Gastrointestinal Infections Flashcards
What are the two methods in which bacterial GI infection agents can cause illness?
Infection - bacterial pathogens develop in the gut after ingestion of contaminated food
Intoxication (poisoning) - bacterial pathogens grow in foods and produce toxins
Give some examples of pathogens that grow in the gut after the ingestion of contaminated food (Infection).
Salmonella
Campylobacter
Pathogenic E.Coli
Give some examples of pathogens that grow in foods and produce toxins to make us ill (intoxication).
Bacillus cereus
Staphylococcus aureus
Describe the clinical syndrome of diarrhoea.
Abnormal frequency and/or fluid stool
Usually indicates small bowel disease
Causes fluid and electrolyte loss
Severity varies from mild and self limiting to fatal
- balance between virulence of the organism and the degree of compromise of the host
Describe the symptoms associated with gastroenteritis.
Nausea, vomiting, diarrhoea and abdominal discomfort
What is the clinical definition of dysentery?
Inflammatory bowel disorder of the large bowel
Causes blood and pus in the faeces
Symptoms include pain, fever and abdominal cramps
What is enterocolitis?
Inflammatory process affecting the small and large bowel
What are the two places in which a GI infection can manifest?
Within the GI tract
Outwith the GI tacit
How do pathogens cause disease when they manifest within the GI tract?
Toxin effects (e.g. Cholera) Cause inflammation de to microbial invasion
How do pathogens cause disease when they manifest outwith the GI tract?
Systemic effect of toxins (e.g. STEC - toxins get into the bloodstream)
- Shigatella toxin from E.Coli
They cause invasive infection of the GI tract with wilder dissemination (e.g. metastatic salmonella infection)
List the barriers to GI infection.
Mouth - lysozyme
Stomach - acid pH
Small intestine
Large intestine
Describe how the small and large intestine protect the body against GI infections.
Small intestine - mucous - bile (antibacterial) - secretory IgA - lymphoid tissue (Peyer's patches) - epithelial turnover - removes adherent bacteria - normal flora - competition Large intestine - epithelial turnover - normal flora
Name some sources of GI infection.
Zoonotic
- symptomatic animals
- asymptomatic shedders - e.g. Reptiles and salmonella carriage
Human carriers
- Typhoid - enteric fever
Environmental sources
- contamination of soil and produce (e.g. Listeria, E.Coli)
Name the four Fs of person-to-person transmission
Faecal-oral - when infectious organisms from human/animal faeces can gain access to the GIT of susceptible host
Food - contamination and cross-contamination
Fluids - water and contaminated juices
Fingers - washing hands
- after the toilets and before preparing or consuming foo and drink
Describe enrichment broth in a laboratory diagnosis of GI infection.
Contains nutrients that promote preferential growth of the pathogen
Describe the selective media in laboratory diagnosis of a GI infection?
Suppress growth of background flora while allowing growth of the pathogen.
Describe differential media in the laboratory diagnosis of a GI infection.
Distinguishes mixed micro organisms on the same plate. Uses biochemical characteristics of micro organisms growing in presence of specific nutrients combined with an indicator that changes colour
- examples include Salmonella and Shigella species which are non-lactose fermenters
What colour does Shigella turn MacConkey’s agar?
It doesn’t change colour - because Shigella is non-lactose fermenting
What colour does E.Coli turn MacConkey’s agar?
Pink - because it is lactose fermenting
With a basic, low-level infection. What is the general treatment?
Given that most mild bacterial infections resolves spontaneously, antibiotics are not given.
Hydration is maintained and can be lifesaving - most important aspect of treatment anyway
When and why is it not appropriate to give antibiotics for treatment of a bacterial infection?
Antibiotic treatment is reserved for severe/prolonged symptoms
This is because the therapy itself
- may prolong symptom duration
- may exacerbate symptoms
- promotes resistance
- may actually be harmful (STEC infection)
How are GI infections controlled?
