Identification of Type 3 Fimbriae in UropathogenicEscherichia coliReveals a Role in Biofilm Formation

Abstract

Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the UnitedStates. Uropathogenic Escherichia coli (UPEC), the most common cause of CAUTI, can form biofilms on indwelling catheters. Here, we identify and characterize novel factors that affect biofilm formation by UPEC strains that cause CAUTI. Sixty-five CAUTI UPEC isolates were characterized for phenotypic markers of urovirulence, including agglutination and biofilm formation. One isolate, E. coli MS2027, was uniquely proficient at biofilm growth despite the absence of adhesins known to promote this phenotype. Mini-Tn5 mutagenesis of E. coli MS2027 identified several mutants with altered biofilm growth. Mutants containing insertions in genes involved in O antigen synthesis (rmlC and manB) and capsule synthesis (kpsM) possessed enhanced biofilm phenotypes. Three independent mutants deficient in biofilm growth contained an insertion in a gene locus homologous to the type 3 chaperone-usher class fimbrial genes of Klebsiella pneumoniae. These type 3 fimbrial genes (mrkABCDF), which were located on a conjugative plasmid, were cloned from E. coli MS2027 and could complement the biofilm-deficient transconjugants when reintroduced on a plasmid. Primers targeting the mrkB chaperone-encoding gene revealed its presence in CAUTI strains of Citrobacter koseri, Citrobacter freundii, Klebsiella pneumoniae, and Klebsiella oxytoca. All of these mrkB-positive strains caused type 3 fimbria-specific agglutination of tannic acid-treated red blood cells. This is the first description of type 3 fimbriae in E. coli, C. koseri, and C. freundii. Our data suggest that type 3 fimbriae may contribute to biofilm formation by different gram-negative nosocomial pathogens.Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States, where it accounts for approximately 40% of all nosocomial infections (49). Although CAUTI is usually asymptomatic, it is a frequent cause of bacteremia and infected patients can also experience fever, acute pyelonephritis, and death (59). The risk of bacteriuria following urethral catheterization is estimated to be 5 to 10% per day (60). Most patients with indwelling urinary catheters for 30 days or longer develop bacteriuria (49).Nosocomial CAUTI is caused by a range of gram-negative and gram-positive organisms, including Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Providencia stuartii, Staphylococcus epidermidis, and Enterococcus faecalis (60). These infections are often polymicrobial and can last from several days to months (29). E. coli is one of the most common organisms isolated from the urine of CAUTI patients. Like uropathogenic E. coli (UPEC) strains that cause cystitis and pyelonephritis, CAUTI E. coli strains possess a range of virulence factors, including adhesins (e.g., P and type 1 fimbriae) and toxins (e.g., hemolysin), and express certain O antigen and capsule (K) types (29). Adherence is important for the colonization of the urinary tra...

Identification of a Conserved Chromosomal Region Encoding Klebsiella pneumoniae Type 1 and Type 3 Fimbriae and Assessment of the Role of Fimbriae in Pathogenicity

“…Furthermore, type 3 fimbriae have been established to play a significant role in K. pneumoniae biofilm formation (9,20,27). Historically, type 3 fimbriae have not been associated with E. coli; however, most recently two independent studies have reported type 3 fimbria expression in E. coli strains (3,36). Intriguingly, in both studies type 3 fimbriae were encoded by conjugative plasmids and found to profoundly enhance the ability of E. coli to form biofilm.…”

Surface Polysaccharide Mutants Reveal that Absence of O Antigen Reduces Biofilm Formation of Actinobacillus pleuropneumoniae

“…Other groups have also shown that capsule expression can affect the biofilm formation of pathogens such as Vibrio vulnificus (45) and Porphyromonas gingivalis (46). For example, capsule synthesis genes (wza and wzc for K. pneumoniae and kpsM for E. coli) were recently shown to negatively affect biofilm formation (47,48). In contrast, our acapsular mutant, strain 33.2, produced a biofilm similar to that formed by the parental A. pleuropneumoniae strain, even though the former exhibited enhanced adherence.…”

“…Surface polysaccharides, including LPS, CPS, and PGA, have been linked to biofilm formation in several bacterial species (17,25,(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51); thus, investigation of their unassessed role in the biofilm formation of A. pleuropneumoniae serotype 1 was the focus of our present study. LPS and CPS have been implicated in both the adhesion and virulence of A. pleuropneumoniae, but their role in biofilm formation is still unclear.…”

Next-Science: A Novel Antimicrobial Agent that Inhibits Biofilm Development by Escherichia coli Clinical Isolates on Urinary Tract Catheters

“…The formation of the biofilm is essential for the development of CAUTI [7]. Factors within the bladder accumulate on the surface of the catheter and facilitate biofilm formation.…”