Bacteria can be resistant to multiple antibiotics and we are fast approaching a time when antibiotics will not work on some bacterial infections. New antimicrobial compounds are urgently necessary. Plants are considered the greatest source to obtain new antimicrobials. This study aimed to assess the antimicrobial activity of four phytochemicals—7-hydroxycoumarin (7-HC), indole-3-carbinol (I3C), salicylic acid (SA) and saponin (SP)—against Escherichia coli and Staphylococcus aureus, either as planktonic cells or as biofilms. These bacteria are commonly found in hospital-acquired infections. Some aspects on the phytochemicals mode of action, including surface charge, hydrophobicity, motility and quorum-sensing inhibition (QSI) were investigated. In addition, the phytochemicals were combined with three antibiotics in order to assess any synergistic effect. 7-HC and I3C were the most effective phytochemicals against E. coli and S. aureus. Both phytochemicals affected the motility and quorum-sensing (QS) activity, which means that they can play an important role in the interference of cell-cell interactions and in biofilm formation and control. However, total biofilm removal was not achieved with any of the selected phytochemicals. Dual combinations between tetracycline (TET), erythromycin (ERY) and ciprofloxacin (CIP) and I3C produced synergistic effects against S. aureus resistant strains. The overall results demonstrates the potential of phytochemicals to control the growth of E. coli and S. aureus in both planktonic and biofilm states. In addition, the phytochemicals demonstrated the potential to act synergistically with antibiotics, contributing to the recycling of old antibiotics that were once considered ineffective due to resistance problems.

Single-and multispecies biofilms formed by six drinking water-isolated bacterial species were used to assess their susceptibilities to sodium hypochlorite (SHC). In general, multispecies biofilms were more resistant to inactivation and removal than single biofilms. Total biofilm inactivation was achieved only for Acinetobacter calcoaceticus single-species biofilms and for those multispecies biofilms without A. calcoaceticus. Biofilms with all bacteria had the highest resistance to SHC, while those without A. calcoaceticus were the most susceptible. A. calcoaceticus formed single biofilms susceptible to SHC; however, its presence in multispecies biofilms increased their resistance to disinfection.The control of drinking water (DW) quality in distribution systems is a major technological challenge to the water industry. DW networks can be regarded as biological reactors which host a wide variety of microorganisms (bacteria, protozoa, and fungi), both in the bulk water and on the pipe surfaces. In DW distribution systems (DWDS), Acinetobacter, Aeromonas, Alcaligenes, Arthrobacter/Corynebacterium, Bacillus, Burkholderia, Citrobacter, Enterobacter, Flavobacterium, Klebsiella, Methylobacterium, Moraxella, Pseudomonas, Serratia, Staphylococcus, Mycobacterium, Sphingomonas, and Xanthomonas have been the predominant bacterial genera detected (2, 3). The Gramnegative bacteria are predominant over the Gram-positive bacteria, and Pseudomonas is the most abundant bacterial organism in supply systems, regardless of the water source. Most of the biomass present in these DWDS is located at the pipe walls. Flemming et al. (7) proposed that 95% of the bacteria were adhered to the surface of pipelines and only 5% were present in the bulk water. The presence and significance of biofilms in DWDS have been repeatedly reported (16,18). Biofilm growth and detachment contribute to the increase in the number of cells in bulk water (5). Some of those microorganisms can be pathogens. Commonly encountered waterborne pathogens are Burkholderia pseudomallei, Campylobacter spp., Escherichia coli, Helicobacter pylori, Legionella pneumophila, Mycobacterium avium, Pseudomonas aeruginosa, Salmonella spp., Shigella spp., Yersinia enterocolitica, and Vibrio cholerae (32). Therefore, biofilm control is important for technical, esthetic, regulatory, and public health reasons.Chlorine disinfection is a key step in the biofilm control process. Residual concentrations must be kept below guidelines to lower the potential to form harmful disinfection byproducts (20). Chlorine, a strong oxidizing agent, is the most commonly used disinfectant due to its effectiveness, stability, easy of use, and low cost. However, biofilm formation and resistance to disinfection have been recognized as important factors that contribute to the survival and persistence of microbial contamination in DW (2). Research into DW biofilm control will help to determine optimal disinfection parameters and lead to knowledgeable decisions regarding the management of DW distribution ne...

