SOLVING PROBLEMS IN BACTERIAL PATHOGENESIS 1. Recent headlines have highlighted
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SOLVING PROBLEMS IN BACTERIAL PATHOGENESIS 1. Recent headlines have highlighted the spread of were previously healthy. MRSA is resistant MRSA infection in the United States. tients who According to the to several commonly prescribed antibiotics that are CDC, MRSA is responsible for over 90,000 serious in- usually effective against gram-positive bacteria (meth fections and over 18,000 hospital stay-related deaths icillin, penicillin, and cephalosporins), and an infec per year in the United States. These strains are tion with a MRSA strain can be deadly un if left responsible for many serious skin and soft tissue in- treated. is subcategorized as community fections, as well as pneumonia. One major acquired (CA-MRSA) or hospital acquired (HA with MRSA is that occasionally the skin can on how the infection is usually spread to other organs of the body with more severe MRSA), depending life-threatening symptoms, including acquired. CA-MRSA strains are still sensitive to ciitis (hence the name "flesh-eating" necrotizing fas- many antibiotics, such as trimethoprim, tetracycline, bacteria) and nec- sepsis pneumonia followed by sistant to these drugs while still sensitive to vanco- and toxic shock, and then death in up to 50% mycin linezolid of cases. A striking finding about these infections is and that they occur even in young immunocompetent pa- (continued)Explanation / Answer
A) mechanism of resistance of MRSA are :
- expression of PC1 beta lactamase that hydrolyzes the beta lactam ring. This makes the antibiotic inactive.
- acquisition of a modified penicillin binding protein , known as PBO 2a, that impart further resistance.
B) trimethoprim resistance : this can be by cell wall impermeability and ectopic expression of the gene called dfrA and reduced susceptibility of DHFR enzymes that have substitutions L41F, F99S, F99Y and H150R that reduce the trimethoprim binding and conferring resistance to trimethoprim.
Tetracycline resistance - this was conferred by the presence of the resistance determining genes tetK, tetL, tetM or tetO present in the MRSA that confer resistance.
3) vancomycin is an antibiotic that belongs to the glycopeptide class of antibiotics. These antibiotics prevent the biosynthesis of bacterial cell wall. While studying the resistance mechanism, bacterial resistance mechanism has still not developed as these bacteria produce either beta lactamases or penicillin binding proteins. Similarly, linezolids are synthetic antibiotics called as oxazolidinones and these disrupt bacterial growth by inhibition of the initiation of translation. Thus, resistance has not yet been imparted.
4.
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