilm-producing MRSA strains (494 and N315). Pharmacokinetic/pharmacodynamic CDC biofilm reactor models with polyurethane coupons were used to evaluate the efficacies of the antibiotic combinations over 72 h. Overall, there were no significant differences observed between the two TLV dosing regimens either alone or in combination with RIF or CPT against these strains. Both TLV dosing regimens and CPT alone demonstrated killing but did not reach bactericidal reduction at 72 h. However, both TLV regimens in combination with RIF demonstrated enhanced activity against both strains, with a rapid decrease in CFU/ml at 4 h that was bactericidal and maintained over the 72-h experiment (-Δ3.75 log10 CFU/ml from baseline; P < 0.0001). Of interest, no enhanced activity was observed for TLV combined with CPT. No development of resistance was observed in any of the combination models. However, resistance to RIF developed as early as 24 h, with MIC values exceeding 32 mg/liter. Our results show that TLV plus RIF displayed therapeutic improvement against biofilm-producing MRSA. These results suggest that TLV at 7.5 and 10 mg/kg q24h are equally effective in eradicating biofilm-associated MRSA strains in vitro.

Efficacy of Telavancin Alone and in Combination with Ampicillin in a Rat Model of Enterococcus faecalis Endocarditis

We first assessed telavancin (TLV) pharmacokinetics in rats after a single subcutaneous dose of 35 mg/kg of body weight. The pharmacokinetic data were used to predict a TLV dose that simulates human exposure, and the efficacy of TLV was then evaluated using a TLV dose of 21 mg/kg every 12 h against Enterococcus faecalis OG1RF (TLV MIC of 0.06 μg/ml) in a rat endocarditis model with an indwelling catheter. Therapy was given for 3 days with TLV, daptomycin (DAP), or ampicillin (AMP) monotherapy and with combinations of TLV plus AMP, AMP plus gentamicin (GEN), and AMP plus ceftriaxone (CRO); rats were sacrificed 24 h after the last dose. Antibiotics were given to simulate clinically relevant concentrations or as used in other studies. TLV treatment resulted in a significant decrease in bacterial burden (CFU per gram) in vegetations from 6.0 log₁₀ at time 0 to 3.1 log₁₀ after 3 days of therapy. Bacterial burdens in vegetations were also significantly lower in the TLV-treated rats than in the AMP (P = 0.0009)- and AMP-plus-GEN (P = 0.035)-treated rats but were not significantly different from that of the AMP-plus-CRO-treated rats. Bacterial burdens from vegetations in TLV monotherapy and TLV-plus-AMP-and-DAP groups were similar to each other (P ≥ 0.05). Our data suggest that further study of TLV as a therapeutic alternative for deep-seated infections caused by vancomycin-susceptible E. faecalis is warranted.

Telavancin activity tested against Gram-positive clinical isolates from European, Russian and Israeli hospitals (2011-2013) using a revised broth microdilution testing method: redefining the baseline activity of telavancin

OBJECTIVES

To reassess the activity of telavancin when tested against Gram-positive clinical pathogens recovered from hospitalized patients in European and adjacent regions using a revised broth microdilution method.

METHODS

11 601 consecutive, non-duplicate isolates originating from 36 institutions among 18 countries recovered between 2011 and 2013 were tested for susceptibility using a revised broth microdilution method for telavancin. Interpretive telavancin breakpoints appropriate for the method were those recently approved by the FDA and EUCAST, as available.

RESULTS

Telavancin (MIC50/90, 0.03/0.06 mg/l; 100.0% susceptible) was equally potent against methicillin-susceptible ((MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus. All Enterococcus faecalis was susceptible to telavancin (MIC50/90, 0.12/0.12 mg/l) and inhibited at the susceptibility breakpoint (i.e. ≤ 0.25 mg/l), except for VanA-phenotype vancomycin-resistant isolates (telavancin MIC, >1 mg/l). Telavancin ( ≤ 0.015/0.03 mg/l) was active against vancomycin-susceptible Enterococcus faecium, while higher MIC values were obtained for VanA strains. Telavancin (both MIC50 and MIC90, ≤ 0.015 mg/l) was potent against Streptococcus pneumoniae, beta-haemolytic streptococci (MIC50/90, ≤ 0.015/0.06 mg/l) and viridans group streptococci (MIC50/90, ≤ 0.015/0.03 mg/l).

