Food Science #2 - Final: Part Two Flashcards
Why is Detection of Foodborne Pathogens needed?
- Epidemiology studies = surveillance, outbreaks, investigation;
- Clinical use = determine treatment;
- Food companies = production control, identify sanitation procedures, and prevent recalls;
- Regulatory research;
- Research
What are the criteria for a good method of detection?
- Speed;
- Sensitivity (false-negatives);
- Specific (false-positives);
- Multiple agents;
- Throughout (ease of use);
- Application in food samples;
- Cost
What are the types of Detection Methods?
- Culture;
- Immunological method;
- Molecular
What are the differences in “culture”?
“A” culture is the microorganisms that grow in a culture medium;
“To” culture means to grow the microorganisms in a culture medium
What is Culture Media?
- Solutions containing all of the nutrients and necessary physical growth parameters necessary for microbial growth;
- EX: Vibrio needs a salt component
What must be remembered when trying to culture bacteria?
Not ALL microorganisms can be grown in ANY given culture medium, and some can’t grow in any known medium
How can culture media be distinguished QUALITATIVELY?
- Solid vs. Broth;
- Non-Synthetic vs. Chemically Defined;
- Reducing - O2 Scavenging;
- Selective (suppresses);
- Differential (distinguishes)
What is Solid Medium (AGAR)?
- Contain a solidifying agent, AGAR;
- Has physical structure (broth has none) — colonies can grow;
- Types =
1. Slants;
2. Stabs;
3. Petri Dishes
What is a Colony?
A pile or mass of a sufficiently large enough number of cells growing on or in solid medium, that they are visible to the naked eye
What is Broth Medium?
LACKING solidifying agent, such as Agar
What is Chemically Undefined or Non-Synthetic Medium?
-Contain at least ONE component that is neither purified nor completely characterized nor even completely consistent from batch to batch;
-Usually have partially DIGESTED PROTEIN from various organisms;
-Solid or broth
EX: Broth from yeast (used for Vit. B)
What is SIMPLE Non-Synthetic Medium?
A SIMPLE non-synthetic medium, operationally defined, is capable of meeting the nutrient requirements of organisms requiring FEW growth factors
What is COMPLEX Non-Synthetic Medium?
- COMPLEX supplies additional (more) growth factors;
- COMPLEX are able to support more fastidious microorganisms than SIMPLE
What is Chemically DEFINED Medium?
- One prepared from PURIFIED ingredients and therefore whose EXACT composition is known;
- Must know EXACTLY what the microorganism’s GROWTH REQUIREMENTS are (trial and error)
What are Pre-Prepared Medium?
-Premixed in an often dehydrated and powdered state
What is Ready-to-Use Media?
- Sterilized and ready to use;
- Particularly useful when lacking an AUTOCLAVE, filtration devices, or desire to use pre-prepared media
What is Enriched Medium?
- Pre-prared medium to which MORE growth factors have been added;
- May be added individually ore in complex mixtures;
- May be chemically DEFINED, chemically Undefined complex/simple;
- EX: Blood Agar (complex medium with whole blood added)
What is Reducing Medium?
- Oxygen scavenging;
- Used for growing OBLIGATE ANAEROBES (ex. clostridium);
- Contain chemicals (reducing agents) that DEPLETE molecular O2
What is Selective Medium?
- Differential growth suppression =
- Supresses the growth of some microorganisms and allowing other;
- SOLID medium is employed with SELECTIVE medium so individual colonies are isolated
Examples of SELECTIVE Medium
- Mannitol Salt Agar = against non-skin flora (used for staph);
- Maccokey Agar = against gram-positive;
- Eosin Methylene Blue = against gram-positive
What is Differential Medium?
- Allows the growth of more than one microorganisms, but with MORPHOLOGICAL DIFFERENCES;
- Almost any medium containing specific substrate and well tailored indicators is differential
Examples of DIFFERENTIAL Medium
- Mannitol Salt Agar (fermentation = YELLOW);
- Blood Agar (hemolysis);
- Macconkey Agar (Lactose = YELLOW);
- Eoisin-Methylene Blue Agar (Green metallic sheen; E. coli)
What in an Enrichment Culture?
- Used to increase the relative concentration of certain microorganisms in the culture prior to plating on solid, selective medium;
- BROTH medium
What is the PURE Culture Technique?
- Method of culturing in which all of the individuals in a culture have descended from a SINGLE individual = CLONING;
- Used to =
1. Inhibit evolutionary change in cultures;
2. Allow characterization of microorganisms WITHOUT CONFOUNDING microorganisms
What is the basis of a Pure Culture?
- to ISOLATE, in colonies, individual cells and their descendants from other colonies of individual cells;
- Usually done on Petri Dishes = Streaking, Spreading, Pouring
When should isolation be repeated?
When isolating from complex mixtures need to re-streak at least once;
- Makes sure than colony is from only a single individual cell;
- After isolation from wild, characterize by inoculation on DIFFERENTIAL media to help identify
What is a Pour Plate?
- A method of melted agar inoculated followed by Petri Dish incubation;
- Used for QUANTIFYING microorganisms in Solid Medium;
- Embedded colonies supply sufficient oxygen deficient environment that can allow growth of microaerophiles
What are the step of making a Pour Plate?
- Cultures are inoculated into melted agar cooled to 45C;
- Liquid is mixed well then poured on petri dish;
- Colonies form WITHIN agar matrix rather than ON top as with streaking/spreading
What is a Spreading Plate?
- Another method of QUANTIFYING microbes on SOLID medium;
- Instead of embedding into agar (pour method), liquid cultures are SPREAD on the agar surface with a hockey stick;
- Advantage = Cultures are never exposed to 45C melted agar temps
What is Preserving Cultures Important?
- Scientific reasons;
- Indentification;
- Vaccine production;
- Industrial use
What are the methods of Preserving Cultures?
- Refrigeration;
- Stabs;
- Slants;
- Lyophilization (Freeze dry);
- Freezing
When is Refrigeration used to preserve cultures?
(4C);
- SHORT periods of times;
- Broth culures — don’t last long;
- Stabs;
- Slants;
- Streak
What is Stabbing?
- Cultures are stabbed deeply into agar using an inoculation needle;
- Stabs are incubated until VISIBLE cultures from, then sealed at stored at RT or lower
What is the Slant Method?
- Cultures may be streaked onto the surface of SOLID medium in a SLANT;
- Slants incubated until visible culture formation then sealed and stored at RT or lower
What is Lyphophilization or Freeze Drying?
- Lypophilization is freeze drying of cultures;
- Frozen and dried under vacuum;
- to REVIVE cultures, REHYDRATED by BROTH;
- LONG TERM storage
How are cultures Frozen with Protection?
- BROTH cultures are pelleted mixed with other ingredients to limit freezer damage and then frozen to −50C to −95C (mostly −80C);
- Thawed and transferred to Broth to REVIVE;
- Effective LONG term method
What is Colony Morphology?
- Gives important clues to IDENTIFY microorganisms;
1. One SIZE of colony;
2. Type of MARGIN;
3. Colony ELEVATION;
4. Colony TEXTURE:
5. LIGHT and transmission;
6. Colony PIGMENTATION
What determines Colony SIZE?
- Dependent not just on the TYPE of organisms but also the growth MEDIUM and NUMBER of colonies and culture MEDIA characteristics;
- Colonies SMALLER when greater than a certain amount are present
How long does it take colony SIZE to stabilize?
-After a day or two of incubation; Exceptions = 1. Slow growers; 2. Conditions that promote slow growth; — Growth will continue past first few days, especially when steps are taken to ensure slow growth
