Current P-fimbriae, bacterialadhesion, and pyelonephritis · P-fimbriae, bacterial adhesion, and pyelonephritis 181 in most clinical isolates of E coli is mannose resistant,'8 this

Archives of Disease in Childhood, 1984, 59, 180-184

Current topics

P-fimbriae, bacterial adhesion, and pyelonephritisJAN WINBERG

Department of Paediatrics, Karolinska Institute, Karolinska Hospital and National Bacteriologic Laboratory,Stockholm, Sweden

Bacterial tropism

Everyday observations usually seem self evident andare often not given the attention they merit.Examples are the fact that I haemolytic streptococcicause sore throat but not pneumonia; gonococcicause urethritis but not urinary tract infection (UTI)(which Escherichia coli do); and bacteria likeNeisseria gonorrhoea and Bordetella pertussis thatcause human disease are often harmless in animals.Bacterial adherence may play a role in this'tropism'.

In nature bacteria often stick to surfaces likestones, leaves, and roots. Epithelial cell surfacesmake no exception. Bacteria belonging to the'normal' flora as well as pathogens may adhere byhydrophobic or electrostatic bonds, or both, of an'unspecific' nature, or through a specific interactionbetween bacterial adhesins and epithelial cellreceptors.'-5 The ability of pathogens to adhere tomucous membranes is now recognised as a potentialfactor in virulence.

Specific bacterial adhesion

Adhesion is often mediated by fimbriae (pili)/' 7proteinacious, hairlike extensions from the bacterialcell surface that may recognise specific receptorstructures, often carbohydrates, on the epithelialcell membrane. These fimbriae have been studiedmostly in E coli in relation to gastroenteritis andUTI, and in N gonorrhoeae.

Haemagglutination was the first observed mani-festation of adhesion in enterobacteriacae. Thepioneering work was done in the 1950s by Duguid etal. but it took almost two decades before the fullimportance of this work was recognised.8

Adherence concept in UTI

The way bacteria reach the kidney in patients withacute pyelonephritis long remained an enigma.

Vesicoureteral reflux (VUR) provided a rationalefor the ascent of bacteria from the bladder to thepelvis, and intrarenal reflux (IRR) for the spreadinto the renal parenchyma.9 Only a minority ofpatients, however, with acute, febrile pyelonephritishave gross VUR shown by micturition urethrocy-stography and still fewer have IRR. "' Furthermore,in many children with VUR the infection stillremains limited to the bladder. The mechanisticconcept of the initiation of urinary tract infectionmay thus need to be amended.

The host and the bacteria. In females with recurrentUTI, the outer urethral orifice and vaginal introitusare usually heavily colonised with Gram negativebacteria, even between infections."' 12 Urogenitalepithelial cells from these patients bind E coli betterthan cells from healthy controls.'-'9 This may be anexpression of a more general biological abnormality,since buccal cells from women prone to UTI alsoshow an increased adhesive capacity.'6 In humansE coli strains isolated from patients with pyelo-nephritis bind better to uroepithelial cells than strainsfrom patients with cystitis and asymptomaticbacteriuria.

Thus, the initiation and progress of urinary tractinfection may be governed by the interaction be-tween host and bacteria. One main task in presentresearch is to identify and characterise the two mainactors: the adhesins of the bacteria and the receptorsof the uroepithelial cells of the host.

Mannose sensitive and mannose resistant adhesion.Bacterial adhesion is divided into mannose sensitive(adhesion inhibited by mannose) and mannoseresistant (adhesion not inhibited by mannose).Mannose sensitive adhesion is common amongE coli pathogens as well as non-pathogens and ismediated by so called type 1 fimbriae,8 but since ithas not so far been shown to play any role in theinitiation of human pyelonephritis it is not men-tioned further. Although the type of adhesion found

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P-fimbriae, bacterial adhesion, and pyelonephritis 181

in most clinical isolates of E coli is mannoseresistant,'8 this is a very crude definition of theadhesin, telling us only that adhesion is not medi-ated by type 1 fimbriae.

