Microbiology Flashcards
What is a coloniser?
just present within a host and is sometimes short lived
What is a pathogen?
microorganism that has the potential to cause tissue damage and disease
What is virulence?
likelihood of the pathogen to cause disease
What are the common infections of the abdomen?
peritonitis, liver abscess, cholangitis, perineal abscesses and
gastroenteritis abscesses
What is the structure of a gram positive bacteria?
thick peptidoglycan wall
What is the structure of a gram negative bacteria?
thin peptidoglycan wall but with many lipopolysaccharides
What is bacteriodes?
gram negative bacilli
What are enterobacteriaceae?
- gram negative and don’t form spores
- pink on agar
- endotoxins and enterotoxins
What bacteria are in the mouth?
strep viridans
What bacteria are in the stomach?
candida
What bacteria are in the large bowel?
- enterococcus eg faecalis
- coliforms
- strict anaerobes
What are the ways to identify bacteria?
- macroscopic: haemolysis
- microscopic: gram stain, organism shape and antigenic properties
- spores
- respiration
What can microbiology be used to test?
blood stool urine wound tissue culture
What is a test used in tayside for blood cultures?
MALDI-TOF
What are the important organisms that can be serotyped?
E.coli, salmonella and shigella
What are general risk factors for gastroenteritis?
- malnutrition
- closed communities
- exposure to contaminated food and water
- winter congregating
- young or older age
What drugs can cause gastroenteritis?
PPIs as they suppress acid so can cause C. diff
What can the immunosuppressed get?
salmonella
What is inoculum size?
different infections require different amount of bug so some diseases only need a small amount of pathogen to cause a problem
What is diarrhoea?
more than three unformed stools in one day with no other known cause, the stools will hold the shape of the container and show a departure from normal bowel habits
What can be used to type stool?
Bristol stool chart
What is dysentery?
diarrhoea with blood and mucus and is associated with fever, abdominal pain and tenesmus eg shigella
What is gastroenteritis?
an illness caused by eating food that has been contaminated with microorganisms, toxins, poisons etc
What does gastroenteritis present with?
diarrhoea, abdominal pain and vomiting
What are the important history questions in gastroenteritis?
food history, medicines, animal contact
What is the bacteria found in reheated rice?
Bacillus cereus is in reheated rice which is a gram positive bacillus that causes vomiting
What is the bacteria found in meat, milk and fish at room temperature?
Staphylococcus is a gram positive coccus
What are the most common invasive pathogens?
campylobacter and salmonella
What are the features of shigella?
- extremely infectious
- shiga toxin binds to receptors, inhibits protein synthesis and causes cell death
What are the features of E.coli?
- shiga-toxin producing
- mostly caused by 0157
- low infectious dose is needed for a problem to occur
- high risk in children and elderly
- comes from food eg raw milk, water or from animals
What is haemolytic uraemia syndrome?
comes from E.coli and treating with antibiotics which causes more toxin to be produced and there is a high mortality
What is the presentation of HUS and how is it identified and treated?
- low platelets and haemoglobin, high LDH, can develop after the bloody diarrhoea has stopped
- send a stool culture for all patients with bloody faeces
- don’t treat with antibiotics, NSAIDS or antimotility agents
- notify public health
Why is PCR not always good?
just because bug is present, doesn’t mean it is the one causing the presentation
What bug comes from uncooked poultry?
campylobacter
What bug comes from person to person spread and gives bloody diarrhoea?
shigella
What bug comes from undercooked meat and unpasteurised milk?
E. coli
What bug comes from milk, beef or eggs and gives sometimes bloody diarrhoea?
salmonella
What bug comes from an endemic area and gives diarrhoea?
vibrio cholerae
What virus comes from person to person spread and mostly in kids?
rotavirus
What virus comes from person to person spread and outbreaks in dense populations?
norovirus
What are the four types of E.coli?
- enterotoxigenic (makes heat stable toxin and is travel related)
- enteropathogenic (can be asymptomatic)
- enteroinvasive (watery diarrhoea)
- enteroaggregative (travellers diarrhoea)
What are the main features of E.coli 0157?
- blood diarrhoea
- children
- elderly
What are the features of campylobacter?
- poultry and raw milk
- treat with supportive or maybe macrolide
- very common
What are the features of salmonella?
- poultry, meat and raw eggs
- non-typhoidal
- D and V, blood and fever
- different antigens called O-antigens
- B,C and D are common locally
What are the features of listeria monocytogenes?
- grows in fridge
- causes fever, muscle aches and diarrhoea
- from unpasteurised milk, deli counter and soft cheese
- gram positive rod
What are the features of viral gastroenteritis?
- Rotavirus: vaccine, winter with kids, low infectious dose and rehydration treatment
- Norovirus: winter vomiting bug, all ages, explosive and sudden diarrhoea, closed communities
What does C diff produce?
toxin A and B
What causes C diff and why?
antibiotics kill off the normal gut flora and C diff will begin to proliferate
What are the symptoms of C diff infection?
- diarrhoea (sometimes bloody)
- abdominal pain
- severe cases have pseudomembranous colitis or bowel perforation
What is the C diff treatment?
less severe = oral metronidazole
severe = oral vancomycin (only time this is given orally and not IV)
What is c diff microbiologically?
gram positive
spore-bearing
bacillus
resistant to disinfectants
How is c diff diagnosed?
look for GDH
look for toxin A and B
no culture
What are the features of rotavirus?
- diarrhoea in the winter
- no blood
- treatment is supportive rehydration
- low infectious dose
- diagnosis is PCR on faeces
- vaccine in UK
What are the features of the noravirus?
- winter vomiting bug
- sudden explosive diarrhoea and vomiting for 2-4 days
- PCR diagnosis
- supportive treatment for dehydration
- still infectious after recovery
- outbreaks are common on cruises and in schools and hospitals
How do you tell if diarrhoea is infectious?
fever?
length of onset
What other infectious apart from diarrhoea diseases are spread by the faecal-oral route?
hepatitis A and E
What are antimicrobials?
all agents that act against all microorganisms so bacteria, fungi, viruses and protozoa
What are antibacterials?
only act on bacteria which includes antibiotics
What are antibiotics?
produced naturally by microorganisms and kill or inhibit growth of other microorganisms
What are the two ways in which antibiotic resistance can be acquired?
- vertical transmission (accumulation of mutations which are then passed on by replication)
- horizontal transmission (resistance genes are swapped from one microbe to another)
What are the main contributors to drug resistance?
prior antibiotic exposure
invasive procedures
prior hospitalization
underlying disease
What are the main areas of impact of antibiotic resistance?
health impact (morbidity and mortality)
economic impact (more treatment costs)
societal impact (lack of trust in healthcare)
Why do we see more resistance recently?
- More sick and chronically ill patients
- More immunocompromised
- More procedures and devices
- More pathogens
- Complacent antibiotic prescribing and increased use of broad-spectrum antibiotics
- Poor infection control
- Lots of patients in small areas
- International travel
What are the main parts of antimicrobial stewardship?
right drug
right dose
right duration
right de-escalation
What are the main rules for prescribing antibiotics?
- Use narrow spectrum
- Follow guidance
- Respond to positive microbiology
- Switch to oral if possible
- Do as short a course as possible
- Don’t give multiple courses if possible
- De-escalate the broad therapy quickly
- Only give surgical prophylaxis for 24 hours
