Heavy Metal Induced Antibiotic Resistance in Bacterium LSJC7

Co-contamination of antibiotics and heavy metals prevails in the environment, and may play an important role in disseminating bacterial antibiotic resistance, but the selective effects of heavy metals on bacterial antibiotic resistance is largely unclear. To investigate this, the effects of heavy metals on antibiotic resistance were studied in a genome-sequenced bacterium, LSJC7. The results showed that the presence of arsenate, copper, and zinc were implicated in fortifying the resistance of LSJC7 towards tetracycline. The concentrations of heavy metals required to induce antibiotic resistance, i.e., the minimum heavy metal concentrations (MHCs), were far below (up to 64-fold) the minimum inhibition concentrations (MIC) of LSJC7. This finding indicates that the relatively low heavy metal levels in polluted environments and in treated humans and animals might be sufficient to induce bacterial antibiotic resistance. In addition, heavy metal induced antibiotic resistance was also observed for a combination of arsenate and chloramphenicol in LSJC7, and copper/zinc and tetracycline in antibiotic susceptible strain Escherichia coli DH5α. Overall, this study implies that heavy metal induced antibiotic resistance might be ubiquitous among various microbial species and suggests that it might play a role in the emergence and spread of antibiotic resistance in metal and antibiotic co-contaminated environments.     

Phenotypic and Safety Assessment of the Cheese Strain Lactiplantibacillus plantarum LL441, and Sequence Analysis of its Complete Genome and Plasmidome

This work describes the phenotypic typing and complete genome analysis of LL441, a dairy Lactiplantibacillus plantarum strain. LL441 utilized a large range of carbohydrates and showed strong activity of some carbohydrate-degrading enzymes. The strain grew slowly in milk and produced acids and ketones along with other volatile compounds. The genome of LL441 included eight circular molecules, the bacterial chromosome, and seven plasmids (pLL441-1 through pLL441-7), ranging in size from 8.7 to 53.3 kbp. Genome analysis revealed vast arrays of genes involved in carbohydrate utilization and flavor formation in milk, as well as genes providing acid and bile resistance. No genes coding for virulence traits or pathogenicity factors were detected. Chromosome and plasmids were packed with insertion sequence (IS) elements. Plasmids were also abundant in genes encoding heavy metal resistance traits and plasmid maintenance functions. Technologically relevant phenotypes linked to plasmids, such as the production of plantaricin C (pLL441-1), lactose utilization (pLL441-2), and bacteriophage resistance (pLL441-4), were also identified. The absence of acquired antibiotic resistance and of phenotypes and genes of concern suggests L. plantarum LL441 be safe. The strain might therefore have a use as a starter or starter component in dairy and other food fermentations or as a probiotic.     

A Comprehensive Insight into Tetracycline Resistant Bacteria and Antibiotic Resistance Genes in Activated Sludge Using Next-Generation Sequencing

In order to comprehensively investigate tetracycline resistance in activated sludge of sewage treatment plants, 454 pyrosequencing and Illumina high-throughput sequencing were used to detect potential tetracycline resistant bacteria (TRB) and antibiotic resistance genes (ARGs) in sludge cultured with different concentrations of tetracycline. Pyrosequencing of 16S rRNA gene revealed that tetracycline treatment greatly affected the bacterial community structure of the sludge. Nine genera consisting of Sulfuritalea, Armatimonas, Prosthecobacter, Hyphomicrobium, Azonexus, Longilinea, Paracoccus, Novosphingobium and Rhodobacter were identified as potential TRB in the sludge. Results of qPCR, molecular cloning and metagenomic analysis consistently indicated that tetracycline treatment could increase both the abundance and diversity of the tet genes, but decreased the occurrence and diversity of non-tetracycline ARG, especially sulfonamide resistance gene sul2. Cluster analysis showed that tetracycline treatment at subinhibitory concentrations (5 mg/L) was found to pose greater effects on the bacterial community composition, which may be responsible for the variations of the ARGs abundance. This study indicated that joint use of 454 pyrosequencing and Illumina high-throughput sequencing can be effectively used to explore ARB and ARGs in the environment, and future studies should include an in-depth investigation of the relationship between microbial community, ARGs and antibiotics in sewage treatment plant (STP) sludge.     

