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Escherichia coli as a pathogen in dogs and catsLothar Beutin

To cite this version:Lothar Beutin. Escherichia coli as a pathogen in dogs and cats. Veterinary Research, BioMed Central,1999, 30 (2-3), pp.285-298. �hal-00902570�

Review article

Escherichia coli as a pathogen in dogs and cats

Lothar Beutin

Robert Koch-Institut, Division of Emerging Bacterial Pathogens,Nordufer 20, 13353 Berlin, Germany

(Received 16 October 1998; accepted 17 December 1998)

Abstraet-Certain strains of Escherichia coli behave as pathogens in dogs and cats causing gastro-intestinal and extra-intestinal diseases. Among the five known groups of diarrhoeagenic E. coli,namely enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli(EIEC), shiga-toxin producing E. cnli (STEC) and enteroaggregative E. coli (EAggEC), only EPECand ETEC were clearly associated with enteric disease in young dogs. ETEC isolates from diar-rhoeic dogs were found to be positive for the hcat-stable enterotoxins STa and STb but negative forheat-labile enterotoxin (LT). Canine ETEC were found to be different from those of other animals andhumans by their serotypes, production of alpha-haemolysin and adhesive factors and by the pro-duction of uncharacterized types of cntcrt>tt>xins by some ETEC. Canine EPEC could be distin-guished from EPEC of humans or other animals by their serotypes and by the eae-protein intimin whichmediates intimate adherence of EPEC to intestinal mucosa cells. STEC were occasionally isolated fromfaeces of healthy and diarrhoeic dogs but their role in canine diarrhoea is not yet well known. EIECand EAggEC were not reported to occur in dogs or cats. Very little is known on diarrhoegenic E. coliin cats and further epidemiological investigations on this subject are needed. Besides its role ingastro-intestinal infections, E. coli can cause infections of the urogenital tract and systemic diseasein dogs and cats. Extra-intestinal pathogenic E. coli strains from dogs and cats belong to a limited num-ber of serotypes and clonal groups and are frequently found as a part of the normal gut flora of theseanimals. Many of these E. coli strains carry P-fimbriae and produce alpha-hacmolysin and a necro-tizing cytotoxin (ChlF1 Some of the frequently isolated types of extra-intestinal pathogenic E. cnlifrom dogs, cats and humans were found to be highly genetically related but showed differences in theirP-fimbrial adhesins which determine host specificity. Transmission of extra-intestinal and enteralpathogenic E. coli between dogs and humans was reported. Further research is needed, however, todetermine the role of dogs and cats as transmission vectors of pathogenic E. coli strains to otheranimals and humans. © Inra/Elsevier, Paris.

Escherichia coli infections / dogs / cats / humans / diarrhoea / extra-intestinal diseases / virulencefactors

Tel.: (49) 30 4547 2484; fax: (49) 30 4547 2673; e-mail: BcutinL@rki.dc

Résumé Escherichia coli, un agent pathogène du chien et du chat. Certaines souches d’Esche-riclrio ioli sont pathogènes pour le chien et le chat, et provoquent des maladies gastro-intestinales etextru-intestinales. Parmi les cinq groupes d’E. coli responsables de diarrhée à savoir E. coli entéro-pathogène (EPEC), E. coli entérotoxinogènc (ETEC), E. culi entéroinvasive (EIEC), E. coli produi-