By breaking the chain of infection
- adequate public health measures (clean drinking water, proper sewage disposal)
- education in hygienic food preparation (avoid cross-contamination, cook food properly and hand hygiene)
- pasteurisation of milk and dairy products
- sensible travel food precautions (wash it, peel it, cook it or forget it)
Describe the microbiology of campylobacter.
These are curved, gram negative bacilli.
They are microaerophilic and thermophilic (42C)
They are cultured on Campylobacter selective agar
C.jejuni are the most important species
Describe the epidemiology of Campylobacter.
Most common food borne infection in the UK
- large animal reservoir (POULTRY, cattle, sheep, rodents and wild birds)
- infection transmitted via contaminated food, milk or water
- 70% of raw retail fresh chicken is infected (becomes safe if cooked properly)
Seasonal peaks of infection in May and September
Person to person spread is rare
Large point source outbreaks are uncommon because once in food, it doesn’t multiply
What is the pathogenesis of Campylobacter?
Bacterial invasion causes inflammation, ulceration and bleeding in the small and large bowel
Can cause bacteraemia (immunocompromised or extremes of age)
Can cause post-infectious demyelination syndrome (Guillain-Barre)
- characterised by ascending paralysis, can cause respiratory paralysis
- can take weeks/months
What are the clinical signs of a campylobacter infection?
Incubation tales 2-5 days
Causes bloody diarrhoea, fever (inflammation of the gut wall) and severe abdominal cramps
Vomiting rarely occurs
Duration is between 2-10 days.
How is Campylobacter treated?
Fluid replacement is sufficient in most cases.
For more severe/persistent disease, Clarithromycin is used
For invasive disease
- Quinolone (ciprofloxacin) or gentamicin is used
What are the best ways to control spread of Campylobacter bacteria?
Reduction in the contamination of raw, retail poultry meat
- followed by adequate cooking
Describe the microbiology of Salmonella bacteria.
It is a gram negative bacilli
It is a member of the Enterobacteriaceae group
Nomenclature confusing
Non-lactose fermenters
XLD plates are most commonly used in clinical labs
How is Salmonella nomenclature confusing?
Most human infections are caused by Salmonella Enterica
However there are over 2000 serotypes defined on a basis of lipopolysaccharide O antigens of the cell wall and flagellar province H antigens
Describe the epidemiology of Salmonella.
Found in cold and warm blooded animals
- acquired from contaminated food (especially pork, poultry and other meat and milk/dairy products)
- waterborne is less common
- large food borne outbreaks can occurs because it can multiply in foodstuffs
Low infectious dose
Secondary spread may be person-to-person
Seasonal peaks in Summer and Autumn
Which salmonella types don’t have an animal reservoir?
S.Typhi and S.Paratyphi
- the causative organisms of enteric fever
- person to person transmission
What is the pathogenesis of Salmonella?
Invasion of the epithelial cells in the distal small intestine causing subsequent inflammation and diarrhoea
Bacteraemia can occur
Can Salmonella have a systemic/distant effect?
Yes, it can metastasise to different organs and cause inflammatory problems there
- joints - septic arthritis
- bones - osteomyelitis
- brain - meningitis
What are the clinical symptoms of Salmonella infections?
Incubation takes 12-72 hours Watery diarrhoea Vomiting is common Fever can occur - associated with more invasive disease Duration is for 2-7 days
What is the treatment for a Salmonella infection?
Fluid replacement is normally sufficient
Antibiotics are used for severe cases and bacteraemia
- Beta-lactams, quinolone so or aminoglycosides
Antibiotics, however, prolong the excretion of Salmonella into the faeces
How can the spread of Salmonella be controlled?
There was an introduction of immunisation of poultry flocks which reduced S.Enteritdis in the UK
Describe the microbiology of the Shigella bacteria.
Gram-negative bacilli
Member of the Enterobacteriaceae family - biochemically similar to E.Coli
Non-lactose fermenters
XLD plates are most commonly used in clinical labs