Introduction To Infection / Microbes Flashcards
What is infection?
It is the invasion of a host’s tissues by micro-organisms AND disease caused by: microbial multiplication, toxins and the host response.
How is infection spread from patient to patient?
By microbiota or ‘commensals’, which are carried on skin and mucosal surfaces (where they are normally harmless), being transferred to other sites (where they can be harmful).
What is a source in terms of infection?
The origin from which a host acquires an infection.
This can be endogenous (arising from a person’s own commensal microbial flora) or exogenous (from an individual, animal or foreign body).
What is an intermediary in terms of infection?
An intermediary is normally a vertebrate animal, which acts as a vehicle for pathogens to grow (normally spread by the sting or a bite of an arthropod). This vertebrate will then subsequently spread the pathogen to other animals who can become infected.
Give an example of an infection that can be spread from Source –> Intermediary –> Patient.
An example would be the Black Death, where fleas (with the bacteria Yersinia Pestis) would infect rats. The bacteria then would grow in rats (the ones who were resistant to the bacteria) who would act as intermediaries of the spread of the plague to humans and other animals.
Outline some other methods of transmission of infection.
Physical contact - e.g. STIs; Airborne spread - e.g. TB; May require a vector - e.g. Malaria and a mosquito.
The environment can be involved in the transmission of infection. Give three examples.
Transmission due to ingestion of contaminated food or water - e.g. Hepatitis A or Cholera; Inhalation of air contaminated by environmental organisms - Mesothelioma (due to asbestos exposure); Contact with contaminated surfaces, including medical devices (Staph / Strep ?!?!)
What are the three methods of horizontal transmission?
Contact: direct, inderect or vectors
Inhalation: droplets or aerosols
Ingestion (faecal-oral route)
What is vertical transmission?
Transmission of infection from mother to child. This can occur before or after birth.
There are 5 stages that micro-organisms must undertake to cause disease. What are they?
Exposure Adherance Invasion Multiplication Dissemination
What are virulence factors?
They are molecules released by a pathogens which allow them to:
Colonisation of a niche in the host (adherance)
Immunoevasion
Immunosuppression
Entry into and out of the host
Receive nutrition from the host
What is the difference between exo- and endotoxins?
They are both virulence factors. Exotoxins are toxins released by living bacterial cells into the body (e.g. cytolytic, AB toxins, superantigens, enzymes). Endotoxins are toxins present in bacterial cells, which are released when the cell disintegrates.
How can virulence factors cause host cellular damage?
Directly or
Damage is consequent to the host immune response
What are the determinants of disease? (Hint: 4 P’s)
Pathogen: virulence factors, inoculum size. antimicrobial resistance;
Patient: site of infection, co-morbidities
Practice: quality of health, immunity
Place: environmental engineering (terraced housing vs. detached?)
When dealing with infections what must we consider? (Hint: Don’t need to remember this, just practical, common-sense questions we must ask)
Is there an infection?
Where is the infection?
What is the cause of the infection?
What is the best treatment?
How do we know patients have an infection? (Hint: HEI)
History: symptoms - focal, systemic / severity / duration; potential exposures
Examination: organ dysfunctions
Investigations: specific & supportive
What are some supportive investigations we can use to diagnose someone with infection?
FBC - neutrophils & lymphocytes; CRP Blood chemistry - liver (ALT, AST; ALP & Bilirubin) & kidney function test (creatinine) Imaging - x-ray, US, MRI Histopathology
How do we know patients have bacterial infections? (Hint: M,C&S)
Specimen types: swabs, fluids, tissues;
M,C&S: microscopy (+/-ve stain on bacterial cells and analysing patient cells - e.g. CSF); culture; antibiotic susceptibility;
Antigen detection;
Nucleic acid detection
How do we know patients have viral infections?
Antigen detection (the virus) Antibody detection (the patient's response) Detecting viral nucleic acid (DNA or RNA)