CONCLUSIONS

Telavancin exhibited potent activity against this contemporary (2011-2013) collection of organisms, inhibiting indicated pathogens at or below the FDA/EUCAST-approved breakpoints for susceptibility. VanA-phenotype enterococci were less susceptible to telavancin, a feature observed using the previous testing method. These results redefine telavancin's activity against isolates from Europe.

Daptomycin Pharmacokinetics and Pharmacodynamics in Septic and Critically Ill Patients

Infections, including sepsis, are associated with high mortality rates in critically ill patients in the intensive care unit (ICU). Appropriate antibiotic selection and adequate dosing are important for improving patient outcomes. Daptomycin is bactericidal in bloodstream infections caused by Staphylococcus aureus and other Gram-positive pathogens cultured in ICU patients. The drug has concentration-dependent activity, and the area under the curve/minimum inhibitory concentration ratio is the pharmacokinetic/pharmacodynamic (PK/PD) index that best correlates with daptomycin activity, whereas toxicity correlates well with daptomycin plasma trough concentrations (or minimum concentration [C min]). Adequate daptomycin exposure can be difficult to achieve in ICU patients; multiple PK alterations can result in highly variable plasma concentrations, which are difficult to predict. For this reason, therapeutic drug monitoring could help clinicians optimize daptomycin dosing, thus improving efficacy while decreasing the likelihood of serious adverse events. This paper reviews the literature on daptomycin in ICU patients with sepsis, focusing on dosing and PK and PD parameters.

Epidemiology of antimicrobial resistance in bloodstream infections

Antimicrobial resistance in bacterial pathogens is a worldwide challenge leading high morbidity and mortality in clinical settings. Multidrug resistant patterns in gram-positive and -negative bacteria have resulted in difficult-to-treat or even untreatable infections with conventional antimicrobials. Since the early identification of causative microorganisms and their antimicrobial susceptibility patterns in patients with bacteremia and other serious infections is lacking in many healthcare institutions, broad spectrum antibiotics are liberally and mostly unnecessarily used. Such practice has, in turn, caused dramatic increases in emerging resistance and when coupled with poor practice of infection control, resistant bacteria can easily be disseminated to the other patients and the environment. Thus, availability of updated epidemiological data on antimicrobial resistance in frequently encountered bacterial pathogens will be useful not only for deciding on empirical treatment strategies, but also devising an effective antimicrobial stewardship program in hospitals.

When sepsis persists: a review of MRSA bacteraemia salvage therapy

MRSA bacteraemia (MRSAB), including infective endocarditis, carries a high mortality rate, with up to 50% of patients failing initial therapy with vancomycin and requiring salvage therapy. Persistent MRSAB can be difficult to successfully eliminate, especially when source control is not possible due to an irremovable focus or the bacteraemia still persists despite surgical intervention. Although vancomycin and daptomycin are the only two antibiotics approved by the US FDA for the treatment of patients with MRSAB as monotherapy, the employment of novel strategies is required to effectively treat patients with persistent MRSAB and these may frequently involve combination drug therapy. Treatment strategies that are reviewed in this manuscript include vancomycin combined with a β-lactam, daptomycin-based therapy, ceftaroline-based therapy, linezolid-based therapy, quinupristin/dalfopristin, telavancin, trimethoprim/sulfamethoxazole-based therapy and fosfomycin-based therapy. We recommend that combination antibiotic therapy be considered for use in MRSAB salvage treatment.

In Vitro Pharmacodynamics of Human Simulated Exposures of Telavancin against Methicillin-Susceptible and -Resistant Staphylococcus aureus with and without Prior Vancomycin Exposure

Telavancin is a lipoglycopeptide with potent activity against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). The activity of telavancin against MRSA and MSSA after prior vancomycin exposure was studied in an in vitro pharmacodynamic model. Two clinical MRSA and two MSSA isolates, all with vancomycin MICs of 2 μg/ml, were subjected to humanized free drug exposures of vancomycin at 1 g every 12 h (q12h) for 96 h, telavancin at 750 mg q24h for 96 h, and vancomycin at 1 g q12h for 72 h followed by telavancin at 750 mg q24h for 48 h (120 h total). The microbiological responses were measured by changes from 0 h in log10 CFU/ml at the end of experiments and area under the bacterial killing and regrowth curves over 96 h (AUBC0-96). The control isolates grew to 8.8 ± 0.3 log10 CFU/ml. Initially, all regimens caused -4.5 ± 0.9 reductions in log10 CFU/ml by 48 h followed by slight regrowth over the following 48 to 72 h. After 96 h, vancomycin and telavancin achieved -3.7 ± 0.9 and -3.8 ± 0.8 log10 CFU/ml changes from baseline, respectively (P = 0.74). Sequential exposure to telavancin after vancomycin did not result in additional CFU reductions or increases, with ultimate log10 CFU/ml reductions of -4.3 ± 1.1 at 96 h and -4.2 ± 1.3 at 120 h (P > 0.05 for all comparisons at 96 h). The AUBC0-96 was significantly smaller for the regimen of telavancin for 96 h than for the regimens of vancomycin for 96 h and vancomycin followed by telavancin (P ≤ 0.04). No resistance was observed throughout the experiment. Against these MRSA and MSSA isolates with vancomycin MICs of 2 μg/ml, telavancin was comparable with vancomycin and its activity was unaffected by prior vancomycin exposure.

