The cellulose synthase BcsA plays a role in interactions of Salmonella typhimurium with Acanthamoeba castellanii genotype T4

Colony phase variation switch modulates antimicrobial tolerance and biofilm formation in Acinetobacter baumannii

Carbapenem-resistant Acinetobacter baumannii causes one of the most difficult-to-treat nosocomial infections. Polycationic drugs like polymyxin B or colistin and tetracycline drugs such as doxycycline or minocycline are commonly used to treat infections caused by carbapenem-resistant A. baumannii. Here, we show that a subpopulation of cells associated with the opaque/translucent colony phase variation by A. baumannii AB5075 displays differential tolerance to subinhibitory concentrations of colistin and tetracycline. Using a variety of microscopic techniques, we demonstrate that extracellular polysaccharide moieties mediate colistin tolerance to opaque A. baumannii at single-cell level and that mushroom-shaped biofilm structures protect opaque bacteria at the community level. The colony switch phenotype is found to alter several traits of A. baumannii, including long-term survival under desiccation, tolerance to ethanol, competition with Escherichia coli, and intracellular survival in the environmental model host Acanthamoeba castellanii. Additionally, our findings suggest that extracellular DNA associated with membrane vesicles can promote colony switching in a DNA recombinase-dependent manner.IMPORTANCEAs a WHO top-priority drug-resistant microbe, Acinetobacter baumannii significantly contributes to hospital-associated infections worldwide. One particularly intriguing aspect is its ability to reversibly switch its colony morphotype on agar plates, which has been remarkably underexplored. In this study, we employed various microscopic techniques and phenotypic assays to investigate the colony phase variation switch under different clinically and environmentally relevant conditions. Our findings reveal that the presence of a poly N-acetylglucosamine-positive extracellular matrix layer contributes to the protection of bacteria from the bactericidal effects of colistin. Furthermore, we provide intriguing insights into the multicellular lifestyle of A. baumannii, specifically in the context of colony switch variation within its predatory host, Acanthamoeba castellanii.

Deciphering Target Protein Cascade in Salmonella typhi Biofilm using Genomic Data Mining, and Protein-protein Interaction

Background

Salmonella typhi biofilm confers a serious public health issue for lengthy periods and the rise in antibiotic resistance and death rate. Biofilm generation has rendered even the most potent antibiotics ineffective in controlling the illness, and the S. typhi outbreak has turned into a fatal disease typhoid. S. typhi infection has also been connected to other deadly illnesses, such as a gall bladder cancer. The virulence of this disease is due to the interaction of numerous genes and proteins of S. typhi.

Objective

The study aimed to identify a cascade of target proteins in S. typhi biofilm condition with the help of genomic data mining and protein-protein interaction analysis.

Methods

The goal of this study was to notice some important pharmacological targets in S. typhi. using genomic data mining, and protein-protein interaction approaches were used so that new drugs could be developed to combat the disease.

Results

In this study, we identified 15 potential target proteins that are critical for S. typhi biofilm growth and maturation. Three proteins, CsgD, AdrA, and BcsA, were deciphered with their significant role in the synthesis of cellulose, a critical component of biofilm's extracellular matrix. The CsgD protein was also shown to have high interconnectedness and strong interactions with other important target proteins of S. typhi. As a result, it has been concluded that CsgD is involved in a range of activities, including cellulose synthesis, bacterial pathogenicity, quorum sensing, and bacterial virulence.

Conclusion

All identified targets in this study possess hydrophobic properties, and their cellular localization offered proof of a potent therapeutic target. Overall results of this study, drug target shortage in S. typhi is also spotlighted, and we believe that obtained result could be useful for the design and development of some potent anti-salmonella agents for typhoid fever in the future.

Two-component system ArcBA modulates cell motility and biofilm formation in Dickeya oryzae

Phytopathogen Dickeya oryzae is a causal agent of rice foot rot disease and the pathogen has an array of virulence factors, such as phytotoxin zeamines, plant cell wall degrading enzymes, cell motility, and biofilms, collectively contributing to the bacterial pathogenesis. In this study, through deletion analysis of predicted regulatory genes in D. oryzae EC1, we identified a two-component system associated with the regulation of bacterial virulence. The two-component system contains a histidine kinase ArcB and a response regulator ArcA, and deletion of their coding genes resulted in changed phenotypes in cell motility, biofilm formation, and bacterial virulence. Electrophoretic mobility shift assay revealed that ArcA bound to the promoters of the bcs operon and bssS, which respectively encode enzymes for the synthesis of celluloses and a biofilm formation regulatory protein. ArcA could also bind to the promoters of three virulence associated transcriptional regulatory genes, i.e., fis, slyA and ohrR. Surprisingly, although these three regulators were shown to modulate the production of cell wall degrading enzymes and zeamines, deletion of arcB and arcA did not seem to affect these phenotypes. Taken together, the findings from this study unveiled a new two-component system associated with the bacterial pathogenesis, which contributes to the virulence of D. oryzae mainly through its action on bacterial motility and biofilm formation.

