A study on the role that quorum sensing play in antibiotic-resistant plasmid conjugative transfer in Escherichia coli

Understanding Stimulation of Conjugal Gene Transfer by Nonantibiotic Compounds: How Far Are We?

A myriad of nonantibiotic compounds is released into the environment, some of which may contribute to the dissemination of antimicrobial resistance by stimulating conjugation. Here, we analyzed a collection of studies to (i) identify patterns of transfer stimulation across groups and concentrations of chemicals, (ii) evaluate the strength of evidence for the proposed mechanisms behind conjugal stimulation, and (iii) examine the plausibility of alternative mechanisms. We show that stimulatory nonantibiotic compounds act at concentrations from 1/1000 to 1/10 of the minimal inhibitory concentration for the donor strain but that stimulation is always modest (less than 8-fold). The main proposed mechanisms for stimulation via the reactive oxygen species/SOS cascade and/or an increase in cell membrane permeability are not unequivocally supported by the literature. However, we identify the reactive oxygen species/SOS cascade as the most likely mechanism. This remains to be confirmed by firm molecular evidence. Such evidence and more standardized and high-throughput conjugation assays are needed to create technologies and solutions to limit the stimulation of conjugal gene transfer and contribute to mitigating global antibiotic resistance.

Bibliometric analysis and visualization of quorum sensing research over the last two decade

Background

Quorum sensing (QS) research stands as a pivotal and multifaceted domain within microbiology, holding profound implications across various scientific disciplines. This bibliometric analysis seeks to offer an extensive overview of QS research, covering the period from 2004 to 2023. It aims to elucidate the hotspots, trends, and the evolving dynamics within this research domain.

Methods

We conducted an exhaustive review of the literature, employing meticulous data curation from the Science Citation Index Extension (SCI-E) within the Web of Science (WOS) database. Subsequently, our survey delves into evolving publication trends, the constellation of influential authors and institutions, key journals shaping the discourse, global collaborative networks, and thematic hotspots that define the QS research field.

Results

The findings demonstrate a consistent and growing interest in QS research throughout the years, encompassing a substantial dataset of 4,849 analyzed articles. Journals such as Frontiers in Microbiology have emerged as significant contributor to the QS literature, highlighting the increasing recognition of QS's importance across various research fields. Influential research in the realm of QS often centers on microbial communication, biofilm formation, and the development of QS inhibitors. Notably, leading countries engaged in QS research include the United States, China, and India. Moreover, the analysis identifies research focal points spanning diverse domains, including pharmacological properties, genetics and metabolic pathways, as well as physiological and signal transduction mechanisms, reaffirming the multidisciplinary character of QS research.

Conclusion

This bibliometric exploration provides a panoramic overview of the current state of QS research. The data portrays a consistent trend of expansion and advancement within this domain, signaling numerous prospects for forthcoming research and development. Scholars and stakeholders engaged in the QS field can harness these findings to navigate the evolving terrain with precision and speed, thereby enhancing our comprehension and utilization of QS in various scientific and clinical domains.

Carbamazepine facilitated horizontal transfer of antibiotic resistance genes by enhancing microbial communication and aggregation

Antimicrobial resistance is a global health security issue of widespread concern. Recent studies have unveiled the potential contribution of non-antibiotics to the emergence of antimicrobial resistance. This study investigated the effect of carbamazepine, a non-antibiotic pharmaceutical, on the fate of antibiotic resistance genes (ARGs) during anaerobic digestion. The results, as revealed by both metagenomic sequencing and absolute quantification, demonstrated that carbamazepine induced the enrichment of ARGs and increased the abundance of ARGs hosts by 1.2-2.1 times. Carbamazepine facilitated microbial aggregation and intercellular communication by upregulating functional genes associated with two-component systems, quorum sensing and type IV secretion systems, thereby increasing the frequency of ARGs conjugation. Furthermore, carbamazepine induced the acquisition of ARGs by pathogens and elevated the overall pathogenic abundance. This study revealed the mechanisms of microbial self-regulation and ARGs transmission under carbamazepine stress, highlighting the potential health risks posed by non-antibiotic pharmaceuticals during the safe disposal of sludge.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Effects of luxS gene on growth characteristics, biofilm formation, and antimicrobial resistance of multi-antimicrobial-resistant Vibrio parahaemolyticus Vp2015094 isolated from shellfish

AIMS

Vibrio parahaemolyticus is an important foodborne pathogen worldwide, which can cause gastroenteritis. This study aimed to investigate the effect of quorum sensing system LuxS/AI-2-related gene luxS on the biological characteristics and antimicrobial resistance of V. parahaemolyticus Vp2015094 from shellfish, which carried a multi-antimicrobial-resistant plasmid.

