Colonization through Escherichia. Coli in infants might have reduced in the critical decades, owing to alters in hospital routines and family lifestyle. In this study, the E. Coli flora was identified in 70 healthy and balanced Swedish infants adhered to for the first year of life. E. Coli was isolated from rectal swabs acquired at 3 d that age and quantified in fecal samples accumulated at 1, 2, 4, and also 8 wk of age and also at 6 and 12 mo of age. Strains to be typed using random enhanced polymorphic DNA, and their virulence element genes were determined by multiplex PCR. Emigration by E. Coli occurred late; just 61% that the babies were positive by 2 mo the age. The turnover of individual strains in the microflora was sluggish (1.5 strains per infant throughout 6 mo, 2.1 throughout 1 y). Environmental factors, such together siblings, pets, or feeding mode, did no influence emigration kinetics or strain turnover rate. Genes encoding kind 1 fimbriae, ns fimbriae, and hemolysin were significantly much more common in E. Coli strains persisting because that at least 3 wk in the microflora than in transient strains. The P-fimbrial course III adhesin gene was an ext common in E. Coli from children who had a cat in their homes than in E. Coli from youngsters without pets (p = 0.01); this adhesin form is typical in E. Coli from cats. The so late colonization and also low E. Coli stress, overload turnover price suggest limited exposure that Swedish babies to E. Coli. Our outcomes confirm that p fimbriae and also other virulence factors facilitate persistence that E. Coli in the human being colonic microflora.

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Escherichia coli is just one of the first bacterial types to colonize the infant"s intestines. In the 1970s, E. Coli usually appeared in the baby"s feces a couple of days after bear (1, 2), as a authorize of its establishment in the minister microflora (3, 4). E. Coli colonizing the newborn infant might originate in the maternal fecal flora (5), however E. Coli strains are likewise commonly spread at maternity wards via the parenting staff, especially throughout periods the high bed-occupancy and also staff workload (6). We have actually recently reported the Staphylococcus aureus has end up being a significant colonizer the the child gut (7), which may be a authorize of reduced competition from various other microbes. E. Coli and other fecal bacteria might be less conveniently spread today, since of boosted hygiene in hospitals and families.

Some E. Coli strains persist in the intestinal microflora of one individual for months or year (resident strains), whereas rather (transient strains) disappear within a few weeks (8). Resident E. Coli strains display particular characteristics that allow them come persist in the intestinal microflora, e.g. The expression of ns fimbriae and also capacity come adhere to colonic epithelial cells (9–12). Ns fimbriae room composed that a fimbrial rod with a guideline adhesin the exists in 3 varieties, termed papG great I, II, and III. These acknowledge the Galα1→4Galβ disaccharide, through slight distinctions in binding specificity (13). The class II variety of the papG adhesin is common among E. Coli leading to pyelonephritis (14), conversely, the course III selection is common in cystitis strains from humans (15), dogs (16), and also cats (17). Intestinal persistence of E. Coli has been connected to the course II range of the adhesin (10). E. Coli strains residents in the human being colonic microflora also much more commonly possess gene for other virulence factors, such as the iron-chelating compound aerobactin (9, 10), and the capsular types K1 and K5, contrasted with colonic transient strains (10).

The current study to be designed to inspection the E. Coli colonization pattern throughout the an initial year of life in Swedish babies born in the late 1990s, in relation to distribution mode and lifestyle factors, such together feeding pattern, family size, and also pet ownership. Separation, personal, instance E. Coli strains were identified, and also their possession of gene for adhesins and other virulence components were related to persistence in the intestinal microflora.


Seventy babies (35 girls and also 35 boys) born in 1998-1999 at the Sahlgrenska university Hospital, Sweden, were included. They were component of a prospective birth-cohort examine aiming to examine the relation between intestinal emigration pattern and also allergy development, and also 60 the 70 infants had actually at the very least one allergy parent. Info was obtained about siblings and also pets, and the parents tape-recorded the baby"s feeding pattern. The documents were confirm by a research nurse that interviewed the parents by telephone in ~ 6 and also 12 mo. Notified consent to be obtained, and also the examine was authorized by the Medical values Committee of Göteborg University.

