Abstract
Multi-drug resistant Acinetobacter baumannii is well-known for its rapid acclimatization in hospital environments. The ability of the bacterium to endure desiccation and starvation on dry surfaces for up to a month results in outbreaks of health care-associated infections. Previously, indole and its derivatives were shown to inhibit other persistent bacteria. We found that among 16 halogenated indoles, 5-iodoindole swiftly inhibited A. baumannii growth, constrained biofilm formation and motility, and killed the bacterium as effectively as commercial antibiotics such as ciprofloxacin, colistin, and gentamicin. 5-Iodoindole treatment was found to induce reactive oxygen species, resulting in loss of plasma membrane integrity and cell shrinkage. In addition, 5-iodoindole rapidly killed three Escherichia coli strains, Staphylococcus aureus, and the fungus Candida albicans, but did not inhibit the growth of Pseudomonas aeruginosa. This study indicates the mechanism responsible for the activities of 5-iodoindole warrants additional study to further characterize its bactericidal effects on antibiotic-resistant A. baumannii and other microbes.
Highlights
Acinetobacter baumannii is a notorious bacterium and is recognized as one of the top seven pathogens in terms of the challenge to our healthcare-delivery systems [1,2]
Of the two most effective indoles, 5-iodoindole inhibited cell growth more than 6-iodoindole, and it was the focus of subsequent studies conducted using the reference A. baumannii American Type Culture Collection (ATCC) 17978 strain
The minimum inhibitory concentrations (MICs) of the 16 halogenated indoles against ATCC 17978 fell in the range 50 to 250 μg/mL and the MICs of 5- and 6-iodoindole were lowest at 50 μg/mL
Summary
Acinetobacter baumannii is a notorious bacterium and is recognized as one of the top seven pathogens in terms of the challenge to our healthcare-delivery systems [1,2]. A. baumannii is a Gram-negative coccobacillus and a ubiquitous opportunistic pathogen that causes nosocomial infections, which include hospital-acquired pneumonia and bloodstream, urinary tract, skin, and soft tissue infections [3,4,5,6]. Due to its multidrug resistance (MDR), A. baumannii thrives in nosocomial environments and prevails in critically ill-patients hospitalized in intensive care units [7,8]. A. baumannii has developed a strategy to survive in dry conditions by forming biofilms, which makes the bacterium extremely difficult to eliminate [10]. Indole and its derivatives, such as 7-hydroxyindole [14], 3-indoleacetonitrile [15,16], 7-fluroindole [17], 2-aminobenzimidazoles [18], 7-benzyloxyindole [19,20] have been reported to attenuate the virulence of and biofilm formation by enterohemorrhagic E. coli O157:H7, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, Paenibacillus alvei, and Agrobacterium tumefaciens [21]
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