Detection and Identification of Probiotic Lactobacillus plantarum Strains by Multiplex PCR Using RAPD-Derived Primers

Lactobacillus plantarum 2035 and Lactobacillus plantarum ACA-DC 2640 are two lactic acid bacteria (LAB) strains that have been isolated from Feta cheese. Both display significant potential for the production of novel probiotic food products. The aim of the present study was the development of an accurate and efficient method for the molecular detection and identification of the above strains in a single reaction. A multiplex PCR assay was designed for each strain, based on specific primers derived from Random Amplified Polymorphic DNA (RAPD) Sequenced Characterized Amplified Region (SCAR) analysis. The specificity of the assay was tested with a total of 23 different LAB strains, for L. plantarum 2035 and L. plantarum ACA-DC 2640. The multiplex PCR assay was also successfully applied for the detection of the above cultures in yogurt samples prepared in our lab. The proposed methodology may be applied for monitoring the presence of these strains in food products, thus evaluating their probiotic character. Moreover, our strategy may be adapted for other novel LAB strains with probiotic potential, thus providing a powerful tool for molecular discrimination that could be invaluable to the food industry.     

Differential Chromosome- and Plasmid-Borne Resistance of Escherichia coli hfq Mutants to High Concentrations of Various Antibiotics

The Hfq protein is a bacterial RNA chaperone, involved in many molecular interactions, including control of actions of various small RNA regulatory molecules. We found that the presence of Hfq was required for survival of plasmid-containing Escherichia coli cells against high concentrations of chloramphenicol (plasmid p27cmr), tetracycline (pSC101, pBR322) and ampicillin (pBR322), as hfq⁺ strains were more resistant to these antibiotics than the hfq-null mutant. In striking contrast, production of Hfq resulted in low resistance to high concentrations of kanamycin when the antibiotic-resistance marker was chromosome-borne, with deletion of hfq resulting in increasing bacterial survival. These results were observed both in solid and liquid medium, suggesting that antibiotic resistance is an intrinsic feature of these strains rather than a consequence of adaptation. Despite its major role as RNA chaperone, which also affects mRNA stability, Hfq was not found to significantly affect kan and tet mRNAs turnover. Nevertheless, kan mRNA steady-state levels were higher in the hfq-null mutant compared to the hfq⁺ strain, suggesting that Hfq can act as a repressor of kan expression.This observation does correlate with the enhanced resistance to high levels of kanamycin observed in the hfq-null mutant. Furthermore, dependency on Hfq for resistance to high doses of tetracycline was found to depend on plasmid copy number, which was only observed when the resistance marker was expressed from a low copy plasmid (pSC101) but not from a medium copy plasmid (pBR322). This suggests that Hfq may influence survival against high doses of antibiotics through mechanisms that remain to be determined. Studies with pBR322Δrom may also suggest an interplay between Hfq and Rom in the regulation of ColE1-like plasmid replication. Results of experiments with a mutant devoid of the part of the hfq gene coding for the C-terminal region of Hfq suggested that this region, as well as the N-terminal region, may be involved in the regulation of expression of antibiotic resistance in E. coli independently.     

