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11 Cards in this Set
- Front
- Back
Why is rRNA used in taxonomical classification of microorganisms?
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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
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Describe three sources of contamination of foods of animal origin.
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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. |
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What are some of the new genera into which organisms formerly classified as Micrococcus have been placed?
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Dermacoccus, Kocuria, Kytococcus, Nesterenkonia, and Stomatococcus
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Describe the general structure of molds.
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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.
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What is a teleomorph?
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The ascomycete or sexual reproductive state – according to the book the most important reproductive state of a fungus; aka “the perfect state”
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Name two genera of molds that are commonly responsible for spoilage of fruits.
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Botrytis, Fusarium, Penicillium, and Trichothecium
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Name and describe the genus of yeast used in the production of breads and beer.
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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.
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Describe the procedure you would follow to determine the source of contamination of a particular food.
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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.
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Should molecular-based methods be used as the definitive way to classify micro-organisms? Why or why not?
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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. |
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Describe how ground meat products become contaminated.
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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. |
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List several types of bacteria and molds that are responsible for spoilage of fresh meats and poultry
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Bacteria: Aeromonas, Pseudomonas, Psychrobacter, Enterococcus
Molds: Penicillium, Mucor, Cladosporium, Rhizopus |