food micro 1

bacteria, archaea, eukarya

what are the 3 domains?

morphology, gram stain (bacteria), biochemical reactions, growth pattern & reproduction (fungi), PCR-based, sequencing-based, protein profiles

what are some classification/identification techniques?

LAB, sporeformers, enteric pathogens, coliforms

what are some different, important bacterial groups?

fission formation

what is the formation of B called?

pseudohyphae

what is C called?

septate hyphae

what is the hyphae of E called?

prokaryotic ribosome

what type of ribosome is this?

eukaryotic ribosome

what type of ribosome is this?

the types of disease, nucleic acid content, morphological structure

classification for virus is usually based on: (3)

human viruses

viruses attack human cells, some cause enteric diseases

bacteriophages

viruses attack bacteria, affect food fermentation, may be used to control bacterial pathogens

beneficial microbes

type of microbe classification: food producing microbes (fermentation --> LAB), probiotics

spoilage microbes

type of microbe classification: organoleptic changes make it unacceptable to customer

pathogenic microbes

type of microbe classification: causes infection or intoxication

microbiological criteria

___ is developed to assess: safety of food, shelf-life, suitability, and adherence to legal requirements (such as GMP)

IFT, FDA, USDA, NSF, etc

microbiological criteria is established by:

culturing (growing in broth/agar), and microscopy (observe/count after staining)

what are the 2 most common detection techniques?

no growth

on culture-dependent methods, there is no accurate results if there is ___

standard plate count (SPC)

method used to determine number of cells in a food product via CFU of microbes per g of food, should use a specific medium --> often TSA

doesn't, individual

SPC ___ count total number of microbes, as it does not allow for ___ cell growth

can determine colony morphology, can be modified to test wide variety of microbes

advantages of SPC

time-consuming due to incubation, can't be used to identify microbes at species level

disadvantages of SPC

to homogenize and release microbes from the food

what is the role of a stomacher or a pulsifier?

count cells

dilutions make it easier to ___ on plates

high microbial load

what is the term for when a sample is too concentrated?

1:9

what is the ratio for dilutions

food

the agar serves as ___ for the microbes, so be sure to pick the suitable plate for the test

dilution(plate)

___ refers to how much of the sample actually ends up on the plate (dilution(tube) x amount sampled)

membrane filtration

if a sample is too diluted, ___ can be used to retain bacteria and create a higher concentration

most probable numbers (MPN)

this method relies on statistical probabilities to estimate the initial number, method of choice for determining the density of indicator organisms

ocular density

what does OD stand for?

less light is detected, higher OD

if there is more cells in a sample that you are viewing with a spectrophotometer, ___ & there is a ___

MPN

what does TEMPO calculate?

nutrients, temperature, oxygen, etc

what does a bacterium require for growth?

complex

___ mediums have many different ingredients that make them up, and can often be selective as well

Eosin Y, Methylene Blue

in EMB Agar, what are the selective agents?

Eosin Y, Methylene Blue, Lactose

in EMB Agar, what are the differential agents?

external

when subjected to an ___ stress (heating/freezing/low pH/etc), microorganisms can be injured

non-selective

injured cells are typically unable to form colonies on ___ media that healthy cells can tolerate

selective

XLD is a ___ medium

non-culturable bacteria

___ do not grow easily in the lab on growth media

viable but nonculturable (VBNC)

cells are viable, but cannot be cultured by typical microbiological methods, they can't form colonies in conventional culture media

Direct Microscopic Count (DMC)

observe microscopically, usually after staining, can be structural (spores, capsule) or differential (gram reaction, viability)

fast, able to observe cellular morphology, some methods are simple and easy

advantages of DMC

relatively high cell density is required to see enough cells to count, some methods require expensive instrument and chemical

disadvantages of DMC

green, red

in BacLight, live bacteria with intact cell membranes fluoresce ___ and dead bacteria with compromised membranes fluoresce ___

polymerase chain reaction (PCR)

DNA extracts from the sample, primer's used to bracket region of interest, dNTP & polymerase used to make copies, dsDNA is separated at 95C and primers anneal to template at 55C

endpoint PCR

PCR test where visualize amplicons in agarose gel after staining DNA

quantitative PCR

PCR test where visualize amplification in real-time due to incorporation of fluorescense molecules; requires a standard curve

digital PCR

PCR test where partition DNA template into thousands of wells first, then monitor fluorescense signal in each well; does not require a standard curve, good for detecting rare target, absolute quantification

sensitivity

___ = inclusivity = true positive rate

specificity

___ = exclusivity = true negative rate

detection limit

___ = analytical sensitivity; the smallest amount of the target (cell, toxin) that can be accurately measured by the method

food contact surfaces

surface monitoring determines if microorganisms are present on ___

low

surface monitoring may be useful on products that are expected to have a ___ microbial load