The purpose of the present study was to evaluate the in vitro antibacterial effects of different classes of important and common dietary phytochemicals (5 simple phenolics - tyrosol, gallic acid, caffeic acid, ferulic acid, and chlorogenic acid; chalcone - phloridzin; flavan-3-ol - (-) epicatechin; seco-iridoid - oleuropein glucoside; 3 glucosinolate hydrolysis products - allylisothiocyanate, benzylisothiocyanate and 2-phenylethylisothiocyanate) against Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes and Staphylococcus aureus. Another objective of this study was to evaluate the effects of dual combinations of streptomycin with the different phytochemicals on antibacterial activity. A disc diffusion assay was used to evaluate the antibacterial activity of the phytochemicals and 3 standard antibiotics (ciprofloxacin, gentamicin and streptomycin) against the four bacteria. The antimicrobial activity of single compounds and dual combinations (streptomycin-phytochemicals) were quantitatively assessed by measuring the inhibitory halos. The results showed that all of the isothiocyanates had significant antimicrobial activities, while the phenolics were much less efficient. No antimicrobial activity was observed with phloridzin. In general P. aeruginosa was the most sensitive microorganism and L. monocytogenes the most resistant. The application of dual combinations demonstrated synergy between streptomycin and gallic acid, ferulic acid, chlorogenic acid, allylisothiocyanate and 2-phenylethylisothiocyanate against the Gram-negative bacteria. In conclusion, phytochemical products and more specifically the isothiocyanates were effective inhibitors of the in vitro growth of the Gram-negative and Gram-positive pathogenic bacteria. Moreover, they can act synergistically with less efficient antibiotics to control bacterial growth.

Intergeneric coaggregation of drinking water bacteria was tested. Acinetobacter calcoaceticus was found not only to autoaggregate but also to coaggregate with four of the five other isolates (Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata, and Staphylococcus sp.). In its absence, no coaggregation was found. Interactions were lectin-saccharide mediated. The putative bridging function of A. calcoaceticus was evidenced by multispecies biofilm studies, through a strain exclusion process.The development of microbial biofilm communities results from a series of processes, including initial surface association and adherence, subsequent multiplication of the constituent organisms, the adherence of other species, and the production of extracellular polymeric substances (17). Many of these events are well described (14,17). The bacterial surface properties coaggregation and coadhesion, along with interspecies relationships, are believed to play a determinant role in the formation of multispecies biofilms in drinking water distribution systems (11,13). Nevertheless, the function of coaggregation in the initial development of biofilms still remains unclear. This adhesion mechanism is highly specific and conveys advantages to microorganisms, including the transfer of chemical signals, exchange of genetic information, protection from adverse environmental conditions, and metabolic cooperation between different species as well as cell differentiation in some populations (18). Coaggregation is mediated by protein-saccharide interactions and blocked by simple sugars (1, 2). Coaggregation interactions contribute to the development of biofilms via the specific recognition and adhesion of single suspended cells to genetically distinct bacteria in a developing biofilm and/or by the subsequent adhesion of previously coaggregated secondary colonizers to the developing biofilm. In both cases, bacterial cells in suspension specifically adhere to those within biofilms through a coadhesion process (12). This study describes the intergeneric coaggregation of six heterotrophic bacteria isolated from drinking water and investigates the roles of surface proteins and saccharides in the coaggregation process. Acinetobacter calcoaceticus was investigated as a bridging organism in drinking water biofilms.Coaggregation assays were performed with six representative drinking water bacteria, Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata, and Staphylococcus sp. The bacteria were isolated, identified by 16S rRNA gene sequencing, and cultivated according to the method of Simões et al. (13). The stationary phase of growth was selected for coaggregation studies (9), and cells from planktonic batch cultures were harvested by centrifugation (20 min at 13,000 ϫ g), washed three times, and resuspended in sterile tap water. A visual coaggregation assay, with some modifications from the method of Cisar et al. (2), was used. Briefly, bacte...