<< Chapter < Page Chapter >> Page >
The short peptide has the following amino acids in a chain: tyr, ser, thr, cys, asp, phe, ile, met. Attached to the cys is an S, attached to the S is a C which also attaches to the met. The C also has a double bonded O. The N-acetylated homoserine lactone has a pentagon with an O on the bottom left corner and a double bonded O attached to the left corner. The top corner is attached to an N which is attached to an R and a C. The C is double bonded to an O and also has an H.
Short peptides in gram-positive bacteria and N-acetylated homoserine lactones in gram-negative bacteria act as autoinducers in quorum sensing and mediate the coordinated response of bacterial cells. The R side chain of the N-acetylated homoserine lactone is specific for the species of gram-negative bacteria. Some secreted homoserine lactones are recognized by more than one species.

Biofilms and human health

The human body harbors many types of biofilms, some beneficial and some harmful. For example, the layers of normal microbiota lining the intestinal and respiratory mucosa play a role in warding off infections by pathogens. However, other biofilms in the body can have a detrimental effect on health. For example, the plaque that forms on teeth is a biofilm that can contribute to dental and periodontal disease. Biofilms can also form in wounds, sometimes causing serious infections that can spread. The bacterium Pseudomonas aeruginosa often colonizes biofilms in the airways of patients with cystic fibrosis , causing chronic and sometimes fatal infections of the lungs. Biofilms can also form on medical devices used in or on the body, causing infections in patients with in-dwelling catheters , artificial joints, or contact lenses .

Pathogens embedded within biofilms exhibit a higher resistance to antibiotics than their free-floating counterparts. Several hypotheses have been proposed to explain why. Cells in the deep layers of a biofilm are metabolically inactive and may be less susceptible to the action of antibiotics that disrupt metabolic activities. The EPS may also slow the diffusion of antibiotics and antiseptics, preventing them from reaching cells in the deeper layers of the biofilm. Phenotypic changes may also contribute to the increased resistance exhibited by bacterial cells in biofilms. For example, the increased production of efflux pumps , membrane-embedded proteins that actively extrude antibiotics out of bacterial cells, have been shown to be an important mechanism of antibiotic resistance among biofilm-associated bacteria. Finally, biofilms provide an ideal environment for the exchange of extrachromosomal DNA , which often includes genes that confer antibiotic resistance.

  • What is the matrix of a biofilm composed of?
  • What is the role of quorum sensing in a biofilm?

Key concepts and summary

  • Most bacterial cells divide by binary fission . Generation time in bacterial growth is defined as the doubling time of the population.
  • Cells in a closed system follow a pattern of growth with four phases: lag , logarithmic (exponential) , stationary , and death .
  • Cells can be counted by direct viable cell count . The pour plate and spread plate methods are used to plate serial dilutions into or onto, respectively, agar to allow counting of viable cells that give rise to colony-forming units . Membrane filtration is used to count live cells in dilute solutions. The most probable cell number (MPN) method allows estimation of cell numbers in cultures without using solid media.
  • Indirect methods can be used to estimate culture density by measuring turbidity of a culture or live cell density by measuring metabolic activity.
  • Other patterns of cell division include multiple nucleoid formation in cells; asymmetric division, as in budding ; and the formation of hyphae and terminal spores.
  • Biofilms are communities of microorganisms enmeshed in a matrix of extracellular polymeric substance . The formation of a biofilm occurs when planktonic cells attach to a substrate and become sessile . Cells in biofilms coordinate their activity by communicating through quorum sensing .
  • Biofilms are commonly found on surfaces in nature and in the human body, where they may be beneficial or cause severe infections. Pathogens associated with biofilms are often more resistant to antibiotics and disinfectants.

Fill in the blank

Direct count of total cells can be performed using a ________ or a ________.

hemocytometer, Petroff-Hausser counting chamber

Got questions? Get instant answers now!

The ________ method allows direct count of total cells growing on solid medium.

plate count

Got questions? Get instant answers now!

A statistical estimate of the number of live cells in a liquid is usually done by ________.

most probable number

Got questions? Get instant answers now!

For this indirect method of estimating the growth of a culture, you measure ________ using a spectrophotometer.

turbidity

Got questions? Get instant answers now!

Active growth of a culture may be estimated indirectly by measuring the following products of cell metabolism: ________ or ________.

ATP, acid from fermentation

Got questions? Get instant answers now!

Matching

Match the definition with the name of the growth phase in the growth curve.

