Escherichia coli and Salmonella Enteritidis dual-species biofilms: interspecies interactions and antibiofilm efficacy of phages

A metagenomic study of antibiotic resistance genes in a hypereutrophic subtropical lake contaminated by anthropogenic sources

Antibiotic resistance genes (ARGs) are a major threat to human and environmental health. This study investigated the occurrence and distribution of ARGs in Lake Cajititlán, a hypereutrophic subtropical lake in Mexico contaminated by anthropogenic sources (urban wastewater and runoff from crop and livestock production). ARGs (a total of 475 genes) were detected in 22 bacterial genera, with Pseudomonas (144 genes), Stenotrophomonas (88 genes), Mycobacterium (54 genes), and Rhodococcus (27 genes) displaying the highest frequencies of ARGs. Among these, Pseudomonas aeruginosa and Stenotrophomonas maltophilia showed the highest number of ARGs. The results revealed a diverse array of ARGs, including resistance to macrolides (11.55 %), aminoglycosides (8.22 %), glycopeptides (6.22 %), tetracyclines (4 %), sulfonamides (4 %), carbapenems (1.11 %), phenicols (0.88 %), fluoroquinolones (0.44 %), and lincosamides (0.22 %). The most frequently observed ARGs were associated with multidrug resistance (63.33 %), with MexF (42 genes), MexW (36 genes), smeD (31 genes), mtrA (25 genes), and KHM-1 (22 genes) being the most common. Lake Cajititlán is a recreational area for swimming, fishing, and boating, while also supporting irrigation for agriculture and potentially acting as a drinking water source for some communities. This raises concerns about the potential for exposure to antibiotic-resistant bacteria through these activities. The presence of ARGs in Lake Cajititlán poses a significant threat to both human and environmental health. Developing strategies to mitigate the risks of antibiotic resistance, including improving wastewater treatment, and promoting strategic antibiotic use and disposal, is crucial. This study represents a significant advancement in the understanding of antibiotic resistance dynamics in a hypereutrophic subtropical lake in a developing country, providing valuable insights for the scientific community and policymakers.

Mutualistic interactions of lactate-producing lactobacilli and lactate-utilizing Veillonella dispar: Lactate and glutamate cross-feeding for the enhanced growth and short-chain fatty acid production

The human gut hosts numerous ecological niches for microbe-microbe and host-microbe interactions. Gut lactate homeostasis in humans is crucial and relies on various bacteria. Veillonella spp., gut lactate-utilizing bacteria, and lactate-producing bacteria were frequently co-isolated. A recent clinical trial has revealed that lactate-producing bacteria in humans cross-feed lactate to Veillonella spp.; however, their interspecies interaction mechanisms remain unclear. Veillonella dispar, an obligate anaerobe commonly found in the human gut and oral cavity, ferments lactate into acetate and propionate. In our study, we investigated the interaction between V. dispar ATCC 17748T and three representative phylogenetically distant strains of lactic acid bacteria, Lactobacillus acidophilus ATCC 4356T, Lacticaseibacillus paracasei subsp. paracasei ATCC 27216T, and Lactiplantibacillus plantarum ATCC 10241. Bacterial growth, viability, metabolism and gene level adaptations during bacterial interaction were examined. V. dispar exhibited the highest degree of mutualism with L. acidophilus. During co-culture of V. dispar with L. acidophilus, both bacteria exhibited enhanced growth and increased viability. V. dispar demonstrated an upregulation of amino acid biosynthesis pathways and the aspartate catabolic pathway. L. acidophilus also showed a considerable number of upregulated genes related to growth and lactate fermentation. Our results support that V. dispar is able to enhance the fermentative capability of L. acidophilus by presumably consuming the produced lactate, and that L. acidophilus cross-feed not only lactate, but also glutamate, to V. dispar during co-culture. The cross-fed glutamate enters the central carbon metabolism in V. dispar. These findings highlight an intricate metabolic relationship characterized by cross-feeding of lactate and glutamate in parallel with considerable gene regulation within both L. acidophilus (lactate-producing) and V. dispar (lactate-utilizing). The mechanisms of mutualistic interactions between a traditional probiotic bacterium and a potential next-generation probiotic bacterium were elucidated in the production of short-chain fatty acids.

Advances in bacteriophage-mediated strategies for combating polymicrobial biofilms

Bacteria and fungi tend to coexist within biofilms instead of in planktonic states. Usually, such communities include cross-kingdom microorganisms, which make them harder to remove from abiotic surfaces or infection sites. Additionally, the produced biofilm matrix protects embedded microorganisms from antibiotics, disinfectants, or the host immune system. Therefore, classic therapies based on antibiotics might be ineffective, especially when multidrug-resistant bacteria are causative factors. The complexities surrounding the eradication of biofilms from diverse surfaces and the human body have spurred the exploration of alternative therapeutic modalities. Among these options, bacteriophages and their enzymatic counterparts have emerged as promising candidates, either employed independently or in synergy with antibiotics and other agents. Phages are natural bacteria killers because of mechanisms of action that differ from antibiotics, phages might answer worldwide problems with bacterial infections. In this review, we report the attempts to use bacteriophages in combating polymicrobial biofilms in in vitro studies, using different models, including the therapeutical use of phages. In addition, we sum up the advantages, disadvantages, and perspectives of phage therapy.