A review of telavancin activity in in vitro biofilms and animal models of biofilm-associated infections

ABSTRACT 

Tissue- and device-associated biofilm infections are important medical problems. These infections are difficult to treat due to a high-level of tolerance to antibiotics. Telavancin has been studied in several in vitro biofilm models and has demonstrated efficacy against staphylococcal and enterococcal-associated biofilm infections, including those formed by methicillin-resistant Staphylococcus aureus. Telavancin was effective against the difficult-to-treat vancomycin- and glycopeptide-intermediate strains of S. aureus in these models. Furthermore, the efficacy of telavancin has been evaluated in several biofilm-related in vivo models, including osteomyelitis, endocarditis and device-associated infections in rabbits. Overall, telavancin exhibited similar or greater efficacy than vancomycin and other comparators in these animal models and maintained activity against vancomycin-intermediate and daptomycin nonsusceptible strains of S. aureus.

Telavancin demonstrates activity against methicillin-resistant Staphylococcus aureus isolates with reduced susceptibility to vancomycin, daptomycin, and linezolid in broth microdilution MIC and one-compartment pharmacokinetic/pharmacodynamic models

Methicillin-resistant Staphylococcus aureus (MRSA) isolates have arisen with reduced susceptibility to several anti-MRSA agents. Telavancin (TLV), a novel anti-MRSA agent, retains low MICs against these organisms. Our objective was to determine the MICs for TLV, daptomycin (DAP), vancomycin (VAN), and linezolid (LZD) against daptomycin-nonsusceptible (DNS) S. aureus, vancomycin-intermediate S. aureus (VISA), heteroresistant VISA (hVISA), and linezolid-resistant (LZD(r)) S. aureus. We also evaluated these agents against each phenotype in pharmacokinetic/pharmacodynamic (PK/PD) models. Seventy DNS, 100 VISA, 180 hVISA, and 25 LZD(r) MRSA isolates were randomly selected from our library and tested to determine their MICs against TLV, DAP, VAN, and LZD via broth microdilution and a Trek panel. Four isolates were randomly selected for 168-h in vitro models to evaluate treatment with TLV at 10 mg/kg of body weight/day, DAP at 10 mg/kg/day, VAN at 1 g every 12 h (q12h), and LZD at 600 mg q12h. The MIC50/90 for TLV, DAP, VAN, and LZD against 70 DNS S. aureus isolates were 0.06/0.125 μg/ml, 2/4 μg/ml, 1/2 μg/ml, and 2/2 μg/ml, respectively. Against 100 VISA isolates, the MIC50/90 were 0.06/0.125 μg/ml, 1/1 μg/ml, 4/8 μg/ml, and 1/2 μg/ml, respectively. Against 170 hVISA isolates, the MIC50/90 were 0.06/0.125 μg/ml, 0.5/1 μg/ml, 1/2 μg/ml, and 1/2 μg/ml, respectively. Against 25 LZD(r) isolates, the MIC50/90 were 0.03/0.06 μg/ml, 1/1 μg/ml, 2/2 μg/ml, and 8/8 μg/ml, respectively. The TLV MIC was >0.125 μg/ml for 10/365 (2.7%) isolates. In PK/PD models, TLV was universally bactericidal at 168 h and statistically superior to all antibiotics against DNS S. aureus strain R2334. These data further establish the potency of TLV against resistant MRSA. The model data demonstrate in vitro bactericidal activity of TLV against hVISA, VISA, DNS S. aureus, and LZD(r) S. aureus strains. Further clinical research is warranted.

