Stress Conditions Induced by Carvacrol and Cinnamaldehyde on Acinetobacter baumannii

Abstract

Acinetobacter baumannii has emerged as a major cause of nosocomial infections. The ability of A. baumannii to display various resistance mechanisms against antibiotics has transformed it into a successful nosocomial pathogen. The limited number of antibiotics in development and the disengagement of the pharmaceutical industry have prompted the development of innovative strategies. One of these strategies is the use of essential oils, especially aromatic compounds that are potent antibacterial molecules. Among them, the combination of carvacrol and cinnamaldehyde has already demonstrated antibacterial efficacy against A. baumannii. The aim of this study was to determine the biological effects of these two compounds in A. baumannii, describing their effect on the rRNA and gene regulation under environmental stress conditions. Results demonstrated rRNA degradation by the carvacrol/cinnamaldehyde mixture, and this effect was due to carvacrol. Degradation was conserved after encapsulation of the mixture in lipid nanocapsules. Results showed an upregulation of the genes coding for heat shock proteins, such as groES, groEL, dnaK, clpB, and the catalase katE, after exposure to carvacrol/cinnamaldehyde mixture. The catalase was upregulated after carvacrol exposure wich is related to an oxidative stress. The combination of thiourea (hydroxyl radical scavenger) and carvacrol demonstrated a potent bactericidal effect. These results underline the development of defense strategies of the bacteria by synthesis of reactive oxygen species in response to environmental stress conditions, such as carvacrol.

Investigating the synergistic antimicrobial effect of carvacrol and zinc oxide nanoparticles against Campylobacter jejuni

“…These general stress response genes were also induced in C. jejuni cells under starving conditions (Klančnik et al, 2006). A recent study of the synergistic antimicrobial effect of carvacrol and cinnamaldehyde against Acinetobacter baumannii observed similar up-regulation of dnaK and groEL in the cells treated with the combined treatment and carvacrol alone (Montagu et al, 2016). Similarly, Burt and colleagues (2007) Conversely, none of the oxidative stress response genes were significantly changed for C.…”

In vivo antibacterial activity of Zataria multiflora Boiss extract and its components, carvacrol, and thymol, against colistin‐resistant Acinetobacter baumannii in a pneumonic BALB/c mouse model

“…Similar results showed that the alcoholic extract of ZMB at low concentrations could inhibit the growth of gram-positive bacteria. 19,20 In kinetic assays, Montagu et al 21 showed that carvacrol had a bacteriostatic effect at 3 hours and a bactericidal effect from 6 to 24 hours. Furthermore, Eftekhar et al 22 reported that ZMB essential oil had considerable in vitro activity against the standard ATCC cultures, as well as the clinical isolates of K. pneumonia.…”

“…28,29 Combination of carvacrol and cinnamaldehyde in vitro against A. baumannii for 0.5, 1, and 2 hours revealed that antibacterial efficacy was related to the rRNA degradation that specifically was due to the carvacrol. 21 It is also possible that the bacterial clearance of the lung tissue culture treated with ZMB may be related to the combination effects of carvacrol and some other components. These factors may cause the bacterial membrane to become less rigid and more permeable to the porins that clear the bacteria (Figures 1 and 2).…”

“…Carvacrol and thymol have been shown to have antimicrobial activity against Escherichia coli , Salmonella spp ., Shigella spp ., Staphylococcus aurous , K. pneumonia, P. aeruginosa and Listeria monocytogenes . According to Montagu et al, carvacrol in combination with thiourea, induces a potent bactericidal effect.…”

Evaluation of Antimicrobial Activity of Cinnamaldehyde against Carbapenem-Resistant Acinetobacter baumannii Nosocomial Isolates

“…Furthermore, A. baumannii is prone to develop biofilms on solid surfaces, including medical devices (Gayoso et al, 2014). Thus, the combination of the vast resistance mechanisms of A. baumannii species and their survival capacity in the hospital environment make them potential nosocomial pathogens (Montagu et al, 2016).…”