Chlorine-stressed Salmonella cells are significantly more engulfed by Acanthamoeba trophozoites and have a longer intracystic survival than the non-stressed cells

In the present study, the effect of sublethal chlorine-induced oxidative stress on the subsequent interaction of Salmonella enterica serovars Enteritidis and Typhimurium with Acanthamoeba castellanii and A. polyphaga was evaluated. Sublethal chlorine concentration was determined using the lag phase extension information and used to prepare chlorine-stressed Salmonella cells. Coculture experiments of Acanthamoeba and Salmonella cells were performed in Page's amoeba saline (PAS) at 25 °C for 2 h. The results showed that the chlorine-stressed Salmonella cells were significantly more engulfed by A. castellanii and A. polyphaga trophozoites than the non-stressed cells. The uptake rates of the chlorine-stressed and non-stressed Salmonella cells were in the range of 14.17-27.34 and 6.51-11.52% for A. castellanii, and in the range of 8.32-17.76 and 2.28-6.12% for A. polyphaga trophozoites, respectively. Moreover, intracystic survival time of chlorine-stressed cells of S. Enteritidis and S. Typhimurium was significantly longer than that of non-stressed cells. While, non-stressed Salmonella cells survived within A. castellanii and A. polyphaga cysts for 13-20 and 8-15 days, chlorine-stressed cells were recovered from A. castellanii and A. polyphaga cysts after 22-32 and 15-24 days, respectively. These results underscore the importance of bacterial exposure to sublethal chlorine concentrations in their interaction with free-living amoebae, and may lead to a better understanding of the parameters affecting the persistence of Salmonella enterica serovars in food-related environments.

The role of Acanthamoeba spp. in biofilm communities: a systematic review

Acanthamoeba spp. have always caused disease in immunosuppressed patients, but since 1986, they have become a worldwide public health issue by causing infection in healthy contact lens wearers. Amoebae of the Acanthamoeba genus are broadly distributed in nature, living either freely or as parasites, and are frequently associated with biofilms throughout the environment. These biofilms provide the parasite with protection against external aggression, thus favoring its increased pathogeny. This review aims to assess observational studies on the association between Acanthamoeba spp. and biofilms, opening potential lines of research on this severe ocular infection. A systematic literature search was conducted in May 2020 in the following databases: PubMed Central^®/Medline, LILACS, The Cochrane Library, and EMBASE^®. The studies were selected following the inclusion and exclusion criteria specifically defined for this review. Electronic research recovered 353 publications in the literature. However, none of the studies met the inclusion criterion of biofilm-producing Acanthamoeba spp., inferring that the parasite does not produce biofilms. Nonetheless, 78 studies were classified as potentially included regarding any association of Acanthamoeba spp. and biofilms. These studies were allocated across six different locations (hospital, aquatic, ophthalmic and dental environments, biofilms produced by bacteria, and other places). Acanthamoeba species use biofilms produced by other microorganisms for their benefit, in addition to them providing protection to and facilitating the dissemination of pathogens residing in them.

Chryseobacterium indologenes and Chryseobacterium gleum interact and multiply intracellularly in Acanthamoeba castellanii

Chryseobacterium indologenes and Chryseobacterium gleum are Gram negative environmental bacteria that have been frequently reported to implicate in fatal nosocomial infections, such as bacteraemia and ventilator-associated pneumonia in immunocompromised individuals in the past decades. The interaction between Chryseobacterium spp. and Acanthamoeba castellanii, a free-living amoeba ubiquitous in the environment, has not been explored previously. In this study, C. indologenes and C. gleum were co-cultured with A. castellanii trophozoites and their interactions were evaluated. Our results showed that when co-cultured with A. castellanii, bacterial numbers of C. indologenes and C. gleum increased significantly (p < 0.05), indicating growth-supporting role of A. castellanii. Specifically, our findings showed that C. indologenes and C. gleum were able to associate, invade and/or taken up by A. castellani trophozoites, and multiply intracellularly at similar rates (p > 0.05). Interestingly, the two Chryseobacterium spp. associated, invaded and/or taken up by A. castellanii at significantly higher rates than Escherichia coli K1, a neuropathogenic bacterial strain known to interact and replicate intracellularly in A. castellanii (p < 0.05). However, the ability of both Chryseobacterium spp. to multiply in A. castellanii was significantly weaker than E. coli K1 (p < 0.001). This is the first time that Chryseobacterium spp. and A. castellanii were shown to interact with each other. The ability to survive intracellularly in A. castellanii may confer protection to C. indologenes and C. gleum and assist in the survival and transmission of Chryseobacterium spp. to susceptible hosts within a hospital setting. Future studies will determine the ability of C. indologenes and C. gleum survival in A. castellanii cysts and the possible molecular mechanisms involved in such interactions.

Type 1 Fimbriae and Motility Play a Pivotal Role During Interactions of Salmonella typhimurium with Acanthamoeba castellanii (T4 Genotype)

Amoebic bacterial interactions are the most ancient form of host pathogen interactions. Here, we investigate the fate of Salmonella typhimurium and Acanthamoeba castellanii T4 genotype upon mutual interactions in a nutrition free environment. The role of type 1 fimbriae and motility of S. typhimurium during interactions with A. castellanii has also been investigated. Deletion of genes encoding the type 1 fimbriae subunit FimA, type 1 fimbriae tip protein FimH, chemotaxis regulatory proteins CheA and CheY and major flagella subunits FliC and FljB was performed through homologous recombination. In vitro association, invasion and survival assays of S. typhimurium wild-type and mutant strains were performed upon co-incubation of bacteria with A. castellanii trophozoites in a nutrition free environment. The deletion gene encoding type 1 fimbriae subunit FimA reduced, whereas the deletion of genes encoding flagella subunits FliC and FljB of flagella enhanced the association capability of S. typhimurium with A. castellanii. Invasion of A. castellanii by Salmonella was significantly reduced upon the loss of type 1 fimbriae subunit FimA and type 1 fimbriae tip protein FimH. Co-incubation of S. typhimurium with A. castellanii in phosphate buffered saline medium stimulated the growth of S. typhimurium wild-type and mutant strains. Viable A. castellanii trophozoites count became significantly reduced upon co-incubation with S. typhimurium within 48 h. Type 1 fimbriae play a pivotal role in the adherence of S. typhimurium to the A. castellanii cell surface. Subsequently, this interaction provides S. typhimurium an advantage in growth.