Lesson 10 Flashcards
-population of bacteria grown in the laboratory
culture
- contains only one single type of bacteria
pure culture
-it is done to keep the bacterial population growing
Subculturing
contains two or more different bacteria.
mixed culture 🧫
if a bacterial culture is left in the same media for too long what will happen?
the cells will use up the available nutrients
excrete toxic metabolites
eventually the entire population will die
is used to obtain a pure culture of an Infectious agent, and also for studies leading to the identification of the pathogen.
Subculturing
- means using practices and procedures to prevent contamination from pathogens.
-
Aseptic technique
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.
Streak plate method
-The piles of bacterial cells observed after an incubation period
Colonies
-Also called as carpet culture, prepared by flooding the surface of the plate with a liquid culture or suspension of the bacterium, pipetting off the excess inoculum and incubating the plate. Also provides a uniform growth of the
bacterium.
Lawn culture
-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.
Stoke culture
-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
Stab culture
-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.
Pour plate culture
-pour plate culture ml needed of molten
15 ml
-the molten agar in tubes is left to cool in a water bath at what degree?
45 degree Celsius
-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.
Shake culture
-This method is used for
(a) blood culture and for sterility,
(b) dilution in the medium, o
r (c) large yields culture. However, it does not provide a pure culture from mixed inocula—the major disadvantage, nor identify a bacteria.
Liquid culture
-may be inoculated by touching with a charged loop or by adding the inoculum with pipettes or syringes.
Liquid culture
-require extra CO2 in the air in which they are grown
Brucella abortus and capnophilic streptococco
, grow better in air supplemented with 5 to 10percent CO2
pneumococcus and gonococcus
-require incubation without oxygen and differ in their requirement and sensitivity to oxygen.
Anaerobic culture method
- will not grow from small inocula unless oxygen is absent and the Eh of the medium is low
Obligate anaerobes
-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.
Surface plating
- are widely used for the isolation of pathogens from specimens such as feces, with varied flora
Enrichment, selective and indicator media
-example is 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.
Selective media
-selenite broth for Salmonella sp, favor the multiplication of particular species as a step towards their isolation in
pure culture.
Enrichment media
-such as Willis and Hobbs medium for Clostridium sp, contain ingredients that change in appearance with particular organisms and so assist their isolation.
Indicator media
-can be used to separate spores from vegetative bacilli but does not guarantee that spores will germinate under subsequent cultural conditions.
Heating at 65°C for 30 minutes or at higher temperatures for shorter periods:
-This method is useful for the isolation of tetanus bacilli from dust and similar sources.
Heating at 65°C for 30 minutes or at higher temperatures for shorter periods
-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.
Pretreatment of specimens with appropriate bactericidal substances
-The temperature and atmosphere chosen for a culture automatically preclude the growth of many bacteria.
Separation of bacteria with different temperature optima
-thermophilic bacteria grow at this temperature
60ºC
will not grow in air
Strict anaerobes
grow less vigorously under anaerobic than under aerobic conditions
facultative anaerobes
- This consists of a tube of semisolid agar, with a narrow tube open at both ends placed in the center of the medium in such a way that it projects above the level of the agar
Cragies tube
- 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
U-tube
-may be isolated from mixtures by inoculation into appropriate animals due to the fact that laboratory animals are highly susceptible to certain organisms
Pathogenic bacteria
can be distinguished from other aerobic
sporulating bacilli by inoculation into mice or guinea pigs.
produce a
fatal septicemia and may be cultured pure from the heart blood.
Anthrax bacilli
-Bacteria of differing sizes may be separated by the use of this .
selective filters.
-are widely used for separating viruses from bacteria.
-
filters
can be isolated from
contaminating organisms by inoculation of an infected specimen into a guinea pig.
is found in a pure state in the resulting lesions.
Tubercle bacillus
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.
Pneumococcus
