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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

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

plate count

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

most probable number

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


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

ATP, acid from fermentation

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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

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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?

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

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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
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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?

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Questions & Answers

Explain Mould
Chinenye Reply
Explain mycoses and it's classification
why do we have hiccups?
Manisha Reply
shakey diaphragm
The antibody binding site is formed primarily by:
Asalla Reply
How many types of MICROORGANISMS do we have?
Hope Reply
Hello friends
What's pathogenesity
Usman Reply
something that causes disease
who is the father of microbiology?
no it is not it also dealt withe fermentation techniques, downstream processing of isolated products etc
Ramchandra Reply
you from
I'm from Bangalore, India
in banglore
what group is Indian
I'm from pune
Why scientists is not studies the drungs or vaccines of a virus, based on common characterstics of virus as living and non-living organisms?
what are the examples of viruses and their causing agent
kolawole Reply
coronavirus in the family of Coronaviridae and the causing agent is common cold where it spread easily compared to hot region.you can correct me if I am wrong.
okay there are major 3 groups (1.Enterovirus=poliovirus, cocksakievirus A&B,echovirus,endovirus etc causing poliomyelities,meningitis, fever,respiratory disease, acute hemorrhagic conjunctivitis, 2.Hepatitis virus- infectious hepatitis , 3.Rotavius incl.coronavius =vomiting, diarrhoea and common co
isthe another virus are coronaviridae
Hai Puja
corona virus is not dangerous but not care is very dangerous..............
he means if we take care we will not be infected
for the question thing first let's classify viruses then it would be easier to deal with zem
Where you all from?
what are five elements that are needed for bacteria to grow?
proper acidity (ph)
salt level
osmotic pressure,oxygen,light
but zey are not only five n we can classify zem as physical and chemical
air in hydrogen and carbon and niterogin
1. Possible complications and outcomes for cutaneous anthrax:
Firoj Reply
chlamydia can it be viral disease?
nyakaraitta Reply
what is microbiology
Sohel Reply
is the study of tiny organisms with the use of microscopes
Is the study of microorganisms
is the biological science of identification and charaterization of micro organisms surrounding the environment
what are the major groups of archae bacteria
Brian Reply
methanogens, halophiles, thermophiles
Right, mali
how can get information
Raage Reply
how i study microbiology
By Reading About It
quickest form
why do our brain needs glucose?
Bijay Reply
b/c our brain works glucose as the other body use insulin
of course why do hairs obtain nutrients yet there is no blood?
can I get a diagram of paramicium
what is the meaning of the term microbiology
Mary Reply
 study of all living organisms that are too small to be visible with the naked eye.
yahh it right
wow lovely
Well said.
study of microscopic organism like protozoa, bacteria, fungi, algea ,viruses betc
what are the career opportunities in microbiology
I don't understand the explanation
Nancy Reply
virus can also culture?
ya same doubt.. virus can also culture?
prabhat explain More
yes we can culture virus. virus culture is a laboratory test in which samples are placed with a cell type that the virus being tested for is able to infect.
the topic is telling us on how the first microscope is been invented by van Lee...., & his own still remains the best although he's was a simple one with one lens while the compound one that was invented by Hooke with two lenses is the one commonly used now.
sorry! Hooke didn't invent it rather he used it in the writing of his book .
what is microbiology
microbiology is the study of microrganisms (unicellular,multicellular) which can be seen under the microscope

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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