H.labeled Cafter drinkand thatinvasivestomachHellcobeComme(a)of Tradi(e)(b)FIGURE 10.4 Biochemical Tests Results, left to right (a) Catalese positive and negative. (b) Sugar fermentation negative, positive (acid and gaspositive (acid only), and uninoculated control. (c) Urease positive and uninoculated control.Severaltional ba strip F(figureadded ting thetional16-hWhat specifically couses the celer to change in the sugar fermentation and urease tests?already present in a bacterial colony. Most, however, requirean incubation period of at least 18 hours.One of the easiest and fastest biochemical tests is an assayfor the enzyme catalase (figure 10.4a). Recall that catalase isan enzyme that many organisms produce to protect againsthydrogen peroxide (see table 4.3), To detect catalase, a smallportion of a colony is transferred to a microscope slide or theinside of a Petri dish, and then a drop of hydrogen peroxide(H2O) is added. If catalase is present, it immediately breaksdown the hydrogen peroxide to form O, and water; the O, canbe observed as bubbles in the reagent. Most bacteria that growin the presence of O2 are catalase-positive. Important excep-tions are the lactic acid bacteria, which include members ofan inverted tube traps any gas produced (figure 10.4b)medium designed to detect urease, an enzyme that degradesurea to produce carbon dioxide and ammonia, contains ureaand a pH indicator (figure 10.4c).The basic strategy for identifying bacteria bused osbiochemical tests relies on a dichotomous key, a series ofalternative choices that lead to the identification of an organism (figure 10.5). In the case of bacterial identification, thechoices are results of laboratory tests such as those listed intable 10.1. Because each test often requires an incubationperiod, however, it would be too time-consuming to proceedone step at a time, In addition, relying on a single biochemicaltest at each step could lead to misidentification. For exampleif a strain that normally gives a positive result fora certain tesloses the ability to produce a key enzyme, it would insteadhave a negative result. Therefore, several different biochemi-cal tests are inoculated at the same time in order to identifythe organism faster and more conclusivelyIn certain cases, biochemical testing can be done without culturing the organism. Helicobacter pylori, the cause ofmost stomach ulcers, can be detected using the breath test,aare detvertedputermicrotwellswideallowof miwastethe genus Streptococcus. Thus, if B-hemolytic colonies growfrom a throat culture but testing reveals they are all catalase-positive, then Streptococcus pyogenes has been ruled out.2 syswithcatalase, p. 101 H Streptococcus pyogenes. p. 535Most biochemical tests rely on a chemical indicator thatchanges color when a compound is degraded. To test for theability of an organism to ferment a given sugar,thatorgan-ism is added to a broth growth medium containing thesugarand a pH indicator. If the organism ferments the sugar, acid iswhichfor the presence of urease. The patient drinks aassaysproduced, which lowers the pH, resulting in a color change;solution containing urea labeled with an isotope of carbon. IfFIGURE 10.5 Dichotomous KeyThis shows an example of steps thatcan be used to distinguish some ofthe common causes of urinary tractinfections. Additional tests may be doneto confirm the identity of the pathogen.Gram stainGram-positive coccusGram-negative rodCatalaseOxidase testWhen identifying organisms, whyare most biochemical tests usuallyinoculated at the same time, ratherPositiveNegativePositiveNegativethan waiting for one result beforestarting the next test?CoagulasePseudomonasEnterococcus sp.LactosefermentationaeruginosaPositiveNegativePositiveNegativeStaphylococcusStaphylococcussaprophyticusE. coli orother coliformaureusProteus sp

Question
Asked Oct 15, 2019

Dichotomous key:
b. Based on the key, bacteria of which genus would appear purple after a Gram-staining test? please refer to the attached photo.