METHODS AND RESULTS

The critical gene luxS related to the synthesis of AI-2 in V. parahaemolyticus Vp2015094 was knocked out by homologous recombination with suicide plasmid. The effect of luxS on the biological characteristics of V. parahaemolyticus was determined by comparing the growth, AI-2 activity, motility, biofilm formation ability, and antibiotic resistance between the wildtype strain and the luxS deletion mutant. Compared with wildtype strain, the production of AI-2, the motility and biofilm formation ability, antimicrobial resistance, and conjugation frequency of luxS deletion mutant strain were decreased. The transcriptome sequencing showed that the transcriptional levels of many genes related to motility, biofilm formation, antimicrobial resistance, and conjugation were significantly downregulated after luxS deletion.

CONCLUSIONS

Quorum sensing system LuxS/AI-2-related gene luxS in V. parahaemolyticus Vp2015094 played an important role in growth characteristics, biofilm formation, antimicrobial resistance, and resistance genes' transfer.

Augmented dissemination of antibiotic resistance elicited by non-antibiotic factors

The emergence and rapid spread of antibiotic resistance seriously compromise the clinical efficacy of current antibiotic therapies, representing a serious public health threat worldwide. Generally, drug-susceptible bacteria can acquire antibiotic resistance through genetic mutation or gene transfer, among which horizontal gene transfer (HGT) plays a dominant role. It is widely acknowledged that the sub-inhibitory concentrations of antibiotics are the key drivers in promoting the transmission of antibiotic resistance. However, accumulating evidence in recent years has shown that in addition to antibiotics, non-antibiotics can also accelerate the horizontal transfer of antibiotic resistance genes (ARGs). Nevertheless, the roles and potential mechanisms of non-antibiotic factors in the transmission of ARGs remain largely underestimated. In this review, we depict the four pathways of HGT and their differences, including conjugation, transformation, transduction and vesiduction. We summarize non-antibiotic factors accounting for the enhanced horizontal transfer of ARGs and their underlying molecular mechanisms. Finally, we discuss the limitations and implications of current studies.

Hypoxia triggers the proliferation of antibiotic resistance genes in a marine aquaculture system

The transmission of antibiotic resistance genes (ARGs) affects the safety of aquaculture animals. Dissolved oxygen (DO) can affect the transmission of ARGs, but its mechanism of action in this process is unclear. We conducted laboratory breeding experiment with low and control DO groups. Combined quantitative PCR and 16S rRNA sequencing to study the effect of DO on the spread of ARGs. Hypoxia treatment significantly increased the accumulation of ammonium and nitrite in aquaculture water, and it increased the relative abundances of ARGs and mobile genetic elements (MGEs), especially the ARGs resistant to drugs in the categories of sulfonamide, (flor)/(chlor)/(am)phenicol, and MLSB (macrolide, lincosamide and streptogramin B) and the MGE intI-1(clinic), by 2.39-95.69 % in 28 days relative to the control DO treatment. Though the abundance of ARG carries, especially the Rhodocyclaceae, Caldilineaceae, Cyclobacteriaceae, Saprospiraceae, Enterobacteriaceae, Sphingomonadaceae families, showed higher abundance in low DO groups, relating to the vertical transmission of ARGs. Hypoxia treatment is more likely to promote the horizontal gene transfer (HGT)-related pathways, including ABC transporters, two component system, and quorum sensing, thus to induce the HGT of ARGs. The changed bacterial proliferation also altered the abundance of MGEs, especially intI-1(clinic), which induced HGT of ARGs as well. Additionally, pearson correlation results revealed that the succession of bacterial community function played the strongest role in ARG proliferation, followed by bacterial community structure and MGEs. Our results highlight the importance of suitable DO concentration in controlling the spread of ARGs especially the HGT of ARGs. In the context of global attention to food safety, our results provide important information for ensuring the safety of aquatic products and the sustainable development of aquaculture.

