Differential expression of nonagglutinating fimbriae and MR/P pili in swarming colonies of Proteus mirabilis

Structure and Assembly of the Proteus mirabilis Flagellar Motor by Cryo-Electron Tomography

Proteus mirabilis is a Gram-negative Gammaproteobacterium and a major causative agent of urinary tract infections in humans. It is characterized by its ability to switch between swimming motility in liquid media and swarming on solid surfaces. Here, we used cryo-electron tomography and subtomogram averaging to reveal the structure of the flagellar motor of P. mirabilis at nanometer resolution in intact cells. We found that P. mirabilis has a motor that is structurally similar to those of Escherichia coli and Salmonella enterica, lacking the periplasmic elaborations that characterize other more specialized gammaproteobacterial motors. In addition, no density corresponding to stators was present in the subtomogram average suggesting that the stators are dynamic. Finally, several assembly intermediates of the motor were seen that support the inside-out assembly pathway.

A light-guiding urinary catheter for the inhibition of Proteus mirabilis biofilm formation

Catheter-associated urinary tract infection (CAUTI) is a leading cause of hospital-acquired infections worldwide causing debilitating illness for patients as well as a significant financial and treatment burden on health services. CAUTI is linked with the build-up of biofilms on catheter surfaces which act as a reservoir for infection. Additionally, urease-producing bacteria such as Gram-negative Proteus mirabilis (PM), can form crystalline biofilms which encrust catheter surfaces ultimately leading to blockages which require immediate removal of the catheter. Currently there are limited treatments available to prevent the formation of biofilms by PM as well as other urinary tract infection causing bacteria. A novel concept for a light-guiding urinary catheter is presented where a silicone elastomer waveguide incorporated along the length of the catheter is used to irradiate the catheter surfaces with antimicrobial blue light (405 nm) to prevent biofilm formation in situ. The prototype device is mass producible while also easy to fabricate in a lab setting for research studies. The inhibitory effect of blue light on PM biofilm formation over a range of irradiances is described for the first time showing an LD90 at 192–345 J/cm2 and total inhibition at 1,700 J/cm2In vitro studies show that the light-guiding catheter (LGC) prototypes exhibit a 98% inhibition in PM biofilm formation inside the catheter lumen at an average estimated irradiance of 30–50 mW/cm2 (324–540 J/cm2 fluence) showing that the concept is highly effective, promising to be a powerful and economical antimicrobial approach to prevent catheter associated biofilm development and blockage.

Pathogenesis of Proteus mirabilis in Catheter-Associated Urinary Tract Infections

Proteus mirabilis (PM) is a Gram-negative rod-shaped bacterium and widely exists in the natural environment, and it is most noted for its swarming motility and urease activity. PM is the main pathogen causing complicated urinary tract infections (UTIs), especially catheter-associated urinary tract infections. Clinically, PM can form a crystalline biofilm on the outer surface and inner cavity of the urethral indwelling catheter owing to its ureolytic biomineralization. This leads to catheter encrustation and blockage and, in most cases, is accompanied by urine retention and ascending UTI, causing cystitis, pyelonephritis, and the development of bladder or kidney stones, or even fatal complications such as septicemia and endotoxic shock. In this review, we discuss how PM is mediated by a catheter into the urethra, bladder, and then rose to the kidney causing UTI and the main virulence factors associated with different stages of infection, including flagella, pili or adhesins, urease, hemolysin, metal intake, and immune escape, encompassing both historical perspectives and current advances.

Proteus spp. as Putative Gastrointestinal Pathogens

Proteus species, members of the Enterobacteriaceae family, are usually considered commensals in the gut and are most commonly recognized clinically as a cause of urinary tract infections. However, the recent identification of Proteus spp. as potential pathogens in Crohn's disease recurrence after intestinal resection serves as a stimulus to examine their potential role as gut pathogens. Proteus species possess many virulence factors potentially relevant to gastrointestinal pathogenicity, including motility; adherence; the production of urease, hemolysins, and IgA proteases; and the ability to acquire antibiotic resistance. Gastrointestinal conditions that have been linked to Proteus include gastroenteritis (spontaneous and foodborne), nosocomial infections, appendicitis, colonization of devices such as nasogastric tubes, and Crohn's disease. The association of Proteus species with Crohn's disease was particularly strong. Proteus species are low-abundance commensals of the human gut that harbor significant pathogenic potential; further investigation is needed.