A review of mechanism analysis methods in multi-species biofilm of foodborne pathogens

Biofilms are an aggregation of microorganisms that have high resistance to antimicrobial agents. In the food industry, it has been widely studied that foodborne pathogens on both food surfaces and food-contact surfaces can form biofilms thereby threatening the safety of the food. In the natural environment, multi-species biofilms formed by more than two different microorganisms are abundant. In addition, the resistance of multi-species biofilms to antimicrobial agents is higher than that of mono-species biofilms. Therefore, studies to elucidate the mechanisms of multi-species biofilms formed by foodborne pathogens are still required in the food industry. In this review paper, we summarized the novel analytical methods studied to evaluate the mechanisms of multi-species biofilms formed by foodborne pathogens by dividing them into four categories: spatial distribution, bacterial interaction, extracellular polymeric substance production and quorum sensing analytical methods.

Laser-Induced Transferred Antibacterial Nanoparticles for Mixed-Species Bacteria Biofilm Inactivation

In the present study, copper and silver nanoparticles with a concentration of 20 µg/cm² were synthesized using the method of laser-induced forward transfer (LIFT). The antibacterial activity of the nanoparticles was tested against bacterial biofilms that are common in nature, formed by several types of microorganisms (mixed-species bacteria biofilms): Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The Cu nanoparticles showed complete inhibition of the bacteria biofilms used. In the course of the work, a high level of antibacterial activity was demonstrated by nanoparticles. This activity manifested in the complete suppression of the daily biofilm, with the number of bacteria decreasing by 5-8 orders of magnitude from the initial concentration. To confirm antibacterial activity, and determine reductions in cell viability, the Live/Dead Bacterial Viability Kit was used. FTIR spectroscopy revealed that after Cu NP treatment, there was in a slight shift in the region, which corresponded to fatty acids, indicating a decrease in the relative motional freedom of molecules.

Host receptor identification of a polyvalent lytic phage GSP044, and preliminary assessment of its efficacy in the clearance of Salmonella

Salmonella and pathogenic Escherichia coli are important foodborne pathogens. Phages are being recognized as potential antibacterial agents to control foodborne pathogens. In the current study, a polyvalent broad-spectrum phage, GSP044, was isolated from pig farm sewage. It can simultaneously lyse many different serotypes of Salmonella and E. coli, exhibiting a broad host range. Using S. Enteritidis SE006 as the host bacterium, phage GSP044 was further characterized. GSP044 has a short latent period (10 min), high stability at different temperatures and pH, and good tolerance to chloroform. Genome sequencing analysis revealed that GSP044 has a double-stranded DNA (dsDNA) genome consisting of 110,563 bp with G + C content of 39%, and phylogenetic analysis of the terminase large subunit confirmed that GSP044 belonged to the Demerecviridae family, Epseptimavirus genus. In addition, the genomic sequence did not contain any lysogenicity-related, virulence-related, or antibiotic resistance-related genes. Analysis of phage-targeted host receptors revealed that the outer membrane protein (OMP) BtuB was identified as a required receptor for phage infection of host bacteria. The initial application capability of phage GSP044 was assessed using S. Enteritidis SE006. Phage GSP044 could effectively reduce biofilm formation and degrade the mature biofilm in vitro. Moreover, GSP044 significantly decreased the viable counts of artificially contaminated S. Enteritidis in chicken feed and drinking water. In vivo tests, a mouse model of intestinal infection demonstrated that phage GSP044 was able to reduce the number of colonized S. Enteritidis in the intestine. These results suggest that phage GSP044 may be a promising candidate biologic agent for controlling Salmonella infections.

Characterization of a novel Jerseyvirus phage T102 and its inhibition effect on biofilms of multidrug-resistant Salmonella

Biofilm, as a complex microbial community, is a serious and major safety concern in the food industry. Interestingly, some phages could effectively disrupt biofilms. This study characterized a novel isolated Salmonella bacteriophage T102, and its ability to control and remove biofilm produced by multidrug-resistant Salmonella. Phage T102 exhibited a broad host range within the Salmonella genus, especially drug-resistant Salmonella. The genome of phage T102 was comprised of 41,941 bp with 49.7% G + C composition, and with no genes associated with antibiotic resistance or virulence factors. The structural protein profile of phage T102 was subjected to SDS-PAGE and UPLC-MS/MS analysis, among them, 34 peptides were consistent with the hypothetical protein sequences annotated in the genome of T102. The biofilm inhibition assay revealed that phage T102 inhibited the formation of 6 h biofilms by two multidrug-resistant S. Typhimurium strains by 43.17 and 32.42%, respectively. 24 h biofilms formed by S. Typhimurium decreased by 54.94 and 53.67%, respectively, after 2 h of exposure to phage T102. Microscopic observation confirmed the inhibition effect of phage T102 on biofilm formation on spiked lettuce. Overall, our results support new research into the application of bacteriophage for biofilm reduction.

