Molecules involved in motility regulation in Escherichia coli cells: a review

Prevalence, Antimicrobial Susceptibility, and Resistance Genes of Extended-Spectrum β-Lactamase-Producing Escherichia coli from Broilers Sold in Open Markets of Dakar, Senegal

Extended-spectrum β-lactamase-producing Escherichia coli (ESBL-Ec) poses a significant public health concern due to its widespread prevalence and resistance to multiple antibiotics. This study aimed to assess the prevalence, resistance profile, and carriage of ESBL-encoding genes in ESBL-Ec isolates from broilers in two markets of Dakar, Senegal. Sampling over a one-year period revealed that 61.7% of broilers carried ESBL-Ec in their cecum. Antibiotic susceptibility testing of 186 ESBL-Ec isolates showed high resistance to β-lactam antibiotics, including ampicillin, ticarcillin, and third-generation cephalosporins. Notably, all isolates were susceptible to imipenem. Multidrug resistance was frequent, with 91.4% of the isolates displaying this phenotype. Comparison between the two markets revealed variations in resistance to quinolones. PCR analysis detected blaCTX-M genes in all isolates, with blaCTX-M-1 being the most prevalent subgroup. Additionally, blaTEM and blaOXA genes were found in 26.3% and 2.7% of isolates, respectively, while no blaSHV genes were detected. Combinations of ESBL genes were common, with blaCTX-M15-blaTEM being the most frequent. These findings highlight the widespread prevalence of ESBL-Ec in broilers from Dakar markets, indicating a potential risk of transmission to humans through the food chain. Effective surveillance and intervention strategies are crucial to mitigate the spread of antimicrobial resistance in humans and animals.

Conditional expression of flagellar motility, curli fimbriae, and biofilms in Shiga toxin- producing Escherichia albertii

Escherichia albertii is an emerging foodborne pathogen. We previously reported that some avian Shiga toxin-producing E. albertii strains exhibited higher or comparable cytotoxicity in Vero-d2EGFP cells with several enterohemorrhagic E. coli (EHEC) outbreak strains. To better understand the environmental persistence of this pathogen, comparative genomics and phenotypic assays were applied to assess adhesion capability, motility, and biofilm formation in E. albertii. Among the 108 adherence-related genes, those involved in biogenesis of curli fimbriae, hemorrhagic E. coli pilus, type 1 fimbriae, and Sfm fimbriae were conserved in E. albertii. All 20 E. albertii strains carried a complete set of primary flagellar genes that were organized into four gene clusters, while five strains possessed genes related to the secondary flagella, also known as lateral flagella. Compared to EHEC strain EDL933, the eight chemotaxis genes located within the primary flagellar gene clusters were deleted in E. albertii. Additional deletion of motility genes flhABCD and motBC was identified in several E. albertii strains. Swimming motility was detected in three strains when grown in LB medium, however, when grown in 5% TSB or in the pond water-supplemented with 10% pigeon droppings, an additional four strains became motile. Although all E. albertii strains carried curli genes, curli fimbriae were detected only in four, eight, and nine strains following 24, 48, and 120 h incubation, respectively. Type 1 fimbriae were undetectable in any of the strains grown at 37°C or 28°C. Strong biofilms were detected in strains that produced curli fimbriae and in a chicken isolate that was curli fimbriae negative but carried genes encoding adhesive fimbriae K88, a signature of enterotoxigenic E. coli strains causing neonatal diarrhea in piglets. In all phenotypic traits examined, no correlation was revealed between the strains isolated from different sources, or between the strains with and without Shiga toxin genes. The phenotypic variations could not be explained solely by the genetic diversity or the difference in adherence genes repertoire, implying complex regulation in expression of various adhesins. Strains that exhibited a high level of cytotoxicity and were also proficient in biofilm production, may have potential to emerge into high-risk pathogens.

