Lab Exam 2 Flashcards
Which group are identified/ isolated using EMB agar media
Inhibit growth of gram positive bacteria
Thus favoring growth of Gram- negative
Allows distinction of lactose fermenters and lactose non fermenters.
Biochemical basis of selectivity and differential ability of EMB media.
Eosin methylene blue agar contains aniline dyes that inhibit growth of gram positive.
Large amounts of acid from outside fermenters
Cause dye to precipitate on the colony surface producing a green color and pink.
Why is EMB a complex media?
Because it uses different dyes to rule out different bacteria growth. This makes it a complex media because it can do several things at once.
E. Coli identification using EMB
Eosin methylene blue agar is used as a selective and differential medium used for isolation and differentiation amount members of Enterbacteriacea.
The enteric gut bacteria.enteric bacteria are facultative lay anarobic gram negative rods.coliforms includeE. Coli
Eosin- pH indicater
EMB agar and their role
Selective and differential used for isolation and differentiation
Gut bacteria
Anaerobic gram- negative rods
Produce acid from lactose fermentation
And those that do not
Methylene blue and eosin which inhibit gram positive bacteria
Lactose makes EMB a differential medium in that it allows distinction between lactose fermenters and lactose non fermenters.
Producing green metallic sheen
Smaller amounts of acid produces pink
Non fermenters produce colorless
Streak plate and put method for colony isolation.
Bacteria from a mixed culture are streaked over the surface of the agar plate.
In a pattern that progressively pulls them farther apart.
Toward the end of the pattern, resulting in colonies should be separate from all others and maybe used ( picked) to start pure cultures.
Common errors in streak plate method.
Getting fresh cells on loop from original culture tube before streaking the second and 3rd section.
Failed to pass through previous sections 2 times.
Put method for colony isolation
Is a method with mixed melted agar and then placed into a petri plate.
Melted agar held with micro staphylococcus bacteria and bacteria that swarm instead of colinize.
Staining types
Simple stain
Differential stain
Special stains
Simple stain
Involves entire organism; shape and basic structures are visible
Including arrangement of cells
Are relatively less value in diagnostic bacteriology.
Differential stain
Involves application of two or more dyes together or separately
Main used to distinguish one group of bacteria from another
Various dyes reacts with different bacterial structural components
Gram stain
Acid fast stain
Spore stain
Real and virtual image
The objective lens magnifies the specimen to produce real image that is projected to ocular lens.
The real image is magnified by ocular lens to produce the virtual image.
Gram staining
Advantages
It’s relatively rapid and an extremely useful tool
Provides suggestive clues during the identification process
It provides valuable information to initiate course of ant microbial treatment
Gram stain
Disadvantage
Often disease causing bacteria don not have distinct stain charteristics.
The stain is not specific enough
The stain is stained poorly
Principle of starch hydrolysis test;
If bacteria are cultured on media contains starch as a sole sugar source some synthesize and secrete an enzyme called
Amylose
Amylase
Belongs to the class of EXOENZYME.
Iodine detects presence or abundance of intact starch around bacterial growth.
Iodine reacts with starch
Does not stain starch
So it leaves a haylow
Interpretations of enzyme tests result such as catalase
Catalase is an enzyme produced by many microbes to neutralize the toxic effect of hydrogen peroxide to generate water and oxygen,
Oxygen is released from the peroxide molecule is observed as a bubble.
Catalase presence can be detected by adding hydrogen peroxide directly onto the bacterial culture, tube or alternatively onto a dry smear of bacterial cell transferred onto a slide.
Lysozyme and their action
Lysozyme is an enzyme found in bodies secretion such as saliva, nasal secretion, tears, and also found in hens eggs ( constipated in white part)
Lysozyme hydrolyses the glycoside bond between the NAG-NAM units (the back bone components) of the bacteria cell wall.
Subsequently making bacterial cell susceptible to osmotic bursting.
Lysozyme action is more pronounced and clear in gram positive than negative walls cells.
Gram positive cells susceptibility to lysozyme action is due to a lack of a protective barrier.
In contrast, gram negative cells have an outer membrane which covers the peptidoglycan layer shields from enzymatic attack of lysozyme.
Acid fast bacteria
Belong to the Mycobacterium and Nocardia sps.
Acid fast bacteria
Bling to gram negative group
These bacteria belong to mycobacterium and Nocardia sps
Mycobacterium sps are responsible for deadly tuberculosis and leprosy in humans.
Acid fast bacteria
Staining these organisms is facilitated by application of heat and phenol(in the primary stain)
Once stained, these cells are able to retain the stain because of the waxy lipid, my colic acid cell wall that are not easily decolerized by acid alcohol, so they appear red.
The waxy coat makes them ( the cell) importable to routine stains; heating and prescence of phenol( in primary stain) facilitates dye uptake easily.
In contrast to acid fast cells, non acid fast cells decolonize readily and can be counter stained with another dye ( methane blue) and thus they appear blue.
BASIS of acid fast staining procedure
Is to isolate specific types of bacteria by the “acid fastness” or the ability to retain dye.
Acid fast bacteria
The appear red because they are not easily decolerized and cannot be counter stained.
Acini cells
Pancreas
Produce pancreatic juice which aids digestion
Pancreatic islet cells
They produce the endocrine hormones of the pancreas.
