Pathogenicity of human and porcine intestinal spirochetes in one-day-old specific-pathogen-free chicks: an animal model of intestinal spirochetosis

Cooperative haemolysis between weakly beta-haemolytic human intestinal spirochaetes and Staphylococcus aureus

Weakly beta-haemolytic spirochaetes related to human intestinal spirochaetosis produced a cooperative haemolysis together with S. aureus consisting of an enhanced haemolysis in the zone of the spirochaetal growth which was overlapped by the zone of activity of the staphylococcal beta-haemolysin. The cooperative haemolysis was observed in sheep blood agar media when the concentration of spirochaetes ranged from 1.5 x 10(3) to 1.5 x 10(8) CFU/ml and the concentration of S. aureus from 4 x 10(3) to 4 x 10(8) CFU/ml. With the increase of the distance between the streaks of the spirochaetes and S. aureus from 3 to 10 mm, the period of incubation needed to observe the cooperative haemolysis also increased from 18 to 72 hours. When the spirochaetes and S. aureus were streaked at the same time and when S. aureus was streaked earlier than the spirochaetes, the phenomenon was observed after anaerobic incubation of the plates for 24-72 hours but not after incubation in 10% CO2 under atmospheric conditions. A cooperative haemolysis was also observed between S. aureus and spirochaetes related to the porcine and avian intestinal spirochaetosis and the spirochaete causing swine dysentery when the same experimental conditions were used which allowed an observation of the phenomenon involving human spirochaetes and S. aureus.

Laboratory identification and enteropathogenicity testing of Serpulina pilosicoli associated with porcine colonic spirochetosis

Pathogenic intestinal spirochetes of swine include Serpulina hyodysenteriae, a strongly beta-hemolytic spirochete that causes swine dysentery, and S. pilosicoli, a weakly beta-hemolytic intestinal spirochete (WBHIS) that causes porcine colonic spirochetosis. Because of the existence of nonpathogenic WBHIS in the normal swine colon, it is important to develop laboratory procedures for accurate identification of S. pilosicoli. The purpose of the present study was to assess hippurate hydrolysis and polymerase chain reaction (PCR) amplification of specific 16S ribosomal RNA (rRNA) sequences for identification of porcine S. pilosicoli. Additionally, the enteropathogenicity of 8 field isolates of porcine S. pilosicoli was determined by challenge exposure of 1-day-old chicks and sequential histologic examination of the cecal mucosa. The field isolates of porcine S. pilosicoli hydrolyzed hippurate and yielded S. pilosicoli-specific products by PCR amplification of 16S rRNA sequences. Although all of the field isolates of porcine S. pilosicoli attached to the cecal epithelium of challenge-exposed chicks by day 21 postinoculation, some isolates had locally invasive phenotypes. We concluded that identification of porcine S. pilosicoli could be made on the basis of results of hippurate hydrolysis and 16S rRNA PCR amplification. Challenge inoculation of 1-day-old chicks followed by histologic examination of the cecal mucosa demonstrated the enteropathogenicity of porcine S. pilosicoli.

Identification and characterization of Serpulina pilosicoli isolates recovered from the blood of critically ill patients

The phenotypic and genetic characteristics of spirochetes isolated from the blood of one U.S. and six French patients with severe clinical disease or impaired immunity were examined. All spirochetes were anaerobic, weakly beta-hemolytic, positive for hippurate hydrolysis, and negative for beta-glucosidase activity. Cell lengths ranged from 4 to 8 microm, and each isolate had between 8 and 12 periplasmic flagella per cell. These features were consistent with the spirochetes' being Serpulina pilosicoli, the agent of intestinal spirochetosis. All isolates were positive in a PCR assay amplifying a portion of the S. pilosicoli 16S rRNA gene, and they all grouped with fecal isolates of S. pilosicoli in multilocus enzyme electrophoresis (MLEE). The blood isolates could be differentiated from each other by MLEE, although the U.S. and two French isolates were closely related. Apparently S. pilosicoli may translocate from the large intestine to establish spirochetemia. The clinical significance of this finding remains uncertain and requires further investigation.

Genetic and phenotypic characterization of intestinal spirochetes colonizing chickens and allocation of known pathogenic isolates to three distinct genetic groups

