Examining the safety of respiratory and intravenous inoculation of Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus in a mouse model

Abstract

Bdellovibrio spp. and Micavibrio spp. are Gram-negative predators that feed on other Gram-negative bacteria, making predatory bacteria potential alternatives to antibiotics for treating multi-drug resistant infections. While the ability of predatory bacteria to control bacterial infections in vitro is well documented, the in vivo effect of predators on a living host has yet to be extensively examined. In this study, respiratory and intravenous inoculations were used to determine the effects of predatory bacteria in mice. We found no reduction in mouse viability after intranasal or intravenous inoculation of B. bacteriovorus 109J, HD100 or M. aeruginosavorus. Introducing predators into the respiratory tract of mice provoked a modest inflammatory response at 1 hour post-exposure, but was not sustained at 24 hours, as measured by RT-qPCR and ELISA. Intravenous injection caused an increase of IL-6 in the kidney and spleen, TNF in the liver and CXCL-1/KC in the blood at 3 hours post-exposure, returning to baseline levels by 18 hours. Histological analysis of tissues showed no pathological changes due to predatory bacteria. Furthermore, qPCR detected predators were cleared from the host quickly and efficiently. This work addresses some of the safety concerns regarding the potential use of predatory bacteria as a live antibiotic.Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus are small, highly motile, uniflagellate Gram-negative bacteria that prey naturally on other Gram-negative bacteria 1,2 . Recently, predatory bacteria have been considered as potential alternatives to traditional antibiotics for treating multi-drug resistant (MDR) Gram-negative bacterial infections. B. bacteriovorus have a predatory lifestyle where they attach to and enter the prey periplasm, multiply by exhausting the nutrients, lyse the cell, and then continue to seek out more prey to invade 1,3,4 . Micavibrio spp., in contrast, attach to, grow and kill prey at the surface of the prey cell in a 'vampire'-like fashion 2,5,6 . Bdellovibrio-and-like organisms (BALOs) are a promising potential novel agent against bacterial pathogens and present several advantages when considering their use for controlling infection 7 . Previous studies have confirmed the ability of predatory bacteria to control a broad range of important human pathogens in vitro, including MDR bacteria 8 , grown both planktonically and in biofilms [9][10][11] . In addition,

Predatory Bacteria Attenuate Klebsiella pneumoniae Burden in Rat Lungs

“…The lack of toxicity due to inoculation with predatory bacteria is in agreement with previous studies demonstrating the safety of introducing predatory bacteria in a variety of animal models (16–19). In particular, we observed similar results in our previous study, in which C57BL/6 mice were intranasally inoculated with high concentrations of viable or heat-killed B. bacteriovorus or M. aeruginosavorus (19).…”

“…Our results seen with the rat model align with our previous study, where intranasal or intravenous inoculation of high doses of either B. bacteriovorus or M. aeruginosavorus in mice caused no tissue pathology and induced only a modest inflammatory response that returned to baseline levels within 24 h postinoculation (19). Furthermore, predatory bacteria were completely cleared from the animals by an innate immune response (possibly via neutrophils) within 48 h postinoculation (19).…”

“…In particular, we observed similar results in our previous study, in which C57BL/6 mice were intranasally inoculated with high concentrations of viable or heat-killed B. bacteriovorus or M. aeruginosavorus (19). In that study, no mouse exhibited either morbidity or any histological abnormalities at up to 50 days postinoculation, signaling that predatory bacteria are nontoxic when inhaled.…”

“…While the safety of administering predatory bacteria into the lungs of mice has already been demonstrated (19), we began by investigating if the predators are compatible with the animal model being used in this study, Sprague-Dawley (SD) rats. To examine the effect on host morbidity of introducing predatory bacteria into the respiratory tract of SD rats, we performed intranasal inoculations of 6.0 × 10 8  PFU/rat of B. bacteriovorus 109J, 1.1 × 10 9  PFU/rat of B. bacteriovorus HD100, or 5.0 × 10 7  PFU/rat of M. aeruginosavorus ARL-13 into rats in three groups containing six rats each.…”

“…Predatory bacteria are unable to invade and prey on mammalian cells (15), mitigating potentially harmful off-target effects. Additionally, predatory bacteria are nonpathogenic in a variety of animal models, including mice, rabbits, guinea pigs, and chicks (14, 16–19). Furthermore, development of genetically stable resistance to predation has yet to be confirmed (20).…”