Subinhibitory antibiotic concentrations promote the horizontal transfer of plasmid-borne resistance genes from Klebsiellae pneumoniae to Escherichia coli

Horizontal gene transfer plays an important role in the spread of antibiotic resistance, in which plasmid-mediated conjugation transfer is the most important mechanism. While sub-minimal inhibitory concentrations (sub-MIC) of antibiotics could promote conjugation frequency, the mechanism by which sub-MIC levels of antibiotics affect conjugation frequency is not clear. Here, we used Klebsiella pneumoniae SW1780 carrying the multi-drug resistance plasmid pSW1780-KPC as the donor strain, to investigate the effects of sub-MICs of meropenem (MEM), ciprofloxacin (CIP), cefotaxime (CTX), and amikacin (AK) on conjugational transfer of pSW1780-KPC from SW1780 to Escherichia coli J53. Our results showed that the transfer frequencies increased significantly by treating SW1780 strain with sub-MIC levels of MEM, CIP, CTX and AK. Transfer frequencies at sub-MIC conditions in a Galleria mellonella were significantly higher than in vitro. To investigate gene expression and metabolic effects, RT-qPCR and LC-MS-based metabolome sequencing were performed. Transcript levels of T4SS genes virB1, virB2, virB4, virB8, and conjugation-related genes traB, traK, traE, and traL were significantly upregulated by exposure to sub-MICs of MEM, CIP, CTX, and AK. Metabolome sequencing revealed nine differentially regulated metabolites. Our findings are an early warning for a wide assessment of the roles of sub-MIC levels of antibiotics in the spread of antibiotic resistance.

Detection and various environmental factors of antibiotic resistance gene horizontal transfer

Bacterial antibiotic resistance in water environments is becoming increasingly severe, and new antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have also attracted the attention of researchers. The horizontal transfer of ARGs in water environments is considered one of the main sources of bacterial resistance in the natural environment. Horizontal gene transfer (HGT) mainly includes conjugation, natural transformation, and transduction, and conjugation has been investigated most. Several studies have shown that there are a large number of environmental factors that might affect the horizontal transfer of ARGs in water environments, such as nanomaterials, various oxidants, and light; however, there is still a lack of systematic and comprehensive reviews on the detection and the effects of the influence factors of on ARG horizontal transfer. Therefore, this study introduced three HGT modes, analysed the advantages and disadvantages of current methods for monitoring HGT, and then summarized the influence and mechanism of various factors on ARG horizontal transfer, and the possible reasons for the different effects caused by similar factors were mainly critically discussed. Finally, existing research deficiencies and future research directions of ARG horizontal transfer in water environments were discussed.

Hormetic dose-response of halogenated organic pollutants on Microcystis aeruginosa: Joint toxic action and mechanism

Quinolones (QNs), dechloranes (DECs), and chlorinated paraffins (CPs) are three kinds of new halogenated organic pollutants (HOPs), which originate from the use of flame retardants, lubricants and pesticides. Since QNs, DECs, and CPs are frequently detected in waters and sediments, it is necessary to investigate the toxic effects of these HOPs with dwelling phytoplankton, especially for cyanobacteria, to explore their potential hormetic effects and contributions to algal blooms. In the present study, we investigate single and joint toxicity of QNs, DECs and CPs on Microcystis aeruginosa (M. aeruginosa), a cyanobacterium that is frequently implicated with algal blooms. The results indicate single QNs and DECs induce marked hormetic effects on the proliferation of M. aeruginosa but CPs do not. The stimulatory effect of hormesis is linked with accelerated replication of DNA, which is considered to stem from the moderate rise in intracellular reactive oxygen species (ROS). Joint toxicity tests reveal that both QNs & CPs mixtures and DECs & CPs mixtures show hormetic effects on M. aeruginosa, but QNs & DECs mixtures show no hormetic effect. QNs & DECs mixtures exhibit synergistic toxic actions, which may be caused by a sharp rise in intracellular ROS simultaneously produced by the agents. Joint toxic actions of both QNs & CPs, and DECs & CPs shift from addition to antagonism as concentration increases, and this shift may mainly depend on the influence of CPs on cell membrane hydrophobicity of M. aeruginosa. This study provides data and toxic mechanisms for the hormetic phenomenon of single and joint HOPs on M. aeruginosa. The hormetic effects of HOPs may benefit the proliferation of M. aeruginosa in the aquatic environment, aggravating the formation of algal blooms. This study also reflects the important role of hormesis in environmental risk assessment of pollutants.

