Bacterial adherence to bladder uroepithelial cells in catheter-associated urinary tract infection

To assess the role of bacterial adherence to uroepithelial cells in the pathogenesis of nosocomial urinary tract infection, we prospectively studied 55 patients with indwelling urinary catheters. We obtained uroepithelial cells from the bladder and urine for culture on the patients' entry into the study and every two to four days during catheterization. In all, 235 collections of uroepithelial cells from these patients were used in an in vitro adherence assay with six gram-negative bacterial strains. With uroepithelial cells from patients who did not have bacterial infections, the adherence of the bacteria used in the assay differed significantly according to species. The least adherence occurred with Escherichia coli GR12; the adherence increased with (in order) Proteus mirabilis, E. coli J96, Klebsiella pneumoniae, Serratia marcescens, and Pseudomonas aeruginosa. With cells collected just before the onset of bacteriuria, adherence of these gram-negative strains was higher in patients in whom gram-negative rod infections developed than in those with gram-positive coccal infections (P = 0.005). Analysis with the Cox proportional-hazards model demonstrated that a significant increase in bacterial adherence to uroepithelial cells in the bladder occurred two to four days before the onset of bacteriuria, but that adherence returned to base-line values with the onset of bacteriuria. These results suggest that a transient increase in the adherence of gram-negative bacteria to bladder epithelial cells may be an important early event in the development of catheter-associated bacteriuria.     

Bacterial motility is a colonization factor in experimental urinary tract infection.

In an experimental urinary tract infection of the mouse, colonization of the urinary bladder by isogenic strains of Salmonella enterica serovar Typhimurium was found to depend on the motility of the bacteria. Strains were obtained by genetic recombination between a highly motile O-6,7 and a poorly motile O-4,5,12 strain. The O antigen did not interfere with the colonization, whereas motility did; flagellated and motile O-6,7 and O-4,5,12 bacteria colonized the bladder equally well.     

Identification of a gene encoding heat-resistant agglutinin in Escherichia coli as a putative virulence factor in urinary tract infection

Escherichia coli causes the vast majority of urinary tract infections (UTI) in both ambulatory and hospital patients. Several uropathogenic virulence factors have been identified, but half of all E. coli isolates that cause UTI have none or only one of the known virulence factors. Thus, it is reasonable to presume that other bacterial factors may be important in UTI pathogenesis. In order to find additional uropathogenic E. coli genes, we used genomic subtraction to identify DNA regions present in a uropathogenic strain of E. coli (1128-11). Genomic subtraction yielded 40 tester-specific fragments, including a novel heat-resistant agglutinin (hra) gene fragment. hra occurred in 55% of 486 UTI strains compared to 28% of 165 rectal strains (P = 0.001). The hra gene in 1128-11 was cloned, sequenced, and found to have 91% homology to the hra gene from E. coli meningitis strain RS218. The genetic organization of genes flanking hra in 1128-11 is distinct from the hra found in E. coli strains J96 and RS218. In our UTI and rectal specimen collections, hra was positively associated with a number of known virulence genes, including pathogenicity island genes hly and cnf, which are absent in 1128-11. The presence of hra in 1128-11 independent of hly/cnf suggests multiple mechanisms by which hra can be acquired by pathogenic E. coli strains. The flanking genes suggest that in 1128-11, hra may be part of a novel variant of a pathogenicity island V.     

Bacterial adherence and humoral immune response in women with symptomatic and asymptomatic urinary tract infection

Purpose: To determine the role of humoral immune response and bacterial adherence in the pathogenesis of symptomatic and asymptomatic urinary tract infection in women. Methods: The study population consisted of 30 women with symptomatic UTI, 30 women with asymptomatic UTI and 30 healthy women as controls. Bacterial adherence to vaginal epithelial cells was studied and the concentration of serum and urine antibodies to mixed coliform antigen and clinical isolate was determined by ELISA. Surface hydrophobicity of the urine isolates was determined. Student’s unpaired t test and Pearson’s correlation coefficient test were used in the statistical analysis. Results: Compared to asymptomatic UTI, significantly more number of bacteria adhered to the epithelial cells of women with symptomatic UTI (P<0.001). All cases of UTI had significantly high concentration of urinary IgG antibody to mixed coliform antigens. Asymptomatic UTI cases had higher concentrations of urinary IgG, IgM and IgA antibodies to clinical isolate. Concentration of sIgA level was more in symptomatic UTI. Significant correlation was observed between urinary IgG and adherence of clinical isolate in case of asymptomatic UTI. Conclusions: The present study showed that greater receptivity of epithelial cells to bacteria may increase the susceptibility to UTI. Humoral immune response and local immunity may modify the pathogenesis of UTI.     