Nine babies were ceded by cesarean section owing to signs of fetal asphyxia (n = 3), maternal epidemic (n = 1), preeclampsia (n = 1), myoma (n = 2), pelvic convulsion (n = 1), or psychological reasons (n = 1). Most infants roomed in v their mother at the maternity ward straight after delivery and left the hospital after an typical of 2.5 d. Seven babies stayed a few days at the neonatal ward prior to being moved to the maternity ward.

All mother commenced breast-feeding, but five babies were breast-fed for less than 2 mo, and thereafter received commercial formula. Solids to be mostly presented by 4 mo that age, however 77% the the infants received breast milk in addition to solids till at the very least 6 mo the age. Fruits and also vegetables were routinely introduced between 4 and also 5 mo the age, porridge and gruel in ~ 4-6 mo of age, and meat in ~ 5-6 mo the age. Fish and also egg were rarely introduced before 6 mo of age.

Isolation the E. Coli native infants" intestinal microflora.

A sample of the rectal flora was obtained 3 d after shipment using a cotton-tipped swab. The swab was put in COPAN"s transportation medium (18) and also transported to the laboratory within 20 h. The swab was streaked on a Drigalski agar plate (19), and the inoculate was spread out to acquire free-lying colonies.

Fecal samples were acquired at 1, 2, 4, and 8 wk of age and at 6 and also 12 mo the age. Feces was collected at residence by the parents and put in a plastic bag in i m sorry an anaerobic setting was created (AnaeroGen Compact, Oxoid, Hampshire, U.K.). The samples were maintained refrigerated until being transported come the laboratory whereby they were processed within 24 h ~ collection. Making use of this procedure, E. Coli counts were not reduced compared with immediate culture as shown in preliminary experiments.

Feces to be diluted serially, plated top top Drigalski agar (19), and incubated aerobically overnight at 37°C. In each sample, individual colony varieties differing in size, shape, color. Or mucoid figure were separately enumerated and subcultured because that purity, and also their types identity was identified using the API20E biotyping mechanism (API equipment SA, La Balme les Grottes, Montalieu-Vercieu, France). Colony species representing E. Coli were conserved at −70°C in Hogner"s freezing medium (20) and also analyzed further.

The limit of detection to be 330 cfu/g feces (represented logarithmically as 102.52). Subdominant strains might be identified if lock differed in morphology and also if their population numbers differed much less than 2 log devices from the dominant colony type. Colony species less frequent than this were overgrown and missed. One to 6 colony varieties were regularly figured out in every sample.

Strain inputting by RAPD.

Different E. Coli strains were figured out by RAPD (21). A tiny amount the bacteria acquired from one overnight culture on tryptic soy agar (TSA) plates was added to 50 μL that HotStarTaq grasp Mix, (Qiagen, Spånga, Sweden) include 6 μM that the primer GTGATCGCAG. The PCR was began with a 95°C 15-min warm activation action for the polymerase, and continued v the complying with temperature profile: 94°C because that 45 s; 30°C because that 120 s; 72°C for 60 s for 4 cycles adhered to by 94°C because that 5 s; 36°C because that 30 s; 72°C because that 30 s because that 26 cycles (the extension step was enhanced by 1 s for every new cycle). The reaction to be terminated in ~ 72°C because that 10 min and cooled come 4°C. The PCR assets were be separate on 8% ready-made Tris-Glycine gels and visualized by silver- staining (21).

All E. Coli isolates native one boy were assayed together, and also their PCR commodities were, once possible, be separated on the exact same gel. 2 isolates with the same profiles were considered to belong come the same strain. If two isolates proved minor differences in RAPD patterns, they were run together in a new PCR and thereafter assigned come the exact same or different strains.

Multiplex PCR for detection the virulence genes in E. Coli strains.

Virulence aspect genes were established using 3 sets that multiplex PCRs, the very first identifying the gene for type 1 fimbriae (fimA), p fimbriae (papC), S fimbriae (sfaD/E), and Dr. Hemagglutinin (draA); the second the course I, class II, and also class III arrays of the P-fimbrial adhesin gene papG; and the 3rd the genes for the capsule K1 (neuB) and K5 (kfiC), aerobactin (iutA), and also hemolysin (hlyA) (10). The primer pairs used have been published formerly (10, 22–25).

