Diagnostic Methods & Bioassays Flashcards
What are the 5 components of diagnostic testing operations and bioassays?
- food type and environment
- sample collection plan
- hazard to be tested
- interpretation and decision based on lab results (hazard limits)
- analytical methods used for detection, enumeration, or quantification
What are the possible objects tested on diagnostic testing?
- meat
- whole edible egg after shell removal
- cheese
- whole fish/shellfish after shell, head, tail, and gut removal
- milk
- water
- utensils, equipment, surfaces
What food and environment sampling are done for diagnostic testing?
FOOD: raw ingredient or products in-process, ready for market, at grocery, or ready to eat
ENVIRONMENT: food contact surface, non-food contact surfaces (floors, drains, carts, equipment housing), water, air
What 4 parts are in the sampling plans?
- sample size
- sample type
- weight/volume per sample
- sampling interval per year
What sample size is recommended for diagnostic tests? What interval is usually used? What additional way does the USDA do?
33-60 —> quarterly
50 samples where 5 samples are collected weekly over 10 weeks
How much weight/volume is recommended for sampling different tests?
- meat: 25 g or 100 cm^2 swab
- whole egg, cheese, or fish/shellfish
- milk/water: 100 mL
- utensils, equipment, surfaces: 100 cm^2 swab
What are the 3 types of hazards in foods used for testing?
- Biological: microbiological, natural toxins, parasites
- Chemical: unapproved food or color additives, allergens, pesticide, natural toxins (mycotoxins, shellfish), drug residues
- Physical: metal, glass, sand, sharp materials
How are samples processed for biological hazards?
- mix sample in broth at 1:4 sample to broth ratio
- dilute each sample 10-fold dilution up to 10^-4
- subculture each dilution 8-48 hours in 5 tubes
How are samples processed for chemical hazards?
- collect samples
- grind, chop, homogenize
- inject 10-20 µL sample into analytical equipment
What quantitative test is used for detecting bacteria?
direct bacteria plating
- 1:4 dilution followed by 10-fold dilution up to 10^-4 and culture in agar
- plate 0.1 mL from test tubes and incubate on plates
- culture and count colonies
What are the 2 types of microbes found in the food supply chain?
- indicators or sanitary (GHP monitoring)
- dangerous pathogens (food safety)
What 3 counts are used to measure sanitary procedures? What are they 3 overall indicators for?
- coliform colony count
- mesophilic or aerobic colony count
- E. coli colony count
food quality, shelf-life, GHP at any stage in food supply chains
What are the 11 major dangerous pathogens that are used as indicators of food safety?
- Salmonella - all foods
- Shigella
- Yersinia
- Listeria - almost all foods
- Bacillus cereus - crop foods
- Vibrio spp. - seafood
- STEC - protein-rich foods
- Campylobacter - poultry, milk, water
- Norovirus
- Cyclospora
- Cryptosporidium
(occur in food at low incidence and in few food/animals)
In what 3 ways are samples of microbiological test interpreted?
- 2-class (qualitative/categorical)
- prevalence limit method
- 3-class (numerical/quantitative)
What prevalence demands corrective actions in pig, poultry, and beef? Recall?
PIG - > 6%
POULTRY - > 14%
BEEF - > 4%
(> 0%)
What are decisions based on in two-class decision plans? How are decisions made?
uses qualitative/categorical for microbial concentration in food samples based on presence/absence of pathogens in a food sample
decisions based on 25 g —> no bacteria = satisfactory; bacteria = potentially hazardous
(present/absent, satisfactory/unsatisfactory, accept/reject)
What are decisions based on in three-class decision plans? How are decisions made?
uses numerical values for microbial concentration in food samples based on cfu/g of pathogens
- < 10^2 = satisfactory
- 10^2 - 10^3 = marginal
- 10^3 - 10^4 = unsatisfactory
(satisfactory/borderline/unsatisfactory, accept/doubtful/unsatisfactory)
Pathogen concentrations detected in food:
What is the likely cause of the necessity for proper hygiene action following decisions based on diagnostic results?
inadequate time and temperature control during cooling, storage, processing, or reheating
slow or inadequate cooling, reheating, or cooking of large production volumes
What is the basis for detecting foodborne contaminants?
central dogma - DNA —> RNA —> protein
- DNA-RNA-protein-based test: culture independent diagnostic test (CDIT)
- microbiology and parasitology
- biological activity assays on host cells, tissues, or animals
What are some tests that use DNA, RNA, proteins/metabolites, or nucleic acids/enzymes/antibodies?
DNA - PCR, nucleic acid probe, DNA microarray, whole genome sequencing, metagenomics
RNA - RNA viruses, mRNA, rtPCR
P/M - ELISA, lateral flow assay, gel diffusion assay, fluorescent anitbody, radioimmunoassay, MALDI-TOF, HPLC
NA/E/A - biosensors; bioreceptors = antibodies, enzymes, cells, DNA, phage, molecules; transducers = electrochemical, optical, mass-based
(CDIT)
How are cells and tissues/animals used in bioassays?
CELLS - Chinese hamster ovary cells, Vero cells, mice spleen cells, human peripheral lymphocytes
TISSUES/ANIMALS - mouse lethality test, monkey and kitten emesis test, rabbit and guinea pig skin tests, rabbit and mice ileal loop test
What are the 2 purposes of microbiological tests for food?
- confirms that food is produced in hygienic conditions with effective sanitation detergents/disinfectants, personnel, hygienic status, sanitation programs, HACCP, GHP, and decontamination
- confirms that food is safe by detecting presence of pathogenic microorganisms
What are bioassays? What are they the standard test for? When are results received?
procedure that requires model organisms, tissues, or host cells to test harmful effects of stimuli (chemical, microbe) on living things
- toxicology
- pathogenicity
- dose-response
12-72 hours
