Inhibitory effect of resveratrol on swimming motility and adhesion ability against Salmonella enterica serovar Typhimurium infection

Salmonella enterica serovar Typhimurium (S. typhimurium) is a common Gram-negative foodborne pathogen that threatens public health and hinders the development of livestock industry. Resveratrol, an important component in grape fruits and seeds, has been shown to possess multiple biological activities, but its potential effects on S. typhimurium-mediated virulence have been rarely reported. In this study, we investigated the effect of resveratrol on S. typhimurium flagella -mediated virulence. The results showed that resveratrol significantly reduced the transcription of flagella genes and swimming motility of S. typhimurium, and also inhibited the transcription of T3SS-related virulence genes with varying degrees inhibiting bacterial growth. Simultaneously, resveratrol significantly reduced the adhesion of S. typhimurium to HeLa cells. Unfortunately, resveratrol does not improve the survival rate of S. typhimurium-infected mice, but it reduces the bacterial load in the liver and spleen of infected mice, and it also has a certain degree of anti-inflammatory activity. In summary, these results indicated that resveratrol has the potential to be developed as an alternative drug or antibacterial agent to prevent Salmonella infection.

Hexanic extract of Achyrocline satureioides: antimicrobial activity and in vitro inhibitory effect on mechanisms related to the pathogenicity of Paenibacillus larvae

INTRODUCTION

Paenibacillus larvae is a spore-forming bacillus, the most important bacterial pathogen of honeybee larvae and the causative agent of American foulbrood (AFB). Control measures are limited and represent a challenge for both beekeepers and researchers. For this reason, many studies focus on the search for alternative treatments based on natural products.

AIM

The objective of this study was to determine the antimicrobial activity of the hexanic extract (HE) of Achyrocline satureioides on P. larvae and the inhibitory activity on some mechanisms related to pathogenicity.

MATERIAL AND METHODS

The Minimum Inhibitory Concentration (MIC) of the HE was determined by the broth microdilution technique and the Minimum Bactericidal Concentration (MBC) by the microdrop technique. Swimming and swarming motility was evaluated in plates with 0.3 and 0.5% agar, respectively. Biofilm formation was evaluated and quantified by the Congo red and crystal violet method. The protease activity was evaluated by the qualitative technique on skim milk agar plates.

RESULTS

It was determined that the MIC of the HE on four strains of P. larvae ranged between 0.3 and 9.37 µg/ml and the MBC between 1.17 and 150 µg/ml. On the other hand, sub-inhibitory concentrations of the HE were able to decrease swimming motility, biofilm formation and the proteases production of P. larvae.

Assessment of the potential of phage-antibiotic synergy to induce collateral sensitivity in Salmonella Typhimurium

This study was designed to evaluate the synergistic effect of phage and antibiotic on the induction of collateral sensitivity in Salmonella Typhimurium. The synergistic effects of Salmonella phage PBST32 combined with ciprofloxacin (CIP) against S. Typhimurium KCCM 40253 (ST^KCCM) were evaluated using a fractional inhibitory concentration (FIC) assay. The CIP susceptibility of ST^KCCM was increased when combined with PBST32, showing 16-fold decrease at 7 log PFU/mL. The combination of 1/2 × MIC of CIP and PBST32 (CIP[1/2]+PBST32) effectively inhibited the growth of ST^KCCM up to below the detection limit (1.3 log CFU/mL) after 12 h of incubation at 37 °C. The significant reduction in bacterial swimming motility was observed for PBST32 and CIP[1/4]+PBST32. The CIP[1/4]+PBST32 increased the fitness cost (relative fitness = 0.57) and decreased the cross-resistance to different classes of antibiotics. ST^KCCM treated with PBST32 alone treatment exhibited the highest coefficient of variation (90%), followed by CIP[1/4]+PBST32 (75%). These results suggest that the combination of PBST32 and CIP can be used to control bacterial pathogens.