sant des toxines Shiga (STEC) et E. coli entéroaggrégatif (EAggEC), seules les EPEC et les ETEC ontété clairement associés à des maladies entériques chez les jeunes chiens. Des isolats d’ETEC issus dechiens diarrhéiques sont positifs en sonde nucléique pour des gènes d’entérotoxines thermostables Staet Stb mais négatifs pour des gènes d’entérotoxines thermolabiles (LT). Les ETEC canins étaientdifférents des ETEC des autres animaux et des humains par leurs sérotypes, par la production del’hémolysine alpha, de facteurs d’adhésions et par la production d’entérotoxines encore non-carac-térisées. Les EPEC canins peuvent être distingués des EPEC des humains ou d’autres animaux par leurssérotypes et par l’intimine (Eae) qui permet l’adhésion intime des EPEC sur les cellules de la muqueuseintestinale. Les STEC, en revanche, ont parfois été isolés des fèces de chiens en bonne santé ainsi quede fèces de chiens diarrhéiques, mais leur rôle dans la diarrhée canine n’est pas encore bien connu. LesEIEC et EAggEC n’ont pas été signalés chez les chiens et les chats. On a peu de renseignementsconcernant la diarrhée due à l’E. coli chez les chats et des études épidémiologiques complémentairessont nécessaires. E. coli peut provoquer également des infections de la voie urogénitale et des affec-tions systémiques chez le chien et le chat. Les souches pathogènes d’E. coli extra-intestinales dechiens et de chats appartiennent à un nombre limité de sérotypes et de clones et font fréquemment par-tie de la flore intestinale normale de ces animaux. Plusieurs de ces souches d’E. Coli produisent desfimbriae de type P, une hémolysine alpha et une cytotoxine nécrosante (CNFI). Les souches d’E. coliisolées d’infections extra-intestinales chez le chien, le chat et l’homme sont génétiquement très simi-laires, néanmoins les séquences de leurs adhésines de type P sont différentes et pourraient déterminerla spécificité d’hôte. La transmission d’E. coli pathogène à localisation extra-intestinale et entériquepathogène entre les chiens et les humains a été signalée. Toutefois, d’autres études sont nécessairespour déterminer le rôle des chiens et chats en tant que vecteurs dans la transmission des souchesd’E. coli pathogènes de l’homme et d’autres animaux. © Inra/Elsevier, Paris.

infections dues à Escherichia coli / chiens / chats / humains / diarrhée / maladies extra-intestinales / facteurs de virulence

1. INTRODUCTION

Dogs and cats belong to those species ofanimals which have been living in a closecommunity with man for many thousandsof years. Large populations of these domes-

tic animals are present in industrializedcountries. For example, the number of dogsand cats living in Germany is estimated to be5 million and 6 million, respectively (pers.comm.). As a consequence, contactsbetween humans, dogs and cats are numer-

ous and the possibility of transmission ofmicro-organisms between these differenthost species is extremely high.

The enterobacterium Escherichia coli isa normal commensal inhabitant of the gutof humans and warm-blooded animals. Asother mammals, dogs and cats are colonizedwith E. coli during the first days of their life[74]. Among the E. coli species, some strainsare known to cause enteric or extra-intesti-nal infections in humans and animals. More-over, some pathogenic E. coli strains aretransmitted between different host speciesand may cause disease in one host but not inthe other. E. coli as a pathogen in dogs andcats was the subject of two earlier reviewarticles [15, 56]. The aim of this review is tosummarize the current state of knowledgeregarding E. coli as a pathogen in dogs andcats and to discuss findings on the relation-ships between E. coli strains which wereisolated from dogs, cats, other animals andhumans.

2. INTESTINAL ESCHERICHIACOLI INFECTIONS

Diarrhoeagenic E. coli which were iso-lated from animals and humans were shownto be heterogeneous for their virulence mark-ers, their specificity for certain hosts andage groups, and for the diseases caused inhuman and animal patients. In regard to thevirulence markers which are associated with

diarrhoea, five groups of enteral pathogenicE. coli were established:

1) enteropathogenic E. coli (EPEC) express-ing colonization factors such as bundleforming pili (bfp) and intimin (eae);

2) enterotoxigenic E. coli (ETEC) express-ing heat-stable (ST) and heat-labile (LT)enterotoxins and different host-specificcolonization antigens;

3) enteroinvasive E. coli (EIEC) carryingthe genes for invasion of intestinal epithe-lial cells;

4) shiga-toxin producing E. coli (STEC)expressing one or more different typesof cytotoxins (Stxl and Stx2);

5) enteroaggregative E. coli (EAggEC)showing a distinct aggregative pattern ofadherence to epithelial cells.