pCTX-M3—Structure,Function, and Evolution of a Multi-Resistance Conjugative Plasmid of a Broad Recipient Range

pCTX-M3 is the archetypic member of the IncM incompatibility group of conjugative plasmids (recently referred to as IncM2). It is responsible for the worldwide dissemination of numerous antibiotic resistance genes, including those coding for extended-spectrum β-lactamases and conferring resistance to aminoglycosides. The IncM plasmids acquired during evolution diverse mobile genetic elements found in one or two multiple resistance regions, MRR(s), grouping antibiotic resistance genes as well as mobile genetic elements or their remnants. The IncM plasmids can be found in bacteria inhabiting various environments. The information on the structure and biology of pCTX-M3 is integrated in this review. It focuses on the functional modules of pCTX-M3 responsible for its replication, stable maintenance, and conjugative transfer, indicating that the host range of the pCTX-M3 replicon is limited to representatives of the family Enterobacteriaceae (Enterobacterales ord. nov.), while the range of recipients of its conjugation system is wide, comprising Alpha-, Beta-, and Gammaproteobacteria, and also Firmicutes.     

The Phagocytosis of Lacticaseibacillus casei and Its Immunomodulatory Properties on Human Monocyte-Derived Dendritic Cells Depend on the Expression of Lc-p75, a Bacterial Peptidoglycan Hydrolase

The human gut symbiont Lacticaseibacillus (L.) casei (previously Lactobacillus casei) is under intense research due to its wide range of immunomodulatory effects on the human host. Dendritic cells (DCs) are crucial players in the direct and indirect communication with lactobacilli in the gastrointestinal tract. Here, we demonstrate that human monocyte-derived DCs (moDCs) are able to engulf L. casei BL23, in which the intact bacterial cell wall and morphology have a key role. The absence of the bacterial cell-wall-degrading enzyme, Lc-p75, in L. casei cells causes remarkable morphological changes, which have important consequences in the phagocytosis of L. casei by moDCs. Our results showed that the Lc-p75 mutation induced defective internalization and impaired proinflammatory and T-cell-polarizing cytokine secretion by bacteria-exposed moDCs. The T helper (Th) 1 and Th17 cell activating capacity of moDCs induced by the mutant L. casei was consequently reduced. Moreover, inhibition of the phagocytosis of wild-type bacteria showed similar results. Taken together, these data suggested that formation of short bacterial chains helps to exert the potent immunomodulatory properties of L. casei BL23.     

Protective Effects of Lactobacillus plantarum Lac16 on Clostridium perfringens Infection-Associated Injury in IPEC-J2 Cells

Clostridium perfringens (C. perfringens) causes intestinal injury through overgrowth and the secretion of multiple toxins, leading to diarrhea and necrotic enteritis in animals, including pigs, chickens, and sheep. This study aimed to investigate the protective effects of Lactobacillus plantarum (L. plantarum) Lac16 on C. perfringens infection-associated injury in intestinal porcine epithelial cell line (IPEC-J2). The results showed that L. plantarum Lac16 significantly inhibited the growth of C. perfringens, which was accompanied by a decrease in pH levels. In addition, L. plantarum Lac16 significantly elevated the mRNA expression levels of host defense peptides (HDPs) in IPEC-J2 cells, decreased the adhesion of C. perfringens to IPEC-J2 cells, and attenuated C. perfringens-induced cellular cytotoxicity and intestinal barrier damage. Furthermore, L. plantarum Lac16 significantly suppressed C. perfringens-induced gene expressions of proinflammatory cytokines and pattern recognition receptors (PRRs) in IPEC-J2 cells. Moreover, L. plantarum Lac16 preincubation effectively inhibited the phosphorylation of p65 caused by C. perfringens infection. Collectively, probiotic L. plantarum Lac16 exerts protective effects against C. perfringens infection-associated injury in IPEC-J2 cells.     

