Abstract
Vibrio parahaemolyticus is a food-borne pathogen recognized as the prominent cause of seafood-borne gastroenteritis globally, necessitating novel therapeutic strategies. This study examined the antimicrobial and antivirulence properties of indole and 16 halogenated indoles on V. parahaemolyticus. Among them, 4-chloroindole, 7-chloroindole, 4-iodoindole, and 7-iodoindole effectively inhibited planktonic cell growth, biofilm formation, bacterial motility, fimbrial activity, hydrophobicity, protease activity, and indole production. Specifically, 4-chloroindole at 20 μg/mL inhibited more than 80% of biofilm formation with a minimum inhibitory concentration (MIC) of 50 μg/mL against V. parahaemolyticus and Vibrio harveyi. In contrast, 7-chloroindole inhibited biofilm formation without affecting planktonic cell growth with a MIC of 200 μg/mL. Both chlorinated indoles caused visible damage to the cell membrane, and 4-chloroindole at 100 μg/mL had a bactericidal effect on V. parahaemolyticus within 30 min treatment, which is superior to the effect of tetracycline at the same dose. The quantitative structure-activity relationship (QSAR) analyses revealed that chloro and bromo at positions 4 or 5 of the indole are essential for eradicating the growth of V. parahaemolyticus. These results suggest that halogenated indoles have potential use in antimicrobial and antivirulence strategies against Vibrio species.
Highlights
Vibrio parahaemolyticus is a Gram-negative, free-living halophilic bacterium mostly found in estuarine, marine, and coastal environments
In order to identify compounds with antimicrobial and antibiofilm properties, indole and 16 halogenated indoles at 20 and 50 μg/mL were initially assessed against V. parahaemolyticus for their ability to inhibit planktonic cell growth and biofilm formation
The halogenated indoles demonstrated a wide range of inhibitory activities on the biofilm formation of V. parahaemolyticus (Figure 1A)
Summary
Vibrio parahaemolyticus is a Gram-negative, free-living halophilic bacterium mostly found in estuarine, marine, and coastal environments. The adaptation of Vibrio species to different aquatic environments and diverse seafood hosts is essential to their survival and colonization (Nithya and Pandian, 2010). V. parahaemolyticus strains possess various virulence factors that include biofilm formation, thermostable hemolysin, adhesins, type III and VI secretion systems, extracellular proteases, motility, and fimbriae activity (Salomon et al, 2013; Letchumanan et al, 2014). Both clinical and environmental isolates of V. parahaemolyticus showed strong biofilm-forming ability, which increases their cell attachment capacity and resistance to disinfectants and antibiotics
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