The multiplex PCRs were performed as previously explained (10), yet with slim modifications. Bacteria from swarms grown ~ above TSA were added to a mixture comprise HotStarTaq grasp Mix (Qiagen) and also 0.45 μM of each primer pair in a last volume the 50 μL. In the 3rd multiplex PCR reaction, the concentration the MgCl2 was enhanced from 1.5 to 2.0 mM. The PCR regimen was started with an initial heat activation action for the Taq polymerase in ~ 95°C because that 15 min. Thereafter, the PCR was run as explained previously (10). PCR assets were be separate by agarose gelatin electrophoresis and also stained v ethidium bromide.

Statistical methods.

Proportions were compared using Fisher"s specific test. Populace counts were contrasted using the Mann-Whitney U test.

Colonization through E. Coli.

Forty-two percent that the 70 babies were conquered by E. Coli 3 d after ~ birth. After ~ this, additional colonization occurred slowly. That took much more than 2 wk before fifty percent of the infants had E. Coli in their stools and also by 2 mo just 61% to be colonized. One child had actually not yet acquired any E. Coli in ~ 1 y the age, and another eight infants (11%), that had earlier been colonized with E. Coli, were again negative by 1 y the age.

Infants yielded by cesarean section confirmed delayed salvation of E. Coli compared with vaginally ceded infants (Fig. 1A), back the difference between the groups did no reach statistical definition at any kind of time. There was no difference in emigration rate between infants v or without siblings, through allergic or nonallergic parents, or in between infants who grew up in a residence with or without pets (Fig. 1, B-D).

Figure 1



Strain turnover.

Individual strains the E. Coli in an child were identified by RAPD. Strain identities were not compared amongst infants. Figure 3 shows the RAPD file of the E. Coli isolates obtained from one infant. Strain “A” was current on every sampling occasions indigenous d 3 and also onward, whereas another strain “B” was only present in the 6-mo sample. Back several nests were frequently selected indigenous a sample, since they differed in morphology and also were doubt to represent different strains, they frequently turned the end to be the same by RAPD (e.g. The 3 isolates in the 4-wk sample).

Figure 3


During the an initial 6 mo the life, 13% the the infants had no E. Coli, 53% brought a single E. Coli strain, 19% had two, 9% had three, and also 7% had four to 6 strains. ~ above average, 1.5 strains per son were identified during the very first 6 mo.

During the an initial year that life, 1.4% had no E. Coli, 39% carried a solitary strain, 31% had two strains, 16% had actually three strains, and also 13% had 4 to six strains. ~ above average, 2.1 different E. Coli strains were uncovered per infant during the an initial year that life. The diversity of the E. Coli flora in conquered infants go not increase with age. Thus, at 3 d and also at 12 mo of age, every infant optimistic for E. Coli harbored on median 1.2 various strains. The mean number of strains secluded in the an initial year was same in kids who were yielded by cesarean ar (n = 9) or vaginally (n = 61; 2.1 matches 2.1) and in youngsters with (n = 30) or there is no (n = 40) elder siblings (2.2 versus 2.1). Infants cultivation up in a family with pet (n = 19) had actually no greater turnover rate of E. Coli in their microflora than infants in pet-free families (n = 51; 1.8 matches 2.2; ns = 0.53). Children of allergic parents (n = 60) had slightly, but insignificantly, under strains than youngsters of nonallergic parental (n = 10; 2.0 versus 2.7; p = 0.42).

Five infants ceased breast-feeding before 2 mo the age, 11 between 2 and also 6 mo, and 54 still received breast milk in ~ 6 mo of age. Infants in the very first and last groups gained equally couple of E. Coli strains during the duration 2-6 mo (0.4 strains per infant).

Genes because that adhesins and other virulence factors in intestinal E. Coli strains.