Accessing the In Vivo Efficiency of Clinically Isolated Phages against Uropathogenic and Invasive Biofilm-Forming Escherichia coli Strains for Phage Therapy

Escherichia coli is one of the most common members of the intestinal microbiota. Many of its strains are associated with various inflammatory infections, including urinary or gut infections, especially when displaying antibiotic resistance or in patients with suppressed immune systems. According to recent reports, the biofilm-forming potential of E. coli is a crucial factor for its increased resistance against antibiotics. To overcome the limitations of using antibiotics against resistant E. coli strains, the world is turning once more towards bacteriophage therapy, which is becoming a promising candidate amongst the current personalized approaches to target different bacterial infections. Although matured and persistent biofilms pose a serious challenge to phage therapy, they can still become an effective alternative to antibiotic treatment. Here, we assess the efficiency of clinically isolated phages in phage therapy against representative clinical uropathogenic and invasive biofilm-forming E. coli strains. Our results demonstrate that irrespective of host specificity, bacteriophages producing clear plaques with a high burst size, and exhibiting depolymerizing activity, are good candidates against biofilm-producing E. coli pathogens as verified from our in vitro and in vivo experiments using Galleria mellonella where survival was significantly increased for phage-therapy-treated larvae.

A New Kayfunavirus-like Escherichia Phage vB_EcoP-Ro45lw with Antimicrobial Potential of Shiga Toxin-Producing Escherichia coli O45 Strain

Lytic bacteriophages are re-considered as a solution to resolve antibiotic-resistant rampage. Despite frequent foodborne outbreaks caused by the top six non-O157 Shiga-toxin-producing Escherichia coli (STEC), the current interventions are not sufficiently effective against each serogroup, particularly O45. Therefore, this study aimed to characterize a new short-tailed phage, vB_EcoP-Ro45lw (or Ro45lw), as an alternative antimicrobial agent for STEC O45 strains. Phage Ro45lw belongs to the Kayfunavirus genus within the Autographiviridae family and shares no close evolutionary relationship with any reference phages. Ro45lw contains a tail structure composed of a unique tail fiber and tail tubular proteins A and B, likely to produce enzymatic activity against the target bacterial cells besides structural function. Additionally, the phage genome does not contain virulent, antibiotic-resistant, or lysogenic genes. The phage has a latent period of 15 min with an estimated burst size of 55 PFU/CFU and is stable at a wide range of pH (pH4 to pH11) and temperatures (30 °C to 60 °C). Regardless of the MOIs (MOI = 0.1, 1, and 10) used, Ro45lw has a strong antimicrobial activity against both environmental (E. coli O45:H-) and clinical (E. coli O45:H2) strains at 25 °C. These findings indicate that phage Ro45lw has antimicrobial potential in mitigating pathogenic STEC O45 strains.

Antimicrobial Resistant E. coli in Pork and Wild Boar Meat: A Risk to Consumers

Antimicrobial-resistant foodborne microorganisms may be transmitted from food producing animals to humans through the consumption of meat products. In this study, meat that was derived from farmed pigs and wild boars was analyzed and compared. Escherichia coli (E. coli) were isolated and tested phenotypically and genotypically for their resistance to quinolones, aminoglycosides and carbapenems. The co-presence of AMR-associated plasmid genes was also evaluated. A quinolone AMR phenotypic analysis showed 41.9% and 36.1% of resistant E. coli derived from pork and wild boars meat, respectively. A resistance to aminoglycosides was detected in the 6.6% of E. coli that was isolated from pork and in 1.8% of the wild boar meat isolates. No resistant profiles were detected for the carbapenems. The quinolone resistance genes were found in 58.3% of the phenotypically resistant pork E. coli and in 17.5% of the wild boar, thus showing low genotypic confirmation rates. The co-presence of the plasmid-related genes was observed only for the quinolones and aminoglycosides, but not for the carbapenems. Wild boar E. coli were the most capable to perform biofilm production when they were compared to pork E. coli. In conclusion, the contamination of pork and wild boar meat by AMR microorganisms could be a threat for consumers, especially if biofilm-producing strains colonize the surfaces and equipment that are used in the food industry.

Characterization of polyvalent Escherichia phage Sa157lw for the biocontrol potential of Salmonella Typhimurium and Escherichia coli O157:H7 on contaminated mung bean seeds

Seeds are one of the primary sources of contamination with foodborne pathogens, such as pathogenic Escherichia coli, and various Salmonella serovars, for produce, particularly sprouts. Due to the susceptibility of sprout growth to chemical-based antimicrobials and the rising issue of antimicrobial resistance, developing innovative antimicrobial interventions is an urgent need. Therefore, the objective of this study was to characterize Escherichia phage Sa157lw (or Sa157lw) for the biocontrol potential of Salmonella Typhimurium and E. coli O157:H7 on contaminated mung bean seeds. Phage Sa157lw was subjected to whole-genome sequencing and biological characterization, including morphology, one-step growth curve, and stress stability tests. Later, antimicrobial activity was determined in vitro and upon application on the mung bean seeds artificially contaminated with E. coli O157:H7 or Salmonella Typhimurium. Sa157lw possessed a contractile tail and belonged to the Kuttervirus genus under the Ackermannviridae family, sharing a close evolutionary relationship with E. coli phage ECML-4 and Kuttervirus ViI; however, tail spike genes (ORF_102 and ORF_104) were the primary region of difference. Comparative genomics showed that Sa157lw encoded a cluster of tail spike genes—including ORF_101, ORF_102, and ORF_104—sharing high amino acid similarity with the counterfeits of various Salmonella phages. Additionally, Sa157lw harbored a unique tail fiber (ORF_103), possibly related to the receptors binding of O157 strains. The genomic evidence accounted for the polyvalent effects of Sa157lw against E. coli O157:H7 and various Salmonella serovars (Typhimurium, Enteritidis, Agona, Saintpaul, and Heidelberg). Furthermore, the phage did not contain any virulence, antibiotic-resistant, or lysogenic genes. Sa157lw had a 30-min latent period on both E. coli O157:H7 and Salmonella Typhimurium, with an estimated burst size of 130 and 220 PFU/CFU, respectively, and was stable at a wide range of temperatures (4–60°C) and pH (pH4 to pH10). The phage application demonstrated a strong anti-E. coli O157:H7 and anti-Salmonella Typhimurium effects in 1.1 and 1.8 log reduction on the contaminated mung bean seeds after overnight storage at 22°C. These findings provide valuable insights into the polyvalent Sa157lw as a potential biocontrol agent of Salmonella Typhimurium and E. coli O157:H7 on sprout seeds.

