ex. 19 Flashcards
(11 cards)
Normal microbial flora aka normal microflora aka commensal
microorganism
The diverse collection of bacteria found in association with the skin and mucous membranes are collectively referred to as the normal microbial flora of the human body.
Colonization of these
areas begins soon after birth as a newborn encounters microbes as it takes its first breath, takes in food, and touches its surroundings and microbes initiate attachment and then multiplication in the respiratory and gastrointestinal tracts, as well as the on the skin and urogenital tract.
Normal flora are often referred to as commensal organisms because they live with humans in a harmonious relationship rather than a disease-causing one.
Most normal flora are saprophytes, living off the
nutrients of dead cells and tissues. Some produce metabolic end products, such as vitamins, which are absorbed by their human hosts and serve to benefit their human hosts.
As an additional bonus, the mere presence of these common microbial inhabitants helps prevent the establishment of
pathogenic bacteria from taking root
Be able to list factors that can cause the composition of your normal
microflora to change
As a host’s age increases, changes in hormones and other body secretions occur and can influence the microbial community.
Diet, climate and physical activities, as well as antibacterial therapy,
can also change the structure of the normal flora community in a host.
The specific growth environments found in the
human body influence the types of normal flora found as well
Know that some areas of the body are supposed to be sterile
“clean catch” urine means someone has a UTI,
urine is supposed to be sterile and should have no growth on the blood agar plate
but bacteria are always in
feces, on skin, and in the throa
causative agent of streptococcal (bacterial) pharyngitis aka Strep throat,
Streptococcus pyogenes
is beta-hemolytic on blood agar (and catalase-
negative
Blood agar plates (BAP) results
Observe the BAP plate (THROAT) and record your results. Recall that this media is differential, but not selective.
Clearing of the blood underneath the colony indicates that the organism is capable of beta-hemolysis.
Greening of the blood underneath the colony indicates that the organism is capable of alpha-hemolysis.
If the blood underneath the colony remains red, this indicates that the
organism is incapable of any type of hemolysis.
You should perform a catalase test on beta-hemolytic colonies that you observe
Be able to identify/differentiate alpha, beta, and gamma hemolysis by
description and by sight by viewing plate (or picture
alpha hemolysis:
refers to the partial lysis of red blood cells and hemoglobin.
This results in a greenish-grey discoloration of the blood around the colonies
beta hemolysis:
which is the complete lysis of red blood cells and hemoglobin.
This results in complete clearing of the blood around the colonies
gamma hemolysis:
No hemolysis
results in no change in the
medium.
Most pathogenic bacteria tend to be
beta (though some alpha, like
Streptococcus pneumoniae
Be able to say the results expected for someone with Strep throat, and if
they do or do not have Strep throat if given the results
(beta-hemolytic on
blood agar and catalase-negative means Strep throat)
MSA plate results
Observe the MSA plate (SKIN) and record your results. Growth indicates the presence of
staphylococci. Yellow media indicates mannitol has been fermented to acids; red media indicates
that mannitol was not fermented to acids.
EMB plate results (fecal)
Observe the EMB plate (FECAL) and record your results. Growth indicates the presence of Gram-negative bacilli.
Dark purple or metallic green colonies indicate the presence of coliform bacteria that ferment lactose to acids.
Colonies with a green metallic sheen specifically indicate the presence of E.coli as a fecal coliform.
Light pink or translucent colonies indicate the presence of non-coliform
bacteria that do not ferment lactose to acids
EMB plate results (urine)
Observe the EMB plate (URINE) and record your results. Growth indicates the presence of Gram-
negative bacilli.
Dark purple or metallic green colonies indicate the presence of coliform bacteria that ferment lactose to acids.
Colonies with a green metallic sheen specifically indicate the presence of E.coli as a fecal coliform.
Light pink or translucent colonies indicate the presence of non-coliform
bacteria that do not ferment lactose to acids.
