The impact of penicillinase on cefamandole treatment and prophylaxis of experimental endocarditis due to methicillin-resistant Staphylococcus aureus

Subtherapeutic Doses of Vancomycin Synergize with Bacteriophages for Treatment of Experimental Methicillin-Resistant Staphylococcus aureus Infective Endocarditis

Background. Recurrent therapeutic failures reported for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infective endocarditis (IE) with vancomycin may be due to poor bactericidal activity. Alternative antibacterial approaches using bacteriophages may overcome this limitation. Objectives. An experimental rat model of MRSA IE (EE) was used to examine the efficacy of vancomycin combined with a 1:1 bacteriophage (phage) cocktail composed of Herelleviridae vB_SauH_2002 and Routreeviridae 66. Methods. Six hours after inoculation with ca. 5 log10 colony forming units (CFU) of MRSA strain AW7, animals were treated with either: (i) saline, (ii) an equimolar two-phage cocktail (bolus of 1 mL followed by a 0.3 mL/h continuous infusion of 10 log10 plaque forming units (PFU)/mL phage suspension), (iii) vancomycin (at a dose mimicking the kinetics in humans of 0.5 g b.i.d.), or (iv) a combination of both. Bacterial loads in vegetations, and phage loads in vegetations, liver, kidney, spleen, and blood, were measured outcomes. Results. Phage cocktail alone was unable to control the growth of strain AW7 in cardiac vegetations. However, when combined with subtherapeutic doses of vancomycin, a statistically significant decrease of ∆4.05 ± 0.94 log10 CFU/g at 24 h compared to placebo was detected (p < 0.001). The administration of vancomycin was found to significantly impact on the local concentrations of phages in the vegetations and in the organs examined. Conclusions. Lytic bacteriophages as an adjunct treatment to the standard of care antibiotics could potentially improve the management of MRSA IE. Further studies are needed to investigate the impact of antibiotics on phage replication in vivo.

Bacteriophages Combined With Subtherapeutic Doses of Flucloxacillin Act Synergistically Against Staphylococcus aureus Experimental Infective Endocarditis

Background

The potential of phage therapy for the treatment of endovascular Staphylococcus aureus infections remains to be evaluated.

Methods and Results

The efficacy of a phage cocktail combining Herelleviridae phage vB_SauH_2002 and Podoviriae phage 66 was evaluated against a methicillin‐sensitive S. aureus strain in vitro and in vivo in a rodent model of experimental endocarditis. Six hours after bacterial challenge, animals were treated with (1) the phage cocktail. (2) subtherapeutic flucloxacillin dosage, (3) combination of the phage cocktail and flucloxacillin, or (4) saline. Bacterial loads in cardiac vegetations at 30 hours were the primary outcome. Secondary outcomes were phage loads at 30 hours in cardiac vegetations, blood, spleen, liver, and kidneys. We evaluated phage resistance 30 hours post infection in vegetations of rats under combination treatment. In vitro, phages synergized against S. aureus planktonic cells and the cocktail synergized with flucloxacillin to eradicated biofilms. In infected animals, the phage cocktail achieved bacteriostatic effect. The addition of low‐dose flucloxacillin elevated bacterial suppression (∆ of −5.25 log₁₀ colony forming unit/g [CFU/g] versus treatment onset, P<0.0001) and synergism was confirmed (∆ of −2.15 log₁₀ CFU/g versus low‐dose flucloxacillin alone, P<0.01). Importantly, 9/12 rats given the combination treatment had sterile vegetations at 30 hours. In vivo phage replication was partially suppressed by the antibiotic and selection of resistance to the Podoviridae component of the phage cocktail occurred. Plasma‐mediated inhibition of phage killing activity was observed in vitro.

Conclusions

Combining phages with a low‐dose standard of care antibiotic represents a promising strategy for the treatment of S. aureus infective endocarditis.

Ru–g-C3N4 as a highly active heterogeneous catalyst for transfer hydrogenation of α-keto amide into β-aminol or α-hydroxyl amide

This work reports a sustainable route for the catalytic transfer hydrogenation (CTH) of α-keto amide into β-aminol via an efficient heterogeneous catalyst wherein ruthenium is incorporated on an active graphite sheet of a carbon nitride support (Ru–g-C₃N₄).

DMF/NaOH/H2O: a metal-free system for efficient and chemoselective reduction of α-ketoamides

A metal-free method for efficient and chemoselective reduction of α-ketoamides using DMF/NaOH/H₂O system has been developed.

