Lesson 10

Question 1

A population of bacteria grown in the laboratory is referred to as a

Answer 1

culture

Question 2

contains only one single type

Answer 2

pure culture

Question 3

contains two or more
different bacteria.

Answer 3

mixed culture

Question 4

bacterial cultures must be periodically transferred, or
__________, to new media to keep the bacterial population growing.

Answer 4

subcultured

Question 5

is used to obtain a pure culture of an
infectious agent, and also for studies leading to the identification of the pathogen.

Answer 5

subculturing

Question 6

means using practices and procedures to
prevent contamination from pathogens.

Answer 6

Aseptic technique

Question 7

Indications for various culture methods:

Answer 7

1. Isolate bacteria in pure culture and identify the same by performing various tests.
2. Demonstrate biochemical, antigenic, and other phenotypic and genomic
   properties of the isolated colonies.
3. Demonstrate susceptibility of the isolated bacteria to antibiotics, bacteriophages,
   bacteriocins, etc.
4. Prepare antigens for various uses.
5. Maintain stock culture.
6. Estimate viable counts.

Question 8

Culture methods

Answer 8

1. Streak plate method
2. Lawn culture
3. Stroke culture
4. Stan culture
   5.Pour plate culture
   6.Shake culture
5. Liquid cultures

Question 9

: The most effective way to isolate a single type of
bacteria from a source that contains many by diluting the individual cells by
spreading them over the surface of an agar plate using a platinum or inoculating
loop of 2–4 mm diameter. On the plate single cells reproduce and create millions
of clones, which all pile up on top of the original cell.

Answer 9

Streak plate method

Question 10

The piles of bacterial cells
observed after an incubation period are called .

Answer 10

colonies

Question 11

: Also called as carpet culture, this method is used for (a)
Antibiotic susceptibility testing by disk diffusion method, (b) Bacteriophage typing,
(c) For preparation of bacterial antigens and vaccines.

Answer 11

Lawn culture

Question 12

Lawn culture : Also called as carpet culture, this method is used for

Answer 12

(a)
Antibiotic susceptibility testing by disk diffusion method, (b) Bacteriophage typing,
(c) For preparation of bacterial antigens and vaccines.

Question 13

provides a pure growth of bacteria for carrying
out slide agglutination and other diagnostic tests. It is carried out in tubes usually
containing slanted nutrient agar slopes.

Answer 13

Stroke culture

Question 14

This method is used for (a) mainly for demonstration of gelatin
liquefaction, (b) demonstration of oxygen requirement of the bacterium under
study, (c) for the maintenance of stock cultures, (d) to study motility of bacteria in
semisolid agar

Answer 14

Stab culture :

Question 15

is used to determine approximate
number of viable organisms in liquids, such as water or urine. It is used to
quantitate bacteria in urine cultures and also to estimate the viable bacterial
count in a suspension.

Answer 15

pour-plate culture

Question 16

: a deep culture of agar or gelatin through which the inoculum is
evenly distributed by shaking before the medium is solidified and which is used
chiefly for the demonstration of anaerobic colonies.

Answer 16

Shake culture

Question 17

Liquid cultures: This method is used for

Answer 17

(a) blood culture and for sterility, (b)
dilution in the medium, or (c) large yields culture. However, liquid cultures does
not provide a pure culture from mixed inocula—the major disadvantage, nor
identify a bacteria.

Question 18

For _______ the incubation is done in an incubator under normal
atmospheric condition.

Answer 18

cultivation of aerobes

Question 19

Incubation of cultures at ____ is standard practice in the
culture of bacteria pathogenic to man.

Answer 19

37°C

Question 20

Culture in an Atmosphere with Added Carbon
Dioxide Some organisms, such as _______ and _________ ,require extra CO2 in the air in which they are grown and others, such as the
pneumococcus and gonococcus, grow better in air supplemented with 5 to 10
percent CO2.

Answer 20

Brucella abortus
capnophilic streptococci

Question 21

Culture in an Atmosphere with Added Carbon
Dioxide Some organisms, such as Brucella abortus and capnophilic streptococci,require extra CO2 in the air in which they are grown and others, such as the
__________and ________, grow better in air supplemented with 5 to 10
percent CO2.

