Tutorial 3 Flashcards
What is the difference between bacteria and archaea?
Features that archaea have that bacteria don’t:
Have unique rRNA sequences
lack peptidoglycan in cell wall
Some have unusual metabolic characteristics
Many live in extreme environments
Features in bacteria that archaea lack:
Ubiquitous and some live in extreme environments
Cyanobacteria produce lots of oxygen
What are viroids and virusoids?
Infectious agents composed of RNA
What are prions?
Infectious proteins
What factors affect generation times between bacterial species?
Environmental pH
Oxygen level
Nutrient availability
Temperature
What are the ways to measure bacterial growth?
Direct method
Indirect method
What are the stages of the bacterial growth curve?
Lag phase
Exponential phase
Stationary phase
Death phase
What happens during lag phase?
Hardly any reproduction while bacteria are adjusting to their environment
What happens during exponential phase?
Constant growth provided nutrients are available in abundance
What happens during stationary phase?
Decreased availability of nutrients causes dying bacteria to equal bacteria reproduction rate
What happens during death phase?
Inversely correlates with log phase where logarithmic decline takes place
What are the categories of growth requirements?
Physical (temp pH osmotic pressure)
Chemical
What are obligate aerobes?
Require oxygen for growth
What are obligate anaerobes?
Cannot survive in presence of oxygen
What are facultative anaerobes?
Can grow with or without oxygen
What are aerotolerant microbes?
Grows in oxygen but doesn’t use it in metabolism
Microaerophile requires only low levels of oxygen for growth
What are some fastidious bacteria?
Mycobacterium tuberculosis (grown in vivo)
Haemophilus influenza (grown on chocolate agar)
What are the types of media?
Solid (agar)
Liquid (broth)
What is the difference between selective and differential media?
Selective medium contains ingredients that prohibit growth of some organisms
Differential medium contains ingredients that can differentiate between organisms
What are some direct methods of measuring bacterial growth?
Direct cell counts
Cell-counting instruments
Viable cell counts
Plate counts
Membrane filtration
Most probable number
What are some indirect methods of measuring bacterial growth?
Measuring biomass
Turbidity (most often used)
Total weight
Chemical constituents
Measuring cell products
Acids and gases produced
What does TSB contain? Why?
tryptone and peptone to support growth of many fastidious organisms
What are kings A and B used for?
To enhance of the fluorescein and pyocyanin pigments of pseudomonas. These broth cultures change to yellow to indicate fluorescein production and green to indicate pyocyanin production
What is beta haemolysis?
Complete degradation of the red blood cells on the agar plate
What is alpha haemolysis?
Partial degradation of red blood cells
What is rogosa agar?
Selective medium for isolation of lactobacilli used to isolate lactobacilli in faeces, saliva, mouth rinsis and dairy products.
It contains acetate which lowers pH and allows lactic bacteria to grow alone.
Low magnesium, manganese and iron ensure optimal growth of lactobacilli. Glucose is used as carbon source
What is Cysteine Lactose Electrolyte Deficient Agar?
Fermentation of lactose results in yellow colonies and L-cysteine causes alkaine reaction that results in blue colonies
What kind of zone does alpha haemolysis produce?
Greenish coloured zones
What is mannitol salt agar?
a selective-differential medium.
It uses a nutrition medium containing 7.5% salt a single major carbon source and an acid base indicator.
Result is growth of salt tolerant, mannitol fermentors of different kinds that show up in different colours
What is CHROMagar Candida?
Selective/differential media for identification of yeasts.
Selective medium for isolation and presumptive isolation of yeasts and filamentous fungi
What is CHROMagar Candida used to detect?
Yeasts and filamentous fungi
What do yeasts look like in CHROMagar Candida culture?
Produce different colours based on species:
Candida albicans green
Candida tropicalis small smooth metallic blue
Candid krusei large rough pale pink to mauve with white colony borders
Candida parapsilosis large smooth white to pale pink colonies
Candida guilliermondii large smooth dark purple with white colony borders
Candida stellatoidea small smooth deep greeny-blue colonies
What is HEKTOEN ENTERIC AGAR?
Selective-differential medium for isolation of food poisoning organisms. Different bacteria produce different colored colonies
How does Hektoen Enteric Agar work?
Contains various sugars as carbon sources which cannot be used by salmonella or shigella.
Peptone metabolism by salmonella and shigella results in an increase in pH turning the indicator blue.
Medium contains thiosulphate which forms black precipitate in presence of hydrogen sulphide and appears black/brown
Shigella does not produce hydrogen sulphide and so it looks green
What is Xylose Lysine Deoxycholate Agar?
XLD agar is another selective+differential medium to isolate pathogens from enteric specimens
How does XLD work?
Xylose is present which can be fermented by salmonella and decarboxylated to keep medium red however hydrogen sulphides make colonies have black center.
Shigella cannot ferment xylose and remains red.
E.coli ferment lactose and sucrose acidifying the medium resulting in yellow colonies
What is MEGA (Membrane Enriched Enterococcus Glucoside Azide Agar)?
Medium used in the membrane filtration analysis of water samples to select for faecal streptococci.
What does MEGA contain?
Sodium azide at a concentration inhivitory to coliform organisms and most other gram negative bacteria.
2, 3, 5 - triphenyl tetrazolium chloride which can be reduced by faecal streptococci to form formazan.
What is MESLS?
Medium used in membrane filtration analysis of water samples to select for faecal coliforms.
How does MESLS work?
Sodium lauryl sulfate acts to inhibit growth of non-coliform bacteria.
Lactose is the sole carbohydrate available and phenol red is the indicator of acidity
How do bacteria selected for look like on MESLS agar?
Lactose fermenting colonies appear yellow while other non-coliform bacteria are pink
What is E.coli used for?
indicator organism for monitoring faecal contamination of water sources.
What are the features of ideal indicator organisms?
Present when pathogens are present
Present only when there is danger of pathogens
Occue in greater numbers than pathogens
Survive in the environment as long as the pathogens are present
Easy to detect
Should not multiply in water and thus distort numbers
What are the limitations of using E.coli for monitoring pollution?
It does not reflect possible presence of protozoa and is not linked with possible viral contaminants such as enteroviruses
What are slope cultures?
agar cultures that are liquid but not broths
What are urea slopes?
slopes used for detection of organisms that can hydrolyse urea by producing urease.
All proteus species have urease which can be differentiated from other members of enterobacteraceae
How does a capsule appear when stained with india ink?
Like a halo around bacteria
What bacteria are detected using ZIEHL NEESON ACID-FAST stain?
Mycobacterium species such as M.tubercolosis or M.leprae
What makes cell wall difficult to penetrate and how is that fixed with ZIEHL-NEELSON ACID-FAST stain?
Mycolic acid in cell walls make cell wall difficult to penetrate. Heat is used to permit entry of the stain.
Acid-fast because positive cells retain colour after being washed with acid
How does kinyoun’s stain work?
Waxy mycolic acid in cell envelope is resistant to drying which improves survival in environment.
Mycolic acid binds with the stain carbol fuchsin and cannot be removed with acid-alcohol during decolourisation step.
How is tuberculosis diagnosed?
Kinyoun’s stain on sample from sputum
What are the staining reagents of kinyoun’s stain?
Kinyoun’s carbol fuchsin
3% acid alcohol
0.3% aqueous methylene blue counterstain
What do acid fast bacteria look like on kinyoun’s stain?
Red against blue background
Non-acid fast bacteria stain blue/purple
Endospore staining
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