Biofilm-associated bacteria are less sensitive to antibiotics than freeliving (planktonic) cells. Furthermore, with variations in the concentration of antibiotics throughout a biofilm, microbial cells are often exposed to levels below inhibitory concentrations and may develop resistance. This, as well as the irresponsible use of antibiotics, leads to the selection of pathogens that are difficult to eradicate. The Centers for Disease Control and Prevention use the terms "antibiotic" and "antimicrobial agent" interchangeably. However, a clear distinction between these two terms is required for the purpose of this assessment. Therefore, we define "antibiotics" as pharmaceutically formulated and medically administered substances and "antimicrobials" as a broad category of substances which are not regulated as drugs. This comprehensive minireview evaluates the effect of natural antimicrobials on pathogens in biofilms when used instead of, or in combination with, commonly prescribed antibiotics.

Antibiotic resistance and recurrence of bacterial vaginosis (BV), a polymicrobial infection, justify the need for novel antimicrobials to counteract microbial resistance to conventional antibiotics. Previously, two series of cationic amphiphiles (CAms) which self-assemble into supramolecular nanostructures with membrane-lytic properties were designed with hydrophilic head groups and nonpolar domains. The combination of CAms and commonly prescribed antibiotics is suggested as a promising strategy for targeting microorganisms that are resistant to conventional antibiotics. Activities of the CAms against ATCC 14018, a representative BV pathogen, ranged from 1.1 to 24.4 μM. Interestingly, the tested healthy species, especially ATCC 39268, were significantly more tolerant of CAms than the selected pathogens. In addition, CAms prevented biofilm formation at concentrations which did not influence the normal growth ability of ATCC 14018. Furthermore, the biofilm minimum bactericidal concentration (MBC-Bs) of CAms against ATCC 14018 ranged from 58.8 to 425.6 μM, while much higher concentrations (≥850 μM) were required to produce ≥3-log reductions in the number of biofilm-associated lactobacilli. The conventional antibiotic metronidazole synergized strongly with all tested CAms against planktonic cells and biofilms of ATCC 14018. The synergism between CAms and the tested conventional antibiotic may be considered a new, effective, and beneficial method of controlling biofilm-associated bacterial vaginosis.

Curcumin, a hydrophobic phenolic compound isolated from tumeric (Curcuma longa), has gained a great attention due to its health benefits and antimicrobial effects. In this study, curcumin nanoparticles (CNPs) were formulated via acusto‐plastic deformation technique, with three differently surface‐charged surfactants‐sodium dodecylsulfate, Tween 20 and cetrimonium bromide (CTAB). The fabricated CNPs were evaluated for their antimicrobial activity against Listeria monocytogenes, one of the most severe foodborne pathogens. Our results demonstrated that the CNPs formulated with positively charged surfactant (CTAB) exhibited the highest antimicrobial activity against L. monocytogenes, indicating that there is a strong relationship between surface charge and antimicrobial activity of curcumin. The enhanced antimicrobial action of CNPs‐CTAB was concluded to be due to the increased cell‐antimicrobial interaction, which resulted from the opposing electrical charges between CNPs‐CTAB and L. monocytogenes cells, as well as increased antimicrobial penetration endowed by the small size. Practical applications In this study, we showed that surface charge as well as the small size of curcumin nanoparticles play a key role in enhancing cell‐antimicrobial interaction and antimicrobial efficacy. The fabricated CNP‐CTAB showed the best antimicrobial activity against Listeria monocytogenes. A size reduction to nano‐scale is a recently developed strategy used to improve drug/food delivery and matching the public demand for effective and safe antimicrobial formulations for control of foodborne pathogens.

Page 5, lines 2-4: "QS compounds include N-acyl-homoserine lactones (AHLs), produced by Gramnegative bacteria, and autoinducing peptides (autoinducer 2 [AI-2]) produced by Gram-positive bacteria" should read "QS compounds include N-acyl homoserine lactones (AHLs) (produced by Gram-negative bacteria), autoinducing peptides (produced by Gram-positive bacteria), and autoinducer 2 (AI-2) (produced by Gram-positive and Gram-negative bacteria)."