Expanding the paradigm for the outer membrane: <i>Acinetobacter baumannii</i> in the absence of endotoxin

Powers, Matthew J.; Trent, M. Stephen

doi:10.1111/mmi.13872

Cited by 55 publications

(55 citation statements)

References 82 publications

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“…Similarly, in a hyperporinated, Δ9 strain of E. coli , where a recombinant pore was introduced in the OM and all nine known TolC-dependent transporters deleted 28 , CBG activity became evident with a MIC of 8 μg/mL. Finally, in an Acinetobacter baumannii deficient in lipooligosaccharide (LOS-), which effectively alters the permeability of the OM 29 , CBG activity was enhanced greater than 128- fold, resulting in a MIC value of 0.5 μg/mL. Overall, these results suggest that cannabinoids face a permeability barrier in Gram-negative bacteria and further imply that cannabinoids inhibit a bacterial process present in Gram-negative pathogens, and likely common to that in Gram-positive pathogens.…”

Section: Resultsmentioning

confidence: 99%

Uncovering the hidden antibiotic potential of Cannabis

Farha

El-Halfawy

Gale

et al. 2019

Preprint

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26The spread of antimicrobial resistance continues to be a priority health concern worldwide, 27 necessitating exploration of alternative therapies. Cannabis sativa has long been known to contain 28 antibacterial cannabinoids, but their potential to address antibiotic resistance has only been 29 superficially investigated. Here, we show that cannabinoids exhibit antibacterial activity against 30 MRSA, inhibit its ability to form biofilms and eradicate stationary phase cells persistent to antibiotics. 31 We show that the mechanism of action of cannabigerol is through targeting the cytoplasmic membrane 32 of Gram-positive bacteria and demonstrate in vivo efficacy of cannabigerol in a murine systemic 33 infection model caused by MRSA. We also show that cannabinoids are effective against Gram-negative 34 organisms whose outer membrane is permeabilized, where cannabigerol acts on the inner membrane. 35Finally, we demonstrate that cannabinoids work in combination with polymyxin B against multi-drug 36 resistant Gram-negative pathogens, revealing the broad-spectrum therapeutic potential for Public Health agencies around the globe have identified antimicrobial resistance as one of the 62 most critical challenges of our time. The rapid and global spread of antimicrobial-resistant organisms in 63 recent years has been unprecedented. So much so that the world health organization (WHO) published 64 its first ever list of antibiotic-resistant "priority pathogens", made up of 12 families of bacteria that pose 65 the greatest threat to human health 1 . Among them, Staphylococcus aureus is the leading cause of both 66 healthcare and community-associated infections worldwide and a major cause for morbidity and 67 mortality 2 , especially with the emergence and rapid spread of methicillin-resistant S. aureus (MRSA), 68 which is resistant to all known β-lactam antibiotics 3 . Worse yet, resistance to vancomycin, linezolid 69 and daptomycin has already been reported in MRSA clinical strains, compromising the therapeutic 70 alternatives for life-threatening MRSA infections 4 . Further, antibiotic-resistant Gram-negative 71 infections have increasingly become a pressing issue in the clinic. Indeed, of the bacteria highlighted 72 by the WHO, 75% are Gram-negative organisms. Among the currently approved antibiotics, the latest 73 discovery of a new drug class dates back to more than 30 years ago. The rapid loss of antibiotic 74 effectiveness and diminishing pipeline beg for the exploration of alternative therapies. 75 Cannabis plants are important herbaceous species that have been used in folk medicine since 76 the dawn of times. Increasing scientific evidence is accumulating for the efficacy of its metabolites in 77 the treatment, for example, of epilepsy, Parkinson disease, analgesia, multiple sclerosis, Tourette's 78 syndrome and other neurological diseases 5 . At a very nascent stage are investigations into the potential 79 of cannabis metabolites as antibacterial therapies. To date, assessments of their antibacterial activ...

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Section: Resultsmentioning

confidence: 99%

Uncovering the hidden antibiotic potential of Cannabis

Farha

El-Halfawy

Gale

et al. 2019

Preprint

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“…Gram-negative bacteria evolved multiple mechanisms of resistance to these peptides, the primary mechanism being the modification or removal of the phosphate groups on lipid A, thereby reducing the net negative charge of the bacterial surface (15). Curiously, Acinetobacter baumannii is one of three species of bacteria (along with Neisseria meningitidis and Moraxella catarrhalis) that can survive in the total absence of lipid A (16)(17)(18)(19). In A. baumannii, this phenotype is selected for in the presence of high concentrations of the CAMPs colistin or polymyxin B (17), both of which are currently used to treat multidrug-resistant Gram-negative pathogens (20).…”

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confidence: 99%

Phospholipid retention in the absence of asymmetry strengthens the outer membrane permeability barrier to last-resort antibiotics

Powers

Trent

2018

Proc. Natl. Acad. Sci. U.S.A.

