Question

1.   What does selective toxicity refer to? Why are penicillins and cephalosporins low in toxicity for humans?

2.  Why are so called 'superbug' strains of bacteria commonly found in hospitals? Cite two reasons why hospitalized patients taking broad-spectrum antimicrobial drugs are more likely to develop such HAI superinfections.

Compare and contrast endotoxins and exotoxins. Why are exotoxins more potent than endotoxins?

3. Assume that you are responsible for decontaminating materials in a large hospital. How would you sterilize each of the following? Briefly justify your answers.

a)    A mattress that was used by a patient who had bubonic plague, but will be used again

b)   Intravenous glucose-saline solutions

c)    Used disposable syringes

d)   Tissue (as in living, flesh) taken from patients

4. A couple, living in West Africa, brings their 4-year old son to the office of their physician on the second day of a visit home to Minnesota. The boy had a mild episode of diarrhea about seven days earlier and would not eat. He seemed to recover, but the mother noticed that the boy was having trouble walking the previous night and had seemed to have trouble dressing himself and walking that day. On examination, the patient had no significant fever (98.9°F) and normal bowel sounds. His chest, ears and eyes were clear. He had no rebound tenderness in the abdomen. The physician noted that the child had poor muscular reflexes in his arms and legs. The child also was a bit lethargic and seemed confused. The family lives in an isolated village in Africa. The mother opposes vaccinations on personal grounds, so the child has only had the initial series of DPT shots and no other typical vaccines. The village where they live has many problems with parasites and insect borne fevers. Urine, stool and blood samples were collected for analysis.

For each of the following questions, mark the box at the left of your answer:

This disease is most likely:

□  an intestinal infection or parasite.

□  a respiratory infection or parasite.

□  a neurological infection or parasite.

□  a urinary tract infection or parasite.

□  Not enough information is given to determine this.

My best guess at a diagnosis is:

□  Haemophilus influenzae meningitis

□  E. coli infection

□  polio

□  a parasitic worm

□  malaria

□  Staphylococcus aureus infection

Which of the following samples could easily provide confirmation of your diagnosis?

□  The stool would show the presence of the worms.

□  The serum would have antibody against polio.

□  The urine would contain H. influenzae organisms.

□  The blood would contain red blood cells with malarial parasites.

□  Only CSF will show the answer.

Would receiving the childhood vaccine series have prevented this problem?

□  yes, without doubt

□  yes, most likely

□  possibly, but living in Africa the pathogen load might be too high

□  no, no vaccine is normally given

□  no way, no vaccine exists

Answer 1

1.Selective toxicity refers to the ability of the drugs to target sites that are relative specific to the microorganism responsible for infection. It selectively kills or inhibits the growth of microbial targets while causing minimal or no harm to the host.

Penicillins and cephalosporins are low in toxicity for humans. Penicillins and cephalosporins are broad spectrum antibiotics having a beta-lactam ring which interfers with the bacterial cell wall synthesis eventually leading to cell lysis and death. As human cells lack cell wall these antibiotics are less toxic to humans.

2.Superbug bacteria are the antibiotic resistant bacteria which are changing an adapting to the given treatments. The infections caused by such super bugs are extremly difficult to treat. Such superbugs are common in hospitals because the patients there are continously exposed to antibiotics and recieve lots of hands on care. Superinfection is the process by which a cell that has previously been infected by one virus gets co-infected with a different strain of the virus or another virus at a later point in time. After antibiotic theraphy is initiated in the patients, the drug sensitive bacteria are readily killed allowing the drug insensitive population of bacteria to amplify over time dueb to the lack of competition for resources necessary for growth. Hence such hospitilized patients taking broad spectrum antibiotics are more likely to devlop super infections.

Endotoxins can be defined as heat stable components of the gram-negative bacterial cell wall. Exotoxins are heat labile proteins that are secreted by some species of bacteria and diffuse readily into the surrounding medium. Endotoxins are not secreted but are released only when the cells are disrupted. They are less potent and less specific. On the other hand Exotoxins are highly potent and cause damage to the host by destroying cells or disrupting normal cellular metabolism.

3. The following items will be sterilized as follows:

a) A mattress used by a patient with bubonic plague: Hepa vacuuming, ultra-violet germicidal radiation, light enzymes mostly to kill remaining colonies.

b) Intravenous glucose-saline solutions: Put it in the autoclave

c) Used disposable syringes: It is disposable i.e. for one time use only, so just throw it away. Also it can be sterilized by ethylene oxide first.

d) Tissue (as in living, flesh) taken from patients: Gamma irradiation and gas sterilization with ethylene oxide can be used to sterilize human tissues taken from the patients; the gas penetrates the tissues.

4) 1) Correct answer is A, an intestinal infection or parasite.

2) Correct answer is C, Polio.

3) Correct answer is B, the serum would have antibody against polio.

4) Correct answer is C, recieving the childhood vaccine series would have possibly prevented this problem, but living in africa the pathogen load might be too high.