Observation of multicellular spinning behavior of Proteus mirabilis by atomic force microscopy and multifunctional microscopy

This study aimed to observe the multicellular spinning behavior of Proteus mirabilis by atomic force microscopy (AFM) and multifunctional microscopy in order to understand the mechanism underlying this spinning movement and its biological significance. Multifunctional microscopy with charge-coupled device (CCD) and real-time AFM showed changes in cell structure and shape of P. mirabilis during multicellular spinning movement. Specifically, the morphological characteristics of P. mirabilis, multicellular spinning dynamics, and unique movement were observed. Our findings indicate that the multicellular spinning behavior of P. mirabilis may be used to collect nutrients, perform colonization, and squeeze out competitors. The movement characteristics of P. mirabilis are vital to the organism's biological adaptability to the surrounding environment.

Merging mythology and morphology: the multifaceted lifestyle of Proteus mirabilis

Proteus mirabilis, named for the Greek god who changed shape to avoid capture, has fascinated microbiologists for more than a century with its unique swarming differentiation, Dienes line formation and potent urease activity. Transcriptome profiling during both host infection and swarming motility, coupled with the availability of the complete genome sequence for P. mirabilis, has revealed the occurrence of interbacterial competition and killing through a type VI secretion system, and the reciprocal regulation of adhesion and motility, as well as the intimate connections between metabolism, swarming and virulence. This Review addresses some of the unique and recently described aspects of P. mirabilis biology and pathogenesis, and emphasizes the potential role of this bacterium in single-species and polymicrobial urinary tract infections.

Repression of motility during fimbrial expression: identification of 14 mrpJ gene paralogues in Proteus mirabilis

Proteus mirabilis alternates between motile and adherent forms. MrpJ, a transcriptional regulator previously reported to repress motility, is encoded at the 3' end of the mrp fimbrial operon in P. mirabilis. Sequencing of the P. mirabilis genome revealed 14 additional paralogues of mrpJ, 10 of which are associated with fimbrial operons. Twelve of these genes, when overexpressed, repressed motility; several distinct patterns of swarming motility were noted. Expression of 10 of the 14 mrpJ paralogues repressed flagellin (FlaA) synthesis. Alignment of the predicted amino acid sequences of MrpJ and its 14 paralogues revealed a conserved consensus motif (SQQQFSRYE) within the helix-turn-helix domain. Site-directed mutagenesis of these residues coupled with linker insertion mutagenesis of MrpJ confirmed the importance of this domain for repression of motility. Gel shift assays demonstrated that MrpJ and another paralogue UcaJ bind directly to the promoter region of the flagellar master regulator flhDC. Thus, P. mirabilis appears to use a related mechanism to inhibit motility during the production of at least 10 of its predicted fimbriae.

Complete genome sequence of uropathogenic Proteus mirabilis, a master of both adherence and motility

The gram-negative enteric bacterium Proteus mirabilis is a frequent cause of urinary tract infections in individuals with long-term indwelling catheters or with complicated urinary tracts (e.g., due to spinal cord injury or anatomic abnormality). P. mirabilis bacteriuria may lead to acute pyelonephritis, fever, and bacteremia. Most notoriously, this pathogen uses urease to catalyze the formation of kidney and bladder stones or to encrust or obstruct indwelling urinary catheters. Here we report the complete genome sequence of P. mirabilis HI4320, a representative strain cultured in our laboratory from the urine of a nursing home patient with a long-term (> or =30 days) indwelling urinary catheter. The genome is 4.063 Mb long and has a G+C content of 38.88%. There is a single plasmid consisting of 36,289 nucleotides. Annotation of the genome identified 3,685 coding sequences and seven rRNA loci. Analysis of the sequence confirmed the presence of previously identified virulence determinants, as well as a contiguous 54-kb flagellar regulon and 17 types of fimbriae. Genes encoding a potential type III secretion system were identified on a low-G+C-content genomic island containing 24 intact genes that appear to encode all components necessary to assemble a type III secretion system needle complex. In addition, the P. mirabilis HI4320 genome possesses four tandem copies of the zapE metalloprotease gene, genes encoding six putative autotransporters, an extension of the atf fimbrial operon to six genes, including an mrpJ homolog, and genes encoding at least five iron uptake mechanisms, two potential type IV secretion systems, and 16 two-component regulators.