A simple judgment method for joint action of antibacterial agents on bacterial resistance

The severe pollution of bacterial resistance induced by the wide and even indiscriminate use of antibacterial agents has posed serious threats to human health and ecological safety. Furthermore, the combined effects of antibacterial agents have a closer relationship with the pollution of bacterial resistance than single antibacterial agent. However, there is little information regarding how multiple antibacterial agents interplay to induce bacterial resistance. Here, we developed a simple judgment method with five basic procedures for the joint action of antibacterial agents on bacterial resistance, involving toxicity determination, mutation frequency determination, conjugative transfer frequency determination, dose-response relationship fitting, key parameters obtaining, and joint resistance action judgment. This proposed approach was validated through investigating the joint resistance action between silver nanoparticle (AgNP) and 1-pyrrolidino-1-cyclohexene (1P1C, a kind of quorum sensing inhibitors). According to the procedures, the mutation unit and conjugative transfer unit for the AgNP-1P1C mixture were calculated to be 64.27 and 5.10, respectively, indicating the antagonism for their joint resistance action. This method can not only benefit the mechanistic explanation for how mixed antibacterial agents stimulate the bacterial resistance, but also guide the environmental risk assessment and clinical use of combined antibacterial agents in the related fields. • We present a novel method to judge the joint resistance action of antibacterial agents, taking the emergence and dissemination of antibiotic resistance genes into account. • Toxicity determination can help to design the mixtures of antibacterial agents and confirm the appropriate test concentration range of antibacterial agents used in mutation frequency and conjugative transfer frequency determination. • The mutation unit and conjugative transfer unit were proposed according to the toxic unit in the judgment of joint toxic action.

The Dynamics of the Antimicrobial Resistance Mobilome of Salmonella enterica and Related Enteric Bacteria

The foodborne pathogen Salmonella enterica is considered a global public health risk. Salmonella enterica isolates can develop resistance to several antimicrobial drugs due to the rapid spread of antimicrobial resistance (AMR) genes, thus increasing the impact on hospitalization and treatment costs, as well as the healthcare system. Mobile genetic elements (MGEs) play key roles in the dissemination of AMR genes in S. enterica isolates. Multiple phenotypic and molecular techniques have been utilized to better understand the biology and epidemiology of plasmids including DNA sequence analyses, whole genome sequencing (WGS), incompatibility typing, and conjugation studies of plasmids from S. enterica and related species. Focusing on the dynamics of AMR genes is critical for identification and verification of emerging multidrug resistance. The aim of this review is to highlight the updated knowledge of AMR genes in the mobilome of Salmonella and related enteric bacteria. The mobilome is a term defined as all MGEs, including plasmids, transposons, insertion sequences (ISs), gene cassettes, integrons, and resistance islands, that contribute to the potential spread of genes in an organism, including S. enterica isolates and related species, which are the focus of this review.

Antimicrobial-induced horizontal transfer of antimicrobial resistance genes in bacteria: a mini-review

The emergence and spread of antimicrobial resistance (AMR) among pathogenic bacteria constitute an accelerating crisis for public health. The selective pressures caused by increased use and misuse of antimicrobials in medicine and livestock production have accelerated the overall selection of resistant bacteria. In addition, horizontal gene transfer (HGT) plays an important role in the spread of resistance genes, for example mobilizing reservoirs of AMR from commensal bacteria into pathogenic ones. Antimicrobials, besides antibacterial function, also result in undesirable effects in the microbial populations, including the stimulation of HGT. The main aim of this narrative review was to present an overview of the current knowledge of the impact of antimicrobials on HGT in bacteria, including the effects of transformation, transduction and conjugation, as well as other less well-studied mechanisms of HGT. It is widely accepted that conjugation plays a major role in the spread of AMR in bacteria, and the focus of this review is therefore mainly on the evidence provided that antimicrobial treatment affects this process. Other mechanisms of HGT have so far been deemed less important in this respect; however, recent discoveries suggest their role may be larger than previously thought, and the review provides an update on the rather limited knowledge currently available regarding the impact of antimicrobial treatment on these processes as well. A conclusion from the review is that there is an urgent need to investigate the mechanisms of antimicrobial-induced HGT, since this will be critical for developing new strategies to combat the spread of AMR.