Tannic acid inhibits Escherichia coli biofilm formation and underlying molecular mechanisms: Biofilm regulator CsgD

Biofilms often engender persistent infections, heightened antibiotic resistance, and the recurrence of infections. Therefor, infections related to bacterial biofilms are often chronic and pose challenges in terms of treatment. The main transcription regulatory factor, CsgD, activates csgABC-encoded curli to participate in the composition of extracellular matrix, which is an important skeleton for biofilm development in enterobacteriaceae. In our previous study, a wide range of natural bioactive compounds that exhibit strong affinity to CsgD were screened and identified via molecular docking. Tannic acid (TA) was subsequently chosen, based on its potent biofilm inhibition effect as observed in crystal violet staining. Therefore, the aim of this study was to investigate the specific effects of TA on the biofilm formation of clinically isolated Escherichia coli (E. coli). Results demonstrated a significant inhibition of E. coli Ec032 biofilm formation by TA, while not substantially affecting the biofilm of the ΔcsgD strain. Moreover, deletion of the csgD gene led to a reduction in Ec032 biofilm formation, alongside diminished bacterial motility and curli synthesis inhibition. Transcriptomic analysis and RT-qPCR revealed that TA repressed genes associated with the csg operon and other biofilm-related genes. In conclusion, our results suggest that CsgD is one of the key targets for TA to inhibit E. coli biofilm formation. This work preliminarily elucidates the molecular mechanisms of TA inhibiting E. coli biofilm formation, which could provide a lead structure for the development of future antibiofilm drugs.

Correlation between antimicrobial resistance, biofilm formation, and virulence determinants in uropathogenic Escherichia coli from Egyptian hospital

BACKGROUND

Uropathogenic Escherichia coli (UPEC) is the main etiological agent behind community-acquired and hospital-acquired urinary tract infections (UTIs), which are among the most prevalent human infections. The management of UPEC infections is becoming increasingly difficult owing to multi-drug resistance, biofilm formation, and the possession of an extensive virulence arsenal. This study aims to characterize UPEC isolates in Tanta, Egypt, with regard to their antimicrobial resistance, phylogenetic profile, biofilm formation, and virulence, as well as the potential associations among these factors.

METHODS

One hundred UPEC isolates were obtained from UTI patients in Tanta, Egypt. Antimicrobial susceptibility was assessed using the Kirby-Bauer method. Extended-spectrum β-lactamases (ESBLs) production was screened using the double disk synergy test and confirmed with PCR. Biofilm formation was evaluated using the microtiter-plate assay and microscopy-based techniques. The phylogenetic groups of the isolates were determined. The hemolytic activity, motility, siderophore production, and serum resistance of the isolates were also evaluated. The clonal relatedness of the isolates was assessed using ERIC-PCR.

RESULTS

Isolates displayed elevated resistance to cephalosporins (90-43%), sulfamethoxazole-trimethoprim (63%), and ciprofloxacin (53%). Ninety percent of the isolates were multidrug-resistant (MDR)/ extensively drug-resistant (XDR) and 67% produced ESBLs. Notably, there was an inverse correlation between biofilm formation and antimicrobial resistance, and 31%, 29%, 32%, and 8% of the isolates were strong, moderate, weak, and non-biofilm producers, respectively. Beta-hemolysis, motility, siderophore production, and serum resistance were detected in 64%, 84%, 65%, and 11% of the isolates, respectively. Siderophore production was correlated to resistance to multiple antibiotics, while hemolysis was more prevalent in susceptible isolates and associated with stronger biofilms. Phylogroups B2 and D predominated, with lower resistance and stronger biofilms in group B2. ERIC-PCR revealed considerable diversity among the isolates.

CONCLUSION

This research highlights the dissemination of resistance in UPEC in Tanta, Egypt. The evident correlation between biofilm and resistance suggests a resistance cost on bacterial cells; and that isolates with lower resistance may rely on biofilms to enhance their survival. This emphasizes the importance of considering biofilm formation ability during the treatment of UPEC infections to avoid therapeutic failure and/or infection recurrence.

Flagella-mediated adhesion of Escherichia coli O157:H7 to surface of stainless steel, glass and fresh produces during sublethal injury and recovery

E. coli O157:H7 can be induced into sublethally injured (SI) state by lactic acid (LA) and regain activity in nutrient environments. This research clarified the role of flagella-related genes (fliD, fliS, cheA and motA) in adhesion of E. coli O157:H7 onto stainless steel, glass, lettuce, spinach, red cabbage and cucumber during LA-induced SI and recovery by plate counting. Results of adhesion showed improper flagellar rotation caused by the deletion of motA resulting in the decreased adhesion. Motility of wildtype determined by diameter of motility halo decreased in SI state and repaired with recovery time increasing, lagging behind changes in expression of flagella-related genes. Flagellar function-impaired strains all exhibited non-motile property. Thus, we speculated that flagella-mediated motility is critical in early stage of adhesion. We also found the effects of Fe2+, Ca2+ and Mn2+ on adhesion or motility of wildtype was independent of bacterial states. However, the addition of Ca2+ and Mn2+ did not affect motility of flagellar function-impaired strains as they did on wildtype. This research provides new insights to understand the role of flagella and cations in bacterial adhesion, which will aid in development of anti-adhesion agents to reduce bio-contamination in food processing.