Strains belonging to either group ofEPEC, ETEC or STEC are known to causedisease in humans and in some species ofanimals, whereas EIEC and EAggEC wereonly isolated from infected humans. Besidesthe recognized groups of diarrhoeagenicE. coli, certain E. coli strains were describedwhich express other types of cyto- andenterotoxins, or adherence factors. The roleof these E. coli strains and their virulencefactors in diarrhoeal disease is not wellknown and requires further investigation.This chapter describes what is known aboutE. coli as an agent of diarrhoea in dogs andcats.

2.1. Verocytotoxic E. coliand shiga-toxin-producingE. coli (STEC)

Verocytotoxic E. coli were first describedin 1977 by their ability to cause damage tocultured Vero cells [43]. Many, but not allverocytotoxic E. coli strains produce shiga-toxins (Stxl, Stx2 and Stx2 variants) [3 1 ]and the latter strains are called shiga-toxin-producing E. coli (STEC) [17J. 1.

Cytotoxic E. coli were isolated from fae-ces of healthy and diarrhoeic dogs and catsin a number of different studies (table o.STEC, however, were only detected amongisolates from dogs [11, 12, 26, 32] (table n.Canine STEC were shown to produce dif-ferent types of shiga-toxins and some ofthese strains showed an enterohaemolyticphenotype and were positive for the plas-mid encoded haemolysin of enterohaemor-rhagic E. coli (EHEC-haemolysin) [12].Other STEC strains from dogs carried boththe genes for heat-stable enterotoxins STapand STb together with stxl or stx2-

sequences [32]. The combined expressionof shiga-toxins and enterotoxins was notfound in STEC from cattle or humans butwas observed in some porcine STEC strainswhich are agents of post-weaning diarrhoeain pigs [33]. The ST-producing STEC strainswere all isolated from diarrhoeic dogs andwere not found in the healthy control group[32]. In contrast, other types of ST-produc-ing ETEC from diarrhoeic dogs were foundto be negative for shiga-toxins [60, 63].STEC carrier rates were not significantly

different between groups of asymptomaticdogs (3.2-12.3% positive) and dogs withdiarrhoea (8.9 % positive) (table n. In onestudy, however, an association between diar-rhoeal disease in dogs and Stx2-producingSTEC strains was found [32]. Further inves-tigations on larger numbers of healthy anddiarrhoeic animals are needed in order tolearn more about the role of STEC strains as

possible enteric pathogens in dogs.Among STEC, strains of serotype

0157:H7 are regarded as the most virulentfor humans and these strains frequentlycause bloody diarrhoea and haemolytic ure-mic syndrome [28[. Two cases were pub-

lished where STEC 0157:H7 were isolatedfrom dogs [41,76]. The dog STEC 0157:H7strains belonged both to the same phage typePT4 which was found associated with21.0 % of STEC 0157:H7 isolates fromhuman patients in Canada [41]. In an out-break investigation, epidemiologicallyrelated 0157:H7 strains were isolated froma dog, other farm animals and from a childwho developed bloody diarrhoea after infec-tion [76]. Thus, asymptomatic dogs mightfunction as vectors of transmission for STEC0157:H7 to humans and other animals.

Verocytotoxic E. coli were isolated at ahigh frequency from healthy and diarrhoeiccats [ I, 11 ]. Stx-genes were not detected,however, in these strains [12] or were notinvestigated [ 1 ]. STEC were not reportedto occur in cats but it is noteworthy toremark that these organisms were investi-gated in only a small number of cats. Thecytotoxins produced by some E. coli iso-lates from cats were not further characterizedfor their pheno- and genotypes; however,heat-stable (ST) or heat-labile enterotoxins(LT) were not detected in these strains [1,141. This finding and the observation that

E. coli producing uncharacterized cytotox-ins were frequently isolated from faecal sam-ples of the healthy control group makes itunlikely that such E. coli strains are closelyassociated with diarrhoea in cats.