Zirconium-MOF-catalysed selective synthesis of α-hydroxyamide via the transfer hydrogenation of α-ketoamide

This work reports the synthesis of α-hydroxy amide and its derivatives using zirconium-based metal–organic frameworks (Zr-MOFs).

Highly enantioselective Ir/f-amphox-catalyzed hydrogenation of ketoamides: efficient access to chiral hydroxy amides

Asymmetric synthesis of chiral hydroxy amides has been successfully accomplished by asymmetric hydrogenation of prochiral α-, β-, γ-, δ-keto amides catalyzed by Ir/f-amphox with up to >99% conversion and >99% ee.

Biomimetic catalytic transformation of toxic α-oxoaldehydes to high-value chiral α-hydroxythioesters using artificial glyoxalase I

Glyoxalase I plays a critical role in the enzymatic defence against glycation by catalysing the isomerization of hemithioacetal, formed spontaneously from cytotoxic α-oxoaldehydes and glutathione, to (S)-α-hydroxyacylglutathione derivatives. Upon the hydrolysis of the thioesters catalysed by glyoxalase II, inert (S)-α-hydroxy acids, that is, lactic acid, are then produced. Herein, we demonstrate highly enantioselective glyoxalase I mimic catalytic isomerization of in-situ-generated hemithioacetals, providing facile access to both enantiomers of α-hydroxy thioesters. Owing to the flexibility of thioesters, a family of optically pure α-hydroxyamides, which are highly important drug candidates in the pharmaceutical industry, were prepared without any coupling reagents. Similar to real enzymes, the enforced proximity of the catalyst and substrates by the chiral cage in situ formed by the incorporation of potassium salt can enhance the reactivity and efficiently transfer the stereochemical information.

In vivo effect of flucloxacillin in experimental endocarditis caused by mecC-positive staphylococcus aureus showing temperature-dependent susceptibility in vitro

Methicillin-resistant Staphylococcus aureus (MRSA) carrying the mecC gene (mecC-MRSA) exhibited at 37°C MICs of oxacillin close to those of methicillin-susceptible S. aureus (MSSA). We investigated whether at this temperature, mecC-MRSA strains respond to flucloxacillin treatment like MSSA strains, using a rat model of endocarditis. Flucloxacillin (human-like kinetics of 2 g intravenously every 6 h) cured 80 to 100% of aortic vegetations infected with five different mecC-MRSA strains. These results suggest that mecC-MRSA infections may successfully respond to treatment with β-lactams.

A quorum sensing small volatile molecule promotes antibiotic tolerance in bacteria

Bacteria can be refractory to antibiotics due to a sub-population of dormant cells, called persisters that are highly tolerant to antibiotic exposure. The low frequency and transience of the antibiotic tolerant “persister” trait has complicated elucidation of the mechanism that controls antibiotic tolerance. In this study, we show that 2’ Amino-acetophenone (2-AA), a poorly studied but diagnostically important small, volatile molecule produced by the recalcitrant gram-negative human pathogen Pseudomonas aeruginosa, promotes antibiotic tolerance in response to quorum-sensing (QS) signaling. Our results show that 2-AA mediated persister cell accumulation occurs via alteration of the expression of genes involved in the translational capacity of the cell, including almost all ribosomal protein genes and other translation-related factors. That 2-AA promotes persisters formation also in other emerging multi-drug resistant pathogens, including the non 2-AA producer Acinetobacter baumannii implies that 2-AA may play an important role in the ability of gram-negative bacteria to tolerate antibiotic treatments in polymicrobial infections. Given that the synthesis, excretion and uptake of QS small molecules is a common hallmark of prokaryotes, together with the fact that the translational machinery is highly conserved, we posit that modulation of the translational capacity of the cell via QS molecules, may be a general, widely distributed mechanism that promotes antibiotic tolerance among prokaryotes.