H.
labeled C
after drink
and that
invasive
stomach
Hellcobe
Comme
(a)
of Tradi
(e)
(b)
FIGURE 10.4 Biochemical Tests Results, left to right (a) Catalese positive and negative. (b) Sugar fermentation negative, positive (acid and gas
positive (acid only), and uninoculated control. (c) Urease positive and uninoculated control.
Several
tional b
a strip F
(figure
added t
ing the
tional
16-h
What specifically couses the celer to change in the sugar fermentation and urease tests?
already present in a bacterial colony. Most, however, require
an incubation period of at least 18 hours.
One of the easiest and fastest biochemical tests is an assay
for the enzyme catalase (figure 10.4a). Recall that catalase is
an enzyme that many organisms produce to protect against
hydrogen peroxide (see table 4.3), To detect catalase, a small
portion of a colony is transferred to a microscope slide or the
inside of a Petri dish, and then a drop of hydrogen peroxide
(H2O) is added. If catalase is present, it immediately breaks
down the hydrogen peroxide to form O, and water; the O, can
be observed as bubbles in the reagent. Most bacteria that grow
in the presence of O2 are catalase-positive. Important excep-
tions are the lactic acid bacteria, which include members of
an inverted tube traps any gas produced (figure 10.4b)
medium designed to detect urease, an enzyme that degrades
urea to produce carbon dioxide and ammonia, contains urea
and a pH indicator (figure 10.4c).
The basic strategy for identifying bacteria bused os
biochemical tests relies on a dichotomous key, a series of
alternative choices that lead to the identification of an organ
ism (figure 10.5). In the case of bacterial identification, the
choices are results of laboratory tests such as those listed in
table 10.1. Because each test often requires an incubation
period, however, it would be too time-consuming to proceed
one step at a time, In addition, relying on a single biochemical
test at each step could lead to misidentification. For example
if a strain that normally gives a positive result fora certain tes
loses the ability to produce a key enzyme, it would instead
have a negative result. Therefore, several different biochemi-
cal tests are inoculated at the same time in order to identify
the organism faster and more conclusively
In certain cases, biochemical testing can be done with
out culturing the organism. Helicobacter pylori, the cause of
most stomach ulcers, can be detected using the breath test,
a
are det
verted
puter
microt
wells
wide
allow
of mi
waste
the genus Streptococcus. Thus, if B-hemolytic colonies grow
from a throat culture but testing reveals they are all catalase-
positive, then Streptococcus pyogenes has been ruled out.
2 sys
with
catalase, p. 101 H Streptococcus pyogenes. p. 535
Most biochemical tests rely on a chemical indicator that
changes color when a compound is degraded. To test for the
ability of an organism to ferment a given sugar,
that
organ-
ism is added to a broth growth medium containing the
sugar
and a pH indicator. If the organism ferments the sugar, acid is
which
for the presence of urease. The patient drinks a
assays
produced, which lowers the pH, resulting in a color change;
solution containing urea labeled with an isotope of carbon. If
FIGURE 10.5 Dichotomous Key
This shows an example of steps that
can be used to distinguish some of
the common causes of urinary tract
infections. Additional tests may be done
to confirm the identity of the pathogen.
Gram stain
Gram-positive coccus
Gram-negative rod
Catalase
Oxidase test
When identifying organisms, why
are most biochemical tests usually
inoculated at the same time, rather
Positive
Negative
Positive
Negative
than waiting for one result before
starting the next test?
Coagulase
Pseudomonas
Enterococcus sp.
Lactose
fermentation
aeruginosa
Positive
Negative
Positive
Negative
Staphylococcus
Staphylococcus
saprophyticus
E. coli or
other coliform
aureus
Proteus sp
help_outline