2.2. Cytotoxic necrotizing toxin(CNF)-producing E. coli

E. coli inducing necrotizing lesions inrabbit skin and morphological changes inHeLa and Vero cell lines were firstdescribed in the mid 1980s [31]. Two typesof cytotoxic necrotizing factors (CNF),CNF1 and CNF2 were described and CNF-

producing E. coli strains were isolated fromhealthy and diseased humans and from dif-ferent species of animals [21, 31, 58]. Pro-duction of CNFI was shown to be closelyassociated with alpha-haemolysin produc-tion and with certain serotypes of E. colistrains isolated from dogs and cats [14, 21,57, 58, 60]. Two lines of genetically closelyrelated CNF1 producing E. coli 06 strainscould be established by analysing isolatesfrom dogs, pigs, cows and humans [21 ].Among CNFI strains from cats and dogs,04 and 06 serogroups were the most fre-

quent [14, 21, 57, 58, 60]. In healthy cats,CNF production was frequently associatedwith E. coli 06:K53:H strains [14]. In anearlier study, strains belonging to the sameserotype were described as verocytotoxicE. coli and these were isolated from healthyand from diarrhoeic cats [1]. Thus, it appearspossible that some of the cytotoxic strainswhich were not further characterized fortheir toxin types might belong to the CNF-producing group of E. coli (table o.

CNF1-producing E. coli were isolatedfrom intestinal and extra-intestinal infec-tions in dogs and cats but also from faeces ofasymptomatic animals [14, 58, 60]. TheCNF-producing strains were found to benegative for other virulence markers asso-ciated with diarrhoeal disease such as shiga-toxins and enterotoxins. In conclusion, thesedata do not indicate that CNF production in

E. coli is associated with diarrhoea in dogsand cats. In contrast, the production of CNFI Iis closely associated with E. coli strainswhich cause extra-intestinal infections in

dogs and cats but the contribution of CNFlto extra-intestinal diseases is not well knownand has to be further investigated.

E. coli producing CNF2 were only rarelyisolated from cats and were not detected in

dogs [14, 58, 60]. In contrast, CNF2-producing E. coli were more associated withbovines [58].

2.3. Enteropathogenic E. coli (EPEC)

Enteropathogenic E. coli (EPEC) belongto different serotypes and are known to beagents of gastro-enteritis in young infantsand in neonatal farm animals [24, 36, 56].According to their virulence markers, somestrains belonging to the EPEC group werelater reclassified as enterotoxigenic E. coli(ETEC), shiga-toxin-producing E. coli(STEC) and enteroaggregative E. coli(EAggEC). Classical EPEC strains are neg-ative for shiga-toxins and enterotoxins butcarry the eae-gene which is located on thechromosomal locus of enterocyte efface-ment (LEE) [24]. Eae-positive EPEC strainscan cause intimate adherence and attachingand effacing (AE) lesions in intestinalepithelial cells of infected humans and ani-mals. Besides eae, a second virulencemarker is present in classical EPEC strainswhich is a plasmid-encoded (bfpA) bundleforming pilus mediating localized adher-ence of EPEC on epithelial cells. The eae-gene was also found inL. coli strains whichdo not belong to the EPEC serotypes andwhich are negative for shiga-toxins. Thesestrains are also called attaching and effacingE. coli (AEEC).

E. coli belonging to some of the classicalhuman EPEC serogroups (026, 044, 055,086, Olll, 0114, 0119, 0125, 0126,0127, 0128, 0142 and 0158) were occa-sionally isolated from diarrhoeic cats [85]and dogs [25, 70, 88!. Because there is only

little data available on these strains, the sig-nificance of the classical EPEC types as pos-sible diarrhoeal agents in dogs and cats isnot known.

AE-lesions were detected in the intestineof two cats with diarrhoea but the causative

agent of the disease was not isolated [59].Except in this study, EPEC were not asso-ciated with diarrhoea in cats. In contrast,EPEC belonging to different serotypes wereisolated from diarrhoeic dogs [9, 15, 25, 38,78]. Some of the eae-positive E. coli strainsfrom dogs were also positive for the eaeBgene (now termed espB), for plasmid-deter-mined EPEC-adherence factor sequences(EAF) and the bfpA-gene, and thus resem-bled human EPEC strains. Enterotoxins,shiga-toxins and haemolysins were notdetected in canine EPEC strains [9, 25, 78].The serotypes of the few canine EPEC iso-lates were heterogeneous (045, 049:H 10,0115, 0118:NM; 0119 and O-untypable)and most of these were different from thoseof human EPEC [25, 78]. In another study,the similarity between cloned eae genes fromEPEC isolates originating from dogs, pigsand humans was investigated. An overallhomology between 81 and 84 % was foundbetween the different eae-protein sequences.However, the eae-protein obtained from thedog strain was found to be serologicallyrelated to the eae of the human EPEC andnot to that of the porcine EPEC strain [3].

