Labs 8, 9, 32, 33, 35-38, 41, 43, X Flashcards
(67 cards)
What is the Standard Plate Count Method?
The official method for quantifying the bacterial number in milk, counting only the living cells.
What is the importance of knowing the number of bacteria in milk?
to prevent contamination and high numbers of bacteria.
What kinds of milk do public health officials check for bacteria and how much bacteria are allowed in each?
-Pasteurized and raw milk.
-Pasteurized milk must have less than 20,000 bacteria and 10 coliforms per ml.
-Raw milk must have less than 300,000 bacteria per ml.
What do high bacterial numbers suggest?
A diseased cow, poor sanitation of milking-devices and milk cans, poor sanitation of milk handlers, contamination of milk during transport to the pasteurization plant, contaminated pasteurization machinery, nd insufficient pasteurization.
What pathogens and diseases can occur due to contaminated milk?
Pathogens such as brucellosis and tuberculosis can be encountered.
Humans can acquire diseases such as cholera, typhoid, dysentery, diphtheria, scarlet fever, and Q fever from contaminated equipment and diseased animals.
What efforts must be made to ensure milk doesnt become contaminated?
-Animals are vaccinated to prevent the transmission of pathogens, and if proper sanitation and sterilization procedures are maintained, milk should not be contaminated.
-Proper refrigeration of milk during transportation.
-Pasteurization.
-Inspections and corrective measures by public health workers.
Purpose of pasteurization?
Pasteurization is used to eliminate any potentially pathogenic bacteria in raw milk.
If milk is not pasteurized correctly, potentially pathogenic bacteria can remain in the milk and be ingested.
Why must milk be properly refrigerated during transportation?
Because natural microbiota in the milk can grow to potentially dangerous levels if it is not refrigerated at the appropriate temperatures.
Leaving food out too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella Enteritidis, Escherichia coli O157:H7, and Campylobacter) to grow to dangerous levels that can cause illness. Bacteria grow most rapidly in the range of temperatures between 40 °F and 140 °F, doubling in number in as little as 20 minutes. This range of temperatures is often called the “Danger Zone.”
How are bacterial numbers in milk quantified?
Serial dilutions and counting using the pour plate method are used to test milk
Serial dilutions is a stepwise dilution (occuring from tube to tube) to reduce the number of organisms in an environment
What are Pour Plates?
Pour plates are a second way in which you can obtain isolated colonies by mechanically diluting a culture. (First is the streak plate).
Pour Plate technique?
The idea behind the use of a pour plate technique is to inoculate a specific volume (one-tenth ml) of material containing a mixture of microorganisms into a tube of melted agar and then pour the agar into a sterile Petri dish (the bacteria and the agar can also be mixed directly in the petri plate).
Adding the organisms to the medium dilutes them; then, when the medium solidifies in the dish, individual cells are kept separate from each other and form colonies.
The pour Plate Method is based on the fact that when an agar medium mixed with microorganisms is incubated, each of the viable microorganisms will multiply forming a separate colon
In some instances, there may be so many bacteria in the inoculum that vou will have to dilute them further to obtain isolated colonies. How do you achieve this?
To do this, you will have to perform a serial dilution (1:10, 1:100,
1:1000 and so on) (Done in Exercise 8. Inoculate one- ml of the desired dilution into the tube of melted agar and pour the agar into the plate (or you can mix the inoculum and the agar in the plate). If you do this with each dilution, you will reach a point where the original inoculum is sufficiently diluted to obtain isolated colonies (Fig. 1).
How does the pour plate differ from the streak plate?
The pour plate differs from the streak plate in that the agar medium is inoculated while it is still liquid, therefore colonies will develop on the surface as well as throughout the medium. Colonies on the surface of the agar medium, where more oxygen is available, are circular and flat; the colonies embedded or trapped in the medium are smaller and spindle shaped.
Causes of contamination in food?
Some reasons for initial contamination include the fact that most foods come from plants or animals which already contain microbes. Contamination can also occur during the harvesting, handling, and processing of foods.
Organisms can either die, survive, or multiply within the food depending on various conditions that the food item provides such as?
-pH, presence or absence of organic acids, water activity, oxidation-reduction potential, temperature, other microbes, preservatives and packaging materials, and the packaging process.
-Also, the relative abundance of carbohydrates, proteins, and fats in the food can determine whether the microbes will thrive or not.
Microbes concerning meats
Meat are products of living animals so they can definitely contain harmful bacteria. Contaminants of food are most commonly found in the colon. Common pathogens are Salmonella, E.coli
Microbes concerning milk
milk is initially sterile, however, the mammary glands of cattle are riddled with microbes and if infections occur there, the infectious pathogens are passed with the milk. Pasteurization of milk kills a lot of these organisms, not not all die. In fact, psychrophilic pathogens are able to amplify in pasteurized, refrigerated milk
Microbes concerning eggs
Microbes concerning Fish and seafood
Microbes concerning Vegetables
Since they come from the soil environments, the pathogens in the soil may be transferred to them or cropping practices that use animal or human wastes are potential sources
What is epidemiology?
the study of the spread of disease through a population
focuses on spread, control, and prevention/treatment of a disease
What is an epidemic?
the spread of a disease over a given time within a specific area or particular population
generally refers to a sudden increase in the number of cases of a disease above what is normally expected
What is a pandemic?
An increase in the prevalence of a disease over a large area over time
A pandemic, however, refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.
What is an index case?
The first person diagnosed with a disease in an epidemic or pandemic
