Investigating Infections Flashcards
Why do we do a microbiological investigation of a patient? What does this achieve?
Targeted treatment
Prognostication
Prevention in others: eg prophylaxis, vaccination,
Epidemiological info: outbreaks, public health and vaccination
Generates research questions
The successful identification of microbe depends on…
Good quality specimens!
Good aseptic techniques
Correctly obtaining the specimen (infection site; commensals; amount and number of samples)
Timing- acute phase of disease, quick transport of the sample
Describe gram positive cell walls
Thick peptidog layer and teichoic acid.
Peptidoglycan cross linkages is penicillin’s target site
Crystal violet in the stain binds to teichoic acid and resists decolouring to leave a purple colour
Describe gram negative cell walls
Gram-neg wall consists of an outer membrane of phospholipids, lipopolysaccs, proteins and protein channels called porins.
Between the outer membrane and cell membrane=periplasmic space. This stores antibiotic inactivating enzymes in some bacteria. Thin peptidog layer in this space.
They pick up red safranin –> look red
Describe how nutrient agar is used for bacterial cultures
What are the other types of agar plates and why are they used to culture and visualise bacteria?
MacConkey agar = bile salts + lactose indicator cultured overnight at 37oC in air;
Campy-blood agar (selective for Camplyobacter jejuni) - incubated at 42c in anaerobic jar- microaerophilic
( These types of plates used bc some organisms need specific growth requirements eg blood etc )
What does it mean si hay haemolysis on blood agar plates?
Describe the optimum growth conditions for different types of bacteria
What are the limitations of using agar plates?
Growth on the agar plate can be due to normal flora, especially from non sterile sites like mucus
Describe blood cultures
Blood is cultured in special growth media to promote bacterial growth
Blood is cultured both aerobically and anaerobically (purple tops) to detect aerobe and anaerobe bacteria.
Give some other ways in which infections are investigated
Biochemical speciation- Metabolic function and sugar utilisation tests which identify Salmonella, Shigella, E.coli
MALDI-TOF MS: Small part of colony is picked off plate and layered onto a steel MALDI plate, then undergoes mass spectroscopy
Quantitative and normal PCR followed by gel electrophoresis
