Food & Water Bacteriology Flashcards
Perishable foods which can support the growth of harmful bacteria
high risk foods
Which is not part of the high risk food group?
(1) All cooked meat and poultry.
(2) gravy, stock, and roll/sandwich fillings
(3) eggs and egg products
(4) vegetable salad [no dressing]
(4)
Which is not part of the high risk food group?
(A)Milk, cream, artificial cream, custards and dairy
products
(B)Canola oil
(C)shell fish and other sea food
(D)cooked rice
(B)
Minimum weight range for food sample analysis
25-30 g
Why must delay be kept to a minimum (in food sample analysis)?
target organism may decline in number & spoilage organisms may increase in number
What are the four factors to consider in food sample collection?
(1) Time
(2) Temperature
(3) Container
(4) Manner of collection:
How much time is the limit between collection and reception into the laboratory?
2 hours
Identify the process used for analysis:
- gives evaluation of total population of aerobic microbes present (# of colonies that develop after incubation)
- Swabs of product are applied in sterile covered plates to culture media that non-selectively support growth.
Aerobic Plate Count
Which is not a disadvantage of the Aerobic Plate Count method?
a. only counts plates with 25-250 colonies
b. may not be done on fermented foods
c. Small colonies may be difficult to see
d. Sometimes hard to distinguish food particles from bacteria
A
Aerobic Plate Count is used for everything except:
a. Check the microbiological quality of final products only
b. Determine whether a food has been subjected to
temperature abuse during production, transport and
storage
c. Estimate the potential storage life of product
d. Check level of contamination in processing envt
A
raw materials also
Identify the food analysis method:
* Involves the use of agar poured at 45˚C, which may kill
some pychrotrophs or psychrophiles, or damage cells and reduce count
* the technique gives both surface and subsurface colonies
Pour Plate Method
Identify the method: Only count plates with 25-250 colonies
Counting Plates
In Membrane Filtration Method, which does not happen?
A. Involves passing a known volume of liquid through a
cadmium acetate with a pore size of 0.45 um
B. Bacteria, yeasts and molds are removed from the liquid and precipitated on the membrane surface
C. When the membrane is transferred to a pad soaked in
nutrient medium or an agar plate and incubated, nutrients diffuse through the membrane so that organisms can grow on the membrane surface giving visible colonies that can be counted
D. none of the above
A
cellulose acetate dapat
MBF as a technique for assessing microbial numbers is
limited to __
clear liquids that do not contain debris or other
materials that will block the filter
False about Membrane Filtration Method
A. Has an advantage of detecting high numbers of organisms in small volumes of liquids
B. Particularly useful for testing treated water supplies for the presence of coliforms
C. both are false
A
Dapat:
Has an advantage of detecting low numbers of organisms
in large volumes of liquids
Most Probable Number is also known as __
multiple tube technique
In multiple tube technique, the number of __ in food samples is estimated if the criterion for a particular organism requires detection of low numbers
CFUs
Which does not happen in Most Probable Number method?
A. Typical MPN technique for food analysis involves replicate tubes in groups of 3 containing liquid (selective/differential media)inoculated with 1 ml of samples from a dilution series
B.The decision as to whether a viable organism has been transferred to a tube is based on growth to give visible turbidity only
C. Both do not happen
D. Both happen
B
The said step is done in conjunction with another distinguishing property of the bacteria
Identify the method
statistical method based on the
probability of transferring a CFU from an original dilution
using multiple samples and is employed in conjunction
with a statistical table
Most Probable Number technique
False about Direct Microscopic Count
a. A small sample of food (0.01ml liquid food or food
homogenate in diluent) is spread as evenly as possible in
a 1 cm2 area etched on a microscope slide
b. the slide is dried, stained with suitable stain and examined with oil immersion lens on
the microscope
c. The numbers of organisms in 25 random microscopic
fields can be counted and a calculation based on the field
diameter, made to give the number of organisms/g or ml
original sample
d. The technique is tedious, and obtaining results takes a few days
D
Which is not a disadvantage of Direct Microscopic Count?
A. The technique cannot distinguish between living and
dead cells
B. The technique is tedious to carry out, particularly when dealing with large number of samples
C. procedure may not be applied to fermented foods
D. The sensitivity range is very limited
E. Limited to liquid and semisolid foods with no debris
C
this disadvantage –> Aerobic Plate Count
Dye reduction test for milk uses what dye?
methylene blue / resazurin
False about indicator organisms
(1) Be present in human feces in small numbers
(2) Be present in feces when the pathogen is present
(3) Survive for a similar period in the environment as pathogen
(4) Be quick and easy to isolate and identify in the laboratory
(1)
large numbers dapat
Trypticase soy-yeast extract (TSYE) broth is used for
a. Salmonella
b. Shigella
c. both of the above
d. none of those mentioned
B
Eosin Methylene Blue medium is used for
a. Salmonella
b. Shigella
c. E. coli
d. none of those mentioned
C
Preston broth is used for
a. Camyplobacter
b. Shigella
c. E.coli
d. none of those mentioned
A
Which is not a characteristic of enterobacteriaceae?
- All are gram negative rods
- All ferment glucose
- All are oxidase positive
- All are facultative anaerobes
- Motile species have peritrichous flagella
3
negative dapat
What does CT-SMAC medium mean, in E.coli lab diagnosis?
Cefixime Tellurite Sorbitol MacConkey
Which is false?
A. Ecoli 157 forms sorbitol negative colonies
B. Yersinia enterocolitica is urease positive
C. Listeria monocytogenes uses cold enrichment
D. Campylobacter jejuni is oxidase negative
D
Which is not used for culturing L. monocytogenes? A. McBride B. Oxford agar C. Buffered Charcoal Yeast Extract Agar D.PALCAM agar
C
False about L. monocytogenes? A.beta Hemolysis on BAP, B. Catalase positive C. presence of hydrogen sulphide D. Blue colonies by Henry's illumination
C
Which L. monocytogenes serotype does not cause outbreaks? A. 1/2a B.1/2b C. 4a D. 4b
c
Campylobacter jejuni grows best in what medium?
Skirrow’s medium
C. jejuni fails to grow at __ degrees Celsius & is sensitive to__
25 degrees Celsius
nalidixic acid
this form of transmission refers to microorganisms transmitted by contaminated items
horizontal transmission
water serial dilution is usually __
1:10
Which is false?
A. PHC Test cannot replace standard water quality tests
B. Presence-Absence Test is both qualitative and quantitative
C. PHC Test detects qualitative organisms
D. Presence-Absence Test is used for monitoring good-quality drinking water
B
qualitative only
Water Safety Plans are founded on the principles of ___.
HACCP (Hazard Assessment
Critical Control point)