The IrgA homologue adhesin Iha is an Escherichia coli virulence factor in murine urinary tract infection

The role of the Escherichia coli iron-regulated gene homologue adhesin (Iha) in the pathogenesis of urinary tract infections (UTIs) is unknown. We performed a series of complementary analyses to confirm or refute the hypothesis that Iha is a virulence factor in uropathogenic E. coli. Fecal E. coli isolates exhibited significantly lower prevalences of iha (range, 14 to 22%) than did clinical isolates from cases of pediatric cystitis or pyelonephritis, adult pyelonephritis or urosepsis, or bacteremia (range, 38 to 74%). Recombinant Iha from E. coli pyelonephritis isolate CFT073 conferred upon nonadherent E. coli ORN172 the ability to adhere to cultured T-24 human uroepithelial cells. In a well-established mouse model of ascending UTI, CFT073 and its derivative UPEC76 (a pap [P fimbriae] mutant version of strain CFT073) each significantly outcompeted their respective iha deletion mutants in CBA/J mice 48 h after bladder challenge (P < 0.03 for urine, both kidneys, and bladders of both constructs, except for bladders of mice challenged with UPEC76 and its deletion mutant, where P = 0.11). These data suggest that Iha(CFT073) is a virulence factor and might be a target for anti-UTI interventions.     

Role of adherence in pathogenesis of Enterococcus faecalis urinary tract infection and endocarditis.

Enterococcus faecalis strains isolated from urinary tract infections (UTIs) and endocarditis were analyzed for their ability to adhere to urinary tract epithelial cells (ECs) and Girardi heart (GH) and human embryonic kidney (HEK) cell cultures. UTI isolates adhered to urinary tract ECs more efficiently than to the cultured cells, at the same time showing the least affinity for GH cells. In contrast, endocarditis isolates adhered to GH cell cultures more readily than to urinary tract ECs. Moreover, although strains isolated from endocarditis adhered to GH cells more efficiently than those derived from UTI, the latter strains adhered to urinary tract cells better than the former. Studies of the ability of GH and HEK cells to internalize E. faecalis showed that for UTI isolates, 9 to 74% of adhered bacteria were internalized, while for endocarditis isolates, the percentage varied from 76 to 82%. All strains were able to associate with human neutrophils; endocarditis strains, however, associated less efficiently than UTI isolates. Growth in serum raised the adherence of all tested strains by at least 1.5- to 3-fold, with the greatest increase being observed in UTI strain adherence to GH cells (8-fold). In contrast, the association of serum-grown cells with polymorphonuclear leukocytes was reduced by two- to fivefold. In both cases, the observed serum-dependent alterations were cancelled by a few subcultures in brain heart infusion broth. These results indicate that adhesive properties are important virulence factors in the pathogenesis of UTI and endocarditis and also suggest that UTI strains showing the highest invasion and adhesive potential invade the kidneys, cause bacteremia, and, after having expressed the serum-dependent surface modification, colonize the heart.     

Intestinal microbiome as a risk factor for urinary tract infections in children

As urinary tract infection (UTI) pathogens originate from the gut, we hypothesized that the gut environment reflected by intestinal microbiome influences the risk of UTI. Our prospective case-control study compared the intestinal microbiomes of 37 children with a febrile UTI with those of 69 healthy children. We sequenced the regions of the bacterial 16S rRNA gene and used the LefSe algorithm to calculate the size of the linear discriminant analysis (LDA) effect. We measured fecal lactoferrin and iron concentrations and quantitative PCR for Escherichia coli. At the phylum level, there were no significant differences. At the genus level, Enterobacter was more abundant in UTI patients with an LDA score?>?3 (log 10), while Peptostreptococcaceae were more abundant in healthy subjects with an LDA score?>?3 (log 10). In total, 20 OTUs with significantly different abundances were observed. Previous use of antimicrobials did not associate with intestinal microbiome. The relative abundance of E. coli was 1.9% in UTI patients and 0.5% in controls (95% CI of the difference—0.8 to 3.6%). The mean concentration of E.coli in quantitative PCR was 0.14 ng/μl in the patients and 0.08 ng/μl in the controls (95% CI of the difference—0.04 to 0.16). Fecal iron and lactoferrin concentrations were similar between the groups. At the family and genus level, we noted several differences in the intestinal microbiome between children with UTI and healthy children, which may imply that the gut environment is linked with the risk of UTI in children.     

