The composition and health effects of the human microbiome are currently topics

Question

The composition and health effects of the human microbiome are currently topics of extensive interest and research. For example, it is becoming increasingly apparent that the initial development of a robust intestinal microflora is dependent on many factors in a newborn's life, beginning with the mode of delivery (vaginal vs. cesarean section). Other potential influences include premature birth, exposure to antibiotics, and even mode of feeding.

Suppose you were interested in the effect of breastfeeding versus formula feeding on the composition of gut flora in newborns. As part of your experiment, stool samples from healthy babies in the study get plated on various agar media. You notice that greater numbers of colonies are recovered when samples are plated on blood agar compared to Luria Bertani (LB) agar. After some diligent subculturing, you isolate several bacterial species capable of slow growth on the blood but not on the LB agar. You correctly surmise that these organisms

Choose one:

A. should be classified as beta-hemolytic.

B. have extensive and complex nutritional requirements not met by LB agar.

C. grow because the blood agar suppresses the growth of faster-growing bacteria.

D. are opportunistic blood pathogens.

E. are Gram-positive and, thus, inhibited by the ingredients in LB agar.

2. Antarctic habitats have rich but poorly described microbial communities. You have traveled to a particularly harsh, dry, and frigid region known as the Mars Oasis in the hopes of learning more about its resident bacteria. After a morning of exploring, you bring back a sample of soil to the laboratory. Microscopic examination of your sample reveals a large number of rods, cocci, and filamentous cells growing together in a tangled mass. You first decide to plate a portion of the sample on a nutrient medium in an attempt to grow isolated colonies. You then apply a dye mixture containing propidium iodide and Syto-9 to your sample and view it using fluorescence microscopy. The rods and cocci both appear green, while the filamentous cells are nearly all red. A few days later you observe your plates and notice that colonies of a uniform appearance have grown. When you observe these cells under the microscope, they are all cocci, similar in appearance to those from your original sample.

A. filamentous cells / rods

B. cocci / rods

C. rods / cocci

D. filamentous cells / cocci

E. rods / filamentous cells

F. cocci / filamentous cells

Explanation / Answer

1. B. have extensive and complex nutritional requirements not met by LB agar.

2. A. filamentous cells / rods

The most likely explanation for your results would be that the filamentous cells were nonviable to begin with, and the rods have specific, but as yet unknown, nutritional requirements.

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