Dual-Species Biofilms Formed by Escherichia coli and Salmonella Enhance Chlorine Tolerance

Outbreaks of Escherichia coli and Salmonella in food might be associated with the cross-contamination of biofilms on food-contact surfaces. The knowledge of the sanitization of mono-species biofilm on the food-contact surface is well established, while mixed-species biofilm occurs more naturally, which could profoundly affect the efficacy of sanitizer.

Genomic characterization of a novel bacteriophage STP55 revealed its prominent capacity in disrupting the dual-species biofilm formed by Salmonella Typhimurium and Escherichia coli O157: H7 strains

Salmonella and Escherichia coli are important foodborne pathogens, forming bacterial biofilms that contribute to their virulence, antimicrobial resistance, and survival on surfaces. Broad lytic phages are promising alternatives to conventional technologies for pathogen biocontrol and reducing biofilms. Herein, we isolated and characterized a novel polyvalent phage STP55 that not only lyse some serotypes of Salmonella, but also some E. coli strains. It had a wide range of pH (4-12) and thermal (30-60 °C) tolerances. The latent time was determined to be 10 min in the one-step growth experiment. Morphological observations by transmission electron microscopy and phylogenetic analysis using terminase gene classified STP55 to family Ackermannviridae in the order Caudovirales, with a complex tail structure. The genome was found to comprise 157,708 bp double-stranded DNA, with 44.57% GC content, 207 predicted ORFs and with no genes associated with antibiotic resistance, toxins, lysogeny, and virulence factors. Particularly, phage STP55 was able to inhibit single- and dual-species biofilms formation by S. Typhimurium ATCC 14028 and E. coli O157: H7, with a reduction percentage of 51.0%, 47.8% and 52.8%, respectively. Moreover, more than 65.0%, 72.9% and 46.2% of an established, single- and dual-species biofilms by S. Typhimurium ATCC 14028 and E. coli O157: H7 were removed after 8 h exposure to the phage STP55, respectively. The elimination effect of STP55 on dual-species biofilm formed on lettuce was further observed by SEM. Overall, our results demonstrated that STP55 is a promising antimicrobial against Salmonella and E. coli.

Tetracycline-loaded magnesium oxide nanoparticles with a potential bactericidal action against multidrug-resistant bacteria: In vitro and in vivo evidence

Worldwide, the emergence of diarrhoea-causing multi-drug resistant (MDR) bacteria has become a crucial problem in everyday life. Tetracycline (TC) is a bacteriostatic agent that has a wide spectrum of antibacterial activity. One potential strategy to enhance the penetration and antibacterial activity of antibiotics is the use of nanotechnology. In this context, this study dealt with the synthesis of TC loading in biocompatible magnesium oxide nanoparticles (MgONPs), its characterization, and the potency of killing against diarrhoea-causing MDR bacteria E. coli and S. flexneri. TC loaded- MgONPs (MgONPs-TC) were characterized by DLS, SEM-EDS, UV-vis spectroscopy, and FTIR techniques with adequate physical properties. Antibacterial and antibiofilm studies indicate that this nanoparticle successfully eradicated both planktonic and sessile forms of those bacteria. It also significantly reduced the production of bacterial EPS, different levels of antioxidant enzymes, and induced reactive oxygen species (ROS) in the bacterial cell as a mode of antibacterial action. In particular, MgONPs-TC were efficient in reducing the colonization of MDR E. coli and S. flexneri in the C. elegans model. Therefore, all these data suggest that MgONPs-TC are a highly promising approach to combating diseases associated with diarrhoea-causing MDR bacteria in the medical field with limited health care budgets.

