Exploration of Bacterial Re-Growth as In Vitro Phenomenon Affecting Methods for Analysis of the Antimicrobial Activity of Chimeric Bacteriophage Endolysins

Characterization of sulopenem antimicrobial activity using in vitro time-kill kinetics, synergy, post-antibiotic effect, and sub-inhibitory MIC effect methods against Escherichia coli and Klebsiella pneumoniae isolates

Sulopenem is an oral and intravenous penem antibiotic in clinical development for treatment of urinary tract and intra-abdominal infections caused by multidrug-resistant pathogens. This study evaluated in vitro antimicrobial activity of sulopenem by post-antibiotic effect (PAE), sub-inhibitory minimal inhibitory concentration PAE effect (PAE-SME), checkerboard testing, and time-kill testing. Testing sulopenem at 1×, 5×, or 10× the baseline MIC resulted in a PAE interval of 0.0-0.7 hours. When exposed to 0.5× the sulopenem MIC following 5× MIC, all isolate/agent combinations had PAE-SME values of >4.8 hours. Checkerboard testing revealed no instances of antagonism between sulopenem and comparator agents-indifference was observed in most sulopenem checkerboard combinations. Sulopenem demonstrated bactericidal activity (≥3 log10 [99.9%] reduction in viable organism counts) in all time-kill assays following 24 hours of incubation at 8× the baseline MIC (6/6), 5/6 displaying this activity within 8 hours. The present antimicrobial parameters seen at concentrations surrounding the MIC support optimization of sulopenem dosing and further development. The oral dosing regimen of sulopenem etzadroxil/probenecid 500 mg/500 mg administered every 12 hours was recently evaluated in two phase 3 clinical trials where sulopenem demonstrated efficacy against amoxicillin-clavulanate in uncomplicated urinary tract infection (uUTI) and against ciprofloxacin in fluoroquinolone-resistant uUTI.IMPORTANCESulopenem is an oral and intravenous penem antibiotic in clinical development for treatment of urinary tract and intra-abdominal infections caused by multidrug-resistant pathogens. This study evaluated sulopenem via broth microdilution susceptibility testing, PAE, sub-inhibitory MIC PAE effect, checkerboard testing, and time-kill testing. The results of this study-interpreted along with recent pharmacodynamic in vitro one-compartment and hollow-fiber infection model work-provide insight into the in vitro activity of sulopenem.

The Engineered Lysin CF-370 Is Active Against Antibiotic-Resistant Gram-Negative Pathogens In Vitro and Synergizes With Meropenem in Experimental Pseudomonas aeruginosa Pneumonia

BACKGROUND

Lysins (cell wall hydrolases) targeting gram-negative organisms require engineering to permeabilize the outer membrane and access subjacent peptidoglycan to facilitate killing. In the current study, the potential clinical utility for the engineered lysin CF-370 was examined in vitro and in vivo against gram-negative pathogens important in human infections.

METHODS

Minimum inhibitory concentration (MICs) and bactericidal activity were determined using standard methods. An in vivo proof-of-concept efficacy study was conducted using a rabbit acute pneumonia model caused by Pseudomonas aeruginosa.

RESULTS

CF-370 exhibited potent antimicrobial activity, with MIC50/90 values (in µg/mL) for: P aeruginosa, 1/2; Acinetobacter baumannii, 1/1; Escherichia coli, 0.25/1; Klebsiella pneumoniae, 2/4; Enterobacter cloacae 1/4; and Stenotrophomonas maltophilia 2/8. CF-370 furthermore demonstrated bactericidal activity, activity in serum, a low propensity for resistance, anti-biofilm activity, and synergy with antibiotics. In the pneumonia model, CF-370 alone decreased bacterial densities in lungs, kidneys, and spleen versus vehicle control, and demonstrated significantly increased efficacy when combined with meropenem (vs either agent alone).

CONCLUSIONS

CF-370 is the first engineered lysin described with potent broad-spectrum in vitro activity against multiple clinically relevant gram-negative pathogens, as well as potent in vivo efficacy in an animal model of severe invasive multisystem infection.

The dual activity of CaONPs as a cancer treatment substance and at the same time resistance to harmful microbes

Nanotechnology holds significant promise for the development of novel and necessary products that enhance human health. Pharmacology and nanotechnology have contributed to developing advanced and highly effective drugs for cancer treatment and combating microbial infections. The microbiological effectiveness against the variety of examined microorganisms was assessed using the time killer curve, scanning electron microscopy (SEM), MIC techniques, and the agar well diffusion method. SEM was utilized to enhance the analysis of the mechanisms underlying the bio-interface interaction and intracellular localization of calcium oxide nanoparticles (CaONPs). The MTT test was used to examine the cytotoxicity of CaONP anticancer activity in various cancer cells, including colon, breast, and hepatic cells. The efficacy of CaONPs as an anticancer medication was elucidated by analyzing the gene expression of both treated and untreated cancer cells. MIC and MBC of CaONPs against Escherichia coli and Staphylococcus epidermidis were 150, 150, 150, and 200 µg/ml, respectively. The MIC and MFC of CaONPs against Candida albicans were 200 µg/ml and 250 µg/ml, respectively. The IC50 values of various CaONPs vary depending on the type of cancer cells. The gene expression analysis of breast cancer cells undergoing treatment revealed the identification of several cancer-controlling genes, namely BAX, BCL2, P53, TERT, KRAS1, KRAS2, and RB1. The study demonstrated the notable antibacterial efficacy of CaONPs, highlighting their potential as cancer therapies.

