Antibiotics are chemical substances that kill or inhibit the growth of bacteria. The success of antibiotics against disease-causing bacteria is one of modern medicine’s great achievements. However, because bacteria adapt quickly to new environmental conditions, many bacteria harmful to humans have developed ways to circumvent the effects of antibiotics, and many infectious diseases are now much more difficult to treat than they were just a few decades ago. Critically ill patients are more likely to require the aid of antibiotics to fight infections, so are more likely to be harmed by the spread of antibiotic-resistant bacteria.
Bacteria contain genetic material called plasmids, which can carry the genes enabling antibiotic resistance. Bacteria share these plasmids among one another via a direct, mechanical transfer between cells, and antibiotic-resistant plasmids can thus spread easily throughout a bacterial population to create a strain of resistant bacteria. Less commonly, a natural chromosomal mutation may confer antibiotic resistance on a bacterium, which can then reproduce and become dominant via natural selection, likely when that colony is exposed to antibiotics. In the absence of human involvement, however, bacteria rarely develop resistance to antibiotics.
On January 1, 2006, the European Union banned the feeding of all antibiotics to livestock for non-therapeutic purposes. This sweeping policy followed a 1998 ban on the non-therapeutic use of four medically-important antibiotics on animals. In the United States, by contrast, animals raised on industrial-scale factory farms are still routinely administered low levels of antibiotics in their feed—not as a cure for ongoing maladies, but primarily as a growth-enhancing agent to produce more meat and also as a prophylactic measure to compensate for overcrowded and unsanitary conditions. Currently, several antibiotics that are used in human medical treatment, such as tetracycline, penicillin and erythromycin, are also administered non-therapeutically to healthy livestock and poultry. This long-term non-therapeutic use of antibiotics in the United States creates the ideal conditions for the development of antibiotic-resistant bacteria, as the drugs kill only the susceptible bacteria, leaving the resistant strains to reproduce and flourish. The newly-resistant bacteria can then spread from farm animals to other animals, including humans.


The author uses the phrase “prophylactic measure” in the third paragraph in order to describe :
A. a measure to reduce the incidence of developing a resistance to antibiotics
B. a contraceptive method to prevent the animals from passing disease to offspring
C. a preemptive attempt to kill or thwart the growth of bacteria in the animals before the animals become ill
D. an antiseptic measure to kill surface bacteria in the surrounding environment
E. a measure that creates a physical barrier that protects the animals from the bacteria in the surrounding environment

How to answer this question without knowledge of the meaning of word 'Prophylactic' ?

Good question. Whenever you encounter this situation, use context to figure out what is going on. Let's take a look at the sentence:

"In the United States, by contrast, animals raised on industrial-scale factory farms are still routinely administered low levels of antibiotics in their feed—not as a cure for ongoing maladies, but primarily as a growth-enhancing agent to produce more meat and also as a prophylactic measure to compensate for overcrowded and unsanitary conditions."

Okay, so the animals are getting low levels of antibiotics NOT to cure them from diseases BUT INSTEAD to:
1) encourage their growth
AND
2) to compensate for unsanitary conditions.

Compensate is an important word. How are the antibiotics going to counterbalance the unsanitary conditions? They must somehow prevent the animals from experiencing the negative effects of the unsanitary conditions; in other words, if they prevent diseases or health problems that could result form these conditions.

If we match this up to the answer choices C is our best answer. Hope this helps!

_________________
Jamie Nelson
ManhattanGMAT Instructor

Thanks Jamie!

I have a question though. Wouldn't D and E serve the same purpose ?

I mean if they (antibiotics) kill bacteria in the surrounding
or create a physical barrier that protects the animals from the bacteria in the surrounding environment then the animals will not experience the negative effects of the unsanitary conditions. Could you please clarify.

Hmm, interesting point. Obviously it helps to know the meaning of the word "prophylactic". Okay, let's take a look at D and E:

D. an antiseptic measure to kill surface bacteria in the surrounding environment
E. a measure that creates a physical barrier that protects the animals from the bacteria in the surrounding environment

I think D and E are less feasible explanations. With D, can we really spray the entire area the animals are in with antibiotics to kill the surface bacteria? Also, I think the "surface bacteria" would provide the GMAT test writers with an additional defense against the belief that this answer choice is the one; they could say that it may not be "surface" bacteria causing the problems.

With E, "physical barrier" is rather vague--are the antibiotics going to make the animal magically grow a bubble around itself? Obviously I'm taking this to the ridiculous, but we have to realize from this passage that antibiotics work to kill bacteria after they are ingested by the animal. For them to work outside of the animal as in D, or to create some "physical barrier" in E, is much less likely than the scenario discussed in C. Again, go with what makes the most sense.

_________________
Jamie Nelson
ManhattanGMAT Instructor