Analysis of the lytic activity of the Serpulina hyodysenteriae hemolysin

Epidemiological and genetic characterization of Clostridium butyricum cultured from neonatal cases of necrotizing enterocolitis in China

Objective:

Laboratory-based characterization and traceback of Clostridium butyricum isolates linked to outbreak cases of neonatal necrotizing enterocolitis (NEC) in a hospital in China.

Methods:

In total, 37 samples were collected during the NEC outbreak. Classical bacteriological methods were applied to isolate and identify Clostridium spp. Meanwhile, 24 samples collected after an outbreak were similarly tested. All Clostridium isolates were identified to species level as either C. butyricum or C. sporogenes. These isolates were subsequently subtyped using pulsed-field gel electrophoresis (PFGE). Genomic DNA was purified from 2 representative C. butyricum isolates and sequenced to completion.

Results:

Of 37 samples collected during the NEC outbreak, 17 (45.95%) were positive for Clostridium spp. One species, C. butyricum, was cultured from 10 samples. Another species cultured from 2 other samples was identified as C. sporogenes. Both of these species were cocultured from 5 samples. Pulsotyping showed that the 15 C. butyricum and the 7 C. sporogenes isolates produced indistinguishable DNA profiles. No NEC cases were reported after disinfection following the outbreak, and all samples collected after the outbreak were negative for Clostridium spp. Whole-genome sequencing (WGS) indicated that sialidase, hemolysin, and enterotoxin virulence factors were located on the chromosomes of 2 C. butyricum isolates.

Conclusions:

The outbreak of NEC was epidemiologically linked to C. butyricum contamination within the hospital. This is the first report of an NEC outbreak associated with C. butyricum infection in China.

Clostridium butyricum Strains and Dysbiosis Linked to Necrotizing Enterocolitis in Preterm Neonates

BACKGROUND

Necrotizing enterocolitis (NEC) is the most common and serious gastrointestinal disorder among preterm neonates. We aimed to assess a specific gut microbiota profile associated with NEC.

METHODS

Stool samples and clinical data were collected from 4 geographically independent neonatal intensive care units, over a 48-month period. Thirty stool samples from preterm neonates with NEC (n = 15) and controls (n = 15) were analyzed by 16S ribosomal RNA pyrosequencing and culture-based methods. The results led us to develop a specific quantitative polymerase chain reaction (qPCR) assay for Clostridium butyricum, and we tested stool samples from preterm neonates with NEC (n = 93) and controls (n = 270). We sequenced the whole genome of 16 C. butyricum strains, analyzed their phylogenetic relatedness, tested their culture supernatants for cytotoxic activity, and searched for secreted toxins.

RESULTS

Clostridium butyricum was specifically associated with NEC using molecular and culture-based methods (15/15 vs 2/15; P < .0001) or qPCR (odds ratio, 45.4 [95% confidence interval, 26.2-78.6]; P < .0001). Culture supernatants of C. butyricum strains from preterm neonates with NEC (n = 14) exhibited significant cytotoxic activity (P = .008), and we identified in all a homologue of the β-hemolysin toxin gene shared by Brachyspira hyodysenteriae, the etiologic agent of swine dysentery. The corresponding protein was secreted by a NEC-associated C. butyricum strain.

CONCLUSIONS

NEC was associated with C. butyricum strains and dysbiosis with an oxidized, acid, and poorly diversified gut microbiota. Our findings highlight the plausible toxigenic mechanism involved in the pathogenesis of NEC.

