what are commensal, opportunistic and primary pathogens
commensal = no disease, normal e.g. lactobacillus, E.coli
opportunistic = occasional disease, e.g. E.coli, staph aureus
primary = highly virulent, mycobacterium tuberculosis
what are the different bacterial shapes?
- cocci -> diplo or cluster
- bacilli -> short rods, long, chains
- curved
- spiral
how do bacteria hold genetic material?
- chromosome -> single circle
- extrachomsomal plasmid
gram neg and pos characterisitcs
neg:
- thin cell wall
- bound by outer membrane
- lipospolysaccharides in outer membrane
- periplasmic space
- pink
pos:
- thick cell wall
- regular structure
- Teichoic acid
- purple
what are the steps of a gram stain?
- Fixation: By Heat
- Crystal violet: Primary Stain
Penetrates the cell wall of Gram positive and negative cells - Mordant or fixer: Iodine
Make an iodine-crystal violet complex - Decolouriser: Alcohol or acetone
Gram-negative bacteria: Alcohol interacts with lips leading to
the loss of the outer membrane and expose thin peptidoglycan
layer. Iodine-crystal violet complex is washed away.
Gram-positive bacteria: Cells become dehydrated trapping
iodine-crystal violet complex in the large multi-layered
peptidoglycan layer - Counterstain: Safrain/ carbol fusion
Gram-positive retain the purple colour and Gram-negative appear
as pink colour (colour of counter stain)
what are Lipopolysaccharides
- gram neg bacteria only
- LPS or “Endotoxin” 3 components:
- O antigen side chain = antigenic variation
- lipid A = toxin
- core polysaccharide
what is a capsule, what does it do
- polysaccharides or polypeptides -> pathogenicity and cell protection, attachment
what are pili vs fimbriae
pili = longer, few per cell, conjugation
fimbriae = attachment to mucosal surfaces
- in gram negatives
- NOT in corynebacteriums
what does a sex pilus do
- Conjugation
I- involves a donor (D) and a
recipient (R) - Transfer of:
Virulence genes (eg fimbriae)
Antibiotic resistance genes
what are flagella
- chemotaxis or motility
- rotate counter clokcwise, dont flex
- require rotary engine for energy
- antigenic -> immune response
what are endospores
- Large Gram positive rods
- Bacillus anthracis (anthrax)
- Clostridium tetani (tetanus)
- Contain DNA and thick cell
layers - Remains dormant
- Extremely resistant to
environmental stress
what are the patterns of haemolysis
alpha = partial (green)
beta = complete (yellow/clear)
gama = none
what does maconkey agar select for
For enteric Gram-negative
bacteria
* Differentiation based on
lactose fermentation
* Crystal violet inhibits
Gram-positive bacteria
what temp and pH do bacteria mostly like
37 degrees
- 7.2-7.6
what are the oxygen classes for bacteria
1.Aerobes: Require oxygen to grow
2. Facultative Anaerobes: Can grow in aerobic/anaerobic condition
3. Aero-tolerant Anaerobes: Anaerobes that can tolerate oxygen but does not require it for growth
4. Strict Anaerobes: Unable to grow in the
presence of oxygen
5. Microaerophilic: Require reduced oxygen concentration for growth
examples of different aerobe classes
aerobes = pseudomonas spp
facultative anaerobe = E.coli
strict anearobe = dichelobacter spp
microaerophilic = brucella spp
how to store bacteria long term
- slopes, freeze dry, -80 degrees
what are the 3 steps of binary fission
- DNA rep
- cell elongation
- cell division
how to calculate bacteria population growth
- exponential
- 2^number of generations
- 2,4,8,16
what are the phases of population growth
- lag phase -> alive but no increase, adjusting
- log phase (exponential) ->growing and dividing
- stationary phase -> nutrient depletion etc stops increase
- death (decline) phase -> can’t keep surviving with no nutrients etc
how is bacterial growth measured
- turbidity = absorbance at 600nm -> Mcfarlan standard and growth curve, appx bacterial count
- count of viable cells -> agar plate at low dilutions of colony -> should be at 3.2 x 10^5 CFU/ml to not have too many or too few
- viable count done during death phase
what is the gold standard to belong to same species of bacteria
- 16S rDNA sequence >98% identical, reassociatiion = 70% match
why is 16S rRNA sequencing used to compare bacteria
- present in all
- function hasn’t changed over time
- large enough for info 1500bp
what are the steps for bacterial ID in a vet lab, who is responsible
- Correct sampling procedure and provision of adequate history*
2) Transport to the Lab to ensure viability of the suspect organism and minimal contamination
* cold chain and right media
3) Growth, identification and antibiotic sensitivity testing of aetiological agent
*responsibility of the veterinarian
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BACTERIA GENERAL30
-
Bacterial Genetics38
-
gram pos -> staphyloccocus20
-
gram pos -> strep and enterococcus25
-
Small gram pos rods: actinobacteria6
-
Small gram pos rods - listeria spp6
-
small gram pos rods: rhodococcus equi, Erysipelothrix rhusiopathiae7
-
Corynebacterium4
-
Large gram pos rods: bacillus spp10
-
gram pos rods - clostridum spp10
-
Enteroobacteriaceae19
-
Salmonella spp, Yersinia spp. & Pseudomonas spp.8
-
Yersinia spp.6
-
Pseudomonas spp.4
-
Burkholderia and Aeromonas2
-
Pasteurella6
-
Actinobacillus spp + others6
-
Respiratory/ Mucosal Pathogens II and Reproductive Pathogens10
-
Brucella Spp.7
-
Campylobacter6
-
Taylorella, Lawsonia intracellularis, Helicobacter and Vibrio8
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gram neg anaerobes and mycoplasma19
-
Spirochaetes & Mycobacterium16
