Violacein is an indole compound, produced by Chromobacterium violaceum, a bacteria present in tropical and subtropical areas. Among its numerous biological activities, its antimicrobial potential stands out. This study aims to determine the antimicrobial activity of VIO on S. aureus in planktonic culture and biofilms. VIO showed excellent antimicrobial activity in inhibiting and killing S. aureus in planktonic cultures and biofilm formation. The minimum bactericidal concentration (5 μg/mL) of VIO caused the death of S. aureus after 3–4 h of exposure and the minimum inhibitory concentration (1.25 μg/mL) of VIO inhibited bacterial growth within the first 8 h of contact. Biofilm formation was also strongly inhibited by VIO (1.25 μg/mL), in contrast to the higher resistance verified for S. aureus in mature biofilm (40 μg/mL). The high bacterial metabolic activity favored VIO activity; however, the good activity observed during phases of reduced metabolism indicates that VIO action involves more than one mechanism. Thus, VIO is a promising molecule for the development of an antimicrobial drug for the eradication of S. aureus infections.

Chitinases are hydrolases that catalyze the cleavage of the β-1,4-Oglycosidic linkages in chitin, a polysaccharide abundantly found in nature. Chitin is an important structural component of the cell wall of most fungi and the exoskeleton of arthropods, including insects and crustaceans. These enzymes are widespread in the living world, being found in organisms from all three domains of life. Due to their hydrolytic activity on chitin, chitinases have great biotechnological potential in different areas, such as human health, agriculture and food technology. The antifungal, insecticidal and nematicidal effects of many chitinases have been intensively investigated in the scientific literature, aiming to exploit these properties to protect crops against phytopathogenic fungi and insect pests and parasitic nematodes. On the other hand, the effects of chitinases on bacteria have been underexploited, possibly because chitin is not present in bacterial cell walls. The aim of this study was to search the scientific literature for works describing chitinases with antibacterial activity. Three bibliographic databases were searched using the keywords “chitinase” and “antibacterial” as descriptors and the chosen articles were selected according to specific inclusion and exclusion criteria. As a result, we identified only 5 reports wherein 6 purified chitinases have been shown experimentally to have antibacterial activity. Three out of these 6 antibacterial chitinases were shown to be bifunctional enzymes, which have chitinase and lysozyme activity. The possible mechanism of action of these antibacterial chitinases is discussed, highlighting their potential as antibacterial agents. Key-words: Antimicrobial, Chitin, Lysozyme, Peptidoglycan, Hydrolases.

Fungal diseases and the progressive development of resistance are a challenge. In this context, Lippia alba (lemon balm) is a species used in folk medicine, being described with antimicrobial potential. The aim of this study was to determine the antifungal activity and modulating effect of the essential oil of Lippia alba (Mill.) N.E. Brown leaves (LaEO). The antifungal activity of LaEO on eight Candida strains was determined by minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC), minimum biofilm inhibition concentration (MBIC), minimum biofilm eradication concentration (MBEC) and time-kill. The checkerboard technique was used to determine the modulating effect of LaEO on antifungal activity. The results indicate the presence of 11 constituents, with a predominance of carvone (58.15%) and limonene (25.37%). LaEO was able to inhibit the growth of all tested microorganisms, with MIC and MLC ranging from 0.078 to 1.25 mg/mL and MBIC and MBEC ranging from 0.156 to 5 mg/mL. The time-kill assay showed that LaEO was able to eliminate the strains after two hours of exposure and the best association was observed for the combination of LaEO and ketoconazole. The results of the study indicate that LaEO has excellent antifungal activity with potential biotechnological application.

The aim of this study was to evaluate the antimicrobial potential of violacein (VIO) on Staphylococcus epidermidis biofilm. The minimum biofilm inhibition concentration (MBIC) and minimum biofilm eradication concentration (MBEC) were determined, as well as the effect of VIO exposure time on microbial viability in mature biofilm. Violacein showed good antibiofilm action, inhibiting biofilm formation and eradicating mature biofilm of S. epidermidis at concentrations of 20 μg.mL⁻¹ and 160 μg.mL⁻¹, respectively. At concentrations equal to MBEC and 2x MBEC, the biofilm was eradicated in 3 h and 2h30min of incubation, respectively.When evaluating VIO modulating effect on the action of clinically-used drugs (vancomycin, cefepime, ciprofloxacin and meropenem), especial synergism was observed in the violacein-ciprofloxacin association, it can completely erradicated the mature biofilm at the concentration of 1/2xMBEC and 1/4xMBEC, respectively. VIO shows good antimicrobial action on S. epidermidis biofilm and has the potential to synergistically modulate the activity of clinically-used antimicrobials. Graphical Abstract