Comparison of the elimination effectiveness of tetracycline and AmpC β-lactamase resistance genes in a municipal wastewater treatment plant using four parallel processes

Municipal wastewater treatment plants (mWWTPs), considered reservoirs of antibiotic resistance genes (ARGs), are selected to compare the contributions of technology and process to ARG removal. Fifteen ARGs (tetA, tetB, tetC, tetE, tetG, tetL, tetM, tetO, tetQ, tetS, tetX, MOX, CIT, EBC, and FOX) and two integron genes (intI1, intI2) were tracked and detected in wastewater samples from a large-scale mWWTP with four parallel processes, including three biological technologies of AAO (anaerobic-anoxic-oxic), AB (adsorption-biodegradation), and UNITANK, two different disinfection technologies, and two primary sedimentation steps. The results showed that ARGs were widely detected, among which tetA and tetM had the highest detection rate at 100%. AAO was the most effective process in removing ARGs, followed by the AB and UNITANK processes, where the separation step was critical: 37.5% AmpC β-lactamase genes were reduced by the secondary clarifier. UV disinfection was more efficient than chlorination disinfection by 47.0% in ARG removal. Both disinfection and primary sedimentation processes could effectively remove integrons, and the swirling flow grit chamber was a more effective primary settling facility in total ARG removal than the aerated grit chamber. The tet genes and AmpC β-lactamase genes were significantly correlated with the water quality indexes of BOD5, CODCr, SS, TP, TOC, pH and NH4+-N (p < 0.05). In addition, the correlation between efflux pump genes and AmpC β-lactamase genes was strongly significant (r2 = 0.717, p < 0.01). This study provides a more powerful guide for selecting and designing treatment processes in mWWTPs with additional consideration of ARG removal.

Hormetic dose-responses for silver antibacterial compounds, quorum sensing inhibitors, and their binary mixtures on bacterial resistance of Escherichia coli

Silver antibacterial compounds (SACs) and quorum sensing inhibitors (QSIs), as the potential antibiotic substitutes, have been recommended to prevent and treat microbial infections for the purpose of controlling the increasingly serious bacterial resistance induced by the abuse of antibiotics. However, there is little information regarding the resistance risk of these compounds, especially their mixtures. In this study, bacterial mutation and RP4 plasmid conjugative transfer among bacteria were used to characterize the bacterial endogenous and exogenous resistance, respectively. The effects of SACs (including silver nitrate (AgNO₃) and silver nanoparticle (AgNP)), QSIs, and their binary mixtures on the bacterial resistance were investigated via setting the frequency of mutation and conjugative transfer in Escherichia coli (E. coli) as the test endpoints. The results indicated that these two endpoints exhibited hormetic dose-responses to each treatment. Furthermore, the joint resistance actions between SACs and QSIs were all judged to be antagonism. Correlation analysis suggested that the promotion of the bacterial resistance in each treatment was closely related to its toxicity. It was speculated that AgNO₃ and AgNP might both release Ag⁺ ions to facilitate the E. coli resistance, while QSIs probably acted on LsrR and SdiA proteins to stimulate the bacterial mutation and accelerate the RP4 plasmid conjugative transfer, respectively. These findings imply that the bacteria may generate targeted stress response to the survival pressure from environmental compounds, displaying hormetic phenomenon in resistance-related test endpoints. This study provides a new insight into the resistance risk induced by SACs and QSIs, benefiting the environmental risk assessment of these compounds from the perspective of bacterial resistance.

The Impact of Direct-Fed Microbials and Phytogenic Feed Additives on Prevalence and Transfer of Extended-Spectrum Beta-Lactamase Genes in Broiler Chicken

Poultry frequently account for the highest prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in livestock. To investigate the impact of direct-fed microbials (DFM) and phytobiotic feed additives on prevalence and conjugation of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, an animal trial was conducted. Lactobacillus agilis LA73 and Lactobacillus salivarius LS1 and two commercial phytogenic feed additives (consisting of carvacrol, cinnamaldehyde, and eugenol) were used as feed additives either alone or as a combination of DFM and phytogenic feed additive. An ESBL-producing E.coli donor and a potentially pathogenic Salmonella Typhimurium recipient were inoculated at 5 × 10⁹ cells/mL in cecal contents from 2-week-old broilers. Conjugation frequencies were determined after 4 h aerobic co-incubation at 37 °C and corrected for the impact of the sample matrix on bacterial growth of donor and recipient. Surprisingly, indigenous Enterobacteriaceae acted as recipients instead of the anticipated Salmonella recipient. The observed increase in conjugation frequency was most obvious in the groups fed the combinations of DFM and phytogenic product, but merely up to 0.6 log units. Further, cecal samples were examined for ESBL-producing Enterobacteriaceae on five consecutive days in broilers aged 27–31 days. All samples derived from animals fed the experimental diet showed lower ESBL-prevalence than the control. It is concluded that Lactobacillus spp. and essential oils may help to reduce the prevalence of ESBL-harboring plasmids in broilers, while the effect on horizontal gene transfer is less obvious.

