Microbiology and Infection Flashcards
Which micro-organism is associated with re-heating rice or starchy foods?
Bacillus cereus
Name a common cause of healthcare associated diarrhoea
Clostridium difficile
Which toxins does clostridium difficile produce?
Toxins A and B
When will Clostridium difficile often become a problem for a patient?
After antibiotic use
The bacteria is a normal part of the gut flora in older patients and infants. After antiobiotic use, much of the gut flora is wiped out allowing for C. diff to proliferate more than it normally could in the presence of competition from the natural flora
What are the symptoms like for C. diff infection?
- Pseudomembraneous colitis - swelling/inflammation of the colon
- Diarrhoea - often bloody
- Abdominal pain
- Bowel perforation
What is the treatment for C. diff infection?
Metronidizaole or vancomycin
Why are vacomycin or metronidazole given in tablet form when treating C. diff infection?
To ensure the drug remains int he gut tube as much as possible
In order to prevent C. diff infection, which antibiotics should be avoided?
The 4Cs
- Clindamycin
- Cephalosporins
- Co-amoxiclav
- Ciprofloxacin
How should hands be disinfected?
Throrough handwashing
(not alcohol hand gel)
What are the main characteristics of C. diff?
- Gram +ve
- Bacilli
- Spore bearing
How can C. diff be diagnosed in the labratory?
- Screening for glutamate dehydrogenase (GHD)
- If GHD is present, toxins A and B are tested for
- If the strain needs to be typed, culturing may be necessary
Why would negative results be obtained for C. diff if the pathogen is present?
There is often intermittent release of toxin from the pathogen
Which virus is likely to infect people before the age of 5 and cause diarrhea and vomiting?
Rotavirus
What is the best treatment for rotavirus?
Oral rehydration
It is short lived and self limiting
When in the year is rotavirus most common?
Winter
What condition can children develop post-infection with rotavirus?
Post-infection malabsorption
This can lead to further diarrhoea
How can rotavirus be diagnosed?
PCR
(on faeces, or vomit)
How can rotavirus be prevented?
Via a live attenuated vaccine
2 doses are given to infants at 2 and 3 months
Norvirus has which classic symptom?
Explosive diarrhoea
How is norovirus spread?
- Faecal/oral
- Droplets
- Person to person contact
What is the incubation time for norovirus?
<24 hours
How can norovirus be diagnosed?
PCR
(on faeces or vomit)
In terms of infection control what is the most important thing to remember about norovirus after infection?
There is a period of around 48 hours after infection of asymptomatic shedding
Patients at this stage are still infectious, yet less so than when symptoms were present
Where is infection with norovirus most common?
In enclosed environments involving close contact
Examples include cruise ships, schools are hospitals
Which chart can be used to determine a type of stool?
The Bristol Stool chart
What time range would classified as short incubation?
1-6 hours
Short term incubation is short because of what?
The incubation time is due to release of preformed toxins from micro-organisms and not proliferation
What are two common causes of short-term incubation?
- Staph aureus
- Bacillus cereus
Why is Bacillus cereus commonyl associated with poorly reheated food?
It has heat resistant spores which can survive adverse conditions
Meats, fish and poultry are associated with which length of incubation time?
Short incubation
They can be associated with Bacillus cereus and Staph aureus
Poorly stored food leads to a massive histamine reaction and toxins tmulate outpouring of fluid into the bowel lumen causing profuse diarrhoea
What timeframe would be classed as medium incubation?
12-48 hours
Which two pathogens are commonly associated with food poisoning and medium incubation times?
- Salmonella
- C. perfingens
What timeframe woul dbe classed as a long incubation time?
2-14 days
Which two pathogens are associated with food poisoning and a long incubation time?
- Campylobacter
- E. coli 0157
What is the most common cause of food poisoning?
Campylobacter
(in the UK)
Salmonella causes food poisoning and is associated with what?
Outbreaks
Which bacteria may cause bacteraemia in immunocompromised patients?
- Campylobacter
- Salmonella
These bacteria can be invasive
Where is a camplobacter infection likely to come from?
- Raw milk
- Raw poultry
How can a campylobacter infection be treated?