Answer 21

pneumococcus
gonococcus

Question 22

require incubation without oxygen and differ in their
requirement and sensitivity to oxygen.

Answer 22

Anaerobic bacteria

Question 23

will not grow from small
inocula unless oxygen is absent and the Eh of the medium is low.

Answer 23

Obligate anaerobes

Question 24

METHODS OF ISOLATING PURE CULTURES

Answer 24

1. Surface plating
2. Use of selective, enrichment or indicator media
3. Selective treatment of the specimen before culture
4. Use of selective growth conditions
5. Separation of motile from non-motile bacteria can be effected using Cragie’s tube
6. Animal inoculation
7. Filters:

Question 25

: a method routinely employed in clinical bacteriology and enables
the isolation of distinct colonies which may be picked out, if necessary for further
purification and study.

Answer 25

Surface plating

Question 26

________ are widely used for the isolation of
pathogens from specimens such as feces, with varied flora.

Answer 26

Enrichment, selective and indicator media

Question 27

such as tellurite media for the diphtheria
bacillus, have been devised so that, the majority of organisms likely to be associated
with those for which the media are used will not grow, and the isolation of pure
cultures is thus facilitated.

Answer 27

Selective media

Question 28

such as selenite broth for Salmonella
sp, favor the multiplication of particular species as a step towards their isolation in
pure culture.

Answer 28

Enrichment media

Question 29

such as Willis and Hobbs medium for
Clostridium sp, contain ingredients that change in appearance with particular
organisms and so assist their isolation.

Answer 29

Indicator media

Question 30

Selective treatment of the specimen before culture:

Answer 30

i. Heating at 65°C for 30 minutes or at higher temperatures for shorter periods
ii. Pretreatment of specimens with appropriate bactericidal substances

Question 31

can be used to separate spores from vegetative bacilli but does not guarantee that
spores will germinate under subsequent cultural conditions.

Answer 31

i. Heating at 65°C for 30 minutes or at higher temperatures for shorter periods:

Question 32

which destroy the unwanted bacteria. This method is the standard
practice for the isolation of tubercle bacilli from sputum and other clinical specimens,
by treatment with alkali, acid or other substances to which most commensals are
susceptible but tubercle bacilli are resistant.

Answer 32

Pretreatment of specimens with appropriate bactericidal substances

Question 33

Use of selective growth conditions:

Answer 33

i. Separation of bacteria with different temperature optima
ii. Cultivation under aerobic or anaerobic conditions

Question 34

Obligate aerobes and
anaerobes may be separated by

Answer 34

cultivation under aerobic or anaerobic conditions

Question 35

also serves the same purpose, inoculation being performed in one
limb and the subculture taken from the other. This method can also be used to obtain
phase variants in Salmonella species.

Answer 35

U-tube

Question 36

Pathogenic bacteria may be isolated from mixtures by inoculation into
appropriate animals due to the fact that laboratory animals are highly susceptible to
certain organisms for example, the mouse to the pneumococcus.

Answer 36

Animal inoculation

Question 37

Animal inoculation
Example:

Answer 37

i. Pneumococcus
ii. Anthrax bacilli
iii. Tubercle bacillus

Question 38

If a mixture of organisms containing the ________, e.g.
in sputum, is inoculated subcutaneously into a mouse, the animal dies of
pneumococcal septicemia in 12 to 48 hours and the organism can be obtained in
pure culture from the heart blood.

Answer 38

pneumococcus

Question 39

_________ can be distinguished from other aerobic
sporulating bacilli by inoculation into mice or guinea pigs. Anthrax bacilli produce a
fatal septicemia and may be cultured pure from the heart blood

Answer 39

Anthrax bacilli

Question 40

_______can be isolated from
contaminating organisms by inoculation of an infected specimen into a guinea pig.
The tubercle bacillus is found in a pure state in the resulting lesions.

Answer 40

tubercle bacillus

Question 41

Bacteria of differing sizes may be separated by the use of selective _____.
____ are widely used for separating viruses from bacteria.

Answer 41

filters