Regulation of major bacterial survival strategies by transcripts sequestration in a membraneless organelle

TmaR, the only known pole-localizer protein in Escherichia coli, was shown to cluster at the cell poles and control localization and activity of the major sugar regulator in a tyrosine phosphorylation-dependent manner. Here, we show that TmaR assembles by phase separation (PS) via heterotypic interactions with RNA in vivo and in vitro. An unbiased automated mutant screen combined with directed mutagenesis and genetic manipulations uncovered the importance of a predicted nucleic-acid-binding domain, a disordered region, and charged patches, one containing the phosphorylated tyrosine, for TmaR condensation. We demonstrate that, by protecting flagella-related transcripts, TmaR controls flagella production and, thus, cell motility and biofilm formation. These results connect PS in bacteria to survival and provide an explanation for the linkage between metabolism and motility. Intriguingly, a point mutation or increase in its cellular concentration induces irreversible liquid-to-solid transition of TmaR, similar to human disease-causing proteins, which affects cell morphology and division.

Interplay between bacterial 5'-NAD-RNA decapping hydrolase NudC and DEAD-box RNA helicase CsdA in stress responses

IMPORTANCE

Non-canonical 5'-caps removing RNA hydrolase NudC, along with stress-responsive RNA helicase CsdA, is crucial for 5'-NAD-RNA decapping and bacterial movement.

Response mechanisms to acid stress promote LF82 replication in macrophages

Background

Adherent-invasive E. coli (AIEC) LF82 is capable of adhering to and invading intestinal epithelial cells, as well as replicating within macrophages without inducing host cell death.

Methods

We compared the transcriptomics of LF82 at pH=7.5 and pH=5.8 by RNA-sequencing, and qRT-PCR verified differentially expressed genes (DEGs). The deletion mutants of DEGs in the treatment group (pH=5.8) compared to the control group (pH=7.5) were constructed by λ recombinant. The replication differences between the mutants and WT infected Raw 264.7 at 24 h.p.i were analyzed by combining LB solid plate count and confocal observation. NH4Cl and chloroquine diphosphate (CQ) were used for acid neutralization to study the effect of pH on the replication of LF82 in macrophages. Na2NO3 was added to RPMI 1640 to study the effect of nitrate on the replication of LF82 in macrophages. 0.3% solid LB was used for flagellar motility assay and Hela was used to study flagellar gene deletion mutants and WT adhesion and invasion ability.

Results

In this study, we found that infection with LF82 results in acidification of macrophages. Subsequent experiments demonstrated that an intracellular acidic environment is necessary for LF82 replication. Transcriptome and phenotypic analysis showed that high expression of acid shock genes and acid fitness genes promotes LF82 replication in macrophages. Further, we found that the replication of LF82 in macrophages was increased under nitrate treatment, and nitrogen metabolism genes of LF82 were upregulated in acid treatment. The replication in macrophages of ΔnarK, ΔnarXL, ΔnarP, and Δhmp were decreased. In addition, we found that the expression of flagellar genes was downregulated in acidic pH and after LF82 invading macrophages. Motility assay shows that the movement of LF82 on an acidic semisolid agar plate was limited. Further results showed that ΔfliC and ΔfliD decreased in motility, adhesion ability, and invasion of host cells, but no significant effect on replication in macrophages was observed.

Conclusion

In this study, we simulated the acidic environment in macrophages, combined with transcriptome technology, and explained from the genetic level that LF82 promotes replication by activating its acid shock and fitness system, enhancing nitrate utilization, and inhibiting flagellar function.