Macrolide antibiotic such as clarithromycin
Generally it is self limiting
What is the most common species of campylobacter?
C. jejuni
What is a common cause of food poisoning unique to salmonella infection?
Reptiles
(salmonella forms part of their natural gut flora)
Aside from reptiles, where may Salmonella eteritidis also be found?
- Poultry
- Raw egg
- Meat
- Moist food at the correct temperature
Salmonella enterica has which two important divisions?
Typhoidal and non-typhoidal
What is the big difference between typhoidal and non-typhoidal salmonella enterica?
Typhoidal has lots of rash, fever and prolonged excretion of salmonella
Salmonella enteritidis is non-typhoidal
True or false?
False
It is a type of typhoidal Salmonella enterica
Which two main antigens are present on salmonella?
O antigens - stick out of the outer membrane
H antigens - present on flagella
How is salmonella typed?
O antigens are taken from the body and agglutinated with an antibody to determine the prsence of salmonella
What is serogrouping and how is it used for salmonella?
It is a technique used to pinpoint the source of infection
It is useful for detecting outbreaks by tracing the same antigens
What do E. coli bacteria produce that is damaging to the body?
Cytotoxins
(shiga-like toxins)
What is enterohaemorrhagic E. coli?
E. coli affecting enterocytes causing haemorrhage
Why are antibiotics not given against gastroenteritis produced due to enterohaemorrhagic E. coli?
It is hard to find out which antibiotic to use soon enough and the wrong one may perpetuate cytotoxin production and intestinal haemorrhage.
Which type of agar is used for culturing EHEC?
Sorbitol McConkey agar
How can shiga-like toxins be identified?
ELISAs
Which potential infection cause has greatest association with EHEC and specifically E. coli 0157?
Minced beef - burgers (over-handled meat)
Other causes
- Raw milk
- Water (private - old wells)
- Person to person contact
- Animal contact
Which strain of E. coli has outbreak potential?
E. coli 0157
In which age bracket is E. coli 0157 most common?
Under 5 years old
Which two conditions may be produced as a result of E. coli 0157 infection?
- Haemorrhagic colitis
- Haemolytic ureamic syndrome (HUS)
Why are shiga-like toxins so deadly to cells?
They bind to receptors on renal cells, RBCs and other cell types inhibiting protein synthesis and resulting in cell death
Which symptoms may be present with haemolytic ureamic syndrome?
- Abdominal pain
- Fever
- Pallor
- Petechiae - small red/purple spots on the skin due to broken capillary walls
- Oliguria - production of abnormally small amounts of urine
When testing the blood, what findings may be present for HUS?
- High WCC
- Low platelets
- Low Hb
- Red cell fragmentation
- High LDL
Which investigations would be undertaken for HUS?
- Urea
- Electrolyte
- FBC
- LFTs
- Clotting
- Urine
- Lactate dehydrogenase
When HUS is present, which drugs are not given?
- Antiobiotics
- Anti-motility agents
- NSAIDS
How can E. coli 0157 be diagnosed?
Selective culture
Sorbitol non-fermenter
What are two of the main diarrhoea-causing viruses?
- Rotavirus
- Norovirus
In children under 5, which virus is the main cause of diarrhoea?
Rotavirus
How can rotavirus be diagnosed?
PCR
(on faeces)
Which type of vaccine is available for rotavirus?
Oral live attenuated vaccine
(available from September 2013)
Before treating patient with suspected norovirus, what must be done to know when to treat the patients?
Watch and wait
Shellfish are associated with which microorganism that can cause diarrhoea?
Norovirus
(also hepatitis A and E)
Acute travellers’ diarrhoea may be treated with which antibiotic for a select few, potentially high profile individuals?
Fluoroquinolone such as ciprofloxacin
(This type of use is not recommended as it is not necessary and abuses the antibiotic system to a degree)
Enteric fever can be caused by which pathogens?
- Salmonella typhi
- Paratyphi
What are the three main treatment options for enteric fever?
- Ceftriaxone - IV
- Ciprofloxacin - useful, yet their is now high resistance
- Azithromycin - oral
What is pre-hepatic jaundice and what may cause it?