Characterization of a T4-like Bacteriophage vB_EcoM-Sa45lw as a Potential Biocontrol Agent for Shiga Toxin-Producing Escherichia coli O45 Contaminated on Mung Bean Seeds

Application of lytic bacteriophages is a promising and alternative intervention technology to relieve antibiotic resistance pressure and control bacterial pathogens in the food industry. Despite the increase of produce-associated outbreaks caused by non-O157 Shiga toxin-producing E. coli (STEC) serogroups, the information of phage application on sprouts to mitigate these pathogens is lacking. Therefore, the objective of this study was to characterize a T4-like Escherichia phage vB_EcoM-Sa45lw (or Sa45lw) for the biocontrol potential of STEC O45 on mung bean seeds. Phage Sa45lw belongs to the Tequatrovirus genus under the Myoviridae family and displays a close evolutionary relationship with a STEC O157-infecting phage AR1. Sa45lw contains a long-tail fiber gene (gp37), sharing high genetic similarity with the counterpart of Escherichia phage KIT03, and a unique tail lysozyme (gp5) to distinguish its host range (STEC O157, O45, ATCC 13706, and Salmonella Montevideo and Thompson) from phage KIT03 (O157 and Salmonella enterica). No stx, antibiotic resistance, and lysogenic genes were found in the Sa45lw genome. The phage has a latent period of 27 min with an estimated burst size of 80 PFU/CFU and is stable at a wide range of pH (pH 3 to pH 10.5) and temperatures (-80°C to 50°C). Phage Sa45lw is particularly effective in reducing E. coli O45:H16 both in vitro (MOI = 10) by 5 log and upon application (MOI = 1,000) on the contaminated mung bean seeds for 15 min by 2 log at 25°C. These findings highlight the potential of phage application against non-O157 STEC on sprout seeds. IMPORTANCE Seeds contaminated with foodborne pathogens, such as Shiga toxin-producing E. coli, are the primary sources of contamination in produce and have contributed to numerous foodborne outbreaks. Antibiotic resistance has been a long-lasting issue that poses a threat to human health and the food industry. Therefore, developing novel antimicrobial interventions, such as bacteriophage application, is pivotal to combat these pathogens. This study characterized a lytic bacteriophage Sa45lw as an alternative antimicrobial agent to control pathogenic E. coli on the contaminated mung bean seeds. The phage exhibited antimicrobial effects against both pathogenic E. coli and Salmonella without containing virulent or lysogenic genes that could compromise the safety of phage application. In addition, after 15 min of phage treatment, Sa45lw mitigated E. coli O45:H16 on the contaminated mung bean seeds by a 2-log reduction at room temperature, demonstrating the biocontrol potential of non-O157 Shiga toxin-producing E. coli on sprout seeds.

Thermoresistance in Black Yeasts Is Associated with Halosensitivity and High Pressure Processing Tolerance but Not with UV Tolerance or Sanitizer Tolerance

ABSTRACT

Black yeasts can survive extreme conditions in food production because of their polyextremotolerant character. However, significant strain-to-strain variation in black yeast thermoresistance has been observed. In this study, we assessed the variability in tolerance to nonthermal interventions among a collection of food-related black yeast strains. Variation in tolerance to UV light treatment, high pressure processing (HPP), sanitizers, and osmotic pressure was observed within each species. The two strains previously shown to possess high thermotolerance, Exophiala phaeomuriformis FSL-E2-0572 and Exophiala dermatitidis YB-734, were also the most HPP tolerant but were the least halotolerant. Meanwhile, Aureobasidium pullulans FSL-E2-0290 was the most UV and sanitizer tolerant but had been shown to have relatively low thermoresistance. Fisher's exact tests showed that thermoresistance in black yeasts was associated with HPP tolerance and inversely with halotolerance, but no association was found with UV tolerance or sanitizer tolerance. Collectively, the relative stress tolerance among strains varied across interventions. Given this variation, different food products are susceptible to black yeast spoilage. In addition, different strains should be selected in challenge studies specific to the intervention.

HIGHLIGHTS

Phage JS02, a putative temperate phage, a novel biofilm-degrading agent for Staphylococcus aureus

Staphylococcus aureus is a biofilm-producing organism that is frequently isolated from various environments worldwide. Because of the natural resistance of S. aureus biofilm to antibiotics, bacteriophages are considered as a promising alternative for its removal. The bacteriophage vB_SauS_JS02 was isolated from livestock wastewater and showed activity against multidrug-resistant (MDR) S. aureus. The phage vB_SauS_JS02 exhibited broad host range and possessed a large burst size (52 PFU/CFU) as well as moderate pH stability (4-11) and appropriate thermal tolerance (40-50 ºC). Electron microscopy and genome sequence revealed that vB_SauS_JS02 belonged to Triavirus genus in Siphoviridae family. Genetic analysis of the 46 kb sequence of vB_SauS_JS02 revealed 66 ORFs. The predicted protein products of the ORFs were clustered functionally into five groups as follows: replication/regulation, DNA packaging, structure/morphogenesis, lysis, and lysogeny. Although the phage vB_SauS_JS02 was a temperate phage, it exhibited a higher inhibiting and degrading activity against planktonic cells (80~90% reduction), even to S. aureus biofilm (∼68% reduction in biofilm formation). Moreover, the removal activity of the phage vB_SauS_JS02 against both planktonic cells and S. aureus biofilms was even better than that of the antibiotic (ceftazidime). In summary, the present study introduced the phage vB_SauS_JS02 as a potential biocontrol agent against biofilm-producing S. aureus after making it virulent. It may be applicable for phage therapy.

