Bacteremic WORLD OF MICROBIOLOGY AND IMMUNOLOGY44•
The presence of an endospore is very useful. Like the
spores of other bacterial species, the endospore of Bacillus
thuringiensisallows the organism to survive inhospitable con-
ditions in a dormant state. Endospores that contain the pro-
toxin crystal can be applied to fields via crop-dusting aircraft.
The protoxin crystal is a hardy structure, and does not
readily dissolve. However, in the gut of insects, where the pH
is very basic, the protoxin can go into solution. When this
happens an insect enzyme splits the molecule. One of the
toxin fragments, the delta endotoxin, confers the lethal effect
to the insect.
The delta endotoxin binds to the epithelial cells lining
the gut wall of the insect. By creating holes in the cells, the
toxin destroys the functioning of the gut, and causes massive
cell death. The larva is unable to eat. Another consequence of
the destruction is a modification of the pH to a more neutral
level that is hospitable for the germination of the endospores.
The resuscitation and growth of Bacillus thuringiensiswithin
the insect gut kills the larva.
The use of Bacillus thuringiensisas an insecticide has
been practiced since the 1930s. In the recent three or four
decades, with the advent of techniques of molecular
rearrangement, the specificity of the bacterium for target
insect pests has been refined. These products now represent
some one percent of the worldwide use of fungicides, herbi-
cides and insecticides.See alsoBacteriocidal, bacteriostaticBBacteremicACTEREMIC
Bacteremic is a term that refers to the ability of a bacterium to
multiply and cause an infection in the bloodstream. The inva-
sion of the bloodstream by the particular type of bacteriais
also referred to as bacteremia.
If the invading bacteria also release toxins into the
bloodstream, the malady can also be called blood poisoning or
septicemia. Staphylococcusand Streptococcusare typically
associated with septicemia.The bloodstream is susceptible to invasion by bacteria
that gain entry via a wound or abrasion in the protective skin
overlay of the body, or as a result of another infection else-
where in the body, or following the introduction of bacteria
during a surgical procedure or via a needle during injection
of a drug.
Depending on the identity of the infecting bacterium
and on the physical state of the human host (primarily with
respect to the efficiency of the immune system), bacteremic
infections may not produce any symptoms. However, some
infections do produce symptoms, ranging from an elevated
temperature, as the immune system copes with the infection,
to a spread of the infection to the heart (endocarditis or peri-
carditis) or the covering of nerve cells (meningitis). In more
rare instances, a bacteremic infection can produce a condition
known as septic shock. The latter occurs when the infection
overwhelms the ability of the body’s defense mechanisms to
cope. Septic shock can be lethal.
Septicemic infections usually result from the spread of
an established infection. Bacteremic (and septicemic) infec-
tions often arise from bacteria that are normal resident on the
surface of the skin or internal surfaces, such as the intestinal
tract epithelial cells. In their normal environments the bacteria
are harmless and even can be beneficial. However, if they gain
entry to other parts of the body, these so-called commensal
bacteria can pose a health threat. The entry of these commen-
sal bacteria into the bloodstream is a normal occurrence for
most people. In the majority of people, however, the immune
system is more than able to deal with the invaders. If the
immune system is not functioning efficiently then the invad-
ing bacteria may be able to multiply and establish an infection.
Examples of conditions that compromise the immune system
are another illness (such as acquired immunodeficiencysyn-
drome and certain types of cancer), certain medical treatments
such as irradiation, and the abuse of drugs or alcohol.
Examples of bacteria that are most commonly associ-
ated with bacteremic infections are Staphylococcus, Strep-
tococcus, Pseudomonas, Haemophilus, and Escherichia coli.
The generalized location of bacteremia produces gener-
alized symptoms. These symptoms can include a fever, chills,
pain in the abdomen, nausea with vomiting, and a general feel-
ing of ill health. Not all these symptoms are present at the
same time. The nonspecific nature of the symptoms may not
prompt a physician to suspect bacteremia until the infection is
more firmly established. Septic shock produces more drastic
symptoms, including elevated rates of breathing and heartbeat,
loss of consciousness and failure of organs throughout the
body. The onset of septic shock can be rapid, so prompt med-
ical attention is critical.
The discovery of bacteria in the blood should be taken
as grounds to suspect bacteremia, because bacteria do not typ-
ically populate blood. Antibiotic therapy is usually initiated
immediately, even if other options, such as the transient entry
of bacteria from a cut, have actually occurred. In addition,
antibiotic therapy is prudent because many bacteremic infec-
tions arise because of an ongoing infection elsewhere in the
body. Along with the prompt start of treatment, the antibiotic
used must be selected with care. Use of an ineffective antibi-Light microscope image of Bacillus bacteria.womi_B 5/6/03 1:09 PM Page 44