Pre-hepatic jaundice is caused by anthing that increases rate of haemolysis
This can be caused by:
- Malaria - can cause red cell fragmentation
- HUS - due to E. coli and shigella - toxins can cause red cell fragmentation
- Sickle cell crisis caused by infection
What is hepatic jaundice?
Any condition affecting the efficiency of liver functioning to a degree that metabolism and excretion of bilirubin is not fast enough to prevent a build of unmetabolised bilirubin in the blood.
This is often due to cell necrosis as a result of some conditions
Acute travellers’ diarrhoea is most likely caused by which pathogen?
Enterotoxigenic E. coli
(also campylobacter, salmonella and shigella)
Which condition is associted with watery profuse diarrhoea within refugee camps, or shanty towns in the developing world?
Cholera
Which investigations should be undertaken for travellers’ diarrhoea?
Stool culture
Stool wet prep - recently passed stool onto microscope slide
Why would haemolytic ureamic syndrome cause jaundice?
Toxins released by E. coli or shigella can cause red cell fragmentation and an increase in bilirubin within the blood
Which pathogen is likely to cause amoebiasis?
Entamoeba histolytica
What does amoebiasis infection involve?
- Diarrhoea - often bloody
- Abdominal pain
- Tissue perforation
- Anaemia (often due to blood loss)
Which investigations could be undertaken for amoebiasis?
- Stool microscopy - gold standard to view cysts
- AXR
- Endoscopy
Which condition involving the liver is more common in men and can prsent moths after returning from the tropics?
Amoebic liver abscess
Amoebic liver abscesses are caused by which pathogen?
Entamoeba histolytica
Which signs and symptoms will be experienced with amoebic liver abscess?
Fever
Upper abdominal pain
Hepatomegaly
Point tenderness over lower right ribs
Which investigations could be undertaken for a suspected amoebic liver abscess?
LFTs - abnormal
CXR - raised hemi diaphragm
USS/CT
Serology - gives indication of immunological memory, this will show whether travellers have picked up the condition abroad or not
Stool microscopy
What is the treatment for amoebic liver abscess?
- Metronidazole or tinidazole
- Paramomycin or diloxcaine - to clear gut pathogens
Which pathogen can cause giardiasis?
Giardia intestinalis
(a flagellated protozoa)
Where is Giardia intestinalis likely to invade?
Duodenum and proximal jejunum
What are the symptoms for giardiasis and how long may they last?
- Diarrhoea
- Abdominal pain
- Weight loss
- Less common: vomiting, blood in the stool, and fever are less common.
Symptoms usually begin 1 to 3 weeks after exposure and without treatment may last up to six weeks.
How is giardiasis spread?
Giardia usually spreads when Giardia lamblia (intestinalis) cysts within faeces contaminate food or water which is then eaten or drunk. It may also spread between people and from other animals.
Travelling in the developing world is a major risk factor
What is the treatment for giardiasis?
When symptoms are present treatment is typically with either tinidazole or metronidazole.
Helminth infections are associated with a high what as part of the body’s immune response?
Eosinophil count
When diagnosing a helminth infection, what is looked for in the stool?
Eggs
(from nematodes (roundworms), trematodes (flukes) or cestodes (tapeworms))
How do helminth infections come about?
Eggs are ingested
These will invade the gut wall, enter the venous system and pas sinto the liver, heart and lungs.
Alveoli are broken into and then the pathogenascends into the tracheobronchially into the gut to proliferate
What causes schistosomiasis?
Trematodes
(flukes)
After an infection causing giardiasis, which intolerance can be obtained?
What must be done to counteract this?
Lactose intolerance
Milk should be avoided for a few weeks after recovering
Schistosomiasis is associated with exposure to what?
Fresh water
What can shistosomiasis cause chronically?
- Hypertension
- Oesophageal varices
- Ascities
- Hepatomegaly
Cestodes (tapeworms) are often caused by which pathogens from which sources?
- Taenia solium (pork)
- Taenia saginatium (beef)
Both pathogens result from undercooked meat containing infectious larval cysts
Taenia solium eggs (often originating from infected and undercooked pork) can cause which condition?
Cysticercosis
Tissue cysts enter muscle and brain (neurocystercercosis) often producing seizures