Differences in flaA gene sequences, swimming motility, and biofilm forming ability between clinical and environmental isolates of Aeromonas species

The flagellin A gene (flaA) sequences, swimming motility, and biofilm forming ability were investigated in order to reveal the genetic and functional differences of flagella between clinical and environmental isolates of Aeromonas species. Twenty-eight clinical and 48 environmental strains of Aeromonas species isolated in Okinawa Prefecture of Japan were used in this study. The full-length flaA genes of these strains were sequenced and aligned, and a phylogenetic tree was constructed. In addition, swimming motility and biofilm forming ability were evaluated by conventional methods. Aeromonas veronii biovar sobria and A. hydrophila clearly divided into clinical and environmental strain clusters in the flaA phylogenetic classification, and the six and 13 specific amino acids respectively, of FlaA of both species were different in clinical and environmental strains. Furthermore, the flaA size of the clinical strain of A. veronii bv. sobria was mainly 909, 924, and 939 bp, and the size of A. hydrophila was 909 bp. The swimming motility of clinical isolates of both species was lower than the environmental isolates; however, the biofilm forming ability of the clinical isolates was high. Thus, the clinical isolates of A. veronii bv. sobria and A. hydrophila had different genetic and functional characteristics of flagellin than the environmental isolates. The characteristics of flagellin could serve as indicators to distinguish between clinical and environmental isolates of the both species. It may contribute to diagnosis of these diseases and the monitoring of clinical strain invasion into the natural environment.

Can only one physiological trait determinate the adverse effect of green fluorescent protein (GFP) incorporation on Vibrio virulence?

Green fluorescent protein (GFP) has been used extensively for in situ animal studies that follow up bacterial infection under epifluorescence microscopy. It is assumed that GFP is acting as a "neutral" protein with no influence on the bacterial physiology. To verify this hypothesis, the virulence of Vibrio splendidus ME9, Vibrio anguillarum NB10, and their respective GFP-tagged strains ME9-GFP and NB10-GFP (transconjugants) was compared in vitro and tested in vivo towards blue mussel (Mytilus edulis) larvae. Results showed that the incorporation of GFP negatively impacted the growth and swimming motility of NB10 in vitro. Correspondingly, the mRNA levels of genes involved in bacterial swimming motility (flaA, flaE, and cheR) were significantly down-regulated in NB10-GFP. As for the strain ME9 on the other hand, GFP incorporation only had a negative effect on swimming motility. However, both the strains NB10-GFP and ME9-GFP showed almost the same virulence as their respective parental strain towards mussel larvae in vivo. Overall, the data presented here demonstrated that incorporation of GFP may cause modifications in cell physiology and highlight the importance of preliminary physiological tests to minimize the negative influence of GFP tagging when it is used to monitor the target localization. The study also supports the idea that the virulence of Vibrio species is determined by complex regulatory networks. Notwithstanding the change of a single physiological trait, especially growth or swimming motility, the GFP-tagged Vibrio strain can thus still be considered usable in studies mainly focusing on the virulence of the strain. KEY POINTS: • The effect of GFP incorporation on physiological trait of Vibrio strains. • The virulence in vibrios could be multifactorial. • The stable virulence of Vibrio strains after GFP incorporation.

Swimming behavior of the multicellular magnetotactic prokaryote 'Candidatus Magnetoglobus multicellularis' near solid boundaries and natural magnetic grains

The magnetotactic yet uncultured species 'Candidatus Magnetoglobus multicellularis' is a spherical, multicellular ensemble of bacterial cells able to align along magnetic field lines while swimming propelled by flagella. Magnetotaxis is due to intracytoplasmic, membrane-bound magnetic crystals called magnetosomes. The net magnetic moment of magnetosomes interacts with local magnetic fields, imparting the whole microorganism a torque. Previous works investigated 'Ca. M. multicellularis' behavior when free swimming in water; however, they occur in sediments where bumping into solid particles must be routine. In this work, we investigate the swimming trajectories of 'Ca. M. multicellularis' close to solid boundaries using video microscopy. We applied magnetic fields 0.25-8.0 mT parallel to the optical axis of a light microscope, such that microorganisms were driven upwards towards a coverslip. Because their swimming trajectories approach cylindrical helixes, circular profiles would be expected. Nevertheless, at fields 0.25-1.1 mT, most trajectory projections were roughly sinusoidal, and net movements were approximately perpendicular to applied magnetic fields. Closed loops appeared in some trajectory projections at 1.1 mT, which could indicate a transition to the loopy profiles observed at magnetic fields ≥ 2.15 mT. The behavior of 'Ca. M. multicellularis' near natural magnetic grains showed that they were temporarily trapped by the particle's magnetic field but could reverse the direction of movement to flee away. Our results show that interactions of 'Ca. M. multicellularis with solid boundaries and magnetic grains are complex and possibly involve mechano-taxis.