The data indicate that EPEC are potentialdiarrhoeic agents, particularly in young dogsand that canine EPEC might be differentfrom EPEC originating from other sources.However, these findings need further con-firmation by examination of larger numbersof diarrhoeic and healthy dogs. At present,not much is known on the epidemiology ofEPEC in dogs nor on their clinical signifi-cance for cats.

2.4. Enterotoxigenic E. coli (ETEC)

Enterotoxigenic E. coli (ETEC) produceone or more different types of enterotoxins

which stimulate intestinal fluid secretion.ETEC infections cause non-bloody, waterydiarrhoea in humans and in young farm ani-mals [36, 51]. ETEC strains are serologi-cally very diverse and express differentadhesion factors which determine their host

specificity [51,54,91]. The toxins producedby ETEC are divided into two major groups:heat-labile toxins (LT) and heat-stable tox-ins (ST). Two types of LT are known, LTIand LTII which show partial homology intheir A-subunit, but no homology in theirB-subunit. In a similar way, two biochemi-

cally unrelated types of heat-stable entero-toxins were described which are designatedas STa and STb. The STa toxin group is fur-ther divided into two related subtypes calledST-porcine (STIa) and ST-human (STh,STIb) [30, 51].ETEC were isolated as diarrhoeal

pathogens from neonatal calves, lambs, kidsand pigs. An association between the ani-mal host and bacterial properties such asserotypes, production of enterotoxins andspecific colonization factors was found [16,33, 35, 36, 56]. ETEC were also isolatedfrom diarrhoeic dogs and were character-ized by a number of methods includingbioassays, such as the infant mouse assayand the ligated ileal loop assay, by serolog-ical tests and by nucleic acid-based detectionmethods. ETEC were found to be associ-ated with 2.7-31.1 % of cases of diarrhoea,particularly in young dogs and were not iso-lated from healthy control groups (table /7).Most canine ETEC strains were found to

express heat-stable enterotoxins which weredetected with the infant mouse assay 140,63 By the use of DNA-specific detectionmethods, most ST-producing canine ETECwere shown to carry the genes for STa, andfewer strains were positive for STb, some-times both toxin types were present in thesame strain [25, 32, 60, 65, 80].ETEC producing the heat-labile entero-

toxin LT1 were not found in dogs (table 1!.Canine E. coli strains which stimulatedintestinal fluid secretion in the ligated ilealloop assay or exerted cytotonic effects on

CHO cells in culture were, however,detected in different investigations [8, 52,53, 81]. The biological activity of thesestrains resembled heat-labile enterotoxin

although they reacted negatively in othertests specific for LT [52, 53, 60 It is there-fore possible that uncharacterized types ofenterotoxins, which are different from thosefound in ETEC from humans and other ani-

mals, are produced by some canine E. coli.In experimental infections, dogs were foundto be susceptible to LT produced by humanETEC strains although they were resistant tocolonization with these ETEC types [66!. j.In contrast to the moderate effect caused byLT, the dogs were found to be more sus-ceptible and did not develop immunity toST [50, 66]. These findings could explainwhy ST-producing strains predominate innatural infections of dogs with ETEC.