Ameliorative Effects of Lactobacillus plantarum HAC01 Lysate on 3T3-L1 Adipocyte Differentiation via AMPK Activation and MAPK Inhibition

Lactobacillus plantarum HAC01 has been shown to effectively treat metabolic diseases. However, the precise pharmacological effects and molecular mechanisms of L. plantarum HAC01 remain unclear. In this study, we investigate the anti-adipogenic effects of L. plantarum HAC01 lysate and its associated mechanism of action. To induce lipid accumulation, 3T3-L1 cells were incubated in differentiation media with or without L. plantarum HAC01 lysate. Our results show that L. plantarum HAC01 lysate treatment not only reduced lipid accumulation during the differentiation of 3T3-L1 cells, but also decreased the expression of adipogenic and lipogenic genes involved in lipid metabolism in a dose-dependent manner. Additionally, L. plantarum HAC01 lysate inhibited CCAAT/enhancer-binding protein (C/EBP) beta within 4 h of differentiation induction and inhibited peroxisome proliferator-activated receptor gamma, C/EBP alpha, and sterol regulatory element-binding proteins within 2 d. Moreover, treatment with L. plantarum HAC01 lysate increased the phosphorylation of adenosine monophosphate-activated protein kinase, an important regulator of energy metabolism, and decreased the phosphorylation of mitogen-activated protein kinase. These results indicate that L. plantarum HAC01 lysate may have anti-adipogenic effects and support its potential as a useful agent for the treatment of obesity.     

Biofilm Spreading by the Adhesin-Dependent Gliding Motility of Flavobacterium johnsoniae: 2. Role of Filamentous Extracellular Network and Cell-to-Cell Connections at the Biofilm Surface

Flavobacterium johnsoniae forms a thin spreading colony on nutrient-poor agar using gliding motility. As reported in the first paper, WT cells in the colony were sparsely embedded in self-produced extracellular polymeric matrix (EPM), while sprB cells were densely packed in immature biofilm with less matrix. The colony surface is critical for antibiotic resistance and cell survival. We have now developed the Grid Stamp-Peel method whereby the colony surface is attached to a TEM grid for negative-staining microscopy. The images showed that the top of the spreading convex WT colonies was covered by EPM with few interspersed cells. Cells exposed near the colony edge made head-to-tail and/or side-to-side contact and sometimes connected via thin filaments. Nonspreading sprB and gldG and gldK colonies had a more uniform upper surface covered by different EPMs including vesicles and filaments. The EPM of sprB, gldG, and WT colonies contained filaments ~2 nm and ~5 nm in diameter; gldK colonies did not include the latter. Every cell near the edge of WT colonies had one or two dark spots, while cells inside WT colonies and cells in SprB-, GldG-, or GldK-deficient colonies did not. Together, our results suggest that the colony surface structure depends on the capability to expand biofilm.     

Genetic Carriers and Genomic Distribution of cadA6—A Novel Variant of a Cadmium Resistance Determinant Identified in Listeria spp.

Listeria monocytogenes is a pathogen responsible for severe cases of food poisoning. Listeria spp. strains occurring in soil and water environments may serve as a reservoir of resistance determinants for pathogenic L. monocytogenes strains. A large collection of Listeria spp. strains (155) isolated from natural, agricultural, and urban areas was screened for resistance to heavy metals and metalloids, and the presence of resistance determinants and extrachromosomal replicons. Of the tested strains, 35% were resistant to cadmium and 17% to arsenic. Sequence analysis of resistance plasmids isolated from strains of Listeria seeligeri and Listeria ivanovii, and the chromosome of L. seeligeri strain Sr73, identified a novel variant of the cadAC cadmium resistance efflux system, cadA6, that was functional in L. monocytogenes cells. The cadA6 cassette was detected in four Listeria species, including strains of L. monocytogenes, isolated from various countries and sources—environmental, food-associated, and clinical samples. This resistance cassette is harbored by four novel composite or non-composite transposons, which increases its potential for horizontal transmission. Since some cadAC cassettes may influence virulence and biofilm formation, it is important to monitor their presence in Listeria spp. strains inhabiting different environments.     