Bacteriophages: A weapon against mixed-species biofilms in the food processing environment

Mixed-species biofilms represent the most frequent actual lifestyles of microorganisms in food processing environments, and they are usually more resistant to control methods than single-species biofilms. The persistence of biofilms formed by foodborne pathogens is believed to cause serious human diseases. These challenges have encouraged researchers to search for novel, natural methods that are more effective towards mixed-species biofilms. Recently, the use of bacteriophages to control mixed-species biofilms have grown significantly in the food industry as an alternative to conventional methods. This review highlights a comprehensive introduction of mixed-species biofilms formed by foodborne pathogens and their enhanced resistance to anti-biofilm removal strategies. Additionally, several methods for controlling mixed-species biofilms briefly focused on applying bacteriophages in the food industry have also been discussed. This article concludes by suggesting that using bacteriophage, combined with other 'green' methods, could effectively control mixed-species biofilms in the food industry.

Synergy between "Probiotic" Carbon Quantum Dots and Ciprofloxacin in Eradicating Infectious Biofilms and Their Biosafety in Mice

Orally administrated probiotic bacteria can aid antibiotic treatment of intestinal infections, but their arrival at their intestinal target site is hampered by killing in the gastrointestinal tract and by antibiotics solely intended for pathogen killing. Carbon-quantum-dots are extremely small nanoparticles and can be derived from different sources, including bacteria. Here, we hypothesize that carbon-quantum-dots inherit antibacterial activity from probiotic source bacteria to fulfill a similar role as live probiotics in intestinal infection therapy. Physico-chemical analyses indicated that carbon-quantum-dots, hydrothermally derived from Bifidobacterium breve (B-C-dots), inherited proteins and polysaccharides from their source-bacteria. B-C-dots disrupted biofilm matrices of Escherichia coli and Salmonella typhimurium biofilms through extensive reactive-oxygen-species (ROS)-generation, causing a decrease in volumetric bacterial-density in biofilms. Decreased bacterial densities leave more open space in biofilms and have enhanced ciprofloxacin penetration and killing potential in an E. coli biofilm pre-exposed to probiotic B-C-dots. Pathogenic carbon-quantum-dots hydrothermally derived from E. coli (E-C-dots) did not disrupt pathogenic biofilms nor enhance E. coli killing potential by ciprofloxacin. B-C-dots were biosafe in mice upon daily administration, while E-C-dots demonstrated a decrease in white blood cell and platelet counts and an increase in C-reactive protein levels. Therefore, the way is paved for employing probiotic carbon-quantum-dots instead of viable, probiotic bacteria for synergistic use with existing antibiotics in treating intestinal infections.

Promising strategies to control persistent enemies: Some new technologies to combat biofilm in the food industry-A review

Biofilm is an advanced form of protection that allows bacterial cells to withstand adverse environmental conditions. The complex structure of biofilm results from genetic-related mechanisms besides other factors such as bacterial morphology or substratum properties. Inhibition of biofilm formation of harmful bacteria (spoilage and pathogenic bacteria) is a critical task in the food industry because of the enhanced resistance of biofilm bacteria to stress, such as cleaning and disinfection methods traditionally used in food processing plants, and the increased food safety risks threatening consumer health caused by recurrent contamination and rapid deterioration of food by biofilm cells. Therefore, it is urgent to find methods and strategies for effectively combating bacterial biofilm formation and eradicating mature biofilms. Innovative and promising approaches to control bacteria and their biofilms are emerging. These new approaches range from methods based on natural ingredients to the use of nanoparticles. This literature review aims to describe the efficacy of these strategies and provide an overview of recent promising biofilm control technologies in the food processing sector.

Understanding the Complex Phage-Host Interactions in Biofilm Communities

Bacteriophages and bacterial biofilms are widely present in natural environments, a fact that has accelerated the evolution of phages and their bacterial hosts in these particular niches. Phage-host interactions in biofilm communities are rather complex, where phages are not always merely predators but also can establish symbiotic relationships that induce and strengthen biofilms. In this review we provide an overview of the main features affecting phage-biofilm interactions as well as the currently available methods of studying these interactions. In addition, we address the applications of phages for biofilm control in different contexts.

The antimicrobial efficacy of remote cold atmospheric plasma effluent against single and mixed bacterial biofilms of varying age

Cold atmospheric plasma (CAP) is a minimal food processing technology of increasing interest in the food industry, as it is mild in nature compared to traditional methods (e.g. pasteurisation) and thus can maintain the food's desirable qualities. However, due to this mild nature, the potential exists for post-treatment microbial survival and/or stress adaptation. Furthermore, biofilm inactivation by CAP is underexplored and mostly studied on specific foods or on plastic/polymer surfaces. Co-culture effects, biofilm age, and innate biofilm-associated resistance could all impact CAP efficacy, while studies on real foods are limited to the food product investigated without accounting for structural complexity. The effect of a Remote and Enclosed CAP device (Fourth State Medicine Ltd) was investigated on Escherichia coli and Listeria innocua grown as planktonic cells and as single or mixed bacterial biofilms of variable age, on a biphasic viscoelastic food model of controlled rheological and structural complexity. Post-CAP viability was assessed by plate counts, cell sublethal injury was quantified using flow cytometry, and biofilms were characterised and assessed using total protein content and microscopy techniques. A greater impact of CAP on planktonic cells was observed at higher air flow rates, where the ReCAP device operates in a mode more favourable to reactive oxygen species than reactive nitrogen species. Although planktonic E. coli was more susceptible to CAP than planktonic L. innocua, the opposite was observed in biofilm form. The efficacy of CAP was reduced with increasing biofilm age. Furthermore, E. coli produced much higher protein content in both single and mixed biofilms than L. innocua. Consequently, greater survival of L. innocua in mixed biofilms was attributed to a protective effect from E. coli. These results show that biofilm susceptibility to CAP is age and bacteria dependent, and that in mixed biofilms bacteria may become less susceptible to CAP. These findings are of significance to the food industry for the development of effective food decontamination methods using CAP.