Infection with intestinal spirochetes has recently been recognized as a cause of lost production in the poultry industry. Little is known about these organisms, so a collection of 56 isolates originating from chickens in commercial flocks in Australia, the United States, The Netherlands, and the United Kingdom was examined. Strength of beta-hemolysis on blood agar, indole production, API ZYM enzyme profiles, and cellular morphology were determined, and multilocus enzyme electrophoresis was used to analyze the extent of genetic diversity among the isolates. The results were compared with those previously obtained for well-characterized porcine intestinal spirochetes. The chicken isolates were genetically heterogeneous. They were divided into 40 electrophoretic types distributed among six diverse genetic groups (groups b to g), with a mean genetic diversity of 0.587. Strains in two groups (groups d and e) may represent new species of Serpulina, and the groups contained only strains isolated from chickens. Three genetic groups contained isolates previously shown to be pathogenic for chickens. These corresponded to the proposed species "Serpulina intermedius," to an unnamed group (group e), and to Serpulina pilosicoli. Two of the chicken isolates (one "S. intermedius" and one S. pilosicoli isolate) were strongly beta-hemolytic, two (both "S. intermedius") had an intermediate level of beta-hemolysis, and the rest were weakly beta-hemolytic. Fourteen isolates of "S. intermedius" produced indole, as did one isolate from group d. Isolates identified as S. pilosicoli resembled porcine isolates of this species, having four to six periplasmic flagella inserted subterminally in a single row at each end of the cell, and had tapered cell ends. All other spirochetes were morphologically similar, having seven or more periplasmic flagella and blunt cell ends. The identification of three genetic groups containing pathogenic isolates provides an opportunity for more detailed epidemiologic studies with these pathogens and for the development of improved diagnostic tests.

Phenotypic and genotypic profiles of human, canine, and porcine spirochetes associated with colonic spirochetosis correlates with in vivo brush border attachment

A group of phenotypically and genotypically distinct weakly beta-hemolytic intestinal spirochetes (WBHIS) have been associated with a diarrheal disease of humans, dogs and swine, designated colonic spirochetosis (CS). Because attachment of spirochetes to the brush border of colonic enterocytes is a consistent feature of CS, it may represent an important virulence mechanism. In this study, pure cultures of WBHIS obtained from humans, dogs, and swine with clinical signs or lesions of CS were compared with Serpulina innocens using biochemical, genotypic and an in vivo brush border attachment assay CS-associated WBHIS did not form genotypic and an in vivo brush border attachment assay CS-associated WBHIS did not form indole, but hydrolyzed hippurate. Analysis of genomic DNA using arbitrarily primed-PCR (AP-PCR) revealed that the CS-associated WBHIS had a closely related pattern which was distinctly different from that of S. innocens. For in vivo brush border attachment assays, one-day old chicks were inoculated by crop gavage with either sterile trypticase soy broth or broth containing either S. innocens or CS-associated WBHIS. On day 7 post-inoculation, the ceca of sham-inoculated control chicks and S. innocens-inoculated chicks had tall columnar enterocytes without spirochetes, and no spirochetes were isolated by culture on selective medium. Focal to segmental attachment of spirochetes to the brush border of superficial enterocytes was present in the ceca of chicks inoculated with WBHIS, and weakly beta-hemolytic spirochetes with effacement of the microvillous brush border of colonic enterocytes. Complete agreement between hippurate hydrolysis, specific- and AP-PCR assays and in vivo brush border attachment studies confirms the enteropathogencity of CS-associated WBHIS.

Comparative histopathology of intestinal infections

Intestinal infections are characterized by a range of histologic changes. Some examples (moving progressively deeper into the tissue from the intestinal lumen) are: 1) Enterotoxigenic E. coli infections are characterized by layers of E. coli adherent to villous epithelium, usually with little or no apparent structural damage to the mucosa. 2) The term enteropathogenic E. coli infection designates a disease characterized by E. coli attached intimately to the epithelial cell surface membrane with effacement of brush border microvilli. 3) Rotavirus infections are characterized by destruction of villous epithelial cells. Parvovirus infections are characterized by destruction of crypt epithelial cells. 4) Some intracellular infections with Campylobacter-like organisms are characterized by epithelial cell hyperplasia. 5) Hemorrhagic colitis in humans, caused by enterohemorrhagic E. coli strains, is characterized by mucosal hemorrhage and edema indicative of vascular necrosis. 6) Most of these lesions are accompanied by some degree of inflammation. Neurophils and lymphocytes mediate some of the structural and functional changes characteristic of these infections. Some changes are mediated directly by microbial products. Additional examples of the complexity of these diseases are: 1) Edema disease of swine is characterized both by adherent E. coli and vascular necrosis (each process mediated by a different bacterial virulence attribute). 2) Rotavirus infections are characterized both by destruction of villous epithelial cells and compensatory hyperplasia of crypt epithelial cells. 3) There is suggestive evidence that enterohemorrhagic E. coli infections may involve: a) destruction of epithelial brush border by attaching-effacing E. coli, b) neutrophil mediated epithelial cell destruction, c) Shiga-like toxin mediated epithelial cell destruction and d) Shiga-like toxin mediated vascular necrosis which in turn causes ischemic damage to epithelium.

Genetic relatedness amongst intestinal spirochaetes isolated from rats and birds

Multilocus enzyme electrophoresis was used to determine genetic relationships amongst 32 intestinal spirochaetes (Serpulina spp.) isolated from rats (17), rheas (7), chickens, (4), ducks (2), a swan (1) and a flamingo (1). The strains were divided into 20 electrophoretic types (ETs), with a mean genetic diversity per locus of 0.62. The results were compared with those previously published for porcine intestinal spirochaetes. One strain from a healthy rat, and three rhea strains which were recovered from cases of necrotizing typhlitis, were grouped in the same ETs as certain porcine strains of Serpulina hyodysenteriae. The rhea strains could be differentiated from these by pulsed-field gel electrophoresis. Fifteen of the rat strains were genetically and phenotypically closely related. In contrast the avian strains were genetically more heterogeneous, with pathogenic isolates located in three different genetic groups.

