FOOD 4150 MIDTERM 1

What is microbiology

The study of organisms that are usually too small to be seen by the unaided eye

What kind of techniques does microbiology use

Sterilization; culture media; isolate and grow organisms

What are the two fundamental types of cells

Prokaryotes and eukaryotes

What is food microbiology

Study of microorganisms which have both beneficial and deleterious effects on quality and safety of raw and processed food

What is a prokaryote

Single-celled organism; genetic material not enclosed by a nuclear membrane

What is present in bacteria in a prokaryote

Peptidoglycan present in cell wall

What are the classifications of microorganisms

Bacteria; archaea; fungi; protozoa; algae; viruses

What is the classification of bacteria

Prokaryotic cell; most have peptidoglycan cell wall and divide by binary fission

What is the classification of archaea

Prokaryotic cell; lack peptidoglycan; includes extreme halophiles and thermophiles

What is the classification of fungi

Eukaryotic cell; unicellular or multicellular

What is the classification of protozoa

Unicellular eukaryote

What is the classification of algae

Unicellular or multicellular eukaryote

What is the classification of a virus

Noncellular entity that is a parasite of cells; consists of nucleic acid core (DNA or RNA) surrounded by protein coat; related to foodborne outbreaks

What is an example of a bacterium

E. coli; Salmonella; S. aureus

What is an example of a fungus

Yeasts and molds such as Aspergillus

What is an example of a protozoan

Cyclospora; Entamoeba

What is an example of a virus

Norovirus (foodborne outbreak)

What is the structure of a prokaryote

Plasma membrane; nucleoid; periplasmic space; cell wall; capsule and slime layers; fimbriae and pili; flagella; endospore

What is the plasma membrane function of a prokaryote

Selectively permeable barrier; nutrient and waste transport; location of metabolic processes; chemotaxis

What is the function of the nucleoid in a prokaryote

Localization of genetic material (DNA)

What is the function of the periplasmic space in prokaryotes

Contains hydrolytic enzymes and binding proteins for nutrient processing and uptake

What is the function of the cell wall in a prokaryotic cell

Provides shape and protection from lysis in diluted solutions

What is the function of the capsule and slime layers in a prokaryotic cell

Resistance to phagocytosis; adherence to surfaces

What is the function of fimbriae and pili in a prokaryote

Attachment to surfaces; mating

What is the function of flagella in a prokaryote

Motility

What is the function of an endospore in a prokaryote

Survival under harsh conditions and environments

In crystal violet Gram stain what is positive and negative

Both Gram + and Gram − appear deep violet

In Gram stain with iodine what is positive and negative

Both remain violet

In Gram stain with alcohol wash what is positive and negative

Gram + remains violet; Gram − becomes colorless

In Gram stain with safranin what is positive and negative

Gram + remains violet; Gram − stains pink or red

Do Gram positive (+) cells appear thick or thin

Thick

Do Gram negative (-) cells appear thick or thin

Thin

What are conditions for bacterial growth

Moisture; temperature; oxygen; pH; nutrients; time

What are the phases of the bacterial population growth curve

Lag phase; exponential phase; stationary phase; decline or death phase

What is the lag phase

Period after inoculation before growth begins; few or no cells

What is the exponential phase

Cells divide rapidly by binary fission; population of live cells increases

What is the stationary phase

When growth ceases but cells remain active; live and few dead cells present

What is the decline or death phase

When nutrients are depleted or toxic waste builds up; more dead cells than live ones

What is taxonomy

Domain or kingdom – Bacteria;

division or phylum – Proteobacteria (Eubacteria);

class – Gamma Proteobacteria;

order – Enterobacteriales;

family – Enterobacteriaceae;

genus – Escherichia;

species – E. coli

What is a virus surrounded by

Protein coat and sometimes an outer membrane

What is the complete virus particle called

Virion

What are the three classes of viruses

Animal; plant; bacterial

What are bacteriophages

Viruses that infect bacteria; use host metabolism to produce new virus particles which are released to infect new cells

What is an endospore

Resistant dormant survival form produced inside a prokaryotic cell; not used for reproduction

What are endospores resistant to

UV and gamma radiation; desiccation; heat; starvation; chemical disinfectants

Can endospores germinate years after formation

Yes they can survive long periods and germinate later

What is the process of endospore formation called

Sporulation

In what phase do endospores start forming

Stationary phase when conditions deteriorate; metabolic activity changes

What is a normal cell called

Vegetative cell

What does stress trigger in Gram + bacteria

Sporulation

How long can spores survive in boiling water

About one hour

What is the endospore cycle

Dormancy; activation; germination; outgrowth; vegetative cell; sporulation

Is meat stew considered a high-risk food in terms of endospore germination

Yes

How can endospores and spores be eliminated

Heat; high-dose irradiation or UV; strong antimicrobial solutions such as chlorine or acids