The ETEC isolated from dogs were dif-ferent from ETEC isolated from other ani-mals or humans by some phenotypical traits.Canine ETEC were attributed to serotypeswhich are rarely or not found among ETECisolated from humans, pigs and calves [54,91 ]. Among canine ETEC, ST-producing042:H37 strains were most frequently foundand were isolated at different geographical

locations [60, 63, 80]. Some canine ETECwere investigated for their fimbriae whichserve in intestinal colonization. None of theETEC isolates examined was positive forK88 (F4), K99 (F5) or CFAI (F2) andCFAII (F3) antigens except some ST-pro-ducing 042:H37 ETEC strains from Nor-way which were positive for K99 fimbriae[25, 53, 63, 64, 80]. The fimbrial antigenK99 is strongly associated with bovineETEC but it is sporadically found in ETECstrains originating from other animals [ 16].

ETEC from human and animal sources

carry their enterotoxin genes on plasmidsof different sizes [91 ]. This was also foundwith ST-producing ETEC strains from dogs[60, 80 Like porcine ETEC, ETEC fromdogs were frequently found to producealpha-haemolysin which is not found inhuman ETEC strains [12, 33, 60, 63, 80].The alpha-haemolysin genes were found tobe encoded on 48 MD size transferable plas-mids in canine ETEC 042:H37 and on52 MD size plasmids in ETEC 070:H-strains. The genes for ST and for alpha-haemolysin were located on different plas-mids [60[.

In contrast to dogs, there is only very lit-tle information available on ETEC in cats.

ETEC were not found among 22 diarrhoeicand 25 healthy cats which were investigatedfor ST by the infant mouse assay and forLT by the Y 1 adrenal cell test [ 1 In anotherstudy, LT-positive E. coli were not foundamong 159 bacterial isolates which origi-nated from 23 healthy cats [ 14].

3. EXTRA-INTESTINALINFECTIONS WITHESCHERICHIA COLI

Certain strains of E. coli can behave as

opportunistic pathogens causing extra-intestinal infections in humans and animals.In dogs and cats, facultative pathogenicE. coli were shown to cause urinary tractinfection (for reviews see [15, 56]), pro-statitis, vaginitis and pyometra J 13, 79, 84],perinatal infections and puppy death [13,67, 94], otitis externa [7], cardiovascularinfections [18[, cholecystititis [47J, septi-caemia and endotoxaemia [37, 77 ] .

3.1. Urinary tract infections (UTI)

E. coli is the bacterium most commonlyisolated from the urine of dogs and cats withurinary tract infections (UTI) [4, 34, 42, 56,92]. The incidence of bladder infection inbitches was found to increase particularlywith their age. In most cases of UTI, theinfecting E. coli strain was isolated in pureculture from urine and a level of 100 000bacteiia/mL or more was proposed as a basisfor distinguishing significant bacteriuriafrom contamination 142, 56]. E. coli wasalso found to be a cause of pyelonephritisin dogs and cats showing non-significantbacteriuria [23, 45, 82J. In contrast, E. coliwas not found to play a role in canine orfeline urolithiasis [69, 83 [.

3.2. Genital infections

Besides its role in UTI, E. coli is themajor pathogen in male dogs with prostati-tis [84 and in bitches with chronic puru-

lent metritis (pyometra). E. coli was iso-lated in 50-85 % of bitches suffering frompyometra [13, 29, 68, 79] and was alsodetected as a cause of pyometra in cats [22]. ] .In dogs with pyometra, quantitative deter-mination of live E. coli in the uterine con-tents yielded high numbers (10&dquo;’-10&dquo;/mL)and the infective E. coli strain was gener-ally present in the pure culture [68, 79]. Fre-quently, bitches with pyometra were foundto suffer simultaneously from UTI and inmost of these cases the same E. coli strain

type was isolated from urine and the uterinecontent [68, 71, 79]. ] .

3.3. Systemic infections

Besides Staphylococcus aureus, E. coliis an important cause of perinatal death ofpuppies and kittens [49, 67, 94]. The infec-tive E. coli strains can be transmitted intra-uterine or by the infected genital tract lead-ing frequently to abortion or to a septicaemicdeath of the puppies in the first days of life[ 13, 44, 67]. Furthermore, subclinical mas-titis of the bitch was found as another impor-tant source of bacterial infection in new-bom puppies [67]. Septicaemic colibacillosiscaused by E. coli strains of the normalintestinal flora was observed as a frequentlyoccurring complication in dogs with par-voviral enteritis [37, 77]. Bacterial endo-carditis may result from systemic E. coliinfection in dogs and UTI was discussed asa source of these blood-borne infections

[18]. E. coli were also isolated from infectedorgans and shown to be a cause of septi-caemia in cats [57, 58, 62].