Non-fermenters in urinary tract infection

Sixty four (4.4%) strains of non-fermenting gram negative bacteria (NFGNB) were isolated out of 1,380 bacterial isolates from 7,784 urine samples, of which 43 were isolated from male patients and 21 from female patients. P. aeruginosa was found to be the commonest (67.2%) followed by A. lwoffi (7.8%), A. anitratus and P. acidovorans testosterani (6.2% each), P. maltophilia and P. denitrificans (4.8% each), P. putida and P. vesiculare (1.5% each). Forty two(65.6%) of these isolates were isolated as pure cultures and 22(34.4%) as predominant organisms. Most of these isolates i.e. 50-88.8% were sensitive to Norfloxacin and Ofloxacin and 22.2% to 66.6% of these isolates were sensitive to Gentamycin and Cephalexin whereas 11.1% of these isolates were sensitive to Co-trimoxazole and Ampicillin. All of these isolates were resistant to Penicillin and Tetracycline.     

Bacterial colonization behaviour: a new virulence strategy in urinary infections?

The urinary bladder resists bacterial colonization and infection by a number of mechanisms, one of which involves the sloughing of colonized uroepithelial cells. Pathogens which thus become detached from bladder tissue are rapidly eliminated upon voiding of urine. During a recent study of bacterial colonization by the urinary pathogen, Proteus mirabilis, we noted that it colonized glass surfaces such that organisms became widely and evenly dispersed over the surface. In contrast, Pseudomonas fluorescens, a non-pathogen in the urinary tract, did not disperse over the surface but colonized and grew in such a manner as to form small clumps or microcolonies. Other investigators have also shown that Escherichia coli, a common urinary pathogen, initially colonizes bladders in a random, widely-dispersed fashion. We propose that successful bladder pathogens will predominantly adopt colonization behaviour that enables them to widely disperse over bladder tissue and, in so doing, avoid being cleared by the desquamation of uroepithelial cells. Colonization behaviour would therefore represent a previously uncharacterized virulence strategy.     

Measurement of urinary lipopolysaccharide antibodies by ELISA as a screen for urinary tract infection.

Five hundred and twenty two clinical urine specimens submitted for routine microbiological examination were tested in parallel by conventional microscopy and culture and for lipopolysaccharide antibodies by an enzyme linked immunoabsorbent assay (ELISA) to assess the ELISA as a screen for urinary tract infection. When the ELISA alone was compared with routine methods the specificity sensitivity, and predictive value of positive and negative tests was 73.2%, 75.7%, 51.1% and 38.5%. For ELISA with microscopy the same variables were 71.1%, 82.2%, and 92.4% and 94.7%, respectively. The ELISA absorbency increased with increasing bacterial numbers, but results varied widely. Only 65.4% of urines which contained greater than or equal to 10(5) bacteria/ml were positive by ELISA; 36.8% of urines with less than 10(3) bacteria/ml were positive by ELISA; 100% of greater than or equal to 10(5) bacteria/ml cultures of Pseudomonas sp (n = 4), Staphylococcus aureus (n = 3), and Streptococcus faecalis (n = 2) were positive by ELISA but only 71.4% of Proteus sp (n = 7), 61.4% coliforms (n = 70), and 25% of coagulase negative staphylococci (n = 4). It is concluded that further development is required before the ELISA can be used for routine screening for urinary tract infection.     

Lactobacillus delbrueckii as the cause of urinary tract infection

Lactobacilli are part of the normal bacterial flora of the vagina and are typically considered contaminants when cultured from urine specimens of female patients. Here we describe the case of a female patient with chronic pyuria and urinary tract symptoms in which Lactobacillus delbrueckii was determined to be the causative microorganism.     

Bacterial adherence to mucosal surfaces: an attribute of virulence

Colonization of mucosal habitats is, with very few exceptions, a necessary prerequisite that must be satisfied for a bacterial organism to be virulent. The mechanism(s) whereby bacteria colonize such habitats is, for the most part, by association with the mucosa and proliferation at that site. However, the precise mechanism(s) of association is not known for most organisms. Direct adherence to the mucosal surface of the small intestine by some enterotoxigenic strains of Escherichia coli (ETEC) has been demonstrated both in vivo and in vitro. Specific surface appendages (pili) on the bacterial cell surface facilitate the direct attachment of bacteria to microvilli and as such have been termed adhesins. The adhesins of ETEC that cause diarrheal disease in pigs have been most extensively studied. Two adhesins, K88 and K99, are genetically encoded on plasmids while a third one, 987P, appears to be encoded on the chromosome. All three adhesins are composed of identical repeating protein subunits with molecular weights of 18,100-26,000 that undergo specific aggregation to form large polymers. These polymers are the active adhesins and appear as pili (synonym: fimbriae) when observed in the electron microscope. The function of these adhesins has been established by construction of mutants or plasmidless strains that do not produce the adhesin and by reintroduction of the adhesin genes back into the mutants. Only cells that produce the adhesins colonize and adhere to the mucosa of the pig intestine in vivo and thus produce diarrheal disease. The interaction of adhesin with the mucosal surface is mediated by specific receptors. Current data indicate that these receptors are glycoconjugates.