Microbiology and Immunology

Petri, Richard Julius WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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such debris as mucus, bacteria, viruses, and dead cells. When

B. pertussisinterferes with this janitorial function, mucus and

cellular debris accumulate and cause constant irritation to the

respiratory tract, triggering the cough reflex and increasing

further mucus production.

Although the disease can occur at any age, children

under the age of two, particularly infants, are greatest risk.

Once an individual has been exposed to B. pertussis, subse-

quent exposures result in a mild illness similar to the common

coldand are thus usually not identifiable as resulting from B.

pertussis.

Whooping cough has four somewhat overlapping

stages: incubation, catarrhal stage, paroxysmal stage, and con-

valescent stage.

An individual usually acquires B. pertussisby inhaling

droplets infected with the bacteria, coughed into the air by an

individual already suffering from whooping cough symptoms.

Incubation occurs during a week to two week period following

exposure to B. pertussis. During the incubation period, the bac-

teria penetrate the lining tissues of the entire respiratory tract.

The catarrhal stage is often mistaken for an exceedingly

heavy cold. The patient has teary eyes, sneezing, fatigue, poor

appetite, and a very runny nose. This stage lasts about eight

days to two weeks.

The paroxysmal stage, lasting two to four weeks, is her-

alded by the development of the characteristic whooping cough.

Spasms of uncontrollable coughing, the “whooping” sound of

the sharp inspiration of air, and vomiting are hallmarks of this

stage. The whoop is believed to occur due to inflammationand

mucous which narrow the breathing tubes, causing the patient to

struggle to get air in, and resulting in intense exhaustion. The

paroxysms can be caused by over activity, feeding, crying, or

even overhearing someone else cough.

The mucus that is produced during the paroxysmal

stage is thicker and more difficult to clear than the waterier

mucus of the catarrhal stage, and the patient becomes increas-

ingly exhausted while attempting to cough clear the respira-

tory tract. Severely ill children may have great difficulty

maintaining the normal level of oxygen in their systems, and

may appear somewhat blue after a paroxysm of coughing due

to the low oxygen content of their blood. Such children may

also suffer from encephalopathy, a swelling and degeneration

of the brain which is believed to be caused both by lack of

oxygen to the brain during paroxysms, and also by bleeding

into the brain caused by increased pressure during coughing.

Seizures may result from decreased oxygen to the brain.

Some children have such greatly increased abdominal pres-

sure during coughing, that hernias result (hernias are the

abnormal protrusion of a loop of intestine through a weaker

area of muscle). Another complicating factor during this

phase is the development of pneumoniafrom infection with

another bacterial agent, which takes hold due to the patient’s

weakened condition.

If the patient survives the paroxysmal stage, recovery

occurs gradually during the convalescent stage, and takes

about three to four weeks. Spasms of coughing may continue

to occur over a period of months, especially when a patient

contracts a cold or any other respiratory infection.

By itself, pertussis is rarely fatal. Children who die of

pertussis infection usually have other conditions (e.g., pneu-

monia, metabolic abnormalities, other infections, etc.) that

complicate their illness.

The presence of a pertussis-like cough along with an

increase of certain specific white blood cells (lymphocytes) is

suggestive of B. pertussisinfection, although it could occur with

other pertussis-like viruses. The most accurate method of diag-

nosis is to culture(grow on a laboratory plate) the organisms

obtained from swabbing mucus out of the nasopharynx (the

breathing tube continuous with the nose). B. pertussiscan then

be identified during microscopic examination of the culture.

In addition to the treatment of symptoms, Treatment

with the antibiotic erythromycin is helpful against B. pertussis

infection only at very early stages of whooping cough: during

incubation and early in the catarrhal stage. After the cilia, and

the cells bearing those cilia, are damaged, the process cannot

be reversed. Such a patient will experience the full progression

of whooping cough symptoms, which will only abate when the

old, damaged lining cells of the respiratory tract are replaced

over time with new, healthy, cilia-bearing cells. However, treat-

ment with erythromycin is still recommended to decrease the

likelihood of B. pertussisspreading. In fact, it is not uncommon

that all members of the household in which a patient with

whooping cough lives are treated with erythromycin to prevent

spread of B. pertussisthroughout the community.

The mainstay of prevention lies in the mass immuniza-

tionprogram that begins, in the United States, when an infant

is two months old. The pertussis vaccine, most often given as

one immunization together with diphtheriaand tetanus, has

greatly reduced the incidence of whooping cough.

Unfortunately, there has been some concern about serious neu-

rologic side effects from the vaccine itself. This concern led

huge numbers of parents in England, Japan, and Sweden to

avoid immunizing their children, which in turn led to epi-

demics of disease in those countries. Multiple carefully con-

structed research studies, however, have provided evidence

that pertussis vaccine was not the cause of neurologic damage.

See alsoBacteria and bacterial infection; History of public

health; Infection and resistance; Public health, current issues;

Vaccination

PETRI DISH•seeGROWTH AND GROWTH MEDIA

PPetri, Richard JuliusETRI, RICHARDJULIUS (1852-1921)

German physician and bacteriologist

Richard Julius Petri’s prominence in the microbiology com-

munity is due primarily to his invention of the growth con-

tainer that bears his name. The Petri dish has allowed the

growth of bacteriaon solid surfaces under sterile conditions.

Petri was born in the German city of Barmen. Following

his elementary and high school education he embarked on

training as a physician. He was enrolled at the Kaiser

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