Question

Susceptibility Lab Study Concepts Case Study Vancomycin-resistant Staphylococcus aureus (VRSA) was isolated from the exit site of a dialysis catheter in a 40-year-old diabetic with a history of peripheral vascular disease, chronic renal failure, and chronic foot ulcers. A few months earlier, the patient's gangrenous toe had been amputated. Following that surgery, the patient developed bacteremia with methicillin-resistant S. aureus from an infected hemodialysis graft. Vancomycin, rifampin, and graft removal successfully treated the infection. A few months later, when the catheter exit site infection appeared, the area was cultured and the catheter removed, successfully treating the infection. A week later, the patient's chronic foot ulcer again appeared infected. Vancomycin-resistant Enterococcus faecalis (VRE) and Klebsiella oxytoca were cultured from the ulcer. The patient recovered after wound care and systemic treatment with trimethoprim/sufamethoxazole. Analysis of the VRSA isolate revealed that it comtained the vanA gene for vancomycin resistance and the mecA gene for oxacillin resistance. Discussion: 1. Provide an explanation of how the Staphylococcus aureus strain ended up with the gene for vancomycin resistance. 2. Describe mechanisms of how genes, such as those responsible for drug resistance, can be transferred between bacterial species. 3. Explain why would this particular patienthave an increased risk for infection with VRSA

Answer 1

1. Initially the patient was identified with VRSA, after this the surgery for gangrenous toe, the patient developed bacterimia with methicillin resistant staphylococcus aureus from an infected hemodialysis graft. Later on he is treated with vancomycin which results in formation of gene resistance to vancomycin as he already positive with vancomycin resistant staphylococcus aureus.

vancomycin became an antibiotic of choice for treatment of MRSA infections. The s. Aureus cell wall lies just beneath the outermost polysaccharide capsule layer. The cell wall has heavily cross linked peptidoglycan. The vancomycin interferes with late peptidoglycan synthesis which results in inhibition of cell wall synthesis  and bound vancomycin pentapeptide complexes accumulate within the cell resulting in vanA operan mediated vancomycin resistance.

3.This particular patient have an increased risk for infection with VRSA because he was suffering chronic renal failure who needs dailysis and S.aureus is most commomly present on the skin and upper respiratory tract and also these infections spread more in hospitals.

2. The mechanism of genes responsible for drug resistance between bacterial species is called horizontal gene transfer. This can occur between same or different bacterial species by different mechanisms. The large proportion of gene transfer is caused by the help of conjugate plasmids, a part of bacterial DNA. The plasmids are a type of small, dispensible chromosomes which replicate separately from main bacterial chromosome and are not needed for bacterial growth snd multiplication but rather carry genes which are helpful to exploit in particular environment conditions like thrive in the presence of potentially lethal antiboitic.