Abstract
Violacein is a bisindole antibiotic that is effective against Gram-positive bacteria while the bacterial predator, Bdellovibrio bacteriovorus HD100, predates on Gram-negative strains. In this study, we evaluated the use of both together against multidrug resistant pathogens. The two antibacterial agents did not antagonize the activity of the other. For example, treatment of Staphylococcus aureus with violacein reduced its viability by more than 2,000-fold with or without B. bacteriovorus addition. Likewise, predation of Acinetobacter baumannii reduced the viability of this pathogen by more than 13,000-fold, regardless if violacein was present or not. When used individually against mixed bacterial cultures containing both Gram-positive and Gram-negative strains, violacein and B. bacteriovorus HD100 were effective against only their respective strains. The combined application of both violacein and B. bacteriovorus HD100, however, reduced the total pathogen numbers by as much as 84,500-fold. Their combined effectiveness was also demonstrated using a 4-species culture containing S. aureus, A. baumannii, Bacillus cereus and Klebsiella pneumoniae. When used alone, violacein and bacterial predation reduced the total population by only 19% and 68%, respectively. In conjunction with each other, the pathogen viability was reduced by 2,965-fold (99.98%), illustrating the prospective use of these two antimicrobials together against mixed species populations.
Highlights
A case in point is the bisindole antibiotic violacein, which is produced by a number of bacterial species[13], including strains of Chromobacterium[14,15], Janthinobacterium[16], Collimonas[17] and Duganella[18]
The best characterized BALO is probably Bdellovibrio bacteriovorus HD100, an obligate predator of bacteria that is known to attack more than 100 different human pathogens[27,28,29,30], including multidrug resistant strains of Acinetobacter baumannii and Klebsiella pneumoniae[28]
Violacein is quite active against S. aureus, killing more than 99% of the culture when added at a concentration of 20 mg/L or greater[18,21,23]
Summary
A case in point is the bisindole antibiotic violacein, which is produced by a number of bacterial species[13], including strains of Chromobacterium[14,15], Janthinobacterium[16], Collimonas[17] and Duganella[18]. The best characterized BALO is probably Bdellovibrio bacteriovorus HD100, an obligate predator of bacteria that is known to attack more than 100 different human pathogens[27,28,29,30], including multidrug resistant strains of Acinetobacter baumannii and Klebsiella pneumoniae[28]. When it attacks its prey, B. bacteriovorus enters the periplasmic space and consumes its prey from within, where this predator grows, septates and eventually lyses the outer membrane of the prey to facilitate its release. B. bacteriovorus and violacein were partnered together and their activities evaluated using individual bacterial and polymicrobial populations, with an emphasis on those that included both Gram-negative and Gram-positive pathogens
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