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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

what are the prokaryotic
Lungu Reply
prokaraytotic is a unicellular organizm that lacks membrane bound nucleus
and whats eukaryotic
eukaryotic cell are cell which contain anuclues and organells
eukaryotes are the cells that have organells which are protected by membranes
Explain on the Francisco reddi did to prove the theory of spontaneous generation
Diana Reply
what is parasite
Abdirizack Reply
designing of aseptic area
Aashish Reply
I don't know
what is rickettsia
what is microbiology
Is the science that works with microorganisms.
richettsa is small microorganisms that cause disease in human like typhus; they are like viruses that can grow only inside living cells, they're transmitted by mites, ticks or lices.
what is plasmid?
plasmid is extra chromosomal body present in bacteria...which have additional genetic functions example... antibiotic resistance genes....etc etc
state the theory of spontaneous generation of micro oranisms and germ theory of disease
what are the advantages of high note numerical aperture
Genius Reply
list if non flagellated pritozoa
Mepung Reply
Can someone that's understanding of the Kreb Cycle please explain & breakdown it down to me in the simplest way without giving me the dictionary version or Google version. Basically in there own words of knowledge....!
please can someone help explain positive and negative feedback in simple term
negative feedback is the arresting of reaction or reverse of the reaction according to the response and postive feed back is the direct response without reversing or arresting a reaction.
pls can someone explained Kinney stone in memorising in shot time
what tyoebif microorganism will be killed by antibiotic trwatmeant
Mary Reply
I don't really don't understand aerobic respiration anaerobic respiration and fermentation. Can someone explain & breakdown this in the simplest way please.
Anaerobic Respiration in which foodstuffs are partially oxidized, with the release of chemical energy, in a process not involving atmospheric oxygen, such as alcoholic fermentation, in which one of the end products is ethanol.
aerobic respiration A type of respiration in which foodstuffs are completely oxidized to carbon dioxide and water, with the release of chemical energy, in a process requiring atmospheric oxygen.
please can someone explain what pseudomonas species and biofilm is?
Fermentation is the growth of cells or microorganisms in bioreactors (fermenters) to synthesize special products. Fermentation in biochemistry refers to the biodegradation of carbon compounds by cells or organisms under anaerobic (lack of oxygen) conditions.
Please under which conditions does pathogens become established in the human tissues and can cause diseases
please the life cycle of plasmodium parasite
who is John Needham
Mary Reply
John Needham is one of the researcher in microbiology. He also experimented when scientists did not believe animals could arise spontaneously ,but did believe microbes could.
okay is he late
by the way what are the list of courses offered by a newly admitted student for microbiology
Needham's experiments with beef gravy and infusions of plants material reinforced this idea.
what drugs are given to a person with Otis nerve problem(ear problem)
Gum Reply
good morning to you all.
Muhammad Reply
Dr.A.K.S.P.G. college Akbarpur Ambedkar Nagar
Shailesh Vishwakarma BSc 1st year
differentiate between eukaryotes en prikaryotes
eukaryotes are organisms with complex cellular structure(presence of nucleus and mitochondrial) like plants and animals whilst prokaryotes are organisms with simple cellular structure (absence of nucleus, mitochondrial) like arthropods.
hello sir
I am Pankaj from bihar
I am study in NDRI karnal in btech in dairy
I am Pankaj from bihar
thanks am studying biomedical sciences in zambia.chikankata
Am a studying Disease Control in Ghana(kintampo)
I'm studying Environmental health in Zimbabwe 🇿🇼
am Joyce mwale studying nursing in Lusaka Zambia
hi pankaj
hi frds iam from India
IAM studying degree (micro biology)
Hi I am microbiologist
Hi friends I'm from Nigeria studying Microbiology
i am biotechnologist from pakistan
hi feds iam from india
hy frnds am from Uganda
am studying nursing/midwifery n kampala
I'm Gum Joseph Kakuu from Ghana,I'm studying RGN in nursing Jirapa.
I'm Hellen from Kenya studying applied biology
I live in india
am studying biotechnology
am maryjoy uwaoma from Nigeria,I am studying microbiology in NSUKKA NIGERIA
Nice meeting You people hear
thanks you.
can someone in there own words in the simplest way breakdown what aerobic respiration anaerobic respiration and fermentation means please and not from the dictionary version...!
what are the cultivation and identification of microorganisms
Algel Reply
ransport media.basic culture media.enriched media..differential media .indetification media
algel th above are some v th basic medias for bacterial growth
factors that can Prone the host to get disease
Linda Reply
what are the factors that prones host to get disease
Not sure about it, can you tell us Linda?
please I want to know the factors that prones host to get disease
please Linda we have internal and external factors. internal factors are within our body cavities.eg mother having TB giving it to her child,and the others. external factors are within our surrounding environment which include our daily activities(bathing, buying food and the others)
I don't understand aerobic respiration anaerobic respiration and fermentation. Can someone that do give me a short & simple breakdown.
pliz kisha ..aerobic respiration is th typ v repiration whre organisms use oxgyen for survival while anaerobic respiration is whre organisms survive without oxgyen at all.these use carbondioxide

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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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