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11 Cards in this Set

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  • Back
Why is rRNA used in taxonomical classification of microorganisms?
16s ribosome subunit highly conserved and therefore excellent chronometer of bacteria over time. Reverse transcriptase is used to sequence rRNA to determine precise phylogenetic relationships
Describe three sources of contamination of foods of animal origin.
1- Animal feeds – primarily Salmonellae to poultry and other farm animals can also be Listeria with dairy and meat animals. Organisms in dry feed are spread throughout animal environment and common in hides.
2- Animal hides – organisms found in milk reflect biota of udder and hide. Organisms can contaminate general environment, milk containers and hands of handlers
3- Food Utensils – the cutting block, knives, and containers in a meat market are contaminated by initial samples, with repeated use there is a build up of organisms and a fairly constant level of contamination of meat-borne organisms.
What are some of the new genera into which organisms formerly classified as Micrococcus have been placed?
Dermacoccus, Kocuria, Kytococcus, Nesterenkonia, and Stomatococcus
Describe the general structure of molds.
Filamentous fungi grow in a tangled mass – the total mass is referred to as the mycelium composed of branches called hyphae. These hyphae may or may not have cross-walls called septa. There are also reproductive shoots usually growing upwards. Most molds can reproduce either sexually or asexually and the morphologies of the two are different.
What is a teleomorph?
The ascomycete or sexual reproductive state – according to the book the most important reproductive state of a fungus; aka “the perfect state”
Name two genera of molds that are commonly responsible for spoilage of fruits.
Botrytis, Fusarium, Penicillium, and Trichothecium
Name and describe the genus of yeast used in the production of breads and beer.
Saccharomyces cervisiae multiply by budding and produce spherical spores in asci. They are diploid and do not ferment lactose. Found in kefir grains and can be isolated from a wide range of foods like dry-cured salami and many fruits. They rarely cause spoilage.
Describe the procedure you would follow to determine the source of contamination of a particular food.
Using a lab I would identify what the contaminant was and then take samples from each step in the processing of that food. I would then try to identify the same contaminant from one of the source samples.
Should molecular-based methods be used as the definitive way to classify micro-organisms? Why or why not?
I don’t believe that molecular-based methods should be used because:
- It only takes into consideration genetic differences, not morphological or physical differences
- It assumes all changes in molecular structure are equal, they aren’t
- It assumes rate of change of all genes is equal and this is not true.
Describe how ground meat products become contaminated.
There are many routes of contamination including:
- The stick knife: used to exsanguinate the animal by cutting the jugular vein – this is not sterile
- Animal hide: organisms on the hide enter via the stick knife – area is not sterilized, others enter through dehaired carcass or onto freshly cut surfaces
- GI tract: punctures during slaughter lead to deposits on fresh surfaces. Rumen contains about 1010 bacteria/g
- Hands of handlers: source of human pathogens to fresh surfaces, gloves not changed between carcasses, can pass organisms from one to another
- Containers: cuts are place in non-sterile containers that are used over and over again. Primary source in ground meats.
- Handling and storage environment: circulating air places organisms on the surfaces of all slaughtered animals
- Lymph nodes: lymph nodes embedded in fat contain large numbers of bacteria, cut through or added to portions that are ground, the bacteria may become prominent.
List several types of bacteria and molds that are responsible for spoilage of fresh meats and poultry
Bacteria: Aeromonas, Pseudomonas, Psychrobacter, Enterococcus
Molds: Penicillium, Mucor, Cladosporium, Rhizopus