Read the passage below. Use the information in the passage and your own knowledge
to answer the questions that follow.
Maggots and Wound Healing
The photograph shows maggots eating dead tissue at a human wound.
At the beginning of the 20th century maggots were widely used to treat wounds.
When penicillin started to be used in the 1940s, the use of maggots to treat
infections by killing bacteria declined. However, the recent increase in infections
caused by antibiotic resistant bacteria such as MRSA (methicillin resistant
Staphylococcus aureus) is creating renewed interest in maggots.
The maggots used in hospitals to treat wounds are bred in a sterile environment.
Green blowfly maggots are used as this species only digests dead tissue and does
not burrow down into live flesh.
It is not fully understood how the maggots work but there are several theories.
The first theory is that they produce an antibiotic in their gut called mirabilicide,
which kills the bacteria they eat. A second theory is that the maggots secrete
enzymes to break down dead tissue, and digest bacteria in the process. A third
theory is that the maggots secrete ammonia as a waste product which changes
the pH of the wound, making it unfavourable for bacteria to reproduce.
Using maggots to treat a wound also helps to speed up the production of
new tissue. One hypothesis is that the wriggling movement of maggots acts
as the stimulus, but there is little evidence to support this view. A more likely
explanation is that the maggots, or their products, stimulate the body’s immune
system to kill bacteria in the wound and allow the healing process to occur.
Doctors have developed a ‘maggot bag’, for applying the maggots to wounds.
The bags take longer to work than if the maggots are free to move in the wound,
so are less useful if the wound needs to be treated quickly. It is expensive to use
maggot bags because they cost much more than a typical wound dressing.