RODAC, Swab rinse

common methods of surface monitoring

ATP measurement

light output is recorded using a luminometer and a readout of the number of photons is obtained

product sampling

type of sampling involving products that are ready to go to market, as well as in-process and raw ingredient samples

environmental sampling/hygeine monitoring

type of sampling involving environment surrounding the food; facility or transport vehicle; i.e. RODAC & Swab rinse

emergency response/emerging issues sampling

type of sampling in response to outbreaks of foodborne illness to help identify the source of the disease-causing pathogen

product sampling plan

includes both sampling procedure & decision; 2-class & 3-class sampling plan; procedure varies, but mostly based on SPC; designed for quality/safety as accepted

product lot

the quantity of product which is produced, handled, and stored within a limited time period under uniform conditions

2-class sampling plan

assigns lot to one of two classes --> the decision is accept or reject; criterion based on n (# sample units tested), m (threshold conc. for unacceptable), & c (max allowable # of units yielding unacceptable results)

3-class sampling plan

criterion based on n, m, c, and M (max # of bacteria/unit; the lot is not acceptable if any sample is above M)

accepted, marginally accepted, rejected

decisions of product sampling can be: (3)

marginally accepted

some counts are greater than m but not greater than M, provided that the # of failed samples is less than c

oxidoreductase

enzyme classification: important in redox reactions; transfer electrons

transferase

enzyme classification: transfer a functional group; ex: methyl or phosphate group

hydrolase

enzyme classification: hydrolysis of various bonds; ex: urease

lyases

enzyme classification: cleave bonds by means other than hydrolysis and oxidation

isomerase

enzyme classification: different arrangment of atoms within a single molecule

ligase

enzyme classification: join two molecules with covalent bonds; ex: DNA ___

translocase

enzyme classification: movement of ions or molecules across membranes; ex: ADP/ATP ___

400x

what is the total magnification when a 40x objective lens is used to view the sample? (by default, the eyepiece is 10x)

the agents are used to neutralize common disinfectants, the cell count will be underestimated

what is the function of the neutralizing agents? what happens to the surface monitoring results if the medium does not contain neutralizing agents?

no

if a student used a RODAC plate to determine the cleanliness of a food-contact surface, and the CFU/in^2 was 15 CFU/in^2, would you consider it a clean surface?

How do you find the total magnification of a microscope?

magnification of ocular lens x magnification of objective

reasons to incubate plates upside down (1)

avoid condensed water from falling onto the cultures

purposes of doing streak plate using quadrant method (3)

- To determine the colony morphology of the microbe

- To obtain isolated colonies

- To obtain pure cultures

what color are gram + bacteria after gram stain (and why)

- purple

- thick layers of peptidoglycan in cell wall retain primary stain

what color are gram - bacteria after gram stain (and why)

- pink

- thinner peptidoglycan layer => ethanol washes out primary stain => counter stain dyes them pink

can gram stain be used on fungi?

- no

- different cell wall structure

- fungal cell walls are made up of chitin and polysaccharides

purpose of iodine in gram stain

forms a complex with the dye, trapping it in gram+ but not gram- bacteria when the decolorizer (ethanol) is applied

why do you need young cultures for gram stain?

old cells can have damaged cell walls, leading to inaccurate results

oxidase test

- tests for presence of the enzyme cytochrome c oxidase

- visible by change of color

- enzyme substrate on dryslide is oxidized by cytochrome c oxidase resulting in color change

- change in color = enzyme is present (+)

catalase test

- tests for presence of the enzyme catalase

- visible by production of bubbles

- catalase breaks down hydrogen peroxide into oxygen and water

- if you see bubbles = catalase is present bc that is the oxygen from breaking down hydrogen peroxide

DMC

direct microscopic count

what method is a hemocytometer used for?

DMC

MF

microscopic factor

You calibrate the ocular micrometer at two different total magnifications, 100x and 1000x. The calibrated distance between the lines of the ocular micrometer is shorter at the lower magnification.

false (but I have literally no clue why)

We learned two plating techniques in the lab -- pour plate and spread plate. Depending on the plating technique, the dilution factor will be different even with the same volume of dilution plated.

False, it should be the same if you plate the same volume of the same dilution on each plate

relationship between catalase and aerobic capacity

If the microorganism is an aerobe, having catalase would be helpful because hydrogen peroxide is dangerous, however it doesn't exactly mean that it is for sure an aerobe

relationship between oxidase test and aerobic capacity

- there are other types of oxidase, so a negative test doesn't imply that the microbe isn't an aerobe or doesn't use ETC

- however, cytochrome c oxidase is used in ETC to reduce oxygen so positive test would imply aerobe

Emperor Leo VI of Byzantium issued an edict that forbade eating blood sausage because he found out the causative agent of botulism.

false, they didn't know the reason back then

Who was the father of canning?

Nicholas Appert

The yeast used in making alcoholic beverages is in the domain:

Eukarya, All yeast are in domain eukarya because they are fungi

Saccharolytic bacteria

Bacteria that are able to hydrolyze complex carbohydrates

All bacteria are either Gram positive or Gram negative

false, some are neither

What are the classification techniques for fungi? (3 and maybe more but these were the ones in the question)

- morphology (what they look like)

- reproduction (asexual vs sexual)

- DNA sequencing

NOT gram stain

coccus

round shape