Bacterial GI Infections Flashcards
Define gastroenteritis
A syndrome characterised by GI symptoms including nausea, vomiting, diarrhoea, and abdominal discomfort
Define diarrhoea
Frequent and/or fluid stool, at least 3 episodes a day
Define dysentery
Blood and pus in the stool, usually with abdominal pain and fever. More common in infection from abroad.
Define enterocolitis
Inflammation involving mucosa of both small and large intestine
What is used to monitor diarrhoea in hospital?
Bristol stool chart
How can GI infections manifest?
Within GI: toxin effects (eg. Cholera), and inflammation due to microbial invasion (eg. Shigellosis)
Outwith GI: systemic effects of toxins (eg. Shiga toxin produced by E.coli), and invasive infection of GIT with wider spread (eg. Metastatic salmonella infection)
What are the barriers to GI infection in the mouth?
Lysozyme
What are the barriers to GI infection in the stomach?
Acid PH
What are the barriers to GI infection in the small intestine?
- mucous
- bile
- secretory IgA
- lymphoid patches (Peyer)
- high epithelial turnover
- normal flora
What are the barriers to GI infection in the large intestine?
- high epithelial turnover
- normal flora
What organisms are part of the normal GIT flora?
- majority are anaerobes
- enterobacteriales eg. E. Coli, Proteus etc.
What are the possible sources of GI infection?
- zoonotic (symptomatic animals/asymptomatic shedders) eg. Salmonella
- human carriers eg. Typhoid
- environmental sources (contamination of soil and produce) eg. Listeria, E. coli
Describe the different modes of transmission of GI infection
- faecal-oral: any means that an infectious organism from human/animal faeces can gain access to the GIT of another host
- 3Fs: food (farm to fork/cross contamination), fluid (contaminated water), fingers (importance of hand hygiene
- person to person: depends on infectious dose and ability to contaminate and persist in environment
Describe the laboratory diagnosis of GI infection
- picking out the infectious pathogen from the normal flora
- enrichment broth: contains nutrients that promote preferential growth of the pathogen
- selective media: suppresses growth of background flora while allowing growth of pathogen
- differential media: distinguishes mixed organisms on the same plate. Uses biochemical characteristics of microorganisms growing in the presence of specific nutrients with a colour indicator
What are important points to note about antibiotic prescribing in GI infections?
- antibiotics are reserved for severe/prolonged symptoms
- they can prolong symptom duration, exacerbate symptoms, promote resistance and can attribute to harmful infection
What are some ways of controlling GI infections?
- adequate public health measures (provision of safe, clean drinking water; proper sewage disposal)
- education in food preparation (hand hygiene; avoid cross contamination; cook foods properly)
- pasteurisation of milk and dairy products
- sensible travel food practices
Describe the microbiology of salmonella
- gram-negative bacilli
- part of enterobacteriales
- non-lactose fermenters
- XLD plates used in labs
Describe the transmission of salmonella
- acquired by contaminated food (esp pork, poultry and other meat/dairy products)
- secondary spread from person to person
- seasonal peaks in summer and autumn
Describe disease features of salmonella
- diarrhoea (due to invasion of epithelial cells in the distal small intestine causing inflammation)
- bacteraemia
- distant organs can become seeded (metastasis)
Clinical features of salmonella
- incubation 12-72
- watery diarrhoea
- vomiting
- fever (usually associated with more invasive disease)
- duration 2-7 days
What is the treatment for salmonella?
- fluid replacement
- antibiotics for severe cases + bacteraemia (beta-lactams, quinolones, or aminoglycosides)
Describe the microbiology of campylobacter
- curved gram-negative bacilli (sea-gull shaped)
- microaerophilic + thermopholic
- culture on campylobacter selective agar
- C. Jejuni most common
Describe the transmission of campylobacter
- large animal reservoir (cattle, poultry, sheep, rodents and birds)
- infection transmitted via contaminated food, milk or water
- person to person spread is rare
- seasonal peaks in May and September
Describe the disease features of campylobacter
- inflammation, ulceration and bleeding in small and large bowel due to bacterial invasion
- bacteraemia
- post infectious Gullain Barre (ascending paralysis - rare)
Describe the clinical features of campylobacter
- incubation 2-5 days
- bloody diarrhoea
- cramping abdominal pain
- usually no vomiting
- fever
- 2-10 days
What is the treatment of campylobacter?
- fluid replacement
- clarithromycin/erythromycin in severe/persistent disease
- quinolone/aminoglycoside in invasive disease
How can salmonella be prevented?
immunisation of poultry flocks leading to reduction of S. enteritidis
How can campylobacter be prevented?
- reduction of contamination in raw, retail poultry meat
- adequate cooking
Describe the microbiology of E. coli
- gram-negative bacilli
- part of enterobacteriales (important in gut flora in humans and animals, virulence factors enable infection)
- 6 diarrhoeagenic groups
Describe the disease features of Enteropathogenic E. Coli
- initial adherence via pili
- formation of characteristic attaching and effacing lesion mediated by intimin protein and TiR (translocated intimin receptor)
- disruption of intestinal microvilli
Describe the clinical features of Enteropathogenic E. Coli
- incubation 1-2 days
- duration 1-several weeks
- watery diarrhoea with abdo pain and vomiting
- fever
Describe the disease features of enterotoxigenic E. Coli
- diarrhoea due to action of 1/2 plasmid-encoded toxins
- Heat labile = structural and functional analogue of cholera toxin
- Heat stable = produced in addition to or instead of LT with similar mode of action
What are the clinical features of Enterotoxigenic E. Coli?
- incubation 1-7 days
- duration 2-6 days
- watery diarrhoea with abdo pain + vomiting
- no fever
Describe the transmission of enterohaemorrhagic E. Coli
- large animal reservoirs
- persistent in environment
- spread through consumption of contaminated food, water, dairy products
- direct environmental contact with animals
- secondary person to person spread
Describe the disease features of enterohaemorrhagic E. Coli
- attaching and effacing lesions (similar to EPEC)
- production of shiga-like toxins, structural and functional analogue of shigella dysenteriae toxin
Describe the clinical features of enterohaemorrhagic E. Coli
- incubation 1-7 days
- duration 5-10 days
- bloody diarrhoea with abdo pain + vomiting
- no fever
- haemolytic uraemic syndrome (10% - thrombocytopenia + acute renal failure)
What is the treatment of E. Coli infections?
- adequate rehydration
- no antibiotics or anti-motilities (can increase risk of haemolytic uraemic syndrome in EHEC)
