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Microbiology > Introduction - The Nature of Infection > Flashcards

Introduction - The Nature of Infection Flashcards

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Biology 101 flashcards
1
Q

List different types of micro-organisms/infectious agents in order of decreasing size

A 
Parasites
Fungi
Bacteria
Viruses
Prion Proteins
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2
Q

Describe the naming of organisms

A

Organisms have 2 names (in italics):
GENUS name - 1st letter is UPPER CASE

SPECIES name - 1st letter is LOWER case

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3
Q

What are prion proteins? Describe what they do and how they can be removed

A

Rare infectious agents that have no DNA/RNA; cause an incurable brain infection (brain matter lost, appears spongy)

Cannot be reliably removed by sterilisation/disinfection so surgical instruments are destroyed after use on such patients

Responsible prion disease like “mad cow disease” (AKA CJD - Creutzfeldt-Jakob Disease)

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4
Q

What are viruses? Describe their structure

A

Very small, obligate, intracellular parasites that contain either RNA or DNA

Can only be seen using an electron microscope

They have a protein coat (capsomere) and/or a lipid envelope

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5
Q

What are the methods used to diagnose a virus?

A

Cell cultures - no common now
Serology - antigen or antibody detection in blood
PCR - to detect the DNA or RNA. Important in giving real-time results as faster than cell culturing

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6
Q

Describe bacterial structure and contents

A

Can be seen with a light microscope

Contain both DNA and RNA and have a single double-stranded chromosome

They can have plasmids (extra pieces of circular DNA that often code for antibiotic resistance)

Have a cell membrane and cell wall and/or a capsule

The flagellae allow movement of the cell

The pili (fimbriae) allow adhesion of cell to surfaces

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7
Q

What are the different bacterial shapes?

A

Coccus (round)
Bacillus (rod-shaped)
Spirochaetes (spirals)

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8
Q

What is Gram Stain?

A

Stains the bacterial cell wall

Gram positive - purple (bacteria have a thicker peptidoglycan wall)

Gram negative - pink (thin bacterial cell wall so do not hold onto stain well)

Both can result from coccus or bacillus bacterial cells

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9
Q

Importance of gram stain

A

Allows guessing of the most likely organism

Also, many antibiotics act on cell wall so this is important in determining what antibiotic to use

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10
Q

Gram stain limitations

A 
Not all organism stain well:
Mycobacterium tuberculosis has a waxy coat that does not take up stain
Treponema pallidum (spirochaete organism; causes syphilis (STD)

Other staining method must therefore be used for these infections

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11
Q

What are commensal bacteria and give examples of regions where they are found

A

Normal bacterial flora that usually not harmful, if in the correct region

Upper respiratory tract
Lower small intestine and large bowel
Vagina
Skin - resident and transient flora (hand-washing effectively rids the transient flora)

Damp areas (armpits, groin) have rich flora

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12
Q

What is a pathogen? What is an opportunistic pathogen

A

A harmful organism

An organism that will probably only cause infection in an immunocompromised individual (e.g: due to immunosuppressants)

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13
Q

What is meant by pathogenicity?

A

Ability of a microorganism to cause disease

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14
Q

What is meant by virulence of a pathogen?

A

The degree of pathogenicity of an organism (how easily it causes disease)

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15
Q

How do bacteria replicate and what do they require?

A

Via binary fission. Require:
Food (any organic material)
Correct temp (37 C for most human pathogens)
Correct pH (7.4 for most human pathogens)

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16
Q

How does binary fission occur?

A

Bacteria undergo nucleic acid replication
2 sets of chromosomes go to opposite sides of cell
Cell wall forms, dividing cell into 2
Bacteria double

17
Q

What are the phases of bacterial growth?

A 
Lag phase (1st part of curve)
Log phase (exponential growth - nutrients available)
Stationary phase (rate of death = rate of regeneration; nutrients not abundant)
Death phase
18
Q

What kinds of atmosphere do bacteria grow in?