3.4. Characteristics of E. coli strainsfrom the normal faecal flora andfrom extra-intestinal infections in

dogs and cats

E. coli strains causing extra-intestinalinfections in dogs and cats were found tobe associated with a few 0-groups whichwere also frequently found in the normal

faecal flora of these animals. It was therefore

suggested that the faecal flora serves as amajor reservoir and a source of infectionwith these strains [22, 29, 46, 89, 90]. Basi-cally the same observations were made forE. coli strains causing extra-intestinal infec-tions in humans [39!.

Serological typing of 0-, K- and H-anti-gens of faecal and extra-intestinal E. colifrom cats and dogs was performed in a num-ber of different studies [1, 5, 10, 14, 21, 27,57, 60, 62, 88-90]. Strains belonging to asmall number of 0-serogroups (02, 04, 06,08, 09, 022, 025, 075 and 083) werefound to dominate among faecal and extra-intestinal isolates from dogs and cats [1, 14,22, 27, 60, 62, 73, 86]. Among these strains,E. coli of serogroups 04 and 06 were most

frequently isolated. Some E. coli serotypes,such as 04:H-, 04:H5, 06:K53:H1 and06:H31 strains were isolated from extra-intestinal and faecal samples of both dogsand cats [1, 10, 14, 21, 27, 60, 62].

Other faecal and extra-intestinal E. coliisolates from dogs and cats were found tobe positive for the K1 or K5 capsular anti-gens. The E. coli K I strains belonged togroups 02, 07, 018, 021 and 083 [I, 10,21, 27, 60, 73, 86]. The K5 antigen wasfound in 06, 021 and 075 strains. Strainsbelonging to 02:K1:H6 and 06:K5:H1 Iserotypes were isolated in different studiesfrom both dogs and cats [ 1, 21, 27, 73, 86 1.E. coli expressing K1 and K5 are also fre-quently occurring in the human faecal floraand are highly associated with neonatalmeningitis, bacteremia and pyelonephritisin humans [39, 55].

Faecal and extra-intestinal E. coli iso-lates from dogs and cats were also found tobe similar for the expression of differentvirulence attributes. Most of these strainsshow haemolytic activity and further inves-tigations revealed that they carry chromo-somally encoded alpha-haemolysin deter-minants [ 10, 60, 61 !. E. coli 04, 06 and075 strains from dogs and cats were foundto be similar for the production of alpha-

haemolysin, CNFl, P-fimbriae and aer-obactin [14, 27, 60, 61, 62, 86!. Enterotox-ins or shiga-toxins were not detected amongfaecal and uropathogenic E. coli isolatesfrom dogs or cats [14, 57, 60].

3.5. Relationships between faecal anduropathogenic E. coli isolated fromdogs, cats and humans

The E. coli strains isolated from the fae-cal flora and from extra-intestinal infectionsof dogs, cats and humans were found to havea similar frequency of certain 0-types, ofsome K- and H-antigens and of typical vir-ulence attributes such as alpha-haemolysin,P-fimbriae, production of CNFI and aer-obactin [19,39,55]. Moreover, some E. colistrains from dogs, cats and humans sharingidentical serotypes such as 04:H5 and06:K13: H 1, were also found to have highlyrelated P-fimbriae serotypes (F12, F13).Uropathogenic E. coli strains from humans,dogs and cats were shown to be highlygenetically related and could be assigned tosix major E. coli clonal groups [87]. Thepredominating serotypes within differenturopathogenic clones were 04:H-, 04:H5,06:Hl; and 06:H31 [21, 87]. Dog andhuman E. coli 02, 04 and 06 strains werealso found to be similar for the chromosomal

position and for the DNA sequences ofalpha-haemolysin determinants and P-fim-briae [46, 61 It was, therefore, suggestedthat the clonally related human and canine E.coli strains might be transmitted as urinarypathogens between dogs and humans [46,86].

