Summary - IPC Module 1

Question 1

Microorganism description

Answer 1

-too small to be seen without the aid of a microscope
-<0.1 mm
-usually unicellular
-also called “germs”, “microbes“, “bugs”

Question 2

Groups of Microorganisms

Answer 2

in order of decreasing size:

1. Protozoa - unicellular animals; move - flagella or ameboid motion (eg microbe Giardia that causes “beaver fever“)
2. Fungi - primitive plants
   yeasts - unicellular (eg. Candida – oral “yeast”)
   molds - multicellular (eg. microbe that causes ringworm/athletes foot)
3. Bacteria - unicellular, no organized nucleus, rigid cell wall (eg. causative agent of Strept throat, Staph infections, Salmonella infections)
4. Viruses - a bit of DNA or RNA surrounded by protein coat and sometimes lipid coat; grow only in other living cells (e.g. influenza virus, mumps, measles, rubell)

Question 3

Size of Microbes

Answer 3

unit of measurement = micrometer = 1/1000 mm

Question 4

Shapes of Bacteria

Answer 4

round = cocci (coccus)
rectangular = rods/bacilli (bacillus)
spiral/curved = spirilla (spirillum)

Question 5

Gram Reaction of Bacteria

Answer 5

1. Bacteria stained with gram’s staining procedure, appear dark blue (gram positive) or red (gram negative); determined by cell wall structure
2. Why the gram reaction is important:
   first step in identifying bacteria (look at shape and gram/color reaction)
   determines effectiveness of antibiotics
   determines effectiveness of disinfectants

Question 6

Bacterial Endospores

Answer 6

1. Only a few bacteria (some gram positive bacilli such as tetanus, gangrene, botulism, anthrax) can form these under adverse conditions (too dry, too cold, lack of nutrients).
2. Spores vegetate (start growing) when growth conditions become good
3. Spores resist drying, heat and disinfectants (i.e. hard to kill)
   heat: may take 121°C to kill
   disinfectants: require high level disinfectant and long exposure time

Question 7

Bacterial Growth

Answer 7

1. Reproduce by binary fission (Time for this to occur (for population to double) = generation time = 15-30 minutes for rapidly growing bacteria, under ideal conditions (enough food, H20, correct temperature))
2. In lab, grow bacteria on culture media
3. Colony = visible mass of bacteria that forms on surface of solid culture media; usually takes 18-24 hours to form from 1 original cell; each colony is a clone - all descendants of a single bacterial cell.

Question 8

Bacteria Growth Curve

Answer 8

4 Phases:

1. Lag - adapting to new environment (no symptoms, incubation phase)
2. Log - max reproduction (full blown symptoms, acute phase)
3. Stationary - no change in # (no better, no worse)

(on the mend)

4. Death - spores may form (convalescence)

Question 9

Viral Characteristics

Answer 9

Distinctive features:
- metabolically inert - can multiply only in living host cells
- contain DNA or RNA, not both
- have protein coat that surrounds nucleic acid ± lipid envelope

Strangely, lipid viruses are generally easier to destroy than those with only a protein coat. (exception Hepatitis B – lipid virus survives 7 days on surfaces)

Question 10

Multiplication of Animal Viruses

Answer 10

1. Attachment to complementary site on host cell membrane
2. Penetration
3. Viral nucleic acid → nucleus: takes command of host cell and directs synthesis of new viral components
4. Synthesis of viral components:
   nucleic acid - in nucleus
   protein coat - in cytoplasm
5. Assembly of viral components
6. Release from host cell

Question 11

Effects of Viruses on Host Cell

Answer 11

Usually host cell dies (lysis; diversion of metabolic pathways; destroyed by host’s own lymphocytes)

Host cell may be transformed into tumor cell

Question 12

Control of Viruses

Answer 12

Antibiotics have NO effect

Antiviral drugs : acyclovir; ZDV etc

More and more anti virals being developed. Problem is that viruses are inside host cells – have to develop drugs which will destroy viruses without destroying host cells