An Introduction To Infection Flashcards
(28 cards)
Describe Louis Pasteur’s germ theory.
Pasteur further demonstrated that fermentation and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation.
He exposed freshly boiled broth to air in vessels that contained a filter to stop all particles passing through to the growth medium, and even with no filter at all, with air being admitted via a long tortuous tube that would not pass dust particles.
Nothing grew in the broths: therefore the living organisms that grew in such broths came from outside, as spores on dust, rather than being generated within the broth.
Explain Kochs postulates
Postulate 1: The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
Postulate 2: The microorganism must be isolated from a diseased organism and grown in pure culture.
Postulate 3: The cultured microorganism should cause disease when introduced into a healthy organism.
Postulate 4: The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
What is an infection?
It is an invasion of host’s tissues by microorganisms
& disease caused by
1) Microbial multiplication
2) Toxins
3) Host response
What is a symptom?
A response to an infection
How do people get infections?
- Physical contact - STIs
- Airborne spread - chickenpox and TB
- Vector - malaria
- Transmission due to ingestion of
contaminated food or water - Inhalation of air contaminated by
environmental organisms - Contact with contaminated surfaces,
including medical devices
What is a microbiota?
Microbiota = “commensals”
- A microbiota is “the ecological community of commensal, symbiotic and pathogenic microorganisms that literally share our body space
- micro-organisms carried on skin and mucosal surfaces
– normally harmless or even
beneficial
– transfer to other sites can be
harmful
What are the modes of transmission?
• Modes of horizontal transmission – Contact • direct • indirect • vectors – Inhalation • droplets • aerosols – Ingestion (faecal-oral transmission)
• Modes of Vertical transmission
– mother to child, before or at birth
How do microorganisms cause disease?
Exposure Adherence Invasion Multiplication Dissemination
Then the: Virulence factors: - Exotoxins - cytolytic - AB toxins - superantigens - enzymes • Endotoxins
This leads to host cellular damage. this can be:
• direct
• consequent to host immune response
What are the differences between bacteria and viruses?
Viruses must invade inside the host cell in order to replicate. They cannot do it alone.
List the pathogen and patient disease determinants
• Pathogen
– virulence factors
– inoculum size
– antimicrobial resistance
• Patient
– site of infection
– co-morbidities
- disease/health state
How do we know patients have an infection?
• history – symptoms • focal, systemic • severity • duration – potential exposures
• examination
– organ dysfunctions
• investigations
– specific
– supportive
What are the supportive investigations that can be carried out to check if a patient has an infection?
• Supportive Investigations
– Full blood count, neutrophils, lymphocytes
– C reactive protein (CRP)
– blood chemistry – liver and kidney function tests
– imaging – x-ray, ultrasound, magnetic
resonance imaging (MRI)
– histopathology
How would you carry out a bacteriology to check if a patient has an infection?
• Bacteriology:
– Specimen types
• swabs, fluids, tissues
– “M,C&S” • microscopy – bacterial cells (e.g.Gram stain) – patient cells e.g. cerebrospinal fluid (CSF) • culture • antibiotic susceptibility
– Antigen detection
– Nucleic acid detection
How can virology based techniques be used to check for possible infections?
– antigen detection (the
virus)
– antibody detection
(the patient’s
response)
– detecting viral nucleic
acid (DNA or RNA)
Who is involved in managing infections?
• All clinicians encounter patients with infections • Specialties whose primary interest is infection: – infectious diseases – medical microbiology and virology - genitourinary medicine – health protection
List 4 hot topics in infection
- new pathogens
- antimicrobial resistance • healthcare infections
- re-labelling of established diseases as infections
What are agar plates?
They are commonly used for the culture of bacteria
What is agar?
Agar is a polysaccharide derived from seaweeds
WHat are the properties of agar plates?
- It melts when heated to around 85 degrees but then when cooled, it doesn’t gel until 34-42 degrees.
- It is clearer than gelatine
- it resists digestion by bacterial enzymes
- It allow for inoculation at 40 degrees in it’s cool sate and yet incubated at 60 degrees without melting
- can be made with additional ingredients to facilitate bacterial growth, including proteins and NaCl.
Why is agar red?
The addition of blood - this makes it an enriched medium as the blood provides nutrients for a number of common bacteria.
What is chocolate agar? What is the purpose of chocolate agar?
In addition of lysed blood in agar makes it a darker brown colour.
It is used because there are some bacteria who cannot grow in the presence of blood cells and so the blood must be lysed to also allow the release of its Intracellular nutrients
What is the purpose of using the ‘Full Blood Count’?
The FBC is used as a broad screening test to check for such disorders as anaemia, infection, and many other diseases. It includes the following:
- White blood cell (WBC) count is a count of the actual number of white
blood cells per volume of blood. Both increases and decreases can be significant. - White blood cell differential: looks at the types of white blood cells
present. There are five different types of white blood cells, each with its own function. The differential classifies a person’s white blood cells into each type: neutrophils (also known as PMNs), lymphocytes, monocytes, eosinophils, and basophils. - The Red Blood Cell count: is a count of the actual number of red blood cells per volume of blood. Both increases and decreases can point to abnormal conditions.
- Haemoglobin measures the amount of oxygen-carrying protein in the
blood. - Haematocrit measures the amount of space red blood cells take up in the
blood. It is reported as a percentage (0 to 100) or a proportion (0 to 1). - Mean corpuscular volume (MCV) is a measurement of the average size of
your RBCs.
When would WBC count increase or decrease?
May be increased with infections, inflammation,
cancer, leukaemia;
Decreased with some medications, some autoimmune conditions, some viral or severe infections, bone marrow failure, enlarged spleen, liver disease, alcohol excess and congenital marrow aplasia (marrow doesn’t develop normally).
When would the % Neutrophil increase or decrease?
This is a dynamic population that varies somewhat from day to day depending on what is going on in the body. Neutrophils are one of the first lines of defence against bacterial infection. Neutrophils can be increased in some bacterial infections and would support a diagnosis. In some infections the white count and neutrophil count can be suppressed.
