Practical 8: Residues of inhibitory substances

This practical, we checked/counted the agar colonies from last week (the ones taken from fish meat). Then, we had theory based on lesson 8.

What are residues of inhibitory substances in food?

They are residues left in the muscle, kidney, or liver tissue of farm animals after medication, which can enter the human body via food.

What does MRL stand for in the context of veterinary drug residues?

Maximum Residue Limit, which is the maximum concentration of residue legally permitted in food. Residues that result from the use of veterinary medicinal products on the animals.

• Expressed in mg/Kg or ug/Kg on a fresh weight basis

What is the purpose of the withdrawal period?

It is the time between the last administration of a veterinary drug and obtaining the product from the treated animal, ensuring that drug concentration corresponds to the MRL.

The use of ATBs?

1. Therapy - treatment

2. Profylaxy - at subtherapeutic conc.

3. Growth promoters - subtherapeutically for production enhancement - increased growth rate and feed efficiency

Regulation (EC) no 1831/2003 in article 11?

Explains that ATBs are not allowed?

why is it not allowed to have residues from ATBs in the meat?

health problems - allergies, Toxicity (tetracyclins, CHLP, STM), and the development of resistance in humans (polyresistance, immunosuppression).

Excretion of ATBs from the body through?

Liver, kidneys, milk and eggs

• After treatment, they can still be present in milk, egg production

• consuming for a long period of time → teratogenic, mutagenic or carcinogenic effects are seen

How to detect residues?

1. Screening test (detection of a group of inhibitory substances possesing similar properties)

2. Confirmatory test (confirm a single compound and its conc. in food)

Define screening tests

rapid, high-volume, low cost, can classsify a large number of samples

confirmatory

low-volume, high cost

• make no false positive and a minimal rate of false-neg. results

• (liquid chromotography, high-performance) ??

What is the role of the PREMI®Test?

It is a microbial inhibition diagnostic test system for detecting antibacterial substances in fresh meat samples.

• bacillus stearothermophilus var. calidolactic (geobacillus stearothermophilus) - most sensitive

What temperature is required for incubating the PREMI®Test?

64 ± 0.5 °C.

How does the agar diffusion test indicate the presence of antibacterial substances?

A clear zone is formed in the agar due to the inhibition of bacterial growth, with the size of the zone proportional to the concentration of the substance.

What type of samples can be used in the agar diffusion test?

Cube-shaped tissue (7 x 7 x 7 mm), paper discs, or metallic cylinders.

What indicates a positive result in the PREMI®Test?

An annular zone of inhibition larger than 3 mm.

What is the required incubation time for Bacillus stearothermophilus var. calidolactis ATCC 10149 in the STAR protocol?

12-15 hours at 55 °C.

What constitutes a positive result in the STAR protocol for Bacillus stearothermophilus var. calidolactis plates?

An annular zone of inhibition larger than 2 mm.