+SURGICAL BACTERIOLOGY+
A _microorganism_ or _microbe_, some species of which cause all
disease, is a minute plant or animal too small, as a rule, to be
visible to the naked eye.
The word _germ_ may be used to designate any microorganism, but it has
so many other meanings and has been so loosely employed even in this
sense, that it cannot be used for accurate scientific description.
_Bacteria_ are minute plants on the order of fungae, many of which are
able to produce fermentation, decomposition or disease.
Although the word _bacterium_ by derivation has the same meaning as
_bacillus_ and indicates a rod shaped fungus, it has been so loosely
employed that it may very well be applied to the entire germal family,
retaining the word bacillus in the narrower sense.
+Description of Bacteria.+ _Schizomycetes_ is the name given all the
bacteria of putrefaction and disease, the former being called
_saprophytic_ and the latter _pathogenic_.
Bacteria are minute fungi, each consisting of a single cell enclosed
in a cell membrane of cellulose which can be demonstrated by iodine,
the latter causing the protoplasm to retract from the cell wall. There
is no nucleus or central core. Some of the bacteria are colorless,
others pigmented, yellow, blue or red. The cells vary in shape and in
size in different species as well as in their mode of growth, and are
named in accordance with these peculiarities. The round or oval cells
are called _cocci_; the rod-shaped organisms are termed _bacilli_. The
cocci are called _micrococci_ or _macrococci_ according to their size;
_diplococci_ or _tetracocci_, according to the production of pairs or
groups of four in their multiplication; _streptococci_, because in
their growth they always form chains of cells; _staphylococci_,
because they grow in irregular clusters resembling bunches of grapes.
Some of the bacteria have the power of motion generally produced by
cilia or flagella and others are motionless.
+Habitat.+ These organisms may truly be said to be omnipresent. Every
thing we wear or use or eat, even the air itself, is impregnated with
them. Pathogenic germs may also be found among these myriads. Every
species has its own particular habitat, where the conditions
especially favor its growth, just as any of the larger plants require
a certain soil, a supply of water, temperature, and proper amount of
light in order to make growth and multiplication possible.
The bacteria in the air are more numerous in dry weather, being
carried up as dust by the wind, for a moist surface holds any bacteria
which may lie upon it. So complete is the action of moisture, that
air, which contained 600 microorganisms when inspired, has been shown
to return from the lungs with almost none, the moist respiratory
surfaces catching and holding the bacteria; so that the expired air is
practically sterilized; this is true even when the expiration is from
diseased lungs. The act of coughing, however, may expel bacteria in
the mucus ejected. The number of bacteria in the air is very variable,
but is much greater in houses than out of doors, and is naturally
increased by attempts to clean the rooms.
+Parasitic Nature.+ The number of species of pathogenic germs is
comparatively small compared with the number of all the varieties of
germs, for the latter are practically innumerable. Indeed, the
wonderful qualities of resistance in animal tissues is the only thing
that makes animal life possible and it is this power of resistance
that allows certain wounds to heal by primary union when left without
protection or care.
The schizomycetes are unable to extract nitrogen from the air or the
soil, like the higher vegetables, and must, therefore, be provided
with a higher nitrogenous compound, such as is produced by vegetable
and animal life. Some of them are able to live upon dead organic
matter, while others cannot exist without living tissues to feed upon
and are therefore true parasites. There are some which are able to
live upon either dead or living tissues and are known as _facultative
parasites_, a class which includes a majority of pathogenic germs.
Some organisms require albuminous matter, others need carbohydrates;
they all require water, carbon, nitrogen, oxygen, and certain
inorganic materials, especially lime and potassium. All organisms
require water. If dried, no form will multiply, and many forms will
die.
The fluids and tissues of the individual may or may not afford a
favorable soil for the germs of a disease, or, in the same person
afford it at one time, and not at another. Some individuals seem to
possess indestructible immunity from, and others are especially prone
to, certain contagious diseases. Impairment of health, by alterating
some subtle condition of the soil, may make a person liable who
previously was exempt.
+Effect of Oxygen.+ Some bacteria need free oxygen; some can live either
with or without free oxygen, while others cannot live at all in the
presence of free oxygen. Those requiring oxygen are called _aerobic_;
those which can live with or without it are called _facultative
aerobic_; those which do not live in free oxygen are called
_anaerobic_.
Bacteria are very sensitive to temperature, few being able to live in
a temperature below 68°F. or 29°C. or above 104°F. or 40°C. The
pathogenic varieties thrive best at about the normal temperature of
the blood. Direct sunlight retards their growth and may kill them.
Freezing renders bacteria motionless and incapable of multiplication,
but it does not kill them; they again become active when the
temperature is raised. The absurdity of employing cold as a germicide
is evident when it is known that a temperature of 200°F. below zero is
not fatal to germ life, cell activities by such a temperature only
being rendered dormant. The high temperatures are fatal to bacteria,
moist heat being more destructive than dry heat, and adult cells are
more easily killed than spores. A temperature less than 212°F. will
kill many organisms and boiling will kill every pathogenic organism
that does not form spores. Some spores are not destroyed after
prolonged boiling and some will withstand a temperature of 120°C. As a
practical fact, however, boiling water kills in a few minutes all
cocci, most bacilli, and all pathogenic spores, though anthrax and
tetanus are harder to kill than are the spores of other bacteria.
Under favorable conditions bacteria multiply rapidly, but when
conditions are unfavorable, they take on a spore formation and remain
in a quiescent state