An Introduction to Microbes and An Infection Model

Question 1

What are the 4 types of microorganisms that cause human disease?

Answer 1

Viruses, bacteria (prokaryotes), fungi and parasites (eukaryotes).

Question 2

List the following in order of size from smallest to largest: proteins, bacteria, viruses, prions, eukaryotic cells (give examples), mycoplasma chlamydia rickettsiae (types of bacteria), worms and mitochondria.

Answer 2

Prions (10-8 m proteins that generate copies of themselves with resilient infectivity), proteins, viruses (can’t see unless under EM), Mycoplasma, Chlamydiae, Rickettsiae, mitochondria, bacteria, eukaryotic cells (yeasts/Protozoa/human cells), worms - potentially on macroscopic scale.

Question 3

Which microorganisms can’t survive outside the host cell and rely on its biochemistry to support metabolism and reproduction?

Answer 3

Viruses and Mycoplasma, Chlamydiae and Rickettsiae.

Question 4

What makes up a virus?

Answer 4

Nucleic acids (DNA/RNA), protein coat, maybe (lipid) envelope with spikes for attaching to specific areas. 
Different classes depend on whether is it has ds or ss nuclei acids, RNA or DNA and if it's gram positive or negative.

Question 5

Viruses may have trophisms, what does that mean?

Answer 5

Preferred certain tissues to replicate in.

Question 6

Transferable DNA may be found in bacteriophages, what are they?

Answer 6

Viruses that infect bacteria.

Question 7

Describe what a bacterium may be made up of.

Answer 7

May have a polysaccharide capsule which may change and is poorly immunogenic, no membrane around chromosomal DNA (prokaryotic) and plasmids which may replicate and be transferred to other bacteria (e.g. Genes for antibiotic resistance or virulence genes).

Question 8

What are the names of the different bacterial shapes?

Answer 8

Coccus/cocci are spherical, Bacillus/bacilli are rods and Spirrilus is zigzag shaped and more rare.
Rods tend to be single, but whether or not cocci are arranged as clusters or chains may help when deciding treatment.

Question 9

How can you tell if a bacterium is gram positive of negative and what does this mean?

Answer 9

Gram positive bacteria have a thick peptidoglycan wall and stain purple, whereas gram negative bacteria have a thinner peptidoglycan wall and stain red (the outer wall of liposaccharide and protein makes the host respond).

Question 10

Aside from gram positive/negative, how may bacteria be classified?

Answer 10

As Aerobes , which can survive in the presence of oxygen, Obligate aerobes which require oxygen for survival, Anaerobes which can survive in the absence of oxygen and Obligate anaerobes that require an oxygen free environment unless they’re able to form spores (doesn’t metabolise/reproduce, just survives and exists).

Question 11

Endotoxins and exotoxins are involved in the mechanisms of bacterial pathogenesis, what else is?

Answer 11

Virulence factors - host entry, adherence to host cell, invasiveness, iron sequestration.

Question 12

What’s the difference between prokaryotes and eukaryotes?

Answer 12

Circular, usually single chromosome (with sometimes extra chromosomal DNA as plasmids) / multiple chromosomes.
No nuclear envelope or nucleoli / present.
No membrane bound organelles / present.
Usually present cell wall, may contain peptidoglycan / present in plant cells, no peptidoglycan.
No carbohydrates or sterols in plasma membrane / some.
Ribosomes are 70S / 80S.

Question 13

What are the 2 types of fungi?

Answer 13

Yeast - single celled

Molds - multicellular

Question 14

What are the 2 types of parasites?

Answer 14

Protozoa - single celled

Helminths - worms, multicellular

Question 15

Describe the Adenovirus.

Answer 15

Group of viruses which can cause upper respiratory tract infection (as well as GI & conjunctivitis). Supportive treatment is needed to relieve symptoms - fluid and rest.

Question 16

Outline the infection model.

Answer 16

Pathogen + patient (mechanism of infection) –> infection –> management –>outcome.

Question 17

Many patient factors will affect the presentation of an infection, name some.

Answer 17

Age, gender, physiological and pathological state & social factors.

Question 18

How might time be considered in relation to an infection? What else might you ask about in terms of the recent past?

Answer 18

Calendar time may be used to consider what’s most likely at a certain time of year and relative time (specific incubation period) can also be considered when diagnosing, to see if it’s likely that symptoms are the result of a particular cause.
The location of the patient, current and patient should be obtained when thinking about infection.

Question 19

The mechanism of an infection/how it’s acquired DNA vary, give some examples.

Answer 19

Contiguous (direct) spread, inoculation, haematogenous, ingestion, inhalation, vector or vertical transmission.

Question 20

After attachment of a microorganism, toxin production, interaction with a host cell and possible resultant inflammation may cause host damage. What are the three stages of subsequent management?

Answer 20

Diagnosis - history, examination, investigations.
Treatment - specific or supportive.
Infection prevention - hospital or community.

The order may be rescheduled in life threatening situations where treatment may be necessary before definite diagnosis to avoid death - try to take blood before IV antibiotics administered.

Question 21

What needs to be asked to ascertain appropriate treatment of infection?

Answer 21

Where is the infection and what is it?

Question 22

What’s the difference between supportive and specific treatment?

Answer 22

Supportive treatment involves symptom relief and physiological restoration, whereas specific treatment may consist of antimicrobials, surgery (drainage, debridement and dead space removal). It all depends on the infection.