Image Transcriptionclose

H. labeled C after drink and that invasive stomach Hellcobe Comme (a) of Tradi (e) (b) FIGURE 10.4 Biochemical Tests Results, left to right (a) Catalese positive and negative. (b) Sugar fermentation negative, positive (acid and gas positive (acid only), and uninoculated control. (c) Urease positive and uninoculated control. Several tional b a strip F (figure added t ing the tional 16-h What specifically couses the celer to change in the sugar fermentation and urease tests? already present in a bacterial colony. Most, however, require an incubation period of at least 18 hours. One of the easiest and fastest biochemical tests is an assay for the enzyme catalase (figure 10.4a). Recall that catalase is an enzyme that many organisms produce to protect against hydrogen peroxide (see table 4.3), To detect catalase, a small portion of a colony is transferred to a microscope slide or the inside of a Petri dish, and then a drop of hydrogen peroxide (H2O) is added. If catalase is present, it immediately breaks down the hydrogen peroxide to form O, and water; the O, can be observed as bubbles in the reagent. Most bacteria that grow in the presence of O2 are catalase-positive. Important excep- tions are the lactic acid bacteria, which include members of an inverted tube traps any gas produced (figure 10.4b) medium designed to detect urease, an enzyme that degrades urea to produce carbon dioxide and ammonia, contains urea and a pH indicator (figure 10.4c). The basic strategy for identifying bacteria bused os biochemical tests relies on a dichotomous key, a series of alternative choices that lead to the identification of an organ ism (figure 10.5). In the case of bacterial identification, the choices are results of laboratory tests such as those listed in table 10.1. Because each test often requires an incubation period, however, it would be too time-consuming to proceed one step at a time, In addition, relying on a single biochemical test at each step could lead to misidentification. For example if a strain that normally gives a positive result fora certain tes loses the ability to produce a key enzyme, it would instead have a negative result. Therefore, several different biochemi- cal tests are inoculated at the same time in order to identify the organism faster and more conclusively In certain cases, biochemical testing can be done with out culturing the organism. Helicobacter pylori, the cause of most stomach ulcers, can be detected using the breath test, a are det verted puter microt wells wide allow of mi waste the genus Streptococcus. Thus, if B-hemolytic colonies grow from a throat culture but testing reveals they are all catalase- positive, then Streptococcus pyogenes has been ruled out. 2 sys with catalase, p. 101 H Streptococcus pyogenes. p. 535 Most biochemical tests rely on a chemical indicator that changes color when a compound is degraded. To test for the ability of an organism to ferment a given sugar, that organ- ism is added to a broth growth medium containing the sugar and a pH indicator. If the organism ferments the sugar, acid is which for the presence of urease. The patient drinks a assays produced, which lowers the pH, resulting in a color change; solution containing urea labeled with an isotope of carbon. If FIGURE 10.5 Dichotomous Key This shows an example of steps that can be used to distinguish some of the common causes of urinary tract infections. Additional tests may be done to confirm the identity of the pathogen. Gram stain Gram-positive coccus Gram-negative rod Catalase Oxidase test When identifying organisms, why are most biochemical tests usually inoculated at the same time, rather Positive Negative Positive Negative than waiting for one result before starting the next test? Coagulase Pseudomonas Enterococcus sp. Lactose fermentation aeruginosa Positive Negative Positive Negative Staphylococcus Staphylococcus saprophyticus E. coli or other coliform aureus Proteus sp

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check_circleExpert Solution
Step 1

Dichotomous means two divisions or classifications. In microbiology, the dichotomous key is defined as a tool that is used to recognize species of different bacteria. The key generally consists of a sequence of organized statements that are arranged into couplets. A couplet contains two descriptions that describe the difference between two species or chosen characters. Based on the differences, the characters of the given specimen are identified.

Step 2

Bacteria are divided into two main groups: gram-positive bacteria and gram-negative bacteria. Gram staining is a method used to recognize these two different species of bacteria. The gram stain distinguishes bacteria based on their physical and chemical properties. If specimens appear purple under a microscope then they are Gram-positive, if bacteria appear red then they are Gram-negative bacteria.

 

Gram-positive bacteria are composed of a thick layer of the cell wall. The main constituent in their wall is peptidoglycan that retains the Gram stain and appeared violet in color. Gram-negative bacteria give a negative test when subjected to Gram staining. The cells of gram-negative bacteria have a thin layer of peptidoglycan layer that permits primary crystal stain to wash out. 

 

Step 3

The dichotomous key given in the figure indicates that Staphylococci aureus and Staphylococcus saprophyticus show positive results when subjected to Gram staining while E. coli and Proteus sp. species show negative result under Gram stain. The positive result indicates purple-colored bacteria and the negative result shows red-colored bacteria under a microscope. Thus, Staphylococci aureus and Staphylococcus saprophyticus are gram-positive and E. coli and Proteus sp. are gram-negative bacteria.

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