___Number of dying cells is higher than the number of cells dividing A. Lag phase
___Number of new cells equal to number of dying cells B. Log phase
___New enzymes to use available nutrients are induced C. Stationary phase
___Binary fission is occurring at maximum rate D. Death phase

D, C, A, B

Got questions? Get instant answers now!

Short answer

Why is it important to measure the transmission of light through a control tube with only broth in it when making turbidity measures of bacterial cultures?

Got questions? Get instant answers now!

In terms of counting cells, what does a plating method accomplish that an electronic cell counting method does not?

Got questions? Get instant answers now!

Order the following stages of the development of a biofilm from the earliest to the last step.

  1. secretion of EPS
  2. reversible attachment
  3. dispersal
  4. formation of water channels
  5. irreversible attachment
Got questions? Get instant answers now!

Infections among hospitalized patients are often related to the presence of a medical device in the patient. Which conditions favor the formation of biofilms on in-dwelling catheters and prostheses?

Got questions? Get instant answers now!

Questions & Answers

what is cell
Avi Reply
is unit of life
Kamaluddeen
Ok
mohamed
who is an industrial microbiologist
Cynthia Reply
I want to know the biochemical composition of bacteria
Josh Reply
It contains peptidoglcon, DNA nd RNA
Asiya
bacteriophage disadvantage
Momina Reply
disease due to __________ abnormalities are termed primary immunodeficiencies
Tayee Reply
Some primary immunodeficiencies are due to a defect of a single cellular or humoral component of the immune system.
Prince
Examples of primary immunodeficiencies include: chronic granulomatous disease, X-linked agammaglobulinemia, selective IgA deficiency etc
Prince
thank you
Nana
explain microbial mutation
Emerald
what is mutation
Cynthia Reply
alteration in genetic makeup
UDEME
Hi, I'm new here. I'm Bello Abdul Hakeem from Nigeria.
BELLO Reply
welcome on board
Kamaluddeen
Thanks brother I'm an undergraduate. I hope to study for MBBS.
BELLO
pls guys help me out
Linda
what is limitation of plate
Linda
limitation of plate load test . there are some that should be considered while performing load test which are given below, this test is usually performed on relatively similar plate ,usually 1 or 2 square foot area the reason is that the plate of greater are the economically not feasible
yemi
iam new here my name shafiu umar from Nigeria
Shafiu
thanks shafiu
gambo
how to differentiate Gram positive from Gram negative bacteria?
Faheem
by the cell membrane
Tim
with gram staining which has 4 steps
Freedom
Mechanism of bacterial pathogenicity
rashida Reply
Toxicity
Ibrahim
write a short note on Algea
najaatu Reply
green minutes plants organisms that are produced in turf.
Prince
Algae is a kind of a photosynthetic organism, which is usually grown in the moist areas. These are usually the simple plants that grow near to the water bodies. It contains a kind of chlorophyll pigments that act as a primary coloring agent.
Avi
they are eukaryotic and most lived in fresh water. they are photosynthetic that's, they contain chlorophyll and store starch in discrete chloroplast.
Prince
are bacteria important to man
just Reply
yes, depending on the type of bacteria .eg the normal florals, the latic acid batteries etc are important to man
Lois
I mean latic acid bacterial
Lois
I don't understand this topic
Jane Reply
what topic is that
Rose
sahi kon hai bhosri ke
saurabh Reply
define metabolism of carbohydrates with example
Thavasi Reply
what is sterilization a
Sani
the process of keep equipment free from bacteria
shar
is it only bacteria?
Lois
no undesirable fungi and contamination also.
Khushbu
what is streak plate method
Offikwu
what is the biofilm
Dimingu
metabolism is the sum of all the biochemical reaction required for energy generation and use of that energy to synthesize cell materials from small molecules in environment.
Alex
boclenia
Pooja
what are granulocytes
Shawnitta Reply
e.coli
Sukhdeep
granulocytes are type of WBCs which contains granules in the cytoplasm
Owili
what is mutation
Cynthia
it is the interchange of genes from their normal sequence
Esther
is an heritable change of the base-pair sequence of genetic material
Elizabeth
suitable example for prokaryotes
Suvetha Reply
one of the possible early sources of energy was
Suvetha
uv radiation and lighting
Anisha
e coli is the example of prokaryotes
Sukhdeep
archaea too
Noel

Get the best Microbiology course in your pocket!





Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?

Ask