Evolution, 4th Edition

EvoluTIonARy BIology 5

Almost every hospital in the world treats casualties in this battle against

changing opponents, but as the use of antibiotics increases, so does the incidence

of bacteria that are resistant to those antibiotics; thus any gains made are almost

as quickly lost (see Figure 1.3). Why is this happening? Do the drugs cause drug-

resistant mutations in the bacteria’s genes? Do the mutations occur even without

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HIV-1 human

SIVcpz chimpanzee

SIVgor gorilla

SIVcpz chimpanzee

SIVmnd mandrill

SIVagm Afr. green monkey

HIV-2 human

SIVsmm sooty mangabey

SIVcol colobus monkey

Lemur

Cat

Rabbit

Horse

FIGURE 1.2 A phylogenetic tree showing

the history by which various immunodefi-

ciency viruses have evolved. Time runs from

left to right, and the common ancestor of

all the viruses is at the left (the “root” of the

tree). One lineage gave rise to the viruses

that infect primates: lemurs, monkeys, and

apes. These simian immunodeficiency viruses

(SIVs) are labeled with abbreviations of the

names of the infected species (e.g., SIVcpz in

chimpanzee). The human immunodeficiency

viruses HIV-2 and HIV-1 arose from SIVs that

infected monkeys and chimpanzees, respec-

tively. (After [25].)

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Qu: Should part (B) y-axis label be worded similarly to (A)? For example: “Prevalence of resistant isolates (%)”

Measure of drug use (volume)

1978 1980 1982 1984 1986 1988 1990 1992

Year

Drug use

Prevalence

of resistant

bacteria

0.9

0.8

40 1.0

1.1

1.2

1.3

1.4

(A) (B)

Prevalence of resistant bacteria (%)

20

0

60

80

100

Number of doses prescribed (millions)

2000 2002 2004 2006 2008 2010

Year

Carbapenem

prescriptions

Third-generation

cephalosporin resistance

Carbapenem

resistance

5

0

10

4

15

20

25

30

Percentage of isolates resistant^2

0

6

8

10

12

14

FIGURE 1.3 Evolution of drug resistance. (A) An increase

in the use of a penicillin-like antibiotic in a community in

Finland between 1978 and 1993 was matched by a dramatic

increase in the percentage of antibiotic-resistant isolates of

the bacterium Moraxella catarrhalisis from middle-ear infec-

tions in young children. (B) Resistance of the pneumonia-

causing bacterium Klebsiella pneumoniae to cephalosporin

and carbapenem antibiotics has recently begun to increase

in the United States. The use of carbapenems approximately

doubled during the period shown. (A after [15]; B after [23].)

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