Rapid bacteriolysis of Staphylococcus aureus by lysin exebacase

Lysins (peptidoglycan hydrolases) are promising new protein-based antimicrobial candidates under development to address rising antibiotic resistance encountered among pathogenic bacteria. Exebacase is an antistaphylococcal lysin and the first member of the lysin class to have entered clinical trials in the United States. In this study, the bacteriolytic activity of exebacase was characterized with time-kill assays, turbidity reduction assays, and microscopy. Three methicillin-susceptible Staphylococcus aureus and three methicillin-resistant S. aureus isolates were tested in time-kill assays over a range of concentrations from 0.25 to 8 × MIC. Exebacase demonstrated a concentration-dependent killing and showed bactericidal activity (≥3 log10 kill achieved relative to the starting inoculum) within 3 h at 1 × MIC against all strains tested. Dose-dependent lysis by exebacase was, furthermore, observed in the turbidity reduction assay, wherein decreases in initial OD600 of 50% were observed within ~15 min at concentrations as low as 4 µg/mL. Membrane dissolution, loss of cytoplasmic material, and lysis were confirmed by video and electron microscopy. The demonstrated rapid bacteriolytic effect of exebacase is an important distinguishing feature of this novel modality. IMPORTANCE To guide the development of an investigational new antibacterial entity, microbiological data are required to evaluate the killing kinetics against target organism(s). Exebacase is a lysin (peptidoglycan hydrolase) that represents a novel antimicrobial modality based on degradation of the cell wall of Staphylococcus aureus. Killing by exebacase was determined in multiple assay formats including time-kill assays, wherein reductions of viability of ≥3 log10 colony-forming units/mL were observed within 3 h for multiple different isolates tested, consistent with very rapid bactericidal activity. Rapid reductions in optical density were likewise observed in exebacase-treated cultures, which were visually consistent with microscopic observations of rapid lysis. Overall, exebacase provides a novel antimicrobial modality against S. aureus, characterized by a rapid cidal and lytic activity.

Bactericidal Activity of Sodium Bituminosulfonate against Staphylococcus aureus

Antibiotic resistance is increasing worldwide making it necessary to search for alternative antimicrobials. Sodium bituminosulfonate is a long-known substance, whose antimicrobial inhibitory activity has recently been re-evaluated. However, to the best of our knowledge, the bactericidal mode of action of this substance has not been systematically characterized. The aim of this study was to investigate the in vitro bactericidal activity of sodium bituminosulfonate by determining the minimal bactericidal concentrations (MBC), as well as the rapidity of bactericidal effect by time-kill curves. Clinical isolates of methicillin-susceptible (MSSA, n = 20) and methicillin-resistant (mecA/mecC-MRSA, n = 20) Staphylococcus aureus were used to determine MBC by a broth microdilution method. Sodium bituminosulfonate (Ichthyol^® light) was tested in double-dilution concentration steps ranging from 0.03 g/L to 256 g/L. For time-kill analysis, two reference and two clinical S. aureus strains were tested with different concentrations of sodium bituminosulfonate (1× minimal inhibitory concentration (MIC), 2× MIC, 4× MIC, 16× MIC and 256× MIC). For MSSA isolates, MBC₅₀, MBC₉₀ and the MBC range were 0.5 g/L, 1.0 g/L and 0.125–1.0 g/L; (MBC/MIC ratio)₅₀, (MBC/MIC ratio)₉₀ and the range of the MBC/MIC ratio were 4, 4 and 1–8, respectively. Among MRSA isolates, MBC₅₀, MBC₉₀ and the MBC range amounted to 0.5 g/L, 1.0 g/L and 0.06–1.0 g/L; (MBC/MIC ratio)₅₀, (MBC/MIC ratio)₉₀ and the range of the MBC/MIC ratio were 2, 4 and 1–8, respectively. Time-kill kinetics revealed a bactericidal effect after 30 min for sodium bituminosulfonate concentrations of 16× MIC and 256× MIC. The bactericidal activity against MSSA and MRSA was demonstrated for sodium bituminosulfonate. The killing was very rapid with the initial population reduced by 99.9% after only short incubation with concentrations of 16× MIC and higher.