Facts of the Case A diabetic patient with chronic renal failure required dialysi
ID: 204857 • Letter: F
Question
Facts of the Case
A diabetic patient with chronic renal failure required dialysis. She also had chronic foot ulcers and poor circulation. She developed an ulcer (abscess) in a toe with methicillin-resistant Staphylococcus aureus (MRSA). A catheter had been used in her toe for drainage. It contained a biofilm and was analyzed. MRSA was isolated which is difficult to treat. This means the S. aureus was resistant to methicillin and another antibiotic needed to be used. The infection with methicillin-resistant Staph aureus was treated with vancomycin. This is a powerful antibiotic that is reserved for use on methicillin-resistant S. aureus and others. The catheter also eventually grew, vancomycin-resistant Enterococcus faecalis (VRE) was also cultured from the foot ulcer. This is a completely different bacterium which is resistant to vancomycin. Within a week or two, vancomycin-resistant Staphylococcus aureus (VRSA) was isolated from this same individual's toe and the catheter. This was the first time a S. aureus strain with this particular trait had been seen in a patient in the U.S. (2002). Now the patient has two bacteria in the toe infection, Staphylococcus that is resistant to methicillin (MRSA) and vancomycin (VRSA) and Enterococcus that is resistant to vancomycin (VRE). Genetic analysis of the VRSA isolate revealed that it contained the most common vancomycin resistance gene (vanA), as well as the mecA gene, which provided resistance to methicillin and oxacillin.
1. A.) What is the difference between genotype and phenotype?
B.) Name the biological molecules that directly control genotype and phenotype?
2. What two genotypes and phenotypes are of particular interest in this case?
3. Does a cell "know" when to develop a useful mutation like vancomycin resistance (this will change the phenotype)?
Explanation / Answer
1. a. Genotype is combination of alleles present on the genome, while phenotype is the combination of genomes expressed.
b. DNA, RNA and protein control the genotype and phenotype, as DNA carries the genotypic data, while RNA and protein carry out the phenotypic expression.
2. The genes for methicillin and vanomycin resistance, and the subsequent resistance of the bacteria are the genotypes and phenotypes of interest.
3. Usually, a cell does not know if a mutation is useful or not. If it is, it increases the fitness of the cell, increasing the numbers for the progeny of that cell.
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