Evaluation of Combination Drug Therapy for Treatment of Antibiotic-Resistant Inhalation Anthrax in a Murine Model

Abstract

Bacillus anthracis is considered a likely agent to be used as a bioweapon, and the use of a strain resistant to the first-line antimicrobial treatments is a concern. We determined treatment efficacies against a ciprofloxacin-resistant strain of B. anthracis (Cip r Ames) in a murine inhalational anthrax model. Ten groups of 46 BALB/c mice were exposed by inhalation to 7 to 35 times the 50% lethal dose (LD 50 ) of B. anthracis Cip r Ames spores. Commencing at 36 h postexposure, groups were administered intraperitoneal doses of sterile water for injections (SWI) and ciprofloxacin alone (control groups), or ciprofloxacin combined with two antimicrobials, including meropenem-linezolid, meropenem-clindamycin, meropenem-rifampin, meropenemdoxycycline, penicillin-linezolid, penicillin-doxycycline, rifampin-linezolid, and rifampinclindamycin, at appropriate dosing intervals (6 or 12 h) for the respective antibiotics. Ten mice per group were treated for 14 days and observed until day 28. The remaining animals were euthanized every 6 to 12 h, and blood, lungs, and spleens were collected for lethal factor (LF) and/or bacterial load determinations. All combination groups showed significant survival over the SWI and ciprofloxacin controls: meropenem-linezolid (P ϭ 0.004), meropenem-clindamycin (P ϭ 0.005), meropenem-rifampin (P ϭ 0.012), meropenem-doxycycline (P ϭ 0.032), penicillindoxycycline (P ϭ 0.012), penicillin-linezolid (P ϭ 0.026), rifampin-linezolid (P ϭ 0.001), and rifampin-clindamycin (P ϭ 0.032). In controls, blood, lung, and spleen bacterial counts increased to terminal endpoints. In combination treatment groups, blood and spleen bacterial counts showed low/no colonies after 24-h treatments. The LF fell below the detection limits for all combination groups yet remained elevated in control groups. Combinations with linezolid had the greatest inhibitory effect on mean LF levels.

A Novel Toll-Like Receptor 2 Agonist Protects Mice in a Prophylactic Treatment Model Against Challenge With Bacillus anthracis

“…Due to the ease of generating antibiotic resistant strains of B. anthracis in the laboratory setting, the Secretary of the Department of Homeland Security issued a Material Threat Determination (MTD) specifically for multi-drug-resistant (MDR) anthrax ( Athamna et al, 2004 ; Heine et al, 2017 ). Public Health Emergency Medical Countermeasures Enterprise (PHEMCE) also recognized MDR B. anthracis as a high-priority threat ( Harris, 2013 ).…”

The roles of antimicrobial resistance, phage diversity, isolation source and selection in shaping the genomic architecture of Bacillus anthracis

“…Five of these genes are commonplace and can be found in the majority of isolates examined, whereas the other five are comparatively rare across the dataset. Given the application of commonly used antibiotic drugs, such as penicillin, doxycycline and ciprofloxacin, to treat B. anthracis infections, the regions where rare antibiotic-resistant gene isolates were sampled may benefit from monitoring, in order to document the persistence of these novel, resistant population clusters and modify antibiotic treatments for effectiveness [ 52, 53 ]. The resistance gene bcII for example, which was found in only six samples, is known to hydrolyse a large number of penicillins ( Table 1 ).…”

Validated Methods for Removing Select Agent Samples from Biosafety Level 3 Laboratories

“…We isolated B. anthracis spores according to Leighton and Doi ( 4 ) and maintained the spores in refrigerated sterile water at »1 × 10 10 CFU/mL. We verified this concentration by serial dilution in sterile water onto sheep blood agar plates as previously stated ( 5 ).…”