One isolate of every E. Coli strain was analyzed by multiplex PCR because that the detection of gene for virulence factors. In addition, numerous isolates native 17 strains were analyzed to assess the consistence the virulence gene carriage. Every isolates the the 17 strains were identical with respect to virulence aspect genes.

Among the 149 strains, gene encoding form 1 fimbriae were lugged by 71%, genes for ns fimbriae by 32%, and for S fimbriae through 26%. Not a solitary strain carried the genes for Dr hemagglutinin. Among the P-fimbriated strains, none brought the class I adhesin, 45% (21 the 47) carried the course II adhesin only, 34% (16 the 47) brought the class III adhesin only, and 8.5% (4 the 47) carried both the course II and class III adhesins, whereas 13% (6 the 47) lacked any type of of this adhesin varieties. Genes encoding the K1 capsule were found in 27%, the K5 capsule in 7%, aerobactin in 29%, and also hemolysin in 23% of the strains.

Certain combinations of virulence genes tend to take place in combinations. We investigated virulence gene associations in the 149 E. Coli strains. The P-fimbrial gene papC to be significantly connected with the S-fimbrial gene sfaD/E (p = 0.0021), the hemolysin gene hlyA (p iutA (p = 0.0061), and the gene because that the K1 capsule neuB (p = 0.0014). PapG class II was linked with hlyA (p = 0.036), iutA (p = 0.0028), and neuB (p = 0.0001), conversely, papG class III was connected with sfaD/E (p = 0.0001) and hlyA (p sfaD/E was significantly connected with hlyA (p neuB (p = 0.019). The aerobactin gene iutA was significantly connected with the K1 gene neuB (p = 0.001).

Strains recovered indigenous 0- come 2-mo-old babies (n = 71) were compared with those recovered native 6- come 12-mo-old infants (n = 78). The previous slightly more often possessed gene for K1 (34% matches 21%) and aerobactin (35% versus 23%) than the latter, but the distinctions were not significant (p = 0.095 and p = 0.11, respectively). The other virulence aspect genes to be equally usual in early and late strains.

Strains an initial appearing in the microflora throughout exclusive breast-feeding (n = 66) were contrasted with strains obtained after discontinuation of breast-feeding (n = 48). Genes for the K1 capsule were significantly an ext common in the strains got by exclusively breast-fed contrasted with weaned babies (32% matches 15%, p = 0.047). Carriage of gene for various other virulence determinants was comparable in the two groups.

E. Coli strains recovered from the five children who had actually a cat in the family carried papG allele III (42% matches 11%, p = 0.011) and the gene for hemolysin (59% versus 18%, ns = 0.021) significantly an ext often 보다 strains from kids whose family members had no pets. Strains diverted from children in households with a dog did no differ significantly from strains isolated from babies without pets.

Virulence variable genes in resident and transient E. Coli strains.

Forty-seven of the 70 infants harbored at the very least one E. Coli strain the persisted in the microflora for at least 3 wk. These strains to be classified together resident. Strains persisting for much shorter periods were characterized as transient, yet strains showing up only in the 2-, 6-, or 12-mo sample were neither identified as resident no one transient, because several months passed between these sampling occasions. A total of 58 E. Coli strains to be classified as resident and 19 together transient. The average time the persistence for the resident strains was 30 wk. Because half of the strains were still current at 12 mo that age, this is one underestimation of the persistence time.

The carriage rate of different virulence factor genes in resident and also transient strains is shown in Table 1. Genes for kind 1 fimbriae, ns fimbriae, and also hemolysin were all significantly much more common in resident 보다 in transient strains. Furthermore, a mix of genes for ns fimbriae and type 1 fimbriae to be 7 times more prevalent amongst resident than amongst transient strains (p = 0.0088) and was, thus, an ext strongly connected with persistence than either p or type 1 fimbriae alone.

