Download Suggested Answers for Insight Questions - McGraw-Hill

Suggested Answers for Insight Questions, Foundations in Microbiology, 7th Edition, listed
by chapter, number, and page location.
A note to the users of these answers: These answers discuss some of the possible ways to
approach the questions. They are not meant to be exhaustive in depth, but can offer information,
suggestions, and points of view that will be helpful in understanding some of the concepts
covered in the Insight and the chapter. Furthermore, they are not the final word--you may have
thought of some other explanations that are just as valid. It is hoped they will serve to stimulate
class discussion and inspire further research.
20.1, pg. 597 – Gram-Negative Sepsis and Endotoxic Shock
One of the problems with a diabetic patient is that they have reduced circulation in their skin, and
this often leads to diabetic ulcers and sores on extremities and surfaces that are exposed to
pressure. Such ulcers will compromise the epithelial barrier, and this provides a route of infection
for even commonplace microbes, whether true pathogens or opportunists. Gram negative rods
are widely distributed in the environment, in the normal flora, and on fomites, so the likelihood of
them becoming inoculated into an ulcer is high. They could readily enter the body and move via
lymphatics into the bloodstream. Their presence in the blood stream means that have freedom
to grow, increase in numbers, cause sepsis, and the cells will give off endotoxins into the
bloodstream as their cell walls break down. Treating the infection with a drug that lyses the cells
will actually make the problem even worse. The final assault will be the effect that endotoxemia
has on organ function, leading to shock.
20.2, pg. 603 – Diarrheal Disease
Microbes can cause damage by destroying cells and tissues of the gut (invasive) or they can alter
the function of intestinal cells and tissues by releasing toxins locally (toxigenic). The first case
may be accompanied by severe ulceration and bloody diarrhea and can be very dangerous if the
intestine perforates into the peritoneal cavity. Toxigenic disease is more insidious and just as
dangerous because the toxins released by the infectious agents disrupt the natural activity of the
intestinal cells and induce them to pump out large quantities of electrolytes and water into the GI
tract. This dehydration and electrolyte loss is not just local in its effects. It can pull water from
fluid compartments, lowering blood pressure and shutting down organ function. The loss of
critical Na+ and Cl- affects muscle and nerve function and may cause heart failure, coma, and
death if the fluids are not replaced.
20.3, pg. 611 – Avoiding Gastrointestinal Infections
In countries where the water supply is not purified, experts recommend soaking all fruits and
vegetables in water with dissolved iodine tablets. Scrubbing the outside surface of some fruits
(apples, tomatoes) and vegetables (peppers, carrots) with detergent and then peeling them could
greatly reduce exposure. The choice of fruits can make a difference. Bananas, oranges, and
other peeled fruit are less likely to be contaminated than are berries that are not peeled. The
most difficult foods to control would be fine greens and sprouts that have many nooks and
crannies to trap microbes. Kitchen practices are also important. Fresh fruits and vegetables
should always be cut with disinfected tools on clean dry surfaces that have not been used for
meats. Such foods should be covered to protect them from mechanical vectors and refrigerated
to slow growth of any microbes that they will no doubt have picked up from soil and water that
cannot be washed away.