Relationship of biofilm-forming ability of with swimming motility, twitching motility and virulence gene distribution

To investigate the relationship of biofilm-forming ability of (PA) with swimming motility, twitching motility and virulence gene distribution. A total of 192 clinical isolates of PA were collected consecutively. Microtiter plate method was used to evaluate the ability to form biofilm. The swimming and twitching motilities were detected by plate method. Polymerase chain reaction (PCR) was used to detect virulence genes. Of the 192 PA clinical isolates, 186 (96.9%) showed biofilm-forming ability. Among them, 36 isolates showed weak biofilm-forming ability, 84 exhibited moderate biofilm-forming ability and 66 showed strong biofilm-forming ability. The diameters of the swimming ring for PA with none biofilm-forming ability, weak biofilm-forming ability, moderate biofilm-forming ability, strong biofilm-forming ability were (9.12±6.76), (18.42±7.51), (19.10±4.77) and respectively. The diameters of the twitching ring for PA in above groups were (8.38±1.50), (17.21±7.42), (18.49±5.62) and respectively. The swimming motility and twitching motility of none biofilm-forming ability group were weaker than biofilm-forming ability groups (all <0.05). Among 192 PA strains, 163 were positive (84.9%), 40 were positive (20.8%), 183 were positive (95.3%), and 189 were positive (98.4%). The positive rate of PA virulence gene , and were different in strains with different biofilm-forming abilities (<0.05). The rate of in the strong biofilm-forming ability group was lower than that in the moderate biofilm-forming ability group (=9.293, <0.01) and the weak biofilm-forming ability group (=9.997, <0.01). The rate of in the strong biofilm-forming ability group was higher than that in the weak biofilm-forming ability group (=10.803, <0.01). Most clinical isolates of PA can form biofilm. Swimming and twitching motilities are related to the formation of biofilm, but not significantly related to strength of biofilm-forming ability. The virulence genes of type Ⅲ secretion system for PA may be related to the biofilm-forming ability.

CdgL is a degenerate nucleotide cyclase domain protein affecting flagellin synthesis and motility in Bacillus thuringiensis

In Bacillus subtilis, motility genes are expressed in a hierarchical pattern - governed by the σ^D transcription factor and other proteins such as the EpsE molecular clutch and SlrA/SlrR regulator proteins. In contrast, motile species in the Bacillus cereus group seem to express their motility genes in a non-hierarchical pattern, and less is known about their regulation, also given that no orthologs to σ^D, EpsE, SlrA or SlrR are found in B. cereus group genomes. Here we show that deletion of cdgL (BTB_RS26690/BTB_c54300) in Bacillus thuringiensis 407 (cry-) resulted in a six-to ten-fold downregulation of the entire motility locus, and loss of flagellar structures and swimming motility. cdgL is unique to the B. cereus group and is found in all phylogenetic clusters in the population except for group I, which comprises isolates of non-motile Bacillus pseudomycoides. Analysis of RNA-Seq data revealed cdgL to be expressed in a three-gene operon with a NupC like nucleoside transporter, and a putative glycosyl transferase for which transposon-based gene inactivation was previously shown to produce a similar phenotype to cdgL deletion. Interestingly, all three proteins were predicted to be membrane-bound and may provide a concerted function in the regulation of B. cereus group motility.

Identification of the genes controlling biofilm formation in the plant commensal Pseudomonas protegens Pf-5

Determinant genes controlling biofilm formation in a plant commensal bacterium, Pseudomonas protegens Pf-5, were identified by transposon mutagenesis. Comprehensive screening of 7500 transposon-inserted mutants led to the isolation of four mutants exhibiting decreased and five mutants exhibiting increased biofilm formation. Mutations in the genes encoding MFS drug resistance transporter, LapA adhesive protein, RetS sensor histidine kinase/response regulator, and HecA adhesin/hemagglutinin led to decreased biofilm formation, indicating that these genes are necessary for biofilm formation in Pf-5. The mutants exhibiting increased biofilm formation had transposon insertions in the genes coding for an outer membrane protein, a GGDEF domain-containing protein, AraC transcriptional regulator, non-ribosomal peptide synthetase OfaB, and the intergenic region of a DNA-binding protein and the Aer aerotaxis receptor, suggesting that these genes are negative regulators of biofilm formation. Some of these mutants also showed altered swimming and swarming motilities, and a negative correlation between biofilm formation and swarming motility was observed. Thus, sessile-motile lifestyle is regulated by divergent regulatory genes in Pf-5.