Table 1 Carriage of genes encoding different virulence factors in resident and transient intestinal E. Coli strains*
Full size table

Several various other combinations that virulence aspect genes were connected with persistence, yet in these situations the mix was not much more strongly associated with persistence than one of the genes alone. Combinations of virulence factors that were much more common in resident 보다 transient strains had S fimbriae and hemolysin (12 that 58 versus 0 of 19, ratio >4.1, ns = 0.032), ns fimbriae and also hemolysin (14 of 58 versus 0 of 19, proportion >4.8, ns = 0.016), P and also S fimbriae (11 that 58 versus 0 that 19, ratio >3.8, ns = 0.056), and kind 1 fimbriae and also hemolysin (13 of 58 matches 0 of 19, proportion >4.5, p = 0.030). Overall, a combination of 4 or more virulence determinants was detected in 36% the the resident versus 5.3% the the transient strains (ratio, 6.8; ns = 0.0088). Conversely, just 5% of the resident strains lugged neither the the tested virulence factors, as contrasted with 37% that the transient strains (ratio, 0.14; ns = 0.0015).


In the present study, the intestinal E. Coli colonization pattern was defined in 70 healthy Swedish babies born in the so late 1990s. E. Coli is a bacterium which can only flourish in the intestines that man and other pets (26). It can, thus, be spread only via fecal contamination. Together contamination may occur during a vaginal delivery, and 45% that vaginally delivered, yet only 12% the cesarean ar delivered, infants were hopeful for E. Coli by 3 d the age. This says that around one third of infants got E. Coli native their mother at delivery, which fits well with various other studies (27, 28).

In the 1970s, at the very least 70% of babies born in Western nations acquired E. Coli throughout their very first week of life (1, 2). Strains spread in the hospital milieu contributed considerably to colonization (29). In occurring countries, practically all infants gain E. Coli in the first week of life (30, 31), consisting of infants ceded by cesarean section (31, 32) In the current study, we listed less than 50% E. Coli emigration by 1 wk of age. Spread out of E. Coli in maternity wards is limited by rooming-in (33). We believe that rooming-in combined with early on discharge from the hospital have reduced early emigration by E. Coli.

It took 6 mo before (almost) all infants were colonized by E. Coli, which is later than it was observed in the 1980s (34). This sluggish acquisition was not led to by the reality that most babies in our study had actually an allergy parent(s), since colonization arisen equally gradually in those with allergic and also nonallergic parents. Brother or pets in the household additionally did not affect E. Coli colonization rate.

Once colonized, the learned infants shown a slow turnover price of separation, personal, instance E. Coli strains in the microflora. Throughout the very first 6 mo the life, a mean variety of 1.5 strains per child were identified, i beg your pardon contrasts sharply to the 8.5 strains discovered on mean in Pakistani babies (35). One may also compare the 2.1 various E. Coli strains found during the very first 12 mo in our study with the typical 4.2 strains found in swedish infants adhered to until 11 or 18 mo the age throughout the 1980s (36). Differences in sampling schedule and variety of selected nests preclude a straight comparison, however one may conclude the the sales of individual E. Coli strains in Swedish babies is at the very least as low together it was in the 1980s, and might also have further decreased since then.

We did no observe any greater variety of E. Coli strains in the microflora of children who shared family members with larger siblings or pets. We additionally did no observe any type of greater turnover of E. Coli strains in between 2 and also 6 mo of age in weaned compared with breast-fed children, indicating that feeds were not a far-ranging source the E. Coli strains. In contrast, in a research performed in the 1980s breast-fed babies harbored under E. Coli strains gradually than bottle-fed infants (37).

The regular intestinal microflora is the significant drive because that the mature of the minister immune mechanism (38). A bacter strain that colonizes the gut activates the gut immune mechanism only transiently, also if it persists in the microflora. The secretory IgA induced in response to the bacterium coats it and also prevents it from translocating across the mucosal obstacle and, hence, from interacting further through the immune system (39). A continuous turnover that strains in the microflora may, therefore, be needed to store the immune system activated. In accordance, Pakistani infants, who space constantly exposed to brand-new E. Coli strains, have actually a strong secretory IgA response against a swimming pool of E. Coli O antigens already at 2 mo the age, conversely, Swedish infants do not reach similar levels till 1-2 y of age (40). The complete secretory IgA concentration in saliva additionally rises much more rapidly in Pakistani 보다 Swedish babies (40).