P-fimbriae and corresponding epithelial receptor(D-galactose -14 - D-galactose)

One research frontier is the definition and chemicalcharacterisation of specific epithelial receptors fordifferent kinds of adhesins within the heterogeneousmannose resistant group; another the purificationand characterisation of the corresponding fimbriae.Two research groups have approached the firstproblem along two different avenues and havelocated a receptor structure for pyelonephritogenicE coli in the same kind of substances-glycosphingolipids associated with the P-bloodgroup system. Kallenius et al, who based their workupon Duguid's original observation that enterobac-teria have specific haemagglutination abilities,showed that pyelonephritogenic E coli specificallyagglutinated human erythrocytes in a mannose

resistant manner and that the agglutination capacitywas proportional to the ability to adhere touroepithelial cells. Systematic work, showed thatthe P-blood group antigens acted as receptors forpyelonephritogenic E coli. 1924 The fimbriae mediat-ing the receptor binding were therefore namedP-fimbriae.22 The P-blood group antigens consist ofdifferent oligosaccaride chains bound to ceramide, asphingo lipid.

About 70 people in the world are known to lackP-antigens-they are of the phenotype p. A keyobservation was that pyelonephritogenic E coli didnot adhere to red cells or epithelial cells from thesesubjects.'9

Continued work has shown that a disaccharide, a

D-galactose - 14 D-galactose, that is part of theoligosaccharide chains of the P-blood group antigensis the minimal receptor active element.20 Theevidence comes from various studies:

(1) Failure of P-fimbriated E coli to agglutinate p

erythrocytes; low adhesion to uroepithelial cellsfrom subjects with phenotype p; isolated P-fimbriaeshow the same binding specificity as wholebacteria.25

(2) Inhibition of agglutination and adhesion bythe D-galactose -

1- D-galactose structure, whichhas been synthesised.

(3) Non-agglutinable erythrocytes are madeagglutinable after passive coating with a smnthesisedglycolipid containing the D-galactose - -4 D-gal-actose disaccharide.

(4) By coating uroepithelial cells with the same

synthetic glycolipid their binding capacity forP-fimbriated bacteria increases.

(5) In vivo, a soluble receptor analogue interfereswith the infectious process.

Svanborg-Eden who has made major contribu-tions in the field of bacterial adhesion in UTI wasearly in the search for a receptor active compound.Together with Leffler26 she independently reportedthat P-blood group antigen related glycosphingo-lipids were functional as receptors for onepyelonephritogenic E coli strain.

Clinical studies

E coli expressing P-fimbriae on their surface werefound in the urine of more than 90% of childrenwith a first, acute, febrile non-obstructedpyelonephritis, but less often in distal infections(Table 1). P-fimbriae most likely help the bacteria toresist the flow of urine by attaching to the uroepithe-lium (Figure), and to the kidney cells where thereceptor active glycosphingolipids are present.'0The P-fimbriated E coli isolated from children

with pyelonephritis also seems to dominate theperiurethral and faecal flora in that child (Table 2).This suggests that faecal colonisation with P-fimbriated E coli may be the first step in the series ofevents leading to overt UTI. The classic antithesis ofthe 'special pathogenicity theory' and the 'preva-lence theory' of initiation of pyelonephritis is not an'either/or', but an 'as well as': specially pathogenicbacteria dominate the faecal flora. Thus, factorspromoting or preventing intestinal colonisation maybe of importance in the pathogenesis of this disease.

Table l Isolation of P-fimbriated E colifrom urine ofpatients with UTI andfrom faeces ofhealthy controls

No (%)

PatientsFebrile symptomatic (clinical pyclonephritis) 35 (94)Afebrile, symptomatic (cystitis) 26 (19)Afebrile, asymptomatic 36 (14)

ControlsFaeces 82 (7)

Table 2 Occurrence of P-fimbriated E coli in periurethralarea and in faeces ofpyelonephritis patients and healthycontrols

Group Periurethral Faecal Dominatingoccurrence occurrence faecal strain(No) No (%) No (%)

Patients (n=10) 10 10 (100) 9 (90)Controls (n=52) ND 5 (10) 1 (2)

ND = not done.

