Week 2

Question 1

How are bacteria classified?

Answer 1

1. Phenotypic:
   a) Physical appearance - morphology, cell wall composition, arrangement, motility, special features (capsule, endospores ect)
   b) Straining patterns (Gram, Acid fast)
   c) Biochemistry/metabolism related to growth - environmental (pH, temp, O2) and nutrition (source of energy, secondary metabolites)
   d) Antigenic structure - serology
2. Genotypic:
   a) Individual gene similarities - compare common and variable regions

Question 2

What does gram staining do?

Answer 2

1. In Gram-positive bacteria, the peptidoglycan forms a thick cell wall
2. In Gram-negative bacteria the peptidoglycan forms a thin layer with an outer membrane

Question 3

What are capsules?

Answer 3

1. Capsules are a polysaccharide or protein
2. They are important for survival and can act as a virulence factor:
   a) Allows bacteria to hide from immune system
   b) Aids sticking to tissues
   c) Extra layer improves survival in extreme conditions

Question 4

What are flagella?

Answer 4

1. Long helical filaments extending from cell surface
2. Enable bacteria to move within their environment
3. Flagella are built of protein components (flagellins) which are strongly antigenic

Question 5

What are pili?

Answer 5

1. Pili are more rigid than flagella and function in attachment either to other bacteria (sex pili) or to host cells (common pili)
2. The presence of many pili may help to prevent phagocytosis, reducing host resistance to bacterial infection

Question 6

What are endospores?

Answer 6

1. Tough, dormant, non reproductive structure of gram-positive rods of genus Clostridium and Bacillus
2. These bacteria can convert from a vegetative state to a dormant state under harsh conditions - can remain dormant for millions of years
3. Highly resistant to heat (boiling), cold, desiccation, radiation, enzyme degradation, chemicals extremes of pH, impenetrable to light

Question 7

What are bacteria toxins?

Answer 7

1. Toxic substances secreted to alter or destroy host cells or hyperstimulate the host immune response
2. Mostly secreted by bacteria for virulence
3. Two main types:
   a) Exotoxins: separate factors released from the pathogen into host tissue
   b) Endotoxins: part of the bacterial cell wall directly activates the immune system when the microbe dies - these can induce clotting, bleeding, inflammation, fever

Question 8

What are firmicutes?

Answer 8

1. Bacteria with a G + C content of less than 50%

2. Include clostridia, mycoplasmas, and other low G + C cocci and bacilli

Question 9

What are actinomycetes?

Answer 9

1. Bacteria that resemble fungi in that they can produce spores and form filaments
2. Include actinomyces, nocardia, and steptomyces

Question 10

What are proteobacteria?

Answer 10

1. Large group of gram-negative bacteria divided into 5 classes:
   a) Alpha
   b) Beta
   c) Gamma
   d) Delta
   e) Epsilon

Question 11

What are bacteroidetes?

Answer 11

1. Three large classes of gram negative, non-spore forming, anaerobic or aerobic, and rod-shaped bacteria

Question 12

What are Staphylococcus?

Answer 12

1. Gram-positive coccus - cells in clusters
2. Normal habitat: humans (and animals associated with them)
   a) Skin - especially nose and perineum
3. Spread via contact and airborne routes
4. Organism survives drying - is tolerant of salt and nitrites
5. 3 main types:
   a) Staph. Aureus (golden staph) - skin infection
   b) Staph. Epidermidis - skin infection
   c) Staph. Saprophyticus - urinary tract infection

Question 13

What are steptococcus?

Answer 13

1. Gram positive cocci
2. Normal habitat: humans and animals - respiratory tract
3. Spread via droplet spread
4. 2 main types of medically significant species:
   a) Steptococcus pyrogenes - throat infections
   b) Steptococcus pneumoniae - throat infection

Question 14

What are enterococcus?

Answer 14

1. Gram positive cocci
2. Normal habitat: gut of humans and animals
3. Spread by
4. More than 30 species - E. faecalis and E. faecium are most medically significant
   a) Cause urinary tract infection, endocarditis, infrequent but severe septicaemia after surgery and in the immunocompromised

Question 15

What are the lactobacillus?

Answer 15

1. Gram positive rods
2. Normal habitat: human NF in the GIT and urinogenital tract
   a) Important probiotic in the GIT
3. Produce H2O2, sodium butyrate and organic acids which inhibit Candida from colonising and forming a biofilm in the vagina

Question 16

What are Corynebacterium?

Answer 16

1. Gram positive rods
2. Natural habitat: usually nasopharynx and occasionally skin of humans
3. Infection spread by aerosol spray - patients may carry toxigenic organism for up to 2-3 months after infection
4. Most significant species: C. diphtheriae - throat infection

Question 17

What are bacillus?

Answer 17

1. Gram positive rods
2. Natural habitat: soil
3. 2 species of medical importance:
   a) B anthracis - infection is usually acquired when spores enter abrasions on the skin or are inhaled
   c) B cereus - spores found on many foods (e.g. rice, vegetables) and infections occur following ingestion of organism

Question 18

Discuss the requirements and effects of temperature on bacterial growth:

Answer 18

1. Bacteriea categorised in philes based on temperature they thrive in:
   a) Psychrophiles - low temperatures
   b) Mesophiles - moderate (~37 degrees C)
   c) Thermophiles - elevated temperature
2. Growth curve varies greatly between groups
   a) Each has a minimum, optimum, and maximum range Diagram 2
3. Different groups cause different problems

Question 19

Summarise the nutrient requirements for bacterial growth, for example special needs for amino acids in media:

Answer 19

1. Bacteria that need carbon sources
   a) Autotroph - produce their own CO2
   b) Heterotroph - need external organic source of carbon
2. Bacteria that can live on simple compounds such as NO3- and glucose
   a) Auxotroph - make all their own amino acids and vitamins
3. Bacteria that require complex compounds
   a) Prototroph - require external vitamins or amino acids
4. Where bacteria get their energy from
   a) Phototroph - sunlight
   b) Chemotroph - organic
5. Bacteria can need a large variety of food sources including:
   a) Carbon source
   b) Nitrogen source
   c) Sulfur
   d) Phosphorus
   e) Trace elements - e.g. Fe

Question 20

Describe the pH relationship with culture media used for isolation and growth of bacteria:

Answer 20

1. Bacteria are categorised in Philes based on what pH environment they thrive in:
   a) Acidophiles
   b) Neutrophiles
   c) Alkaphiles

Question 21

Explain the relevance of oxygen on growth of anaerobes, aerobe, and facultative growth:

Answer 21

1. Obligate aerobes - need O2 to grow
2. Facultative anaerobes - can use O2 but can also grow without it
3. Obligate anaerobes - die in the presence of O2

Question 22

What are different types of media?

Answer 22

1. Defined medium
   a) Has a defined general amount of medium
   b) Will not grow all bacteria - some need more specific contents
2. Complex medium
   a) Contains peptones or yeast extract or vitamins etc
   b) Fastidious bacteria that need these contents can grow
3. Selective medium
   a) Allow specific targeted bacteria to grow by altering environment to be highly specific
   b) E.g. alter salt levels, pH, nutrients etc

Question 23

What are Listeria?

Answer 23

1. Gram-positive rods
2. Natural habitat: widely distributed in nature - survives well in cold
   a) Reaches food chain via silage as well as more directly via vegetables
3. L. monocytogenes are most medically significant - cause meningitis and sepsis in neonates as well as infections in the immunocompromised