Genome-wide screening of genes required for swarming motility in Escherichia coli K-12

Escherichia coli K-12 has the ability to migrate on semisolid media by means of swarming motility. A systematic and comprehensive collection of gene-disrupted E. coli K-12 mutants (the Keio collection) was used to identify the genes involved in the swarming motility of this bacterium. Of the 3,985 nonessential gene mutants, 294 were found to exhibit a strongly repressed-swarming phenotype. Further, 216 of the 294 mutants displayed no significant defects in swimming motility; therefore, the 216 genes were considered to be specifically associated with the swarming phenotype. The swarming-associated genes were classified into various functional categories, indicating that swarming is a specialized form of motility that requires a wide variety of cellular activities. These genes include genes for tricarboxylic acid cycle and glucose metabolism, iron acquisition, chaperones and protein-folding catalysts, signal transduction, and biosynthesis of cell surface components, such as lipopolysaccharide, the enterobacterial common antigen, and type 1 fimbriae. Lipopolysaccharide and the enterobacterial common antigen may be important surface-acting components that contribute to the reduction of surface tension, thereby facilitating the swarm migration in the E. coli K-12 strain.

In vivo expression of the mannose-resistant fimbriae of Photorhabdus temperata K122 during insect infection

Photorhabdus temperata K122 is an entomopathogenic bacterium symbiotically associated with nematodes of the family Heterorhabditidae: Surface fimbriae are important for the colonization of many pathogenic bacteria, and here we report the nucleotide sequence and analysis of the expression of a 12-kbp fragment encoding the mannose-resistant fimbriae of P. temperata (mrf). The mrf gene cluster contains 11 genes with an organization similar to that of the mrp locus from Proteus mirabilis. mrfI (encoding a putative recombinase) and mrfA (encoding pilin), the first gene in an apparent operon of nine other genes, are expressed from divergent promoters. The mrfI-mrfA intergenic region contains inverted repeats flanking the mrfA promoter. This region was shown to be capable of inversion, consistent with an ON/OFF regulation of the operon. In in vitro liquid cultures, both orientations were detected. Nevertheless, when we analyzed the expression of all of the genes in the mrf locus by semiquantitative reverse transcription-PCR during infection of Galleria mellonella (greater wax moth) larvae, expression of mrfA was not detected until 25 h postinfection, preceding the death of the larvae at 32 h. In contrast, mrfJ (a putative inhibitor of flagellar synthesis) was expressed throughout infection. Expression of mrfI was also detected only late in infection (25 to 30 h), indicating a possible increase in inversion frequency at this stage. In both in vitro liquid cultures and in vivo larval infections, the distal genes of the operon were expressed at substantially lower levels than mrfA. These results indicate the complex regulation of the mrf cluster during infection.

Swarming motility

Swarming involves differentiation of vegetative cells into hyperflagellated swarm cells that undergo rapid and coordinated population migration across solid surfaces. Cell density, surface contact, and physiological signals all provide critical stimuli, and close cell alignment and the production of secreted migration factors facilitate mass translocation. Flagella biogenesis is central to swarming, and the flhDC flagellar master operon is the focal point of a regulatory network governing differentiation and migration.

Sliding motility in mycobacteria

Mycobacteria are nonflagellated gram-positive microorganisms. Previously thought to be nonmotile, we show here that Mycobacterium smegmatis can spread on the surface of growth medium by a sliding mechanism. M. smegmatis spreads as a monolayer of cells which are arranged in pseudofilaments by close cell-to-cell contacts, predominantly along their longitudinal axis. The monolayer moves away from the inoculation point as a unit with only minor rearrangements. No extracellular structures such as pili or fimbriae appear to be involved in this process. The ability to translocate over the surface correlates with the presence of glycopeptidolipids, a mycobacterium-specific class of amphiphilic molecules located in the outermost layer of the cell envelope. We present evidence that surface motility is not restricted to M. smegmatis but is also a property of the slow-growing opportunistic pathogen M. avium. This form of motility could play an important role in surface colonization by mycobacteria in the environment as well as in the host.