Challenges of Enteric Pathogen Detection
Medical Scientists worldwide are faced with new challenges on a daily basis. Clinical Microbiology
Laboratories continually experience an increase in workload without securing additional staff or resources. Traditional culture techniques can take up to 2 - 6 days to yield results, these methods call for more staffing requirements and put additional strains on already busy Clinical Medical Scientists.
EntericBio realtime revolutionises the standard faecal / stool pathogen test and allows rapid detection of enteric pathogens within 3 hours.
Types of Enteric Pathogens
The genus Salmonella comprises two species - S. enterica and S. bongori. These species have more than 2,500 serovars, differentiated on the basis of their somatic and flagellar antigens.
Salmonella isolates from humans are serotypes of Salmonella enterica. Gastroenteritis is the most common condition caused by Salmonella species. Symptoms include abdominal pain, diarrhoea, nausea and vomiting, often accompanied by fever.
Strains of Escherichia coli that produce the toxins stx1 & stx2 are termed Verotoxigenic E. coli (VTEC). The toxins are termed “shiga-like” due to their similarity to the toxin of Shigella dysenteriae. Infections vary in severity from mild to bloody diarrhoea and may occur in any age group, although it is more common in children. VTEC are capable of causing two types of disease, namely haemorrhagic colitis and haemolytic uraemic syndrome (HUS). HUS is a life-threatening disease characterized by thrombocytopenia, hemolytic anemia and acute renal dysfunction. Serogroup O157 is the most common cause of these illnesses, but at least 150 non-O157 VTEC serotypes have been reported as agents of both sporadic and outbreak-associated disease.
The genus Campylobacter contains 25 species but only some of those have been firmly established as a cause of human gastroenteritis. Campylobacter jejuni accounts for approximately 90% of reported infections with the majority of the remainder caused by Campylobacter coli and Campylobacter lari.
Members of the genus Vibrio are Gram-negative, straight or curved, motile rods
Several Vibrio spp. are considered human pathogens and have been implicated in gastroenteritis. This includes species such as V. cholerae (toxigenic and non-toxigenic serogroups) and V. parahaemolyticus. Most cases of Vibrio-caused gastroenteritis can be linked to consumption of raw or undercooked seafood.
The genus Shigella consists of four species - S. sonnei, S. flexneri, S. boydi and S. dysenteriae. These species are characterised serologically on the basis of the O antigen only, as Shigella spp. lack the H antigen.
Infection with Shigella spp. manifests as a range of symptoms from watery diarrhoea to dysentery with frequent small volume faeces containing blood, mucus and pus. The diarrhoea may be accompanied by fever and abdominal cramps.
Clostridium difficile is a Gram positive, spore forming, strictly anaerobic rod and a significant cause of nosocomial disease. C. difficile is the causative agent of several antibiotic-associated diarrheal diseases; these syndromes are collectively known as C. difficile infections (CDI). Toxigenic strains produce two toxins: A (enterotoxin) and B (cytotoxin) that cause the characteristic mucosal damage associated with Clostridium difficile infection. Toxin B is an essential virulence factor in C. difficile while toxigenic strains that lack toxin A have been reported. The demonstration of C. difficile toxins in diarrhoeal stools in conjunction with clinical data is an important tool in the diagnosis of CDI.
Yersinia enterocolitica species are divided into 6 biotypes (1A, 1B, 2-5), depending on their genomic characteristics. Main symptoms of yersiniosis include abdominal pain with fever and diarrhoea and often mimic other diseases such as appendicitis or Crohn’s disease11, therefore accurate and fast detection of Y. enterocolitica infection is important for patient management decisions and avoidance of unnecessary surgical procedures.
Traditional laboratory methods using light microscopy to identify these parasites tend to be labour intensive and subjective and molecular methods have been shown to improve detection of these parasites in patients.
Cryptosporidium is a genus of apicomplexan
protozoans that contains at least seven species
associated with human diseases with the most
frequently isolated species being C. hominis and C. parvum. C. hominis is mainly found in humans while C. parvum can also be isolated from cattle and other ruminants.
Entamoeba is a genus of single-cell protozoan parasites within which at least six species can be found in humans among which Entamoeba histolytica is the only pathogenic species. The symptoms of amoebiasis include diarrhoea (mild to severe), often with mucus and blood and may occur several months after the initial infection with E. histolytica. Furthermore, the infection may become chronic and spread extra-intestinally, mostly to the liver or to the brain, where it is associated with higher mortality rates. Microscopic examination of stools does not allow differentiation between E. histolytica and non-pathogenic E. dispar species as these two are morphologically indistinguishable. Therefore, molecular-based detection methods offer increased specificity for the detection of E. histolytica in patients in a diagnostic setting.