57 terms

Microbiology Lab Final

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Populations or communities of microogranisms that attach and grow on a solid surface that has been exposed to water
biofilms
Microorganisms that form biofilms are usually encased in _____
an extracellular polysaccharide
An example of a floating biofilm
A pellicle found on some liquid culture media
Allows the bacteria to float near the surface and get oxygen while getting nutrients form the liquid
pellice
As bacterial cells grow, gene expression in bacterial cells changes in a process called _______.
quorum sensing
The ability of bacteria to communicate and coordinate behavior
quorum sensing
a chemical produced and secreted by bacteria that use quorum sensing
Inducer. As the inducer diffuses into the surrounding medium, other bacterial cells move toward the source and begin producing inducer.
Biofilms are not just layers of cells. A biofilm is usually composed of _____ and _____ through which __________.
Pillars and channels through which water can flow, bringing nutrients and taking away wastes
How did we observe biofilms in class?
A slide was dipped in a hay-infusion preparation, dyed, and observed under a microscope.
What different types of microorganisms were observed in the biofilm exercise? What was the most abundant?
I saw a lot of rods, so possibly bacterial rods. Some larger rods arranged like a puzzle were the most abundant.
How is a biofilm beneficial to bacteria?
Biofilms allow bacteria to survive under conditions in which they otherwise would not survive on their own. Biofilms are more resistant to antibiotics and more difficult for the immune system to destroy.
Is a natural biofilm a pure culture?
Rarely. Some biofilms consist of a single species or multiple species. Those consisting of single species like the H. pylori biofilm in the stomach, are pure cultures.
What cell structures help bacteria attached to a solid surface?
fimbriae, polysaccharides, glycocallyces
What is a quorum in law?
A consensus between members of a group
How is quorum in law relating to quorum sensing in bacteria?
Members of a group of bacteria all agree to produce and secrete an inducer
Why is quorum sensing important for biofilm formation?
Because ALL members of a group of bacteria must agree to produce and secrete an inducer to attract other bacteria cells toward the source, which then begins to secrete the inducer, bringing more and more cells to create a biofilm.
Bacteria are the second most common cause of artificial implant failures in humans. In these cases, why isn't an infection usually detected from cultures of blood or tissue?
The bacteria are most likely located within the cavity of the artificial implants, which is not detectable in blood or tissue cultures. A biofilm may have formed in these patients, making them resistant to their antibiotics.
Suggest a reason why dental researchers were the first to become aware of the importance of biofilms to disease.
Because plaque is a very common biofilm that forms on teeth and can cause cavities. So they may have discovered that by consistently making an effort to remove these biofilms, you can prevent cavities.
Why are biofilms of major concern in industry when disinfectants are utilized?
Because disinfectants are usually incapable of killing a biofilm.
Infection control personnel in a hospital isolated Mycobacterium chelanae from 27 patients. All the patients had undergone an endoscopic procedure. Endoscopes were processes after each use with an automated disinfector, which washed the endoscopes with a detergent solution, disinfected them with 2% glutaraldehyde for 10 minutes, and rinsed them with sterile water. What was the source of infection?
Disinfectants don't kill biofilms, so it is possible that there was a biofilm on the endoscopic tool.
A 3-year-old boy was treated with amoxicillin for a middle-ear infection. He has been better for a few days after completing antibiotic therapy when the infection recurred. Amoxicillin was again prescribed because the S. pneumoniae isolated from ear fluid was amoxicillin sensitive. Again the boy was better after completing the antibiotic therapy, but the infection recurred. What is the underlying cause of the recurrent infections?
There was a biofilm in his ears, so the antibiotic killed some bacteria, but the other bacteria remained. Biofilms send out an inducer to attract bacteria to join the biofilm and then those bacteria also start to transmit an inducer and it is a vicious cycle. So the antibiotic may have worked against the biofilm to get rid of enough bacteria to make him feel better, but then when the antibiotic was stopped the biofilm was able to start growing again causing the same problem. So perhaps the boy needs to be on the antibiotic for a longer amount of time to kill all present bacteria.
What is a major limitation of dilution techniques?
