Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Syphilis

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ally eliminated the disease in the country. However, vigilance

is necessary to maintain this record. In Great Britain, where

swine fever had been eliminated by 1966, it reappeared in

2000.

Such is not the case around the world. In many coun-

tries, swine fever remains a problem. Belgium and France

experienced heavy economic losses in 1997, for example.

African swine fever is a major problem affecting swine in

countries such s Gambia, Ghana, and Madagascar, and there

have also been outbreaks in more northern countries (e.g.,

Italy in 1999 and Portugal in 2000).

In countries such as the United States, swine entering

the country are quarantined for 90 days to ensure that the

swine do not harbor the virus that has yet to be evident as an

infection.

Currently there is no treatment for either swine fever,

save slaughter of the infected animals. In this regard, swine

fever is similar to foot and mouth disease that afflicts cattle

and sheep. The use of a vaccineconsisting of weakened but

living virus has been an effective preventative measure for

swine fever. However, unless the vaccinationinvolves the

total swine population in the target region, the prevention of

infection will not be absolute.

See alsoVirology

SSynchronous growthYNCHRONOUS GROWTH

Synchronous growth is the growth of bacteriasuch that all the

bacteria are at the same stage in their growth cycle (e.g., expo-

nential phase, stationary phase). Because the same cellular

reactions occur simultaneously throughout the bacterial popu-

lation, synchronous growth permits the detection of events not

normally detectable in a single cell or in a population consist-

ing of bacteria in various stages of growth.

In a normal batch cultureof fluid, or on an agarplate,

bacteria in the population exhibit a range of sizes, ages, and

growth rates. In contrast, the bacteria in a synchronized cul-

ture are virtually identical in terms of these parameters.

Synchronized growth is imposed in the laboratory. A

population of bacteria can be filtered to obtain bacteria of a

certain size range. Usually, the filter that is used has very small

holes. All but the smallest bacteria in a population are

excluded from passing through the filter. Because the smallest

bacteria are frequently the youngest bacteria, the filtering

method selects for a population comprised of bacteria that

usually have just completed a division event. When the bacte-

ria are suspended in fresh growth medium the population will

subsequently grow and then divide at the same rate.

Bacteria of the same size can also be recovered using

special techniques of centrifugation, where the bacteria in the

fluid that is spinning around in a centrifuge are separated on

the basis of their different densities. The smallest bacteria will

have the lowest density and so will move furthest down the

centrifuge tube.

Another method of obtaining a synchronous bacterial

population involves the manipulation of some environmental

factor that the bacteria depend on for growth. Typically, the

factor is a nutrient that the bacteria cannot manufacture, and so

is required to be present in the medium. In the alternative, an

agent (e.g., an antibiotic) can be added that does not kill the

bacteria but rather halts their growth at a certain point. Again,

once the bacteria are added to fresh medium, the growth of all

the bacteria will recommence from the point of blockage in the

cell cycle.

Synchronous growth can only be maintained for a few

rounds of growth and division. Ultimately, the inherent ran-

domness of bacterial population growth again dominates. In

other words, not all the bacteria will continue to divide at

exactly and differences in size and other attributes will once

again appear in the population. For those few generations,

however, much useful information can be extracted from a

synchronously growing population.

See alsoBacterial growth and division; Laboratory techniques

in microbiology

SSyphilisYPHILIS

Syphilis is a chronic, degenerative, sexually transmitted dis-

ease caused by the bacterium Treponema pallidum.Although

modern treatments now control the disease, its incidence

remains high worldwide, making it a global public healthcon-

cern. Spread by sexual contact, syphilis begins as a small,

hard, painless swelling, called a primary (or Hunter’s) chan-

cre. The disease is very contagious in the early stages. The ini-

tial sore will usually pass away in about eight weeks, but the

disease will then spread through the body and lodge in the

lymph nodes, causing a skin rash to appear in two to four

months along with fever and headaches. This second stage can

last two to six weeks. After a latent period, which can extend

for years, the disease can appear in various bodily organs and

it can be spread to others.

The earliest records of syphilis are those of Spanish

physician Rodrigo Ruiz de Isla, who wrote that he treated

syphilis patients in Barcelona in 1493. He further claimed that

the soldiers of explorer Christopher Columbus contracted the

disease in the Caribbean and brought it back to Europe in 1492.

However, others challenge this position. Some medical histori-

ans believe that syphilis has been present from ancient times

but was often mislabeled or misdiagnosed. Italian physician

and writer Girolamo Fracastoro gave the disease its name in his

poem “Syphilis sive morbus Gallicus” (Syphilis or the French

Disease), published in 1530, during the height of a European

epidemic. However, for centuries, the disease was called pox or

the great pox. At that time, the treatment was mercury, used in

vapor baths, as an ointment, or taken orally. The mercury

increased the flow of saliva and phlegm to wash out the poi-

sons, but it also caused discomfort, such as loss of hair and

teeth, abdominal pains, and mouth sores. Through the cen-

turies, a milder form of the disease evolved and often became

confused with gonorrhea. In 1767, physician John Hunter

infected himself with fluid from a patient who had gonorrhea

to prove these were two different diseases. Unknown to Hunter,

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