Bacteriology L2

Question 1

Factors required for bacterial growth
Sources of metabolic energy:

Answer 1

Aerobic respiration: requires oxygen
Anaerobic respiration: other final electron acceptors than oxygen
Fermentation: lactic-acid, acetic acid, carbon-dioxide, proteolytic
Photosynthesis: converting light energy into chemical energy

Question 2

Factors required for bacterial growth
Gaseous requirements: oxygen and carbon dioxide

Answer 2

Aerobes: cannot grow without oxygen
Facultative anaerobes: grow under both aerobic and anaerobic conditions
Anaerobes: only grow in absence of free oxygen
Microaerophiles: require oxygen in lower levels than present in atmosphere (2-10% O2)
Capnophiles: require carbon dioxide for optimal growth

Question 3

Factors required for bacterial growth
Environmental factors:

Answer 3

Nutrients (e.g source of C, N and H, minerals, growth factors, vitamins, trace elements)
pH (most pathogenic bacteria grow best at 7.2-7.4)
Ionic strength and osmotic pressure
Light
Temperature (most are mesophilic)

Question 4

Bacteria replicates by

Answer 4

Binary fission

Question 5

Generation time

Answer 5

length of time required for a single bacterial cell to yield two daughter cells (30min- 20h)

Question 6

Bacteria growth curve with 4 phases

Answer 6

Lag phase
Exponential/ logarithmic phase
Maximal stationary phase
Decline/ Death phase

Question 7

Lag phase

Answer 7

increase in cell size, active metabolism of cells but no division

Question 8

Exponential/ Logarithmic phase

Answer 8

cells multiply at maximum rate

Question 9

Maximal stationary phase

Answer 9

Due to exhaustion of nutrients or accumulation of toxic products, growth is ceased, balance between slow multiplication and death rate (note: spore formation occurs)

Question 10

Decline/ Death phase

Answer 10

progressive death of cells

Question 11

Methods for counting bacteria

Answer 11

Microscopic counting
Colony counting (CFU/mL)

The size of bacteria populations is expressed as the number or density of cells present

Question 12

Microscopic counting

Answer 12

Direct smear: counts carried out on a fixed and stained smear from a defined volume of fluid
Counting chamber: counts carried out on a fixed volume of bacterial suspension using a calibrated slide

Question 13

Colony counting (CFU/ mL)

Answer 13

Spread plate method: following serial ten-fold dilution of bacterial suspension, a fixed volume is spread on the surface
Pour plate method: following serial ten-fold dilution, 0.1mL of each dilution is placed in Petri dishes and 20mL agar is added

Question 14

Bacterial colony

Answer 14

a visible mass of bacteria all originating from a single mother cell. Thus a bacterial colony constitutes a clone of bacteria all genetically alike
Bacteria grow on solid media as colonies
When counting bacteria, a colony-forming unit (CFU) is used to estimate the number of viable bacteria

Question 15

Phylogenetic tree of life

Answer 15

diagram representing evolutionary relationships among organisms
Based on comparative gene sequence analyses of conserved genes (16S, 23S, rRNA)
Recent development towards whole genome-based phylogeny

Question 16

Taxonomy

Answer 16

study of bacterial identification
-permits accurate identification
-precise naming for efficient communication
-group similar organisms

Question 17

Polyphasic taxonomy

Answer 17

classification of bacteria as evaluated by both genotypic, phylogenetic and phenotypic properties
-morphology and motility
-metabolism and physiology
-biochemical characteristics (e.g fatty acid composition)
-DNA profiling, GC ratio, multilocus sequence typing (MLST)
-16S rRNA gene sequencing
-Whole genome sequencing

Question 18

Species

Answer 18

basic taxonomic unit
group or population composed of similar individuals that are capable of interbreeding naturally and are reproductively isolated from other groups

Question 19

Symbiont

Answer 19

organism living in symbiosis (the living together of two dissimilar organisms)

Question 20

Mutualism

Answer 20

two organisms of different species in symbiotic relationship in which both benefit from it

Question 21

Commensalism

Answer 21

relation between two species in which one obtains food or other benefits from the other without either harming or benefiting the latter

Question 22

Pathogen

Answer 22

infectious agent= microorganism that can cause disease upon colonization of the host

Question 23

Obligate pathogen

Answer 23

microorganism which must infect a host and cause disease in order to multiply and be transmitted from one host to another

Question 24

Facultative pathogen

Answer 24

microorganism which can infect and multiply in hosts but is also capable of multiplying in the environment

Question 25

Opportunistic pathogen

Answer 25

microorganism which does not ordinarily cause disease but which, under certain conditions (e.g impaired host immunity) becomes pathogenic

Question 26

Infectious disease Host

Answer 26

Breed age, sex, genotype Physiology and 'damage' Immunity

Question 27

Infectious disease Pathogen

Answer 27

(geno)type Virulence, resistance, survival Route, vector tropism Inoculation dose

Question 28

Infectious disease Environment

Answer 28

Housing, management, hygiene Nutrition Disease control

Question 29

Infectious disease

Answer 29

represents complex interactions between host, pathogen and environment

Question 30

Disease

Answer 30

a disorder of structure or funtion in the host