Bacteriophage - A Promising Alternative Measure for Bacterial Biofilm Control

Bacterial biofilms can enhance bacteria's viability by providing resistance against antibiotics and conventional disinfectants. The existence of biofilm is a serious threat to human health, causing incalculable loss. Therefore, new strategies to deal with bacterial biofilms are needed. Bacteriophages are unique due to their activity on bacteria and do not pose a threat to humans. Consequently, they are considered safe alternatives to drugs for the treatment of bacterial diseases. They can effectively obliterate bacterial biofilms and have great potential in medical treatment, the food industry, and pollution control. There are intricate mechanisms of interaction between phages and biofilms. Biofilms may prevent the invasion of phages, and phages can kill bacteria for biofilm control purposes or influence the formation of biofilms. At present, there are various measures for the prevention and control of biofilms through phages, including the combined use of drugs and the application of phage cocktails. This article mainly reviews the function and formation process of bacterial biofilms, summarizes the different mechanisms between phages and biofilms, briefly explains the phage usage for the control of bacterial biofilms, and promotes phage application maintenance human health and the protection of the natural environment.

All Treatment Parameters Affect Environmental Surface Sanitation Efficacy, but Their Relative Importance Depends on the Microbial Target

Environmental sanitation in food manufacturing plants promotes food safety and product microbial quality. However, the development of experimental models remains a challenge due to the complex nature of commercial cleaning processes, which include spraying water and sanitizer on equipment and structural surfaces within manufacturing space. Although simple in execution, the physical driving forces are difficult to simulate in a controlled laboratory environment. Here, we present a bench-scale bioreactor system which mimics the flow conditions in environmental sanitation programs. We applied computational fluid dynamic (CFD) simulations to obtain fluid flow parameters that better approximate and predict industrial outcomes. According to the CFD model, the local wall shear stress achieved on the target surface ranged from 0.015 to 5.00 Pa. Sanitation efficacy on six types of environmental surface materials (hydrophobicity, 57.59 to 88.61°; roughness, 2.2 to 11.9 μm) against two different microbial targets, the bacterial pathogen Listeria monocytogenes and Exophiala species spoilage fungi, were evaluated using the bench-scale bioreactor system. The relative reduction ranged from 0.0 to 0.82 for Exophiala spp., which corresponded to a 0.0 to 2.21 log CFU/coupon reduction, and the relative reduction ranged from 0.0 to 0.93 in L. monocytogenes which corresponded to a 0.0 to 6.19 log CFU/coupon reduction. Although most treatment parameters were considered statistically significant against either L. monocytogenes or Exophiala spp., contact time was ranked as the most important predictor for L. monocytogenes reduction. Shear stress contributed the most to Exophiala spp. removal on stainless steel and Buna-N rubber, while contact time was the most important factor on HDPE (high-density polyethylene), cement, and epoxy.IMPORTANCE Commercial food manufacturers commonly employ a single sanitation program that addresses both bacterial pathogen and fungal spoilage microbiota, despite the fact that the two microbial targets respond differently to various environmental sanitation conditions. Comparison of outcome-based clusters of treatment combinations may facilitate the development of compensatory sanitation regimes where longer contact time or greater force are applied so that lower sanitizer concentrations can be used. Determination of microbiological outcomes related to sanitation program efficacy against a panel of treatment conditions allows food processors to balance tradeoffs between quality and safety with cost and waste stream management, as appropriate for their facility.

Phage cocktail strategies for the suppression of a pathogen in a cross-feeding coculture

Cocktail combinations of bacteria-infecting viruses (bacteriophages) can suppress pathogenic bacterial growth. However, predicting how phage cocktails influence microbial communities with complex ecological interactions, specifically cross-feeding interactions in which bacteria exchange nutrients, remains challenging. Here, we used experiments and mathematical simulations to determine how to best suppress a model pathogen, E. coli, when obligately cross-feeding with S. enterica. We tested whether the duration of pathogen suppression caused by a two-lytic phage cocktail was maximized when both phages targeted E. coli, or when one phage targeted E. coli and the other its cross-feeding partner, S. enterica. Experimentally, we observed that cocktails targeting both cross-feeders suppressed E. coli growth longer than cocktails targeting only E. coli. Two non-mutually exclusive mechanisms could explain these results: (i) we found that treatment with two E. coli phage led to the evolution of a mucoid phenotype that provided cross-resistance against both phages, and (ii) S. enterica set the growth rate of the coculture, and therefore, targeting S. enterica had a stronger effect on pathogen suppression. Simulations suggested that cross-resistance and the relative growth rates of cross-feeders modulated the duration of E. coli suppression. More broadly, we describe a novel bacteriophage cocktail strategy for pathogens that cross-feed.