Baseline activity of telavancin against Gram-positive clinical isolates responsible for documented infections in U.S. hospitals (2011-2012) as determined by the revised susceptibility testing method

Telavancin had MIC50 and MIC90 values of 0.03 and 0.06 μg/ml (100.0% susceptible), respectively, against methicillin-resistant and -susceptible Staphylococcus aureus. Telavancin was active against vancomycin-susceptible Enterococcus faecalis (MIC50/90, 0.12/0.12 μg/ml; 100% susceptible) and Enterococcus faecium (MIC50/90, 0.03/0.06 μg/ml), while higher MIC values were obtained against vancomycin-resistant E. faecium (MIC50/90, 1/2 μg/ml) and E. faecalis (MIC50/90, >2/>2 μg/ml). Streptococci showed telavancin modal MIC results of ≤ 0.015 μg/ml, except against Streptococcus agalactiae (i.e., 0.03 μg/ml). This study reestablishes the telavancin spectrum of activity against isolates recovered from the United States (2011-2012) using the revised broth microdilution method.

The ATTAIN trials: efficacy and safety of telavancin compared with vancomycin for the treatment of hospital-acquired and ventilator-associated bacterial pneumonia

ABSTRACT: Hospital-acquired bacterial pneumonia (HABP) is the second most common nosocomial infection in the USA and the leading cause of mortality among hospital-acquired infections. An increasing proportion of HABP cases are the result of infection with methicillin-resistant Staphylococcus aureus (MRSA). Telavancin is a once-daily injectable, semisynthetic lipoglycopeptide antimicrobial with bactericidal activity against susceptible Gram-positive pathogens, including MRSA. The two methodologically identical Phase III ATTAIN studies demonstrated that telavancin was noninferior to vancomycin for the treatment of HABP, including ventilator-associated bacterial pneumonia, due to S. aureus (including methicillin-sensitive S. aureus and MRSA). Telavancin showed a similar safety profile to vancomycin, except that in patients with moderate-to-severe renal impairment, there was increased mortality, which warrants caution when using telavancin in this population. Now approved in the USA for the treatment of HABP, including ventilator-associated bacterial pneumonia, caused by susceptible isolates of S. aureus when other alternatives are not suitable, telavancin offers another therapeutic option.

Alternative mutational pathways to intermediate resistance to vancomycin in methicillin-resistant Staphylococcus aureus

BACKGROUND

 We used 2 in vitro experimental systems to compare phenotypic and genotypic changes that accompany selection of mutants of methicillin-resistant Staphylococcus aureus (MRSA) strain JH1 with low-level vancomycin resistance similar to the type found in vancomycin-intermediate S. aureus (VISA).

METHODS

 The previously described MRSA strain JH1 and its vancomycin-intermediate mutant derivative JH2, both of which were recovered from a patient undergoing vancomycin chemotherapy, were used in this study. Mutants of JH1 were selected in vitro by means of a pharmacokinetic/pharmacodynamic (PK/PD) model of simulated endocardial vegetations (SEVs) and by exposure to vancomycin in laboratory growth medium. Phenotypic abnormalities of JH1 mutants generated by each in vitro experimental system were compared to those of JH2, and whole genomes of 2 in vitro JH1 mutants were sequenced to identify mutations that may be associated with an increased vancomycin minimum inhibitory concentration.

RESULTS

 JH1R1 was selected from the PK/PD model, and JH1R2 was selected in laboratory growth medium. Both mutants displayed reduced vancomycin and daptomycin susceptibility and phenotypic alterations (eg, thicker cell walls and abnormal autolysis) that are typical of in vivo VISA mutants. Genome sequencing of JH1R1 identified point mutations in 4 genes, all of which were different from the mutations described in JH2, including 1 mutation in yycG, a component of the WalKR sensory regulatory system. Sequencing of the JH1R2 genome identified mutations in 7 genes, including 2 in rpoB.

CONCLUSION

 Our findings indicate that JH1 is able to develop VISA-type resistance through several alternative genetic pathways.