The Lactococcal dgkB (yecE) and dxsA Genes for Lipid Metabolism Are Involved in the Resistance to Cell Envelope-Acting Antimicrobials

The emergence of antibiotic-resistant bacteria led to an urgent need for next-generation antimicrobial agents with novel mechanisms of action. The use of positively charged antimicrobial peptides that target cytoplasmic membrane is an especially promising strategy since essential functions and the conserved structure of the membrane hinder the development of bacterial resistance. Aureocin A53- and enterocin L50-like bacteriocins are highly cationic, membrane-targeting antimicrobial peptides that have potential as next-generation antibiotics. However, the mechanisms of resistance to these bacteriocins and cross-resistance against antibiotics must be examined before application to ensure their safe use. Here, in the model bacterium Lactococcus lactis, we studied the development of resistance to selected aureocin A53- and enterocin L50-like bacteriocins and its correlation with antibiotics. First, to generate spontaneous resistant mutants, L. lactis was exposed to bacteriocin BHT-B. Sequencing of their genomes revealed single nucleotide polymorphisms (SNPs) in the dgkB (yecE) and dxsA genes encoding diacylglycerol kinase and 1-deoxy-D-xylulose 5-phosphate synthase, respectively. Then, selected mutants underwent susceptibility tests with a wide array of bacteriocins and antibiotics. The highest alterations in the sensitivity of studied mutants were seen in the presence of cytoplasmic membrane targeting bacteriocins (K411, Ent7, EntL50, WelM, SalC, nisin) and antibiotics (daptomycin and gramicidin) as well as lipid II cycle-blocking bacteriocins (nisin and Lcn972) and antibiotics (bacitracin). Interestingly, decreased via the SNPs accumulation sensitivity to membrane-active bacteriocins and antibiotics resulted in the concurrently increased vulnerability to bacitracin, carbenicillin, or chlortetracycline. It is suspected that SNPs may result in alterations to the efficiency of the nascent enzymes rather than a total loss of their function as neither deletion nor overexpression of dxsA restored the phenotype observed in spontaneous mutants.     

Plasmids as Key Players in Acinetobacter Adaptation

This review briefly summarizes the data on the mechanisms of development of the adaptability of Acinetobacters to various living conditions in the environment and in the clinic. A comparative analysis of the genomes of free-living and clinical strains of A. lwoffii, as well as the genomes of A. lwoffii and A. baumannii, has been carried out. It has been shown that plasmids, both large and small, play a key role in the formation of the adaptability of Acinetobacter to their living conditions. In particular, it has been demonstrated that the plasmids of various strains of Acinetobacter differ from each other in their structure and gene composition depending on the lifestyle of their host bacteria. Plasmids of modern strains are enriched with antibiotic-resistant genes, while the content of genes involved in resistance to heavy metals and arsenic is comparable to plasmids from modern and ancient strains. It is concluded that Acinetobacter plasmids may ensure the survival of host bacteria under conditions of various types of environmental and clinical stresses. A brief overview of the main mechanisms of horizontal gene transfer on plasmids inherent in Acinetobacter strains is also given.     

A Comparative Genomic and Safety Assessment of Six Lactiplantibacillus plantarum subsp. argentoratensis Strains Isolated from Spontaneously Fermented Greek Wheat Sourdoughs for Potential Biotechnological Application

The comparative genome analysis of six Lactiplantibacillus plantarum subsp. argentoratensis strains previously isolated from spontaneously fermented Greek wheat sourdoughs is presented. Genomic attributes related to food safety have been studied according to the European Food Safety Authority (EFSA) suggestions for the use of lactic acid bacteria (LAB) in the production of foods. Bioinformatic analysis revealed a complete set of genes for maltose, sucrose, glucose, and fructose fermentation; conversion of fructose to mannitol; folate and riboflavin biosynthesis; acetoin production; conversion of citrate to oxaloacetate; and the ability to produce antimicrobial compounds (plantaricins). Pathogenic factors were absent but some antibiotic resistance genes were detected. CRISPR and cas genes were present as well as various mobile genetic elements (MGEs) such as plasmids, prophages, and insertion sequences. The production of biogenic amines by these strains was not possible due to the absence of key genes in their genome except lysine decarboxylase associated with cadaverine; however, potential degradation of these substances was identified due to the presence of a blue copper oxidase precursor and a multicopper oxidase protein family. Finally, comparative genomics and pan-genome analysis showed genetic differences between the strains (e.g., variable pln locus), and it facilitated the identification of various phenotypic and probiotic-related properties.     

