Microbiology

1. What are the advantages and disadvantages of the different types of light and electron microscopes discussed in Chapter 3 that are used to study microorganisms? Focus your response in terms of the following parameters:
   • Range of magnification
   • Resolving ability
   • Sample preparation
   • Possible states of sample (e.g. whole organism, part of, living, non-living, etc.)
2. What type of microscope would you use to investigate each of the following scenarios and why (your answer to question 1 will help):
   • Determine the relative sizes of two eukaryotic cells.
   • Determine how many bacteria are dying after a chemical treatment.
   • Determine where in a eukaryotic cell a particular protein is localized.
   • Identify a virus from a contaminated sample.
   • Visualize the sensory hairs on the surface of an ant’s antennae.
3. What are advantages and disadvantages of the differential staining techniques discussed in Chapter 3 that are used to study microorganisms? Focus your response in terms of the following parameters:
   • Ease and cost of sample preparation
   • Why you would use it (i.e. what information is imparted)
   • Specificity of identification
   • Chance of false positives or negatives

In this activity you have the opportunity to apply your understanding of microbial growth and how to control it to solve the case studies.

1. Explain why is each of these is often resistant to disinfectants.
   1. Mycobacterium
   2. Pseudomonas
   3. Bacillus
2. Entamoeba histolytica and Giardia lamblia were isolated from the stool sample of a 45- year- old man, and Shigella sonnei was isolated from the stool sample of an 18- year- old woman. Both patients experienced diarrhea and severe abdominal cramps, and prior to onset of digestive symptoms both had been treated by the same chiropractor. The chiropractor had administered colonic irrigations (enemas) to these patients. The device used for this treatment was a gravity- dependent apparatus using 12 liters of tap water. There were no check valves to prevent backflow, so all parts of the apparatus could have become contaminated with feces during each colonic treatment. The chiropractor provided colonic treatment to four or five patients per day. Between patients, the adaptor piece that is inserted into the rectum was placed in a “hot- water sterilizer.” What two errors were made by the chiropractor?
3. Between March 9 and April 12, five chronic peritoneal dialysis patients at one hospital became infected with Pseudomonas aeruginosa. Four patients developed peritonitis (inflammation of the abdominal cavity), and one developed a skin infection at the catheter insertion site. All patients with peritonitis had low- grade fever, cloudy peritoneal fluid, and abdominal pain. All patients had permanent indwelling peritoneal catheters, which the nurse wiped with gauze that had been soaked with an iodophor solution each time the catheter was connected to or disconnected from the machine tubing. Aliquots of the iodophor were transferred from stock bottles to small in- use bottles. Cultures from the dialysate concentrate and the internal areas of the dialysis machines were negative; iodophor from a small in- use plastic container yielded a pure culture of P. aeruginosa. What improper technique led to this infection?
4. Eleven patients received injections of methylprednisolone and lidocaine to relieve the pain and inflammation of arthritis at the same orthopedic surgery office. All of them developed septic arthritis caused by Serratia marcescens. Unopened bottles of methylprednisolone from the same lot numbers tested sterile; the methylprednisolone was preserved with a quat. Cotton balls were used to wipe multiple- use injection vials before the medication was drawn into a disposable syringe. The site of injection on each patient was also wiped with a cotton ball. The cotton balls were soaked in benzalkonium chloride, and fresh cotton balls were added as the jar was emptied. Opened methylprednisolone containers and the jar of cotton balls contained S. marcescens. How was the infection transmitted? What part of the routine procedure caused the contamination?

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Using what you’ve learned from reading and videos, compose answers to the following questions and post them on the discussion board. Please number your answers so we can reference them easily. Please respond thoughtfully and in your own words, being sure to back up each statement of fact with cited sources. Your response to each question should be at least 125 words.

1. Haemophilus influenzae requires hemin (X factor) to synthesize cytochromes and NAD (V factor) from other cells. For what does it use these two growth factors? What disease(s) does H. influenzae cause?
2. The bacterial enzyme streptokinase is used to digest fibrin (blood clots) in patients with atherosclerosis. Why doesn’t injection of streptokinase cause a streptococcal infection? How do we know the streptokinase will digest fibrin only and not other tissues?
3. Based on biochemical tests and oxygen usage, how would you identify and classify, respectively, the following microbes:
   1. Staphylococcus aureus
   2. Pseudomonas aeruginosa
   3. Bacillus subtilis
   4. Escherichia coli

In addition, thoughtfully and objectively critique responses from two of your peers. Be specific in your critique. If you find something your peer said to be interesting, then state specifically why. If you find an error in something your peer said, then politely point out the error and cite the sources supporting your statement. Be sure to focus your critique on the facts presented and not on the person or anything in the response that may be interpreted as opinion. Note: opinion is not asked for in any of these questions.