Experimental infection of newly weaned pigs with human and porcine strains of Serpulina pilosicoli

Cultures of Serpulina pilosicoli 95/1000, isolated from a pig with porcine intestinal spirochetosis (PIS), and S. pilosicoli WesB, isolated from an Aboriginal child with diarrhea, were used to infect 5-week-old newly weaned pigs. Four of 12 pigs infected with strain 95/1000 and 2 of 12 pigs infected with strain WesB became colonized and developed watery, mucoid diarrhea within 2 to 11 days postinfection. Affected pigs all had moderate subacute mucosal colitis, with gross and histological changes similar to those previously reported in both natural and experimentally induced cases of PIS. Silver-stained histological sections of the colon and cecum from affected pigs demonstrated spirochetes within dilated intestinal crypts, where they were associated with neutrophilic exocytosis and mucus secretion. Sections from one pig infected with strain 95/1000 showed large numbers of spirochetes attached by one end to the colonic epithelium, a feature consistent with PIS. This study confirms the role of S. pilosicoli in the etiology of PIS and provides evidence that S. pilosicoli strains of human origin have pathogenic potential in an animal model.

Light microscopic and ultrastructural changes in the ceca of chicks inoculated with human and canine Serpulina pilosicoli

Light microscopic and ultrastructural changes were observed in chicks challenged with North American Serpulina pilosicoli, a weakly beta-hemolytic intestinal spirochete (WBHIS) associated with human and canine intestinal spirochetosis. Chicks in control groups received trypticase soy broth or canine Serpulina innocens. The birds were necropsied at weekly intervals, and the ceca were processed for bacteriologic and pathologic examinations. No WBHIS were isolated from the ceca of chicks in the control groups, but WBHIS with genotypes similar to the parent isolates were isolated from the ceca of chicks inoculated with human and canine S. pilosicoli. Gross examination revealed no significant changes in the ceca of chicks at any time post-inoculation. Light microscopic examination revealed no spirochetal attachment in the ceca of chicks in control groups. In contrast, focal to diffuse thickening of the brush border of the surface epithelium along with dilation of the crypt lumina and mild focal lamina propria heterophil infiltration were present in the ceca of chicks inoculated with human and canine S. pilosicoli. Scanning electron microscopic examination revealed focal to confluent spirochetal attachment mainly in the furrow region at the periphery of the crypt units. Transmission electron microscopic examination revealed spirochetes attached to the brush border of the cecal epithelium, causing effacement of the microvilli and disruption of the terminal web microfilaments. The cecal epithelium of chicks inoculated with the canine S. pilosicoli also had caplike elevations of the apical membrane at the point of attachment of the spirochetes together with large numbers of vesicles in the cytoplasm immediately beneath the terminal web and evidence of spirochetal invasion beyond the mucosal barrier. The changes observed suggested that the mechanism of attachment of human and canine S. pilosicoli to the cecal epithelium of chicks was analogous to but different from that described previously for other attaching and effacing gastroenteric bacterical pathogens of human beings and animals.

Phenotypic characteristics of Serpulina pilosicoli the agent of intestinal spirochaetosis

The phenotypic characteristics of three Serpulina pilosicoli strains isolated from humans with diarrhoea (WesB, Kar, Hrm7) and two porcine S. pilosicoli strains isolated from pigs with intestinal spirochaetosis (1648, 3295), were compared with the type strain of the species P43/6/78T (T = type strain) and other intestinal spirochaetes within the genus Serpulina. All S. pilosicoli strains had a characteristic ultrastructural appearance, displayed similar growth rates, hydrolysed hippurate, lacked beta-glucosidase activity, utilised D-ribose as a growth substrate, and had similar sensitivities to rifampicin and spiramycin. The only consistent phenotypic characteristic that differentiated human strains from porcine strains of S. pilosicoli was that the human strains all utilised the pentose sugar D-xylose. These distinguishing phenotypic traits appear useful for identifying S. pilosicoli.

Pulsed-field gel electrophoresis for sub-specific differentiation of Serpulina pilosicoli (formerly 'Anguillina coli')

Pulsed-field gel electrophoresis (PFGE) was developed for subspecific differentiation of Serpulina pilosicoli, and was applied to 52 isolates recovered from cases of intestinal spirochaetosis (IS) in pigs, dogs, human beings and various avian species. The technique was highly sensitive, differentiating the isolates into 40 groupings. Only six groups contained more than one isolate; in five of these groups isolates with the same banding pattern were either from pigs in the same herds (four groups), or from humans in the same community: the sixth group contained two identical Australian porcine isolates from unrelated herds in different states. Overall S. pilosicoli isolates were genetically diverse, but in some cases isolates cultured from the same or different animal species were closely related. This suggested the likelihood of cross-species transmission, including zoonotic spread. PFGE was a powerful tool for epidemiological studies of S. pilosicoli and also allowed examination of genetic relationships between isolates.