Other studies indicated, however, thatthe genetically related canine and humanuropathogenic E. coli strains had differentadhesins (minor fimbrial subunit) whichdetermine the receptor specificity of P-(F12)fimbriae [27, 72, 73, 75]. Phenotypically,most uropathogenic E. coli from dogs werefound to agglutinate dog but not human ery-throcytes and to adhere to canine but not tohuman uroepithelial cells, whereas most

human E. coli strains showed the oppositepicture [27, 73]. It was therefore suggestedthat the variation in the Galal-4Ga1 recep-tor specificity is a mechanism for shiftinghost specificity in E. coli from humans anddogs and that this variation has evolved inresponse to the topography of host cellularreceptors [75]. The differences found in thefimbrial receptor specificity betweenuropathogenic E. coli from dogs and humanscould indicate that these strains are specificfor their host, despite their clonal related-ness.

4. CONCLUSION

There is little information available aboutE. coli causing disease in dogs and cats com-pared to the number of investigations whichwere performed on E. coli as a pathogen ofhumans, pigs and cattle. Among the fivegroups of diarrhoeagenic E. coli, only ETECand EPEC strains were clearly associatedwith gastro-intestinal disease in young dogsand very little is known on the epidemiologyof these strains, their adhesion mechanismsand their host specificity. Although E. colibelonging to the STEC group were alreadyisolated from dogs, it is not clear if theseare associated with disease in dogs or cats.Further research on this subject is needed,particularly in view of a global health prob-lem which is caused by STEC infections inhumans [93]. Further investigations are alsonecessary on those E. coli strains whichwere isolated from diarrhoeic dogs andwhich were shown to produce ’unconven-tional’ enterotoxins or cytotoxins.

Very few data are available on E. coli asa possible agent of diarrhoea in cats. E. colistrains belonging to one of the five differentpathogroups associated with diarrhoeal dis-ease were not found among clinical isolatesfrom cats. However, only a small numberof diarrhoeic and healthy cats were investi-gated, and epidemiological studies involvinglarger numbers of animals and appropriatedetection methods are needed. Studies for

detection of diarrhoeal pathogens should bebased on the identification of virulencemarkers which are associated with diarrhoealdisease. In contrast, serotyping of clinicalisolates was not found to be suitable as a

screening method for diarrhoeagenic E. colistrains in dogs and cats [6, 88].

Uropathogenic E. coli from dogs and catswere found to be similar to human

uropathogenic strains with regard to theirserotypes, clonal types and virulenceattributes. The role of alpha-haemolysin,P-fimbriae, capsular antigens and aerobactinin the pathogenicity of these strains isalready well known. However, further stud-ies are needed on the role of CNF1 which is

closely associated with normal faecal andextra-intestinal E. coli strains in dogs, catsand humans.

Dogs and cats might also play an impor-tant role as E. coli transmission vectors toother animals or man. Several studies indi-cate that transmission of clonally relatedfaecal and uropathogenic E. coli typesbetween humans, dogs and cats has occurredand might still happen [20, 81, 87]. How-ever, the frequency of transmission ofuropathogenic E. coli between differentmammalian hosts is not known and the dif-ferences found between the P-fimbrialadhesins of E. coli strains from dogs andhumans indicate that these strains are host

specific.

Recent findings indicate that the trans-mission of diarrhoeagenic E. coli strainsoccurs between dogs and humans. Asymp-tomatic dogs were identified as carriers ofhuman pathogenic STEC including E. coli0157:H7 strains and could thus play a rolein outbreaks of STEC infections in humans

[41, 76]. Diarrhoeic dogs were identified asan important source of bacterial contami-nation of the environment in apartments of

dog holders which might contribute to thespread and transmission of pathogenic E.coli strains [48]. Thus, further researchshould be directed towards detecting andcharacterizing diarrhoeagenic E. coli types

in dogs and cats, their host specificity andthe possible exchange of pathogenic strainsbetween animals and humans.

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