Mechanisms of daptomycin resistance in Staphylococcus aureus: role of the cell membrane and cell wall

The bactericidal, cell membrane-targeting lipopeptide antibiotic daptomycin (DAP) is an important agent in treating invasive Staphylococcus aureus infections. However, there have been numerous recent reports of development of daptomycin resistance (DAP-R) during therapy with this agent. The mechanisms of DAP-R in S. aureus appear to be quite diverse. DAP-R strains often exhibit progressive accumulation of single nucleotide polymorphisms in the multipeptide resistance factor gene (mprF) and the yycFG components of the yycFGHI operon. Both loci are involved in key cell membrane (CM) events, with mprF being responsible for the synthesis and outer CM translocation of the positively charged phospholipid, lysyl-phosphotidylglycerol (L-PG), while the yyc operon is involved in the generalized response to stressors such as antimicrobials. In addition, other perturbations of the CM have been identified in DAP-R strains, including extremes in CM order, resistance to CM depolarization and permeabilization, and reduced surface binding of DAP. Moreover, modifications of the cell wall (CW) appear to also contribute to DAP-R, including enhanced expression of the dlt operon (involved in d-alanylation of CW teichoic acids) and progressive CW thickening.

Addition of ceftaroline to daptomycin after emergence of daptomycin-nonsusceptible Staphylococcus aureus during therapy improves antibacterial activity

Antistaphylococcal beta-lactams enhance daptomycin activity and have been used successfully in combination for refractory methicillin-resistant Staphylococcus aureus (MRSA) infections. Ceftaroline possesses MRSA activity, but it is unknown if it improves the daptomycin potency comparably to other beta-lactams. We report a complex patient case of endocarditis who was treated with daptomycin in combination with ceftaroline, which resulted in clearance of a daptomycin-nonsusceptible strain. An in vitro pharmacokinetic/pharmacodynamic model of renal failure was used to simulate the development of daptomycin resistance and evaluate the microbiologic effects of daptomycin plus ceftaroline treatment. Combination therapy with daptomycin and ceftaroline restored daptomycin sensitivity in vivo and resulted in clearance of persistent blood cultures. Daptomycin susceptibility in vitro was increased in the presence of either ceftaroline or oxacillin. Daptomycin at 6 mg/kg of body weight every 48 h was bactericidal in the model but resulted in regrowth and daptomycin resistance (MIC, 2 to 4 μg/ml) with continued monotherapy. The addition of ceftaroline at 200 mg every 12 h after the emergence of daptomycin resistance enhanced bacterial killing. Importantly, daptomycin plus ceftaroline as the initial combination therapy produced rapid and sustained bactericidal activity and prevented daptomycin resistance. Both in vivo- and in vitro-derived daptomycin resistance resulted in bacteria with more fluid cell membranes. After ceftaroline was added in the model, fluidity was restored to the level of the initial in vivo isolate. Daptomycin-resistant isolates required high daptomycin exposures (at least 10 mg/kg) to optimize cell membrane damage with daptomycin alone. Ceftaroline combined with daptomycin was effective in eliminating daptomycin-resistant MRSA, and these results further justify the potential use of daptomycin plus beta-lactam therapy for these refractory infections.

Telavancin in therapy of experimental aortic valve endocarditis in rabbits due to daptomycin-nonsusceptible methicillin-resistant Staphylococcus aureus

A number of cases of both methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains that have developed daptomycin resistance (DAP-R) have been reported. Telavancin (TLV) is a lipoglycopeptide agent with a dual mechanism of activity (cell wall synthesis inhibition plus depolarization of the bacterial cell membrane). Five recent daptomycin-susceptible (DAP-S)/DAP-R MRSA isogenic strain pairs were evaluated for in vitro TLV susceptibility. All five DAP-R strains (DAP MICs ranging from 2 to 4 μg/ml) were susceptible to TLV (MICs of ≤0.38 μg/ml). In vitro time-kill analyses also revealed that several TLV concentrations (1-, 2-, and 4-fold MICs) caused rapid killing against the DAP-R strains. Moreover, for 3 of 5 DAP-R strains (REF2145, A215, and B(2.0)), supra-MICs of TLV were effective at preventing regrowth at 24 h of incubation. Further, the combination of TLV plus oxacillin (at 0.25× or 0.50× MIC for each agent) increased killing of DAP-R MRSA strains REF2145 and A215 at 24 h (∼2-log and 5-log reductions versus TLV and oxacillin alone, respectively). Finally, using a rabbit model of aortic valve endocarditis caused by DAP-R strain REF2145, TLV therapy produced a mean reduction of >4.5 log(10) CFU/g in vegetations, kidneys, and spleen compared to untreated or DAP-treated rabbits. Moreover, TLV-treated rabbits had a significantly higher percentage of sterile tissue cultures (87% in vegetations and 100% in kidney and spleen) than all other treatment groups (P < 0.0001). Together, these results demonstrate that TLV has potent bactericidal activity in vitro and in vivo against DAP-R MRSA isolates.