A positive interaction between inhibitors of protein synthesis and cefepime in the fight against methicillin-resistant Staphylococcus aureus

Quinupristin-dalfopristin (Q-D) synergizes with cefepime for the treatment of methicillin-resistant Staphylococcus aureus (MRSA). Here, we studied whether the synergism was restricted to MRSA and if it extended to non-beta-lactam cell wall inhibitors or to other inhibitors of protein synthesis. Three MRSA and two methicillin-susceptible S. aureus (MSSA) strains were tested, including an isogenic pair of mecA (-)/mecA (+) S. aureus Newman. The drug interactions were determined by fractional inhibitory concentration (FIC) indices and population analysis profiles. The antibacterial drugs that we used included beta-lactam (cefepime) and non-beta-lactam cell wall inhibitors (D-cycloserine, fosfomycin, vancomycin, teicoplanin), inhibitors of protein synthesis (Q-D, erythromycin, chloramphenicol, tetracycline, linezolid, fusidic acid), and polynucleotide inhibitors (cotrimoxazole, ciprofloxacin). The addition of each protein inhibitor to cefepime was synergistic (FIC ≤ 0.5) or additive (FIC > 0.5 but < 1) against MRSA, but mostly indifferent against MSSA (FIC ≥ 1 but ≤ 4). This segregation was not observed after adding cotrimoxazole or ciprofloxacin to cefepime. Population analysis profiles were performed on plates in the presence of increasing concentrations of the cell wall inhibitors plus 0.25 × minimum inhibitory concentration (MIC) of Q-D. Cefepime combined with Q-D was synergistic against MRSA, but D-cycloserine and glycopeptides were not. Thus, the synergism was specific to beta-lactam antibiotics. Moreover, the synergism was not lost against fem mutants, indicating that it acted at another level. The restriction of the beneficial effect to MRSA suggests that the functionality of penicillin-binding protein 2A (PBP2A) was affected, either directly or indirectly. Further studies are necessary in order to provide a mechanism for this positive interaction.

Gentamicin-susceptible or gentamicin-resistant methicillin-resistant Staphylococcus aureus: a case-case study

Gentamicin-susceptible methicillin-resistant Staphylococcus aureus (GS-MRSA) strains are replacing gentamicin-resistant MRSA (GR-MRSA) strains. We showed that exposure to other patients harboring GS-MRSA was the major risk factor for GS-MRSA acquisition, and that antimicrobial exposure, especially to beta-lactams, was strongly associated with acquisition of GR-MRSA but not GS-MRSA. Gentamicin use was significantly associated with GR-MRSA acquisition in univariate analysis only.

LB11058, a new cephalosporin with high penicillin-binding protein 2a affinity and activity in experimental endocarditis due to homogeneously methicillin-resistant Staphylococcus aureus

LB11058 is a new synthetic cephalosporin with good affinity for staphylococcal penicillin-binding protein 2a (PBP2a). LB11058 was tested in vitro and in rats with experimental aortic endocarditis against three methicillin-resistant Staphylococcus aureus (MRSA) strains, one penicillinase-negative strain (strain COL), and two penicillinase-producing strains (COL-Bla+ and P8-Hom). The MICs of LB11058 for the organisms were 1 mg/liter. The MICs of vancomycin and ceftriaxone were 1 and >/=64 mg/liter, respectively. In population analysis profiles, none of the MRSA strains grew at >/=2 mg of LB11058/liter. Rats with endocarditis were treated for 5 days. LB11058 was highly bound to serum proteins in rats (>/=98%). However, binding was saturable above a threshold of 250 mg/liter. Therefore, continuous concentrations of 250 mg/liter in serum were infused to ensure a free fraction (>/=5 mg/liter) above the drug's MIC for the entire infusion period. Control treatments included simulation of human serum kinetics produced by intravenous vancomycin (1 g twice daily, free drug concentration above MIC, >/=90% of infusion period) or ceftriaxone (2 g/24 h, free drug concentrations above the MIC, 0% of infusion period). LB11058 successfully treated 10 of 10 (100%) and 13 of 14 (93%) of rats infected with COL-Bla+ and P8-Hom, respectively. This was comparable to vancomycin (sterilization of 8 of 12 [66%] and 6 of 8 [75%] rats, respectively). Ceftriaxone was inactive. Low concentrations of LB11058 (5 and 10 mg/liter, continuously infused) in serum were ineffective, as predicted by the pharmacodynamic parameters. At appropriate doses, LB11058 was highly effective both in vitro and in vivo. This finding supports the development of this beta-lactam with high PBP2a affinity for the treatment of MRSA infections.

Infective endocarditis

Despite improvements in health care, the incidence of infective endocarditis has not decreased over the past decades. This apparent paradox is explained by a progressive evolution in risk factors; while classic predisposing conditions such as rheumatic heart disease have been all but eradicated, new risk factors for infective endocarditis have emerged. These include intravenous drug use, sclerotic valve disease in elderly patients, use of prosthetic valves, and nosocomial disease. Newly identified pathogens, which are difficult to cultivate--eg, Bartonella spp and Tropheryma whipplei--are present in selected individuals, and resistant organisms are challenging conventional antimicrobial therapy. Keeping up with these changes depends on a comprehensive approach, allying understanding of the pathogenesis of disease with the development of new drugs for infective endocarditis. Infection by staphylococci and streptococci is being dissected at the molecular level. New ideas for antimicrobial agents are being developed. These novel insights should help redefine preventive and therapeutic strategies against infective endocarditis.