A

Aerobic
Microaerophilic
Anaerobic

19
Q

What are aerobic bacteria?

A

Grow in the presence of oxygen

Many will also grow anaerobically but not as well

20
Q

What are microaerophilic bacteria?

A

Grown in an atmosphere with reduced oxygen concentration with enriched with CO2

21
Q

What are anaerobic bacteria?

A

Only “strict” anaerobes

Grow in an atmosphere of no oxygen

22
Q

What toxins do bacteria produce?

A

These are enzymes

Exotoxin (mainly gram positive bacteria) - produced inside cell and exported from it

Endotoxin (mainly gram negative bacteria) - part of the outer membrane of the cell wall and usually only released for membrane when cell dies

23
Q

What are some effects of bacterial toxins?

A

Interact with immune cells causing release of cytokines

Damage red and white blood cells, leading to “leaky” small blood vessels; causes decreased BP and affects blood clotting.
Leads to sepsis and septic shock

24
Q

What are spores?

A

Inactive, hardy forms of bacteria that cannot replicate but can survive adverse conditions for many years (they are thick coats containing DNA)

Produced by some gram positive bacilli

25
Q

Steps of spore formation

A

Chromosome condensation and septum formation

Calcium dipicolinate accumulates in the core of the developing spore

26
Q

How are bacteria classified?

A

Gram positive/negative
Atmosphere in which they grow
Shape (bacilli/cocci)
Other: biochemical tests, coagulase, types of haemolysis on blood

27
Q

Bacteria diagnostic methods

A 
Microscopy
Culture
Detection of antigen
Detection of antibodies in blood
PCR
NAATS - (Nucleic Acid Amplification Tests) detection of organism's DNA/RNA
28
Q

Describe steps in bacterial cell culture

A

Culture samples on agar plates to allow bacterial growth

Use specialised tests to help identify organism, like biochemical reaction

Provide info on which antibiotics will be most effective:
Sensitive (S) - can be used to treat infection
Resistant (R) - cannot be used to treat infection

Gradually replaced by PCR

29
Q

Length of time for bacteriology tests

A

Microscopy - same day
PCR - same day (sometimes batched)
Agar culturing and antibiotic sensitivity tests - 48 hrs (24 to grow organism and 24 for sensitivity)
Serology - same day (often batched)
TB culture - 4-12 weeks (can be detected using PCR faster)

30
Q

Give examples of fungi and what they do

A

Moulds - complex structures that produce spores (spread in air currents) and hyphae (filaments that invade organic tissue). Do not stain with gram stain. Most common cause of fungal infection is Aspergillus spp

Yeast - single cell reproduce by BUDDING - not binary fission (mother cell gives rise to several budding daughter cells). Most common cause of fungal infection is Candida spp. Stain as large gram +ve oval structures

31
Q

Why are antibiotics not used to kill fungi?

A

Cell wall different from bacteria.

Special anti-fungal drugs used

32
Q

Describe parasites and their structure

A

Complex interaction with the host - “life cycle”

Structures are varied, from single-celled organisms (protozoa) to more complex organisms

33
Q

Give an example of a parasite with a simple life cycle and a complex life cycle

A

Giardidis - human host only

Shistosoma - worm whose life cycle involves humans and snails

34
Q

What is sterilisation?

A

Destruction and removal of 99.9% of microorganisms and spores (may not inactivate prion proteins)

35
Q

What are the methods of sterilisation?

A

Steam and pressure (autoclaves)
Dry heat in oven at 160C for over an hour
Exposure to ethylene oxide gas - explosive so must be done carefully
Gamma irradiation

36
Q

What is disinfection? What are powerful and mild disinfectants used for?

A

Removal/destruction of PATHOGENIC microorganisms to make item safe

Powerful - medical equipment that does not need to be sterile

Milder - hands, patient’s skin (antispectics)

37
Q

Methods of disinfection?

A

Hot Water

Chemical: bleach and handwash

Microbiology (13 decks)

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