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182 Winberg

Figure Transmission electron micrograph showing a P-fimbriated E coli adhering to a periurethral cell. B is a bacterialcell; C is cytoplasm ofperiurethral cell. The arrow points to a fimbriae-like structure anchoring bacterium to periurethralcell surface. (Reproduced by courtesy ofInfection and Immunity.27

Svenson et al have developed a P-specific particleagglutination test (PPA-test) by means of whichP-fimbriated bacteria can be identified by a simpleslide agglutination.28 This opens new possibilities forstudying the occurrence of P-fimbriated E coli.

Experimental infections

Experimental E coli pyelonephritis is difficult toinduce in animals with a normal urinary tract,29possibly because of the absence of relevant receptorstructures for the inoculated bacteria. An exceptionis the monkey, in several species of which glyco-sphingolipids corresponding to the antigens of thehuman-P-blood group system are present in kidneytissue and on blood cells. Consequently, P-fimbriated E coli adhere well to uroepithelial andred blood cells and, when inoculated into the

urinary tract, cause persistent bacteriuria and acuteand chronic pyelonephritis. Non-adhering, non-P-fimbriated E coli are less infectious.30 3 In vivoexperiments in the monkey have shown that infec-tion can be prevented by the simultaneous adminis-tration of P-fimbriated E coli and a synthetic solublereceptor analogue. This is evidence for in vivorelevance of the P-fimbriae.24 Svanborg-Eden etal,32 recently reported that globotetraose (a P-bloodgroup specific oligosaccharide) interfered withbacterial adhesion and blocked experimental infec-tion in the mouse.

Vaccination with highly purified P-fimbriae25 canalso modify experimental infection and protectagainst severe renal damage. These findings suggestthat antifimbrial antibodies may be protective (un-published data). In vitro they preventadherence.25 3

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P-fimbriae, bacterial adhesion, and pyelonephritis 183

Future development and speculations

It is still unclear why some patients, mainly females,have a large number of infections, while others arenever infected. Direct measurement of P-fimbriaereceptor density or availability, or both, on epithe-lial cells suggest that women prone to infection havemore of these receptors than others.34The finding of faecal dominance of P-fimbriated

E coli in infected patients may have implications fortreatment. For example, persistence of P-fimbriatedE coli in the faecal flora may increase the risk forrecurrence.The crucial question whether colonisation of the

gut with P-fimbriated bacteria predisposes to UTIhas been examined. By means of the PPA testnosocomial spread of P-fimbriated E coli amongstaff and patients has been shown in a hospital ward.A retrospective study suggested that infants caredfor earlier in this ward had an increased incidence ofpyelonephritis.The significance of small bacterial counts in the

urine in infants with pyuria and clinical symptomscompatible with pyelonephritis is obscure. P-fimbriation-shown by means of the PPA test-ofthe few isolated E coli may in these instancessupport the idea that pyelonephritis can be associ-ated with low bacterial numbers.35The protective effect of vaccination of monkeys

with a highly purified P-fimbriae preparationsuggests that immunity plays a role in thedefence against infection. The very first infection ina small infant will hit a host unprotected by anti-fimbrial immunity and may therefore be especiallydangerous. This may provide another rationalefor early diagnosis and treatment of infants withpyelonephritis.

Adhesins and receptors other than the P-antigenrelated ones will probably soon become character-ised. Their role in the pathogenesis of UTI, as wellas the role of other factors such as the mucous gelcovering epithelial cells awaits further elucidation.

In summary, acute and recurrent UTI are com-plex biological events. Recent advances in theunderstanding of the host/parasite interactions on amolecular level will help us to understand thedelicate complexity of the pathogenesis ofpyelonephritis and should lead to better manage-ment and prevention of renal damage.

Supported by Swedish Medical Rescarch Council grant no 16X 765.

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