Bacterial Identification Flashcards
Bacterial streak plate technique:
What does it mean if a medium is selective vs differential? How is MacConkey’s agar a good example of both?
SELECTIVE = isolate a particular type of microorganism by giving a specific condition for the growth
DIFFERENTIAL = identify and differentiate microorganisms from a closely-related group with the help of unique growth patterns
selects against Gram positive bacteria and differentiates between the lactose utilizers of the growing Gram negative bacteria
What does it mean to inoculate an agar plate?
gradual dilution of an inoculum of bacteria over the surface of an agar plate to produce single isolated pure colonies
What are 6 major characteristics used to identify colonies on the surface of an agar plate?
- SURFACE: smooth. glistening, rough, granular, wrinkled, dry, powdery
- WHOLE COLONY: circular, filamentous, irregular, rhizoid, punctiform
- ELEVATION: flat, raised, convex, pulvinate, umbonate
- MARGIN: entire, undulate, curled, lobate, serrate, filamentous
- SIZE: diameter, pinpoint, small, medium, large
- COLOR: pigmentation
What are the 2 major ways that bacterial can be characterized microscopically?
- size, shape, grouping: bacilli, cocci, clusters, chains
- Gram staining: G+, G-, refractile spore
What are the 2 ways of testing bacterial motility?
- WET MOUNT: direct microscopic observation of bacteria in liquid to see if it will move around
- MOTILITY CULTURE: soft agar is inoculated by being stabbed by a contaminated applicators; nonmotile species will grow in a straight line and motile species will move and grow through out the medium
Why are serological tests able to identify bacteria? What antigens are produced by flagella, LPS on the cell wall, and capsules?
each species has unique antigenic components
H antigens = flagella, protein
O antigens = LPS, polysaccharides
K antigens = capsule, polysaccharides, protein
What is slide agglutination? What bacteria is commonly screened in this method?
antibodies against a specific, known bacteria are suspended in saline and antiserum containing an unknown bacteria - if bacteria are seen to clump together with the marked antibodies, the identity of the bacteria can be matched to the known antibody
- SIMPLE, INEXPENSIVE, QUICK
Salmonella
What is the major advantage to identifying bacteria using ELISA, latex agglutination and Western Blotting?
don’t need to isolate pathogen - can just use patient’s serum
How is carbohydrate utilization tested for in a bacterial colony using the Durham tube?
the media is innoculated within the media and incubated
- if the red media turns yellow, it indicates that the pH is dropping and the growing bacteria is fermenting carbohydrates
- if bubbles form in the upside-down Durham tube, the bacteria is also producing gases
What is the purpose of Triple Sugar Iron medium?
differentiate enteric bacteria based on their abillity to ferment sugars, produce hydrogen sulfide, and/or produce gas
How does the deamination, sesulfurylation, an decarboylation of peptide bonds affect the environment?
DEAMINATION using deaminase produced NH4+ and OH-, alkalizing the pH
DESULFURYLATION using desulfurylase produces FeS, produces and insoluble black material
DECARBOXYLATION using decarboxylase produces RH and CO2, alkalizing the pH
How does sugar fermentation, sugar oxidization, and amino acids carboxylations affect pH of the environment?
SF: produces acids, dropping pH
SO: produces weak acids, no major effect on pH
AAC: produces bases, increasing pH
What is an enterotube?
multiple-test system which combines nine biochemical tests (different media with a specific substrate in each compartment) useful in the identification of members of the family Enterobacteriaceae
What is the API 20E System?
a better test for enteric Gram negative bacteria compared to the enterotube
biochemical panel for identification and differentiation of members of the family Enterobacteriaceae using a generated numeric porofile that can be matched to bacterial ID/DNA