Evaluation of growth and motility in non-photosynthetic Azospirillum brasilense exposed to red, blue, and white light

Azospirillum brasilense is a non-photosynthetic rhizobacterium that promotes the growth of plants. In this work, we evaluated the effects of different light qualities on the growth, viability, and motility in combination to other culture conditions such as temperature or composition of the culture medium. Exponential cultures of A. brasilense Az39 were inoculated by drop-plate method on nutritionally rich (LB) or chemically defined (MMAB) media in the presence or absence of Congo Red indicator (CR) and exposed continuously to white light (WL), blue light (BL), and red light (RL), or maintained in dark conditions (control). The exposure to BL or WL inhibited growth, mostly in LB medium at 36 °C. By contrast, the exposure to RL showed a similar behavior to the control. Swimming motility was inhibited by exposure to WL and BL, while exposure to RL caused only a slight reduction. The effects of WL and BL on plant growth-promoting rhizobacteria should be considered in the future as deleterious factors that could be manipulated to improve the functionality of foliar inoculants, as well as the bacterial effects on the leaf after inoculation.

The cold shock family gene cspD3 is involved in the pathogenicity of Ralstonia solanacearum CQPS-1 to tobacco

Cold shock proteins (Csps) are small and highly conserved proteins that have target RNA- and DNA-binding activities. Csps play roles in different cellular processes and show functional redundancy. Ralstonia solanacearum, the agent of bacterial wilt, has 4 or 5 Csps based on genome analysis. However, the functions of all Csps in R. solanacearum remain unclear. According to phylogenetic analysis, the Csps from R. solanacearum are clustered into a group with CspD from E. coli. Here, we studied the role of CspD3, which was closer to CspD of E. coli in the phylogenetic tree. A cspD3 deletion strain was constructed to assess its effect on the phenotype of R. solanacearum, including growth, biofilm formation, motility, and virulence. The results showed that cspD3 of R. solanacearum was not necessary for normal growth, cold-shock adaptation, or biofilm formation. However, deletion of cspD3 in R. solanacearum CQPS-1 led to increased swimming motility, and the mean diameters of swimming haloes produced by the ΔcspD3 mutant were 1.3-fold larger than those produced by wild-type strain and 1.2-fold larger than those produced by the complemented strain. More importantly, the virulence of the cspD3 deletion mutant on susceptible tobacco plants was significantly attenuated compared to the wild-type strain. At 20 days after inoculation, the disease index of the ΔcspD3 mutant was 2.27, which was reduced by 1.6-fold relative to the wild-type strain. To assess the molecular response influenced by cspD3, the expressions of the main motility-associated genes and virulence-associated genes including flgM, fliA, pehS, pehR, hrpG, xpsR, and prhI in R. solanacearum were measured. The results showed that the expressions of hrpG, xpsR, and prhI were significantly decreased in cspD3 deletion mutant. Collectively, our findings showed that Csps are involved in the regulation of motility and virulence in R. solanacearum.

The effect of the sub-minimal inhibitory concentration and the concentrations within resistant mutation window of ciprofloxacin on MIC, swimming motility and biofilm formation of Pseudomonas aeruginosa

OBJECTIVE

To explore the effect of sub-minimal inhibitory concentration (sub-MIC) and concentrations within resistant mutation window (MSW) of ciprofloxacin (CIP) on minimal inhibitory concentration (MIC), swimming motility and biofilm formation of Pseudomonas aeruginosa, and also to investigate the correlation between swimming motility and genes expression of lasI, lasR, rhlI, rhlR and pqsR.