E. Coli populace numbers continued to be high during the an initial 6 mo the life, however decreased 10-fold between 6 and also 12 mo of age. The populations of facultative bacteria diminish together the anaerobic microflora becomes more complex (41, 42). This has actually been reported to occur currently in the an initial weeks in previously studies (30, 43). The late decrease in E. Coli populace numbers watched here can reflect delay acquisition the a facility anaerobic microflora in the Swedish babies born today. Us have noted very high fecal numbers of S. Aureus (7) and coagulasenegative staphylococci (unpublished observations) in the babies examined here, i m sorry we translate as a authorize of decreased competition from other bacteria in the minister microflora.

Virulence genes were determined in the E. Coli strains colonizing the infants" intestines. The carriage prices of these genes were comparable to those it was observed in E. Coli isolated indigenous the minister flora of sweden schoolgirls in the 1970s (10), but greater than among E. Coli isolated native Pakistani babies (9), i m sorry confirms the commensal E. Coli populations might differ in various geographic locations (35, 44).

Analysis the E. Coli virulence gene carriage in relation to lifestyle factors revealed the E. Coli acquired during exclusive breast-feeding significantly much more often had actually the gene because that K1 보다 those acquired during formula-feeding. This could be an er effect, as K1 tended to be much more common in E. Coli strains acquired during the first 2 mo 보다 in strains gained later, but it could likewise be the other way around; the tendency of K1 strains to colonize newborn infants could be regarded the fact that lock are often breast-fed. Previous studies have instead discovered the reverse: a decreased emigration by E. Coli moving K1 and P fimbriae in breast-fed babies (45, 46).

Another detect was the the course III variety of the papG adhesin situated on ns fimbriae, and the gene because that hemolysin, to be both significantly much more common in E. Coli in the microflora of kids with a cat in the family, contrasted with E. Coli diverted from kids growing increase in pet-free households. One might speculate the E. Coli from a family cat might be transferred to the infant, due to the fact that E. Coli causing urinary tract infection in cats and also dogs frequently carry the papG III adhesin type, and these strains arise native the intestinal flora that the animals (16, 17). We witnessed no effect on E. Coli gene carriage by dog-ownership. Maybe the parents allow cats to have actually closer contact with the infant compared with dogs. Infants cultivation up through pets have actually lesser threat of emerging allergy (47, 48), which might an outcome from exposure to microbes through protective properties.

Resident and transient strains were contrasted for virulence gene carriage rates. We have actually previously shown that E. Coli strains persisting in the intestinal microflora much more often lug the genes for p fimbriae, K1 or K5 capsule, and aerobactin than transient strains in the very same hosts (9, 10). In the current study, ns fimbriae and kind 1 fimbriae, and especially the combination of these two adhesins, to be significantly linked with minister persistence. Ns fimbriae and type 1 fimbriae confer follow to colonic epithelial cell (49), and kind 1 fimbriae bind to the carbohydrate chains of secretory IgA, a significant component of breast-milk (50). Interaction with secretory IgA appears to enhance intestinal survive of type 1-fimbriated E. Coli, due to the fact that these are decreased in IgA-deficient individuals (51).

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The gene because that hemolysin was also much more common amongst resident than transient strains. Hemolysin, i m sorry is toxicity to a variety of cell types (52), enhances colonization by diarrheogenic E. Coli in the pig tiny intestine (53). Hemolysin might add to persistence by attacking enterocytes and also releasing nutrient for the bacteria. In this context, the is interesting to note that E. Coli in the huge intestine shows up to use membrane lipids as its main nutrient source (54). The association in between hemolysin and also persistence could likewise be indirect, as several different virulence element genes occur together, sometimes carried on so-called pathogenicity archipelago in the genome (55–57). Indeed, 36% that the resides strains lugged four or much more virulence factor genes, contrasted with 5.3% of the transient strains. Pathogenic E. Coli belong to details phylogenetic subgroups (58). Further studies may identify whether the strains that space successful in colonizing the large intestine belong come the very same subgroups, and also whether they own pathogenicity islands. These might rather it is in termed “fitness islands,” as previously said (59), if they very first aid in minister colonization and also then confer pathogenicity come E. Coli getting to extraintestinal sites.