What is heat sterilization in regard to endospores

moist heat using water

What is DNA

Genetic material with complementary base pairing A–T and C–G (RNA uses A–U and C–G)

What is a pathogen

A microorganism such as a virus; bacterium; parasite; or fungus capable of causing disease in a host

What are virulence factors

Molecular traits of pathogens that enhance their ability to cause disease in a host

What is whole-genome sequencing

Process of determining the complete DNA sequence of an organism’s genome

What is aseptic technique

A procedure for handling cultures to eliminate contamination by unwanted microorganisms

What does aseptic technique involve

Disinfecting work area and hands; using sterile supplies; minimizing exposure to air; using flame or biosafety cabinet

What are two goals of aseptic technique in the lab

Prevent contamination of the environment or self; prevent contamination of lab samples

What is sample collection at a food processing facility

Collect randomized lots; package properly; maintain correct temperature (some samples refrigerated); deliver to lab within 24 h

What is sample reception in the lab

Record date and client; number of samples; measure temperature (≤ 5 °C) with laser thermometer; check container integrity before processing

What are different types of culture media

Physical state; chemical composition; functional type

What is physical-state media

Liquid; semisolid; solid (convertible or non-convertible)

What is chemically defined (synthetic) versus non-synthetic media

Known composition vs. complex undefined composition

What are the functional types of media

Enriched; general-purpose; selective; differential; enumeration; assay; specimen-transport

What are examples of general-purpose and selective media

Nutrient agar = general purpose; nutrient broth = general purpose; MacConkey agar = selective enumeration; agar plate count = enumeration

When processing a sample what are the two key steps

Enumeration and detection

What is enumeration

Serial dilution (buffer peptone water; peptone water; citrate buffer; saline); plating; incubation; counting; reporting

What is detection

Enrichment for pathogen growth, allows rapid cell multiplication for storage or testing

What is aerobic plate count (APC)

Method providing a general estimate of viable aerobic bacteria; excludes obligate anaerobes and microaerophiles

What assumptions does APC make

Each colony arises from a single bacterium; bacterial clumping may cause colonies to arise from multiple cells

How are APC results reported

Colony-forming units per gram or milliliter (CFU/g or CFU/mL)

What do APC results indicate

Sanitation of product; predicted shelf-life; overall safety; sanitation efficiency

What are types of samples analyzed in microbiology

Liquid; solid; sponge or swab

How much sample is used for microbiological analysis

1:10 dilution (1 g/mL sample in 9 mL diluent)

What are the steps of the pour-plate method

Inoculate empty plate; add melted nutrient agar; swirl; allow colonies to grow within and on the medium

What are the steps of the spread-plate method

Inoculate solid medium; spread inoculum evenly; colonies grow only on surface

What is the equation for dilution

(Weight of sample × dilution factor) − weight of sample = volume of diluent needed

What is the goal of serial dilution

Reduce microbial concentration to achieve countable colonies (25–250 per plate)

If more than 300 colonies are observed how is it reported

Too numerous to count (TNTC)

What is an indicator microorganism

Organism reflecting microbial quality; used to detect process failure or post-process contamination

What is an indicator organism

Selected surrogate marker species such as coliforms; E. coli; Listeria

What do indicators of quality measure

Microbes or metabolic products used to assess existing quality or predict shelf-life

How is shelf-life determined

By initial microbial load and quality indicators

What are types of microbiological indicators

Total plate count (TPC) or plate count to quantify bacterial populations

What does microbial quality indicate

High TPC suggests poor quality and impending spoilage

Why are coliforms microbiological indicators

Aerobic or facultative anaerobic; Gram-negative; non-spore-forming; rod-shaped bacteria that ferment lactose with acid and gas within 48 h at 37 °C

What does the presence of coliforms indicate

High possibility of fecal contamination or lack of sanitation; increased likelihood of pathogen presence

Do positive coliforms confirm pathogen presence

No; they only indicate possible contamination

Is coliform normally present in raw food

Yes; type must be determined to assess safety

Is coliform present in heat-processed food

No; heat destroys them

What is fecal coliform or E. coli

Lactose-fermenting subgroup of coliforms found in fecal material; indicates poor sanitation and handling

What is Enterococcus

Gram-positive; facultative anaerobe; catalase-negative; from fecal material of animals; salt tolerant; resistant to freezing

What is microbiological criterion

Acceptability of a product or lot based on presence/absence or number of microorganisms and toxins per unit

What are the three types of microbiological criteria

Standards; guidelines; specifications

How can microbial criteria be used

To define and verify compliance with microbiological requirements

What is a lot

Quantity of product produced or stored under uniform conditions in a limited period