Bacterial envelope stress responses: Essential adaptors and attractive targets

Millions of deaths a year across the globe are linked to antimicrobial resistant infections. The need to develop new treatments and repurpose of existing antibiotics grows more pressing as the growing antimicrobial resistance pandemic advances. In this review article, we propose that envelope stress responses, the signaling pathways bacteria use to recognize and adapt to damage to the most vulnerable outer compartments of the microbial cell, are attractive targets. Envelope stress responses (ESRs) support colonization and infection by responding to a plethora of toxic envelope stresses encountered throughout the body; they have been co-opted into virulence networks where they work like global positioning systems to coordinate adhesion, invasion, microbial warfare, and biofilm formation. We highlight progress in the development of therapeutic strategies that target ESR signaling proteins and adaptive networks and posit that further characterization of the molecular mechanisms governing these essential niche adaptation machineries will be important for sparking new therapeutic approaches aimed at short-circuiting bacterial adaptation.

Regulation of flagellar motility and biosynthesis in enterohemorrhagic Escherichia coli O157:H7

ABSTARCTEnterohemorrhagic Escherichia coli (EHEC) O157:H7 is a human pathogen that causes a variety of diseases, such as hemorrhagic colitis and lethal hemolytic uremic syndrome. Flagellum-dependent motility plays diverse roles in the pathogenesis of EHEC O157:H7, including its migration to an optimal host site, adherence and colonization, survival at the infection site, and post-infection dispersal. However, it is very expensive for cellular economy in terms of the number of genes and the energy required for flagellar biosynthesis and functioning. Furthermore, the flagellar filament bears strong antigenic properties that induce a strong host immune response. Consequently, the flagellar gene expression and biosynthesis are highly regulated to occur at the appropriate time and place by different regulatory influences. The present review focuses on the regulatory mechanisms of EHEC O157:H7 motility and flagellar biosynthesis, especially in terms of flagellar gene regulation by environmental factors, regulatory proteins, and small regulatory RNAs.

Advances and prospects in metabolic engineering of Escherichia coli for L-tryptophan production

As an important raw material for pharmaceutical, food and feed industry, highly efficient production of L-tryptophan by Escherichia coli has attracted a considerable attention. However, there are complicated and multiple layers of regulation networks in L-tryptophan biosynthetic pathway and thus have difficulty to rewrite the biosynthetic pathway for producing L-tryptophan with high efficiency in E. coli. This review summarizes the biosynthetic pathway of L-tryptophan and highlights the main regulatory mechanisms in E. coli. In addition, we discussed the latest metabolic engineering strategies achieved in E. coli to reconstruct the L-tryptophan biosynthetic pathway. Moreover, we also review a few strategies that can be used in E. coli to improve robustness and streamline of L-tryptophan high-producing strains. Lastly, we also propose the potential strategies to further increase L-tryptophan production by systematic metabolic engineering and synthetic biology techniques.

Prevalence of lipase producer Aspergillus niger in nuts and anti-biofilm efficacy of its crude lipase against some human pathogenic bacteria

Nuts are the natural source of healthy lipids, proteins, and omega-3. They are susceptible to fungal and mycotoxins contamination because of their high nutritional value. Twenty-five species comprising 12 genera were isolated from 80 samples of dried fruits and nuts using the dilution plate method. Peanut recorded the highest level of contamination followed by coconut; almond and raisin were the lowest. Aspergillus was the most prevalent genus and A.niger, was the most dominant species. The morphological identification of the selected A.niger isolates as they were detected in high frequency of occurrence was confirmed by using 18SrRNA sequence. Ochratoxin biosynthesis gene Aopks was detected in the tested isolates. Lipase production by the selected A.niger isolates was determined with enzyme activity index (EAI) ranging from 2.02 to 3.28. A.niger-26 was the highest lipase producer with enzyme activity of 0.6 ± 0.1 U/ml by the trimetric method. Lip2 gene was also detected in the tested isolates. Finally, the antibacterial and antibiofilm efficiency of crude lipase against some human pathogens was monitored. Results exhibited great antibacterial efficacy with minimum bactericidal concentration (MBC) of 20 to 40 µl/100 µl against Escherichiacoli, Pseudomonasaeruginosa, Proteusmirabilis, and Methicillin-resistant Staphylococcusaureus (MRSA). Interestingly, significant anti-biofilm efficacy with inhibition percentages of 95.3, 74.9, 77.1 and 93.6% was observed against the tested pathogens, respectively.