A Two-in-One Strategy: Target and Nontarget Site Mechanisms Both Play Important Role in IMI-Resistant Weedy Rice

The introduction of Clearfield technology allows the use of imidazolinone (IMI) herbicides to control weedy rice. Imidazolinone herbicides stop the acetolactate synthase (ALS) enzyme from synthesizing branched-chain amino acids, resulting in the death of the plant. Since the launch of Clearfield technology in Malaysia in 2010, many farmers have replaced traditional cultivars with Clearfield (CL) rice lines (MR220-CL1 and MR220-CL2). This technology was initially effective; however, in recent years, local farmers have reported the reduced efficacy of IMI herbicides in controlling the spread of weedy rice. Under IMI herbicide treatment, in previous weedy rice studies, the target-site resistance (TSR) mechanism of the ALS gene has been suggested as a key factor conferring herbicide resistance. In our study, a combination of ALS gene sequencing, enzyme colorimetric assay, and a genome-wide association study (GWAS) highlighted that a non-target-site resistance (NTSR) can be an alternative molecular mechanism in IMI-resistant weedy rice. This is supported by a series of evidence, including a weak correlation between single nucleotide polymorphisms (SNPs) within the ALS exonic region and ALS enzyme activity. Our findings suggest that the adaptability of weedy rice in Clearfield rice fields can be more complicated than previously found in other rice strains.     

Lactiplantibacillusplantarum ATG-K2 Exerts an Anti-Obesity Effect in High-Fat Diet-Induced Obese Mice by Modulating the Gut Microbiome

Obesity is a major health problem. Compelling evidence supports the beneficial effects of probiotics on obesity. However, the anti-obesity effect of probiotics remains unknown. In this study, we investigated the anti-obesity effects and potential mechanisms of Lactiplantibacillus plantarum ATG-K2 using 3T3-L1 adipocytes and high-fat diet (HFD)-induced obese mice. 3T3-L1 cells were incubated to determine the effect of lipid accumulation with lysate of L. plantarum ATG-K2. Mice were fed a normal fat diet or HFD with L. plantarum ATG-K2 and Orlistat for 8 weeks. L. plantarum ATG-K2 inhibited lipid accumulation in 3T3-L1 adipocytes, and reduced body weight gain, WAT weight, and adipocyte size in HFD-induced obese mice, concurrently with the downregulation of PPARγ, SREBP1c, and FAS and upregulation of PPARα, CTP1, UCP1, Prdm16, and ND5. Moreover, L. plantarum ATG-K2 decreased TG, T-CHO, leptin, and TNF-α levels in the serum, with corresponding gene expression levels in the intestine. L. plantarum ATG-K2 modulated the gut microbiome by increasing the abundance of the Lactobacillaceae family, which increased SCFA levels and branched SCFAs in the feces. L. plantarum ATG-K2 exhibited an anti-obesity effect and anti-hyperlipidemic effect in 3T3-L1 adipocytes and HFD-induced obese mice by alleviating the inflammatory response and regulating lipid metabolism, which may be influenced by modulation of the gut microbiome and its metabolites. Therefore, L. plantarum ATG-K2 can be a preventive and therapeutic agent for obesity.     