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113

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The outer membrane of Gram-negative bacteria is a critical barrier that prevents entry of noxious compounds. Integral to this functionality is the presence of lipopolysaccharide (LPS) or lipooligosaccharide (LOS), a molecule that is located exclusively in the outer leaflet of the outer membrane. Its lipid anchor, lipid A, is a glycolipid whose hydrophobicity and net negative charge are primarily responsible for the robustness of the membrane. Because of this, lipid A is a hallmark of Gram-negative physiology and is generally essential for survival. Rare exceptions have been described, including , which can survive in the absence of lipid A, albeit with significant growth and membrane permeability defects. Here, we show by an evolution experiment that LOS-deficient can rapidly improve fitness over the course of only 120 generations. We identified two factors which negatively contribute to fitness in the absence of LOS, Mla and PldA. These proteins are involved in glycerophospholipid transport (Mla) and lipid degradation (PldA); both are active only on mislocalized, surface-exposed glycerophospholipids. Elimination of these two mechanisms was sufficient to cause a drastic fitness improvement in LOS-deficient The LOS-deficient double mutant grows as robustly as LOS-positive wild-type bacteria while remaining resistant to the last-resort polymyxin antibiotics. These data provide strong biological evidence for the directionality of Mla-mediated glycerophospholipid transport in Gram-negative bacteria and furthers our knowledge of asymmetry-maintenance mechanisms in the context of the outer membrane barrier.

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“…Rather than LPS, A . baumannii synthesizes LOS, an analogous version of LPS lacking the O‐antigen (Powers and Trent, ).…”

Section: Introductionmentioning

confidence: 99%

“…LPS plays a critical role in protecting the cells against the host immune defenses and noxious compounds such as cationic antimicrobial peptides and antibiotics (Raetz and Whitfield, 2002;Simpson and Trent, 2019). Rather than LPS, A. baumannii synthesizes LOS, an analogous version of LPS lacking the O-antigen (Powers and Trent, 2018).…”

Section: Introductionmentioning

confidence: 99%

The UDP‐GalNAcA biosynthesis genes gna‐gne2 are required to maintain cell envelope integrity and in vivo fitness in multi‐drug resistant Acinetobacter baumannii

Crépin

Ottosen

Chandler

et al. 2019

Molecular Microbiology

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Acinetobacter baumannii infects a wide range of anatomic sites including the respiratory tract and bloodstream. Despite its clinical importance, littleis known about the molecular basis of A. baumannii pathogenesis. We previously identified the UDP-N-acetyl-d-galactosaminuronic acid (UDP-GalNAcA) biosynthesis genes, gna-gne2, as being critical for survival in vivo. Herein, we demonstrate that Gna-Gne2 are part of a complex network connecting in vivo fitness, cell envelope homeostasis and resistance to antibiotics. The ∆gna-gne2 mutant exhibits a severe fitness defect during bloodstream infection. Capsule production is abolished in the mutant strain, which is concomitant with its inability to survive in human serum. In addition, the ∆gna-gne2 mutant was more susceptible to vancomycin and unable to grow on MacConkey plates, indicating an alteration in cell envelope integrity. Analysis of lipid A by mass spectrometry showed that the hexa-and hepta-acylated species were affected in the gna-gne2 mutant. Finally, the ∆gna-gne2 mutant was more susceptible to several classes of antibiotics. Together, this study demonstrates the importance of UDP-GalNAcA in the pathobiology of A. baumannii. By interrupting its biosynthesis, we showed that this molecule plays a critical role in capsule biosynthesis and maintaining the cell envelope homeostasis.

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Expanding the paradigm for the outer membrane: Acinetobacter baumannii in the absence of endotoxin

Cited by 55 publications

References 82 publications

Uncovering the hidden antibiotic potential of Cannabis

Uncovering the hidden antibiotic potential of Cannabis

Phospholipid retention in the absence of asymmetry strengthens the outer membrane permeability barrier to last-resort antibiotics

The UDP‐GalNAcA biosynthesis genes gna‐gne2 are required to maintain cell envelope integrity and in vivo fitness in multi‐drug resistant Acinetobacter baumannii

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