In vitro prevention of the emergence of daptomycin resistance in Staphylococcus aureus and enterococci following combination with amoxicillin/clavulanic acid or ampicillin

155

140

We studied an ampicillin-and vancomycin-resistant Enterococcus faecium (VRE) isolate from a patient with endocarditis and bacteremia refractory to treatment with daptomycin (6 mg/kg of body weight) plus linezolid. Blood cultures cleared within 24 h of changing therapy to daptomycin (12 mg/kg) plus ampicillin. We examined the effects of ampicillin on daptomycin-induced growth inhibition and killing, surface charge, and susceptibility to several prototypical host defense cationic antimicrobial peptides. MICs and time-kill curves with daptomycin were assessed in the presence and absence of ampicillin. The impact of ampicillin on surface charge was assessed by flow cytometry and a poly-L-lysine binding assay. The effects of ampicillin preexposures upon VRE killing by five distinct cationic peptides of different structure, charge, origin, and mechanism of action were analyzed using the epidermal cathelicidin LL-37, thrombin-induced platelet microbicidal proteins (tPMPs), and a synthetic congener modeled after tPMP microbicidal domains (RP-1), human neutrophil peptide-1 (hNP-1), and polymyxin B (bacteria derived). Fluoroscein-Bodipy-labeled daptomycin was used to evaluate daptomycin binding to VRE membranes in the presence or absence of ampicillin. In media containing ampicillin (25 to 100 mg/liter), daptomycin MICs decreased from 1.0 to 0.38 mg/liter. Based on time-kill analysis and an in vitro pharmacodynamic model, ampicillin enhanced daptomycin activity against the study VRE from a bacteriostatic to a bactericidal profile. VRE grown in ampicillin (25 to 150 mg/liter) demonstrated an incremental reduction in its relative net positive surface charge. When grown in the presence (versus absence) of ampicillin (25 and 100 mg/ liter), the VRE strain (i) was more susceptible to killing by LL-37, tPMPs, hNP-1, and RP-1 but not to polymyxin B and (ii) exhibited greater binding to Bodipy-labeled daptomycin. We conclude that ampicillin induces reductions in net positive bacterial surface charge of VRE, correlating with enhanced bactericidal effects of cationic calcium-daptomycin and a diverse range of other cationic peptides in vitro. While the mechanism(s) of such ␤-lactam-mediated shifts in surface charge remains to be defined, these finding suggest a potential for ␤-lactam-mediated enhancement of activity of both daptomycin and innate host defense peptides against antibiotic-resistant bacteria.

Section: Discussionmentioning

confidence: 99%

Ampicillin Enhances Daptomycin- and Cationic Host Defense Peptide-Mediated Killing of Ampicillin- and Vancomycin-Resistant Enterococcus faecium

Sakoulas

Bayer

Pogliano

et al. 2012

155

140

“…Published reports on the combination of DAP and FOF are few and have not addressed the effect of FOF on DAP resistance development (6,31,33). More data are available on the addition of RIF, which has been shown previously to delay the emergence of DAP resistance (12,20) and can significantly enhance clearance of complex MRSA infection when given in combination with DAP (1,38), possibly by suppressing the emergence of resistance to both agents (15). Combination therapy with DAP ϩ CLR has been shown to be superior to either antibiotic alone in the eradication of biofilms (29), but there have been no reports of macrolide antibiotics suppressing the emergence of DAP resistance.…”

Section: Discussionmentioning

confidence: 99%

“…Of note, Entenza and colleagues demonstrated that beta-lactam antibiotics significantly decrease the emergence of DAP resistance during a week-long subinhibitory exposure in Gram-positive isolates from a laboratory collection. Rifampin (RIF) and gentamicin (GEN) were shown to have comparatively little effect, delaying the onset of resistance by no more than 1 day (12).…”

mentioning

confidence: 99%

Altering the Proclivity towards Daptomycin Resistance in Methicillin-Resistant Staphylococcus aureus Using Combinations with Other Antibiotics

Berti

Wergin

Girdaukas

et al. 2012

ABSTRACTDaptomycin (DAP) is increasingly used as a part of combination therapy, particularly in complex methicillin-resistantStaphylococcus aureus(MRSA) infections. While multiple studies have reported the potential for synergy between DAP and adjunctive anti-infectives, few have examined the influence of adjunctive therapy on the emergence of DAP resistance. This study examined eight adjunctive antimicrobial combinations with DAPin vitroand the emergence of DAP resistance over time (up to 4 weeks) using clinical isolates of DAP-susceptible MRSA (MIC, 0.5 μg/ml) in which DAP resistance subsequently developed during patient therapy (MIC, 3 μg/ml). In addition to DAP susceptibility testing, selected strains were examined for phenotypic changes associated with DAP resistance, including changes to cell wall thickness (CWT) and cell membrane alterations. The addition of either oxacillin or clarithromycin in medium containing DAP significantly inhibited the development of DAP resistance through the entirety of the 4-week exposure (10- to 32-fold MIC reduction from that of DAP alone). Combinations with rifampin or fosfomycin were effective in delaying the emergence of DAP resistance through the end of week one only (week one MIC, 0.5 μg/ml; week four MIC, 24 μg/ml). Cell wall thickening was observed for all antibiotic combinations regardless of their effect on the DAP MIC (14 to 70% increase in CWT), while changes in cell membrane fluidity were variable and treatment dependent. DAP showed reduced activity against strains with DAP MICs of 1 to 12 μg/ml, but cell membrane integrity was still disrupted at concentrations achieved with doses greater than 10 mg/kg of body weight. The emergence of DAP resistance in MRSA is strongly influenced by the presence of subinhibitory concentrations of adjunctive antimicrobials. These data suggest that combining DAP with oxacillin or clarithromycin may delay the development of DAP resistance in cases requiring prolonged antibiotic therapy.

“…The more that unbound cytochrome c is detected in the supernatant, the more that a positive charge exists on the bacterial cell surface. SA113 and SA113 null mutant dltA strains were used as controls (dltA positive and negative, respectively) (32 (10 7 CFU/ml) were exposed in MH broth-50 g/ml Ca 2ϩ to stepwise, 2-fold-increasing concentrations of DAP alone for 7 consecutive days (12). After 24 h of incubation at 37°C, the tubes displaying the highest antibiotic concentration and still showing turbidity were used to inoculate a new series of tubes containing antibiotic dilutions.…”

Section: Methodsmentioning

confidence: 99%

β-Lactams Increase the Antibacterial Activity of Daptomycin against Clinical Methicillin-Resistant Staphylococcus aureus Strains and Prevent Selection of Daptomycin-Resistant Derivatives

Mehta

Singh

Plata

et al. 2012

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