Organisms present in limited amount may be diluted out on plates filled with dominant bacteria
Contain chemicals that prevent the growth of unwanted bacteria without inhibiting the growth of the desired organism
selective media
usually liquid media, contain chemicals that enhance the growth of desired bacteria
enrichment media
Contain various nutrients that allow the investigator to distinguish one bacterium from another by how they metabolize or change the media with a waste product
differential media
What were the results in the nutrient agar?
All bacteria showed positive growth
What were the result in the mannitol salt agar?
E. coli and P. aeruginosa showed negative growth and S. aureus showed positive growth
What were the results in the EMB agar?
E. coli and P. aeruginosa showed positive growth and S. aureus showed negative growth
How did the results observed on the mannitol salt and EMB correlate to the Gram reaction of the bacteria?
Gram-positive bacteria showed growth in the mannitol salt agar. Gram-negative bacteria showed growth in the EMB agar.
What is the purpose of peptone in the media?
To provide nutrients to the bacteria. It is the source of carbon, nitrogen and energy for growth.
What is the purpose of agar in the media?
To solidify the bacteria in the media
What ingredient makes mannitol salt selective?
High salt concentration
What was the color of the 2 bacteria that showed growth on the EMB agar?
E. coli was a metallic green. P. aeurginosa was colorless.
What was the color of the 2 bacteria that had growth on the mannitol salt agar?
S. aureus showed yellow colonies. S. epidermidis showed white colonies.
Nutrient agar that contains vancomycin is _____ for ______.
Selective for vancomycin resistant organisms
Minimal salts agar that contains detergent as a carbon source is _____ for _____.
Selective for heterotrophs
Nutrient agar with tellwrite (coagulase indicator) is ____ for ________.
Differential for staph aureus
Chemicals for controlling the growth of microbes
Antimicrobial agents
Chemical agents used on inanimate objects to lower the level of microbes on their surfaces
Disinfectants
Chemicals used on living tissue to decrease the number of microbes
antiseptics
Result in bacterial death
bactericidal agents
cause temporary inhibition of growth
bacteriostatic agents
Things to consider when selecting an antimicrobial agent
pH, solubility, toxicity, organic material present, cost
standard method for measuring the effectiveness of a chemical agent
American Official Analytical Chemist's use-dilution test
3 bacteria used in American Official Analytical Chemist's use-dilution test
Staphylococcus aureus, Salmonella enterica, Pseudomonas aeruginosa
Was your test chemical effective? Briefly explain.
Yes, there was no growth shown past the initial control phase, in which there was no disinfectant mixed with bacteria.
Was it more effective than the lab disinfectant? Briefly explain.
They were the same. Neither the Clorox or lab disinfectant displayed growth.
Was your test chemical bactericidal or bacteriostatic?
Cannot tell from just this one test.
Was this a fair test? Is it representative of the effectiveness of the test substance?
No. The test is artificial. Testing the disinfectant against bacteria in a test tube is not representative of the effectiveness of the disinfectant against microbes in the environment. Test tube tests test for efficacy. Effectiveness can only be tested out in the environment.
How could the procedures used in this experiment be altered to measure bacteriostatic effects?
Resubculture the organisms to grow them under different conditions
In the use-dilution test , a chemical is evaluated by its ability to kill dried Clostridium sporogenes or Bacillus subtilis endospores. Why is this considered a stringent test?
Because chemicals do not penetrate bacterial endospores and the number of endospores used is higher than would be expected in normal use of the disinfectant
In the table provided, which disinfectant is most effective?
The cholorohexidine is the most effective, because it had a very low DRT value while also only being present in a small volume
What is DRT value?
Stand for decimal reduction time. It is the length of time it takes to kill 90% of a test population of bacteria
Did your results differ from your expected results? Briefly explain why or why not.
Yes. My microbiota increased using water, perhaps because it just spread microbiota from other parts of my hands to my fingers.
What is a surgeon trying to accomplish with a 10 minute scrub with a brush followed by an antiseptic?
He is trying to actually mechanically AND chemically expel organisms down the drain.
How do normal microbiota and transient microbiota differ?
Normal microbiota are essentially permanent, while transient microbiota are present for only days or weeks.
If most of the normal microbiota and transient microbiota aren't harmful, then why must hands be scrubbed before surgery?
Because these microbiota could be harmful to an immune compromised patient.