METHODS

The collected strains were incubated under four different concentrations for 5 days. The MIC and mutant prevention concentration (MPC) were measured by the agar dilution method. The diameter of turbid cycle was used to signify the swimming motility. The biofilm formation was measured by the crystal violet stain method. The genes expression of lasI, lasR, rhlI, rhlR and pqsR were measured by RT-PCR.

RESULTS

A total of 11 P. aeruginosa which sensitive to CIP were collected. The incubation within concentrations of MSW made MICs to CIP increased more obviously than under sub-MIC (P < 0.05). The swimming motility showed a trend of being inhibited first and then promoted over time under sub-MIC (P < 0.05), whereas, it was promoted under concentrations within MSW. The biofilm formation was significantly promoted under the concentration of 4×MIC (P < 0.05). Under sub-MIC, the genes expression of rhlR and pqsR had a middle level positive correlation with the promotion of the swimming motility (P < 0.05, r = 0.788 and P < 0.05, r = 0.652, respectively).

CONCLUSIONS

Under the concentration of sub-MIC (0.5×MIC) and the concentrations within MSW (1×MIC, 2×MIC and 4×MIC), the effect of CIP on MICs, swimming motility and biofilm formation of P.aeruginosa was quite different. The genes expression of rhlR and pqsR had a middle level positive correlation with the promotion of the swimming motility.

Inhibition of Staphylococcus aureus and Pseudomonas aeruginosa Biofilm and Virulence by Active Fraction of Syzygium cumini (L.) Skeels Leaf Extract: In-Vitro and In Silico Studies

Syzygium cumini L. Skeels (Myretacae family) is a native plant of the Indian subcontinent which has wide socio-economical importance and is well known for its ant diabetic activity. The present study aimed to investigate the antibiofilm activity of purified fraction (EA) from S. cumini leaf extract against P. aeruginosa and S. aureus. The EA did not show any effect on growth of P. aeruginosa and S. aureus at the concentration of 900 µg/ml. At this concentration EA showed biofilm inhibition up to 86 ± 1.19% (***P < 0.0001) and 86.40 ± 1.19% (***P < 0.0001) in P. aeruginosa and S. aureus respectively. SEM examination also confirmed the reduction in biofilm formation. Further EA also disrupted some virulence phenotypes in P. aeruginosa and S. aureus. Bioactive compounds detected by GC-MS showed their possible molecular interaction with RhlG/NADP active-site complex (PDB ID: 2B4Q), LasR-TP4 complex (PDB ID: 3JPU) and Pseudaminidase (PDB ID: 2W38) from P. aeruginosa. The in vitro biofilm inhibition, virulence factor inhibition and the mode of interaction of bioactive components in Syzygium cumini with QS proteins of bacteria reported in this study might be an affordable and effective alternative method of controlling quorum sensing/biofilm-associated infections.

Comparative genomics of Pseudomonas syringae pathovar tomato reveals novel chemotaxis pathways associated with motility and plant pathogenicity

The majority of bacterial foliar plant pathogens must invade the apoplast of host plants through points of ingress, such as stomata or wounds, to replicate to high population density and cause disease. How pathogens navigate plant surfaces to locate invasion sites remains poorly understood. Many bacteria use chemical-directed regulation of flagellar rotation, a process known as chemotaxis, to move towards favorable environmental conditions. Chemotactic sensing of the plant surface is a potential mechanism through which foliar plant pathogens home in on wounds or stomata, but chemotactic systems in foliar plant pathogens are not well characterized. Comparative genomics of the plant pathogen Pseudomonas syringae pathovar tomato (Pto) implicated annotated chemotaxis genes in the recent adaptations of one Pto lineage. We therefore characterized the chemosensory system of Pto. The Pto genome contains two primary chemotaxis gene clusters, che1 and che2. The che2 cluster is flanked by flagellar biosynthesis genes and similar to the canonical chemotaxis gene clusters of other bacteria based on sequence and synteny. Disruption of the primary phosphorelay kinase gene of the che2 cluster, cheA2, eliminated all swimming and surface motility at 21 °C but not 28 °C for Pto. The che1 cluster is located next to Type IV pili biosynthesis genes but disruption of cheA1 has no observable effect on twitching motility for Pto. Disruption of cheA2 also alters in planta fitness of the pathogen with strains lacking functional cheA2 being less fit in host plants but more fit in a non-host interaction.