LsaA, an antigen involved in cell attachment and invasion, is expressed by Lawsonia intracellularis during infection in vitro and in vivo

Lawsonia intracellularis has been identified recently as the etiological agent of proliferative enteropathies, which are characterized by intestinal epithelial hyperplasia and associated moderate immune responses. This disease complex has been reported in a broad range of animals, prevalently in pigs, and L. intracellularis has been linked with ulcerative colitis in humans. L. intracellularis is an obligate intracellular bacterium, and the pathogenic mechanisms used to cause disease are unknown. Using in vitro-grown organisms as a source of genomic DNA, we identified a Lawsonia gene which encodes a surface antigen, LsaA (for Lawsonia surface antigen), associated with attachment to and entry into cells. The deduced amino acid sequence of this protein showed some similarity to members of a novel protein family identified in a number of other bacterial pathogens but for which roles are not fully defined. Transcription of this gene was detected by reverse transcription-PCR in L. intracellularis grown in vitro in IEC18 cells and in bacteria present in ileal tissue from infected animals. Immunohistochemistry with specific monoclonal antibody and immunoblotting with sera from infected animals demonstrated that LsaA protein is synthesized by L. intracellularis during infection. Expression of this gene during infection in vitro and in vivo suggests that this surface antigen is involved during infection, and phenotypic analysis indicated a role during L. intracellularis attachment to and entry into intestinal epithelial cells

Comparative pathology of bacterial enteric diseases of swine

Enteric bacterial infections are among the most common and economically significant diseases affecting swine production worldwide. Clinical signs of these infections include diarrhea, reduced growth rate, weight loss, and death of preweaned, weanling, grower-finisher, young and adult age breeding animals. The most common etiological agents include Escherichia coli, Clostridium perfringens, Lawsonia intracellularis, Salmonella enterica, and Brachyspira (Serpulina) spp. With the exception of Brachyspira (Serpulina) hyodysenteriae, the cause of swine dysentery, and Lawsonia intracellularis, the cause of proliferative enteropathy, the pathological changes seen with these agents closely resemble the diseases occurring in human beings. Histological changes in the intestines of swine with enteric bacterial infections include bacterial colonization without significant damage (e.g., certain enterotoxigenic E. coli and C. perfringens type A), attaching and effacing lesions with enteropathogenic E. coli and Brachyspira pilosicoli, the cause of colonic spirochetosis, inflammation with S. enterica, and necrotizing and hemorrhagic lesions with certain C. perfringens. Extraintestinal spread of bacteria and/or toxins occurs with some serotypes of E. coli and most serotypes of S. enterica. Enteric bacterial diseases of swine have been used as models to study the pathogenesis of similar diseases of human beings. Several of these pathogens are also important causes of food-borne disease in humans.

Characterization of a haemolysin from Mycobacterium tuberculosis with homology to a virulence factor of Serpulina hyodysenteriae

Scrutiny of sequence data from the Mycobacterium leprae genome sequencing project identified the presence of a gene encoding a 268-amino-acid polypeptide which is highly similar to a pore-forming haemolysin/cytotoxin virulence determinant, TlyA, from the swine pathogen Serpulina hyodysenteriae. Using degenerate oligonucleotide primers based on the TlyA sequences, the Mycobacterium tuberculosis homologue was amplified and this product was used to obtain the clone and sequence a 2.5 kb fragment containing the whole M. tuberculosis tlyA gene. tlyA encodes a 267-amino-acid protein with a predicted molecular mass of 28 kDa. TlyA homologues were identified by PCR in M. leprae, Mycobacterium avium and Mycobacterium bovis BCG, but appeared absent in Mycobacterium smegmatis, Mycobacterium vaccae, Mycobacterium kansasii, Mycobacterium chelonae and Mycobacterium phlei. The M. tuberculosis gene appeared to be the first gene in an operon containing at least two other genes. Introduction of the M. tuberculosis tlyA gene into M. smegmatis using a mycobacterial shuttle expression plasmid converted non-haemolytic cells into those exhibiting significant haemolytic activity. Similarly, inducible haemolytic activity was observed in sonicated bacteria when tlyA was expressed as a His6-tagged fusion protein in Escherichia coli. tlyA mRNA was detected in both M. tuberculosis and M. bovis BCG using RT-PCR, confirming that this gene is expressed in organisms cultured in vitro.