Biofilm formation is a trait commonly found among CAUTI isolates and results in the
growth of bacteria on the inner surface of the PLX4032 mouse urinary catheter. Biofilm formation promotes encrustation and protects the bacteria from the hydrodynamic forces of urine flow, host defenses and antibiotics . A perquisite to biofilm growth is adherence to the catheter surface. A number of mechanisms by which Gram-negative pathogens mediate adherence to biotic and abiotic surfaces have been described and include fimbriae (e.g. type 1, type 3, type IV, curli and conjugative pili), cell surface adhesins (e.g. autotransporter proteins such as antigen 43, UpaH and UpaG) and flagella [5–16]. The expression of type 3 fimbriae has been described from many Gram-negative pathogens [17–28]. Type 3 fimbriae are 2-4 nm wide and 0.5-2 μm long surface organelles that are characterised by their ability to mediate agglutination of tannic acid-treated human RBC (MR/K selleck chemicals llc agglutination) . Several studies have clearly demonstrated a role for type 3 fimbriae in biofilm formation [17, 28, 30–33]. Type 3 fimbriae also mediate various
adherence functions such as binding to epithelial cells (from the respiratory and urinary tracts) and extracellular matrix proteins (e.g. collagen V) [31, 34–36]. Type 3 fimbriae belong to the chaperone-usher class of fimbriae and are encoded by LXH254 datasheet five genes (mrkABCDF) arranged in the same transcriptional orientation [29, 37]. The mrk gene cluster is similar to other fimbrial operons of the chaperone-usher class in that it contains genes encoding major (mrkA) and minor (mrkF)
subunit proteins as well as chaperone- (mrkB), usher- (mrkC) and adhesin- (mrkD) encoding genes [37, 38]. A putative regulatory gene (mrkE) located upstream Carbohydrate of mrkA has been described previously in Klebsiella pneumoniae . The mrk genes have been shown to reside at multiple genomic locations, including the chromosome , on conjugative plasmids [17, 30] and within a composite transposon . Transfer of an mrk-containing conjugative plasmid to strains of Salmonella enterica serovar Typhimurium, Klebsiella pneumoniae, Enterobacter aerogenes and Kluyvera species has also been demonstrated . Taken together, these data strongly support spread of the mrk genes between Gram-negative pathogens by lateral gene transfer. Recently, we identified and characterised the role of type 3 fimbriae in biofilm formation from an Escherichia coli strain isolated from a patient with CAUTI . We also demonstrated that the mrkB chaperone-encoding gene and the ability to mediate MR/K agglutination was common in uropathogenic Klebsiella pneumoniae, Klebsiella oxytoca and Citrobacter koseri strains (86.7%, 100% and 100% of strains, respectively) but rare in uropathogenic E. coli and Citrobacter freundii strains (3.2% and 14.3% of strains, respectively) .