Autoinducer-2 influences tetracycline resistance in Streptococcus suis by regulating the tet(M) gene via transposon Tn916

The concern over increasing resistance to tetracyclines (TCs), such as tetracycline and chlortetracycline, necessitates exploration of new approaches to combating infection in antimicrobial therapy. Given that bacteria use the chemical language of autoinducer 2 (AI-2) signaling molecules in order to communicate and regulate group behaviors, we asked whether the AI-2 signaling influence the tetracyclines antibiotics susceptibility in S. suis. Our present work demonstrated that MIC increased when exogenous AI-2 was added, when compared to the wild type strain. When grown in the presence of sub-MIC of antibiotics, it has been shown that exogenous AI-2 increases growth rate and biofilm formation. These results suggest that the TCs resistance in S. suis could involve a signaling mechanism. Base on the above observations, transcriptomic analyses showed significant differences in the expression of tet(M) of tetracyclines resistance genes, as well as differences in Tn916 transposon related genes transcription, as judged by RT-PCR. Our results provide strong evidence that AI-2 signaling molecules is may involve in TCs antibiotic resistance in S. suis by regulating tet(M) gene via Tn916 transposon. This study may suggest that targeting AI-2 signaling in bacteria could represent an alternative approach in antimicrobial therapy.

Medicinal Plant Compounds for Combating the Multi-drug Resistant Pathogenic Bacteria: A Review

BACKGROUND

Globally, people utilize plants as the main source of remedy to heal various ailments. Medicinal plants have been utilized to treat ailments since the invention of modern scientific systems of medicine. The common remedy of infectious diseases mainly depends on the inhibition capacity of compounds or killing potential. The issue may give a clue for the development of a novel antimicrobial agent.

METHODS

Currently, microorganisms which are resistant towards antibiotics are probably a matter of serious concern for the overall well-being of health. At the moment, new therapeutic targets aside from the microorganism wall-based activities are in progress. For instance, the autoinducer molecules produced by the quorum sensing system are used to control antibiotic resistance and biofilm formation.

RESULTS

This therapeutic target is well-studied worldwide, however, the scientific data are not updated and only current studies started to gain insight into its perspective as a target to struggle against infectious diseases. Microbial resistance against antimicrobial compounds is a topic of serious concern in recent time.

CONCLUSION

Hence, this paper aims to confer a current overview of the novel compounds, quorum sensing, quorum quenching, biofilm formation in the development of antibiotic resistance and an update on their importance as a potential target for natural substances.

Isolation and Characterization of N-acyl Homoserine Lactone-Producing Bacteria From Cattle Rumen and Swine Intestines

Quorum sensing systems regulate gene expression in response to bacterial population density. Acyl-homoserine lactones are a class of quorum sensing molecules found in cattle rumen that are thought to regulate the gene expression of enterohemorrhagic Escherichia coli and thus help this pathogen survive in animal gastrointestinal tracts. However, the specific bacteria that produce these signaling molecules in bovine and porcine gastrointestinal tracts are unknown. Here we developed methods to concentrate gastrointestinal fluids and screen the bacteria that produce acyl-homoserine lactones. We isolated a Pseudomonas aeruginosa strain YZ1 from cattle rumen, and an Aeromonas hydrophila strain YZ2 from pig intestine. Mass spectrometry analysis of culture supernatants indicated at least three specific classes of acyl-homoserine lactones produced by YZ1, and a C4-acyl-homoserine lactone produced by YZ2. Transformation of E. coli with P. aeruginosa or A. hydrophila luxI homologs,which can produce short- or long-chain acyl-homoserine lactones conferred upon E. coli the ability to synthesize acyl-homoserine lactones and affected gene expression, motility, and acid tolerance of E. coli. This is the first study reporting the isolation and characterization of acyl-homoserine lactone synthase-positive bacteria from cattle rumen and swine intestines.