The MexJK Multidrug Efflux Pump Is Not Involved in Acquired or Intrinsic Antibiotic Resistance in Pseudomonas aeruginosa,but Modulates the Bacterial Quorum Sensing Response

Multidrug efflux pumps are critical elements in both intrinsic and acquired antibiotic resistance of bacterial populations. Consequently, most studies regarding these protein machineries focus on this specific phenotype. Nevertheless, different works show that efflux pumps participate in other aspects of bacterial physiology too. Herein, we study the Pseudomonas aeruginosa multidrug efflux pump MexJK. Previous studies, using model strains lacking MexAB-OprM and MexCD-OprJ efflux pumps, support that MexJK can extrude erythromycin, tetracycline, and triclosan. However, the results here reported indicate that this potential increased extrusion, in a mutant overexpressing mexJK, does not alter the antibiotics susceptibility in a wild-type genetic background where all intrinsic multidrug efflux pumps remain functional. Nevertheless, a clear impact on the quorum sensing (QS) response, mainly in the Pqs-dependent QS regulation network and in the expression of Pqs-regulated virulence factors, was observed linked to mexJK overexpression. The production of the siderophore pyoverdine strongly depended on the level of mexJK expression, suggesting that MexJK might participate in P. aeruginosa pyoverdine-dependent iron homeostasis. All in all, the results presented in the current article support that the functions of multidrug efflux pumps, as MexJK, go beyond antibiotic resistance and can modulate other relevant aspects of bacterial physiology.     

Alleviation of LPS-Induced Inflammation and Septic Shock by Lactiplantibacillus plantarum K8 Lysates

We previously showed that Lactiplantibacillus plantarum K8 and its cell wall components have immunoregulatory effects. In this study, we demonstrate that pre-treatment of L. plantarum K8 lysates reduced LPS-induced TNF-α production in THP-1 cells by down-regulating the early signals of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB). The down-regulation of signals may be caused by the induction of negative regulators involved in toll-like receptor (TLR)-mediated signaling. However, co-treatment with high concentrations of L. plantarum K8 lysates and lipopolysaccharide (LPS) activated the late signaling of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-κB pathways and resulted in the induction of absent in melanoma 2 (AIM2) inflammasome-mediated interleukin (IL)-1β secretion. Intraperitoneal injection of L. plantarum K8 lysates in LPS-induced endotoxin shock mice alleviated mortality and reduced serum tumor-necrosis factor (TNF)-α, IL-1β, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. In addition, the mRNA levels of TNF-α, IL-1β, and IL-6 decreased in livers from mice injected with L. plantarum K8 followed by LPS. Hematoxylin and eosin (H&E) staining of the liver showed that the cell size was enlarged by LPS injection and slightly reduced by L. plantarum K8 lysate pre-injection followed by LPS injection. Macrophage infiltration of the liver also decreased in response to the combination injection compared with mice injected with only LPS. Taken together, our results show that although L. plantarum K8 lysates differentially regulated the production of LPS-induced inflammatory cytokines in THP-1 cells, the lysates inhibited overall inflammation in mice. Thus, this study suggests that L. plantarum K8 lysates could be developed as a substance that modulates immune homeostasis by regulating inflammation.     

Outer Membrane Vesicles Derived from Klebsiella pneumoniae Are a Driving Force for Horizontal Gene Transfer

Gram-negative bacteria release Outer Membrane Vesicles (OMVs) into the extracellular environment. Recent studies recognized these vesicles as vectors to horizontal gene transfer; however, the parameters that mediate OMVs transfer within bacterial communities remain unclear. The present study highlights for the first time the transfer of plasmids containing resistance genes via OMVs derived from Klebsiella pneumoniae (K. pneumoniae). This mechanism confers DNA protection, it is plasmid copy number dependent with a ratio of 3.6 times among high copy number plasmid (pGR) versus low copy number plasmid (PRM), and the transformation efficiency was 3.6 times greater. Therefore, the DNA amount in the vesicular lumen and the efficacy of horizontal gene transfer was strictly dependent on the identity of the plasmid. Moreover, the role of K. pneumoniae-OMVs in interspecies transfer was described. The transfer ability was not related to the phylogenetic characteristics between the donor and the recipient species. K. pneumoniae-OMVs transferred plasmid to Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Burkholderia cepacia. These findings address the pivotal role of K. pneumoniae-OMVs as vectors for antimicrobial resistance genes spread, contributing to the development of antibiotic resistance in the microbial communities.