BAL9141, a novel extended-spectrum cephalosporin active against methicillin-resistant Staphylococcus aureus in treatment of experimental endocarditis

The therapeutic efficacy of BAL9141 (formerly Ro 63-9141), a novel cephalosporin with broad in vitro activity that also has activity against methicillin-resistant Staphylococcus aureus (MRSA), was investigated in rats with experimental endocarditis. The test organisms were homogeneously methicillin-resistant S. aureus strain COL transformed with the penicillinase-encoding plasmid pI524 (COL Bla+) and homogeneously methicillin-resistant, penicillinase-producing isolate P8-Hom, selected by serial exposure of parent strain P8 to methicillin. The MICs of BAL9141 for these organisms (2 mg/liter) were low, and BAL9141was bactericidal in time-kill curve studies after 24 h of exposure to either two, four, or eight times the MIC. Rats with experimental endocarditis were treated in a three-arm study with a continuous infusion of BAL5788 (formerly Ro 65-5788), a carbamate prodrug of BAL9141, or with amoxicillin-clavulanate or vancomycin. The rats were administered BAL9141 to obtain steady-state target levels of 20, 10, and 5 mg of per liter or were administered either 1.2 g of amoxicillin-clavulanate (ratio 5:1) every 6 h or 1 g of vancomycin every 12 h at changing flow rates to simulate the pharmacokinetics produced in humans by intermittent intravenous treatment. Treatment was started 12 h after bacterial challenge and lasted for 3 days. BAL9141 was successful in the treatment of experimental endocarditis due to either MRSA isolate COL Bla+ or MRSA isolate P8-Hom at the three targeted steady-state concentrations and sterilized >90% of cardiac vegetations (P < 0.005 versus controls; P < 0.05 versus amoxicillin-clavulanate and vancomycin treatment groups). These promising in vivo results with BAL9141 correlated with the high affinity of the drug for PBP 2a and its stability to penicillinase hydrolysis observed in vitro.

Quinupristin-dalfopristin combined with beta-lactams for treatment of experimental endocarditis due to Staphylococcus aureus constitutively resistant to macrolide-lincosamide-streptogramin B antibiotics

Quinupristin-dalfopristin (Q-D) is an injectable streptogramin active against most gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). In experimental endocarditis, however, Q-D was less efficacious against MRSA isolates constitutively resistant to macrolide-lincosamide-streptogram B (C-MLS(B)) than against MLS(B)-susceptible isolates. To circumvent this problem, we used the checkerboard method to screen drug combinations that would increase the efficacy of Q-D against such bacteria. beta-Lactams consistently exhibited additive or synergistic activity with Q-D. Glycopeptides, quinolones, and aminoglycosides were indifferent. No drugs were antagonistic. The positive Q-D-beta-lactam interaction was independent of MLS(B) or beta-lactam resistance. Moreover, addition of Q-D at one-fourth the MIC to flucloxacillin-containing plates decreased the flucloxacillin MIC for MRSA from 500 to 1,000 mg/liter to 30 to 60 mg/liter. Yet, Q-D-beta-lactam combinations were not synergistic in bactericidal tests. Rats with aortic vegetations were infected with two C-MLS(B)-resistant MRSA isolates (isolates AW7 and P8) and were treated for 3 or 5 days with drug dosages simulating the following treatments in humans: (i) Q-D at 7 mg/kg two times a day (b.i.d.) (a relatively low dosage purposely used to help detect positive drug interactions), (ii) cefamandole at constant levels in serum of 30 mg/liter, (iii) cefepime at 2 g b.i.d., (iv) Q-D combined with either cefamandole or cefepime. Any of the drugs used alone resulted in treatment failure. In contrast, Q-D plus either cefamandole or cefepime significantly decreased valve infection compared to the levels of infection for both untreated controls and those that received monotherapy (P < 0.05). Importantly, Q-D prevented the growth of highly beta-lactam-resistant MRSA in vivo. The mechanism of this beneficial drug interaction is unknown. However, Q-D-beta-lactam combinations might be useful for the treatment of complicated infections caused by multiple organisms, including MRSA.