Activity of telavancin compared to other agents against coagulase-negative staphylococci with different resistotypes by time kill

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.

Salicylanilide carbamates: Promising antibacterial agents with high in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA)

A series of twenty-one salicylanilide N-alkylcarbamates was assessed for novel antibacterial characteristics against three clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus ATCC 29213 as the reference and quality control strain. The minimum inhibitory concentration was determined by the broth dilution micro-method with subsequent subcultivation of aliquots to assess minimum bactericidal concentration. The bactericidal kinetics was established by time-kill assay. Ampicillin, ciprofloxacin and vancomycin were used as reference antibacterial drugs. All the tested compounds exhibited highly potent anti-MRSA activity (⩽ 0.008-4 μg/mL) comparable or up to 250× higher than that of vancomycin, the standard in the treatment of serious MRSA infections. 4-Chloro-2-(3,4-dichlorophenylcarbamoyl)phenyl butylcarbamate and 4-chloro-2-(3,4-dichlorophenylcarbamoyl)phenyl ethylcarbamate were the most active compounds. In most cases, compounds provided reliable bacteriostatic activity, except for 4-chloro-2-(4-chlorophenylcarbamoyl)phenyl decylcarbamate exhibiting bactericidal effect at 8h (for clinical isolate of MRSA 63718) and at 24h (for clinical isolates of MRSA SA 630 and MRSA SA 3202) at 4× MIC. Structure-activity relationships are discussed.

In vitro bactericidal activity of 4- and 5-chloro-2-hydroxy-N-[1-oxo-1-(phenylamino)alkan-2-yl]benzamides against MRSA

A series of nine substituted 2-hydroxy-N-[1-oxo-1-(phenylamino)alkan-2-yl]benzamides was assessed as prospective bactericidal agents against three clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus ATCC 29213 as the reference and quality control strain. The minimum bactericidal concentration was determined by subculturing aliquots from MIC determination onto substance-free agar plates. The bactericidal kinetics of compounds 5-chloro-2-hydroxy-N-[(2S)-3-methyl-1-oxo-1-{[4-(trifluoromethyl)phenyl]amino}butan-2-yl]benzamide (1f), N-{(2S)-1-[(4-bromophenyl)amino]-3-methyl-1-oxobutan-2-yl}-4-chloro-2-hydroxybenzamide (1g), and 4-chloro-N-{(2S)-1-[(3,4-dichlorophenyl)amino]-3-methyl-1-oxobutan-2-yl}-2-hydroxybenzamide (1h) was established by time-kill assay with a final concentration of the compound equal to 1x, 2x, and 4x MIC; aliquots were removed at 0, 4, 6, 8, and 24 h time points. The most potent bactericidal agent was compound 1f exhibiting remarkable rapid concentration-dependent bactericidal effect even at 2x MIC at 4, 6, and 8 h (with a reduction in bacterial count ranging from 3.08 to 3.75 log₁₀ CFU/mL) and at 4x MIC at 4, 6, 8, and 24 h (5.30 log₁₀ CFU/mL reduction in bacterial count) after incubation against MRSA 63718. Reliable bactericidal effect against other strains was maintained at 4x MIC at 24 h.

Novel rate-area-shape modeling approach to quantify bacterial killing and regrowth for in vitro static time-kill studies

In vitro static concentration time-kill (SCTK) studies are a cornerstone for antibiotic development and designing dosage regimens. However, mathematical approaches to efficiently model SCTK curves are scarce. The currently used model-free, descriptive metrics include the log10 change in CFU from 0 h to a defined time and the area under the viable count versus time curve. These metrics have significant limitations, as they do not characterize the rates of bacterial killing and regrowth and lack sensitivity. Our aims were to develop a novel rate-area-shape modeling approach and to compare, against model-free metrics, its relative ability to characterize the rate, extent, and timing of bacterial killing and regrowth from SCTK studies. The rate-area-shape model and the model-free metrics were applied to data for colistin and doripenem against six Acinetobacter baumannii strains. Both approaches identified exposure-response relationships from 0.5- to 64-fold the MIC. The model-based approach estimated an at least 10-fold faster killing by colistin than by doripenem at all multiples of the MIC. However, bacterial regrowth was more extensive (by 2 log10) and occurred approximately 3 h earlier for colistin than for doripenem. The model-free metrics could not consistently differentiate the rate and extent of killing between colistin and doripenem. The time to 2 log10 killing was substantially faster for colistin. The rate-area-shape model was successfully implemented in Excel. This new model provides an improved framework to distinguish between antibiotics with different rates of bacterial killing and regrowth and will enable researchers to better characterize SCTK experiments and design subsequent dynamic studies.