Rapid detection of enterotoxigenic clostridium perfringens by real-time fluorescence resonance energy transfer PCR

Sensitive quantification of Clostridium perfringens in human feces by quantitative real-time PCR targeting alpha-toxin and enterotoxin genes

BACKGROUND

Clostridium perfringens is a widespread pathogen, but the precise quantification of this subdominant gut microbe remains difficult due to its low fecal count (particularly in asymptomatic subjects) and also due to the presence of abundant polymerase-inhibitory substances in human feces. Also, information on the intestinal carriage of toxigenic C. perfringens strains in healthy subjects is sparse. Therefore, we developed a sensitive quantitative real-time PCR assays for quantification of C. perfringens in human feces by targeting its α-toxin and enterotoxin genes. To validate the assays, we finally observed the occurrence of α-toxigenic and enterotoxigenic C. perfringens in the fecal microbiota of healthy Japanese infants and young adults.

METHODS

The plc-specific qPCR assay was newly validated, while primers for 16S rRNA and cpe genes were retrieved from literature. The assays were validated for specificity and sensitivity in pre-inoculated fecal samples, and were finally applied to quantify C. perfringens in stool samples from apparently healthy infants (n 124) and young adults (n 221).

RESULTS

The qPCR assays were highly specific and sensitive, with a minimum detection limit of 10(3) bacterial cells/g feces. Alpha-toxigenic C. perfringens was detected in 36% infants and 33% adults, with counts ranging widely (10(3)-10(7) bacterial cells/g). Intriguingly, the mean count of α-toxigenic C. perfringens was significantly higher in infants (6.0±1.5 log10 bacterial cells/g), as compared to that in adults (4.8±1.2). Moreover, the prevalence of enterotoxigenic C. perfringens was also found to be significantly higher in infants, as compared to that in adults. The mean enterotoxigenic C. perfringens count was 5.9±1.9 and 4.8±0.8 log10 bacterial cells/g in infants and adults, respectively.

CONCLUSIONS

These data indicate that some healthy infants and young adults carry α-toxigenic and enterotoxigenic C. perfringens at significant levels, and may be predisposed to related diseases. Thus, high fecal carriage of toxigenic C. perfringens in healthy children warrants further investigation on its potential sources and clinical significance in these subjects. In summary, we present a novel qPCR assay for sensitive and accurate quantification of α-toxigenic and enterotoxigenic C. perfringens in human feces, which should facilitate prospective studies of the gut microbiota.

Characterization of the plasmidic or chromosomal cpe gene and metabolic activities in Clostridium perfringens isolates from food in San Luis--Argentina

Food poisoning and non-food poisoning illnesses due to C. perfringens (by enterotoxin production) have been associated to chromosomal or plasmidic location of the cpe gene, respectively. Clostridial pathogenicity has been correlated to protease and azoreductase production. The aim of this work was: i) to assess the sanitary-hygienic quality of dehydrated soups (100 samples) consumed in San Luis - Argentina; ii) to verify the presence of C. perfringens in these food products using the "Most Probable Number" method (MPN) and plate-counting methods; iii) to characterise enterotoxigenicity in strain isolates by RPLA; iv) to determine the chromosomal or plasmidic location of the cpe gene in enterotoxigenic strains previously isolated from food in our lab, using PCR; v) to correlate chromosomal cpe and spore heat-resistance; vi) to compare protease activity in cpe+ and cpe- strains; and vii) to compare azoreductase activity in cpe+ and cpe- strains. Twenty-six isolates had a count a 3-43 bacteria g(-1) count using MPN; 7.7% exceeded the Argentine Food Code (CAA) limit. All isolates showed protease activity: enterotoxigenic isolates had higher protease activity than non-enterotoxigenic isolates. All isolates showed azoreductase activity: enterotoxigenic isolates had higher activity and shorter reducing times. Enterotoxigenic isolates showed chromosomal location for the gene responsible for the enterotoxin.

The identification and characterization of Clostridium perfringens by real-time PCR, location of enterotoxin gene, and heat resistance

Clostridium perfringens carrying the enterotoxin gene is an important cause of both foodborne and non-foodborne diarrheal disease. Rapid identification of isolates carrying the enterotoxin gene is invaluable for outbreak investigation whilst information on the genomic location of the enterotoxin (cpe) gene can improve our understanding of disease transmission. This paper describes the validation of a real-time polymerase chain reaction (PCR) assay for the identification of C. perfringens and assessment of the potential to cause diarrhea, together with an investigation into the genomic location of the cpe genes in isolates from confirmed incidents of C. perfringens diarrhea. The real-time assay was shown to be specific for the identification of 253 C. perfringens cultures and gave results concordant with those from motility nitrate and lactose gelatine media, the Nagler reaction, and a conventional block-based PCR assay. The cpe gene was detected in 223 of 253 C. perfringens cultures isolated in association with human gastrointestinal disease. A subset of cpe-positive C. perfringens isolates associated with separate incidents of diarrheal disease were investigated further for plasmid or chromosomal location of the cpe gene using a multiplex PCR assay. The cpe gene was plasmid encoded in two isolates from cases of sporadic diarrhea and six isolates from cases of food poisoning. The cpe gene from the remaining 11 isolates from different food poisoning outbreaks was found to be chromosomally encoded. One of the C. perfringens strains with a plasmid encoded cpe gene formed spores of high heat resistance and five formed spores that were sensitive to heating. Eight of the isolates with a chromosomal cpe gene formed heat-resistant spores, and two formed spores with an intermediate heat resistance.