Micro Lab Exam #2

Front 1

milk and food

Back 1

-are nutrients, unlike water
-provide an excellent growth medium for bacteria in suitable
temperatures
-even a few pathogens in them is serious because it can support an increase in bacterial numbers
-bacterial count in milk and food is the most reliable method to determine sanitary quality (health, safety, cleanliness)

Front 2

water

Back 2

lacks essential nutrients for pathogens (heterotrophs), unless contaminated by organic material (sewage)

Front 3

the numbers (quantity) of bacteria

Back 3

-not the quality, that determines the safety of milk and food (unlike water)

Front 4

the most commonly isolated microorganisms in milk are

Back 4

Staph e,
micrococcus species
E. coli
Staph A
Salmonella

Front 5

bodies of cows and unsanitary handling in milk

Back 5

the usual sources of these organisms in milk

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milk was first pasteurized due to this pathogenic bacteria

Back 6

mycobacterium tuberculosis (TB)

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pasteurization

Back 7

a brief, mild heating of a liquid, (milk, wine, beer, cider) that kills pathogenic and spoilage microorganisms without destroying the quality or flavor of the liquid

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milk with a high bacterial count may indicate

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1) diseased udder
2) unsanitary handling of milk
3) unfavorable storage conditions

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what a high bacterial count means

Back 9

that there is a greater likelihood of disease transmission

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what low bacterial count means

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that it is possible to have pathogens when counts are within acceptable nos. EXCEPT for the fact that milk was pasteurized
ie brucellosis and TB

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if milk is properly refrigerated

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-process in which milk is unlikely to cause disease or spoilage in a short period of time (shelf life), even if bacteria were heat-resistant during pasteurization
-it is this milk that cause milk to spoil eventually

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standard plate count (SPC)

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1) serial dilution
2) pour plate method

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viable count

Back 13

is very accurate because living bacteria that grew into OBSERVABLE colonies can be isolated and counted

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the total number of living bacteria in the 1.0 ml of milk sample

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the number of colonies on the plate; dilution factor on that plate

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within 30-300 colonies

Back 15

no. of colonies can be counted on that plate

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less than 30 colonies

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number that is not considered accurate because they may be due to randomly introduced contaminant bacteria

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more than 3oo colonies

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is not accurate because they are too many to count they can overlap

Front 18

water

Back 18

-is seldom, if ever pure in nature
-even if contains large numbers of bacteria may still be safe to drink
-it is the specific human pathogen in water that determines its quality
-water from streams & lakes that contain autotrophs & saprophytic heterotrophs (make their own food) are non-pathogenic & safe
-pathogens are parasitic heterotrophs

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potable

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safe for drinking, still has bacteria/no human pathogens

Front 20

enteric diseases (Gastrointestinal)

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-are diseases spread principally by the fecal-oral route through contaminated water
-since these enteric human pathogens are not normally found in water, unless it is contaminated with sewage, it is much easier to detect the presence of a sewage indicator microorganism
-dysentery, typhoid fever, cholera

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the routine examination of water for presence of pathogens would be tedious & difficult because

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1) when such pathogens are present in water, their numbers may be too low to detect and might be missed
2) by the time these pathogens are detected it may be too late to prevent the spread of disease caused by these microorganisms

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coliform group

Back 22

-where E coli belongs, most frequent bacteria, most familiar
-facultative anaerobes (able to breathe, use oxygen or switch to ATP)
- (G-)
-non-endospore formers
-bacilli, random, rod-shaped
-fermetns lactose sugar to produce gas

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presumptive test for water quality

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1) inoculate lactose broth tubes with a water sample
2) incubate at 37*C for 48 hrs & look for gas production
3) if gas production occurs, then one can presume (maybe) that coliforms are present in the sample and maybe E. coli
-BUT some G+ microorganisms can also form gas from lactose broth to a second test, the confirmed test, is done on positive presumptive test tubes

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Durham tube

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a small, inverted gas-collecting tube in lactose broth. It indicates the presence of gas by a small air bubble trapped within it

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E. coli

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-since the sewage indicator, is always found in the intestines (normal microbiota)
-are normally not present in soil or water, it can be assumed that their presence in water indicagtes that sewage has contaminated the water supply
-the presence of sewage indicator microorganisms indicateds that human pathogens may also be present

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why E. coli is the standard sewage indicator microorganism for these reasons

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1) is not normally present in water or soil, it is is only found in the large intestine of warm-blooded animals and humans
2) is easy to identify by using selective/differential media
3) survive longer in water than many enteric pathogens so it makes them easy to identify

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confirmed test

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test used to see if the sewage indicator in bacteria, E. coli was present in the water sample