Hormetic Promotion of Biofilm Growth by Polyvalent Bacteriophages at Low Concentrations

Interactions between bacteriophages (phages) and biofilms are poorly understood despite their broad ecological and water quality implications. Here, we report that biofilm exposure to lytic polyvalent phages at low concentrations (i.e., 10²-10⁴ phages/mL) can counterintuitively promote biofilm growth and densification (corroborated by confocal laser scanning microscopy (CLSM)). Such exposure hormetically upregulated quorum sensing genes (by 4.1- to 24.9-fold), polysaccharide production genes (by 3.7- to 9.3-fold), and curli synthesis genes (by 4.5- to 6.5-fold) in the biofilm-dwelling bacterial hosts (i.e., Escherichia coli and Pseudomonas aeruginosa) relative to unexposed controls. Accordingly, the biofilm matrix increased its polysaccharide and extracellular DNA content relative to unexposed controls (by 41.8 ± 2.3 and 81.4 ± 2.2%, respectively), which decreased biofilm permeability and increased structural integrity. This contributed to enhanced resistance to disinfection with chlorine (bacteria half-lives were 6.08 ± 0.05 vs 3.91 ± 0.03 min for unexposed controls) and to subsequent phage infection (biomass removal was 18.2 ± 1.2 vs 32.3 ± 1.2% for unexposed controls), apparently by mitigating diffusion of these antibacterial agents through the biofilm. Overall, low concentrations of phages reaching a biofilm may result in unintended biofilm stimulation, which might accelerate biofouling, biocorrosion, or other biofilm-related water quality problems.

Characterization of a Lytic Bacteriophage vB_EfaS_PHB08 Harboring Endolysin Lys08 Against Enterococcus faecalis Biofilms

Enterococcus faecalis is an opportunistic pathogen that causes illnesses ranging from urinary tract infections to sepsis in humans and animals. However, the overuse of antibiotics has increased rates of drug resistance among E. faecalis isolates. Bacteriophages and their derivatives have recently been identified as good candidates for the treatment of drug-resistant bacterial infections. Here, we isolated a virulent E. faecalis phage, PHB08, using the double-layer plate method. The bioactivity of the phage was determined via one-step growth curve testing and bacterial killing assays, and whole-genome sequencing was performed using the Illumina HiSeq platform. In addition, protein expression and antibiofilm assays were performed to investigate the activity of the phage lysin. Results showed that PHB08 has a 55,244-bp linear double-stranded DNA genome encoding 91 putative coding sequences. PHB08 inhibited the growth of host strain EF3964 at 37 °C in tryptic soy broth (TSB) medium, while in vegetable models, PHB08 caused a 4.69-log decrease in viable E. faecalis cells after 24 h. Both PHB08 and its endolysin lys08 showed antibiofilm activity against E. faecalis biofilms, which was enhanced by Mn²⁺ ions. Thus, virulent phage PHB08 and endolysin lys08 may be good candidates for reducing and/or eradicating E. faecalis infections.

A Novel Tail-Associated O91-Specific Polysaccharide Depolymerase from a Podophage Reveals Lytic Efficacy of Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) strains are important zoonotic foodborne pathogens, causing diarrhea, hemorrhagic colitis, and life-threatening hemolytic uremic syndrome (HUS) in humans. However, antibiotic treatment of STEC infection is associated with an increased risk of HUS. Therefore, there is an urgent need for early and effective therapeutic strategies. Here, we isolated lytic T7-like STEC phage PHB19 and identified a novel O91-specific polysaccharide depolymerase (Dep6) in the C terminus of the PHB19 tailspike protein. Dep6 exhibited strong hydrolase activity across wide ranges of pH (pH 4 to 8) and temperature (20 to 60°C) and degraded polysaccharides on the surface of STEC strain HB10. In addition, both Dep6 and PHB19 degraded biofilms formed by STEC strain HB10. In a mouse STEC infection model, delayed Dep6 treatment (3 h postinfection) resulted in only 33% survival, compared with 83% survival when mice were treated simultaneously with infection. In comparison, pretreatment with Dep6 led to 100% survival compared with that of the control group. Surprisingly, a single PHB19 treatment resulted in 100% survival in all three treatment protocols. Moreover, a significant reduction in the levels of proinflammatory cytokines was observed at 24 h postinfection in Dep6- or PHB19-treated mice. These results demonstrated that Dep6 or PHB19 might be used as a potential therapeutic agent to prevent STEC infection.IMPORTANCE Shiga toxin-producing Escherichia coli (STEC) is an important foodborne pathogen worldwide. The Shiga-like toxin causes diarrhea, hemorrhagic colitis, and life-threatening hemolytic uremic syndrome (HUS) in humans. Although antibiotic therapy is still used for STEC infections, this approach may increase the risk of HUS. Phages or phage-derived depolymerases have been used to treat bacterial infections in animals and humans, as in the case of the "San Diego patient" treated with a phage cocktail. Here, we showed that phage PHB19 and its O91-specific polysaccharide depolymerase Dep6 degraded STEC biofilms and stripped the lipopolysaccharide (LPS) from STEC strain HB10, which was subsequently killed by serum complement in vitro In a mouse model, PHB19 and Dep6 protected against STEC infection and caused a significant reduction in the levels of proinflammatory cytokines. This study reports the use of an O91-specific polysaccharide depolymerase for the treatment of STEC infection in mice.