1B Some methods for detecting microorganisms(2)

Microbial Analysis of Foods

Analyzing food and environmental samples for the presence of spoilage and pathogenic microorganisms and toxins is a standard practice to ensure food safety and quality.

Ultimate goal of microbial analysis of food

To ensure that the food products that we will handle are safe and has quality

Viable counts

limitations in detumination or what we only dependu. Viable County are colonies that we see in the petri plate that we can count.

Conventional methods

are usually plate count methods obtained from homogenization, dilution, and inoculation to specific media

Conventional/Traditional methods

• plating techniques like from the old era times

• Use of agar and petri plates also peptone water

• always done or practice

Rapid methods

Fast paced methods

Culture-based

use media/cultured media in where we will culture our microorganisms

Non-cultured-Based

• no use of agar

• we check the DNA/RNA of our microorganisms

Can a rapid method also be culture-based?

Yes! Rapid methods just involve culturing bacteria with faster techniques (e.g., color change, fluorescence) that provide results in less time (12 hours vs. 24+ hours)

Factors to consider in detection methods

• solid foods should be liquidized/homogenized for dilution purposes.

• The target organism is normally in the minority of the microbial population and may not be uniformly distributed in food

• The target organism may be physically and metabolically injured

Aerobic plate count

indicates the general microbial load and hence the shelf life of the product

Presence of fecal organisms

could indicate the efficacy of food processing

Standard Methods Agar (SMA)

is used for APC determination

Potato Dextrose Agar (PDA) acidified with 10% Tartaric Acid

is commonly used for Yeast and Mold determination

Violet Red Bile Agar (VRBA)

used for coliform and E-coli determination.

The general sequence of isolating foodborne pathogens

Enrichment -> Selective Isolation -> Subculture -> Confirmation

Pre-enrichment

we ensure that the bacteria/microorganism or pathogen of interest adapt in the environment.

Enrichment

After e-coli adaptation in the environment of coconut water. It needs to be enrich, thus we enhance the environment so pathogens can grow there more. Because it is not just the microorganism present in the sample. We need it to be more/increase in amount.

Selective isolation

we used specialized agar or colorant to see that when microorganisms react at this particular confirmation method, we could actually confirm that this is the presence of our target pathogen

Subculture

To get the microorganism for we already confirm its presence

Confirmation

To check if what we isolate are the microorganism of interest

Metabolically injured

A cell that is not able to form a colony on a minimal salts medium is said to be (??)

Most probable number

MPN method for coliform determination in water

BGLB tubes with turbidity but no gas

This test result indicates possible coliform presence in milk, but without gas production. While not definitive, it can be suggestive of coliform contamination

MPN methods

is a method for estimating the bacteria’s number in a food or water sample

Multiple Tube Method

• most common method in determination of E-coli and coliform but some methods don't need it

• it is used usually for water since e-coli is common in water

Most probable number

is used for calculation/estimation of e-coli and coliforms

MPN/g column

is the estimated number of microorganisms

Fecal

means feces of animals, human etc

E-coli

A subgroup of fecal coliforms

E-coli

all of these are total coliforms and is just fraction of fecal coliform

Total coliform

are wide and range of group bacterias

Positive EC tubes

are used and pour in the EMBA to determine E.Coli

Chromocult agar

a selective and differential chromogenic culture medium for the microbiological analysis of water samples. Can grow in both E.coli & total coliforms

Ingredients that hinder growth of substantially injured cells

• Increasing salt concentration

• Deoxycholate lauryl sulfate

• Bile salts

• Detergents

• Antibiotics

Substantial injury

implies damage to structures within the cells

Substantially injured cells

Cells have injury or damage in their structures or cell walls. This injury is reversible by repairing given that they have a suitable growth condition

Eosin methylene blue agar (EMB)

selective media for e-coli

Chromocult agar

alternative for e-coli

Bismuth sulfite agar (BSA)

type of agar media used to isolate Salmonella

Mannitol lysine crystal violet brilliant green (MLCB) agar

a selective and diagnostic agar for the isolation of salmonellae, other than Salmonella typhi and Salmonella paratyphi, from feces and foods

Baird-Parker Agar with egg yolk and potassium tellurite

is a selective medium for the detection and enumeration of coagulase-positive staphylococci (Staphylococcus aureus and other species)

Brilliant Green Bile Agar (BLGB)

used for the presumptive identification and enrichment of total coliforms

Potato dextrose Agar w/ tartaric acid

is a general purpose medium for yeasts and molds

Selenite Cystine Broth

a medium used for the selective isolation of Salmonella and some species of Shigella

Ottaviani and agosti agar

used for the detection and enumeration of Listeria monocytogenes in food and environmental samples.

Selective media

ontain ingredients that hinder growth of sublethally injured cells

Conventional methods

are labor intensive and time consuming

Enzyme Linked Immunosorbent Assay (ELISA)

• Rapid but can’t isolate microorganisms

• Capture antibodies specific for our target analyte/protein

• used in pregnancy test/COVID-19 test (kit)

• are both qualitative and quantitative

ATP Bioluminescence Techniques and Hygiene Monitoring

Primarily used for hygiene monitoring

Protein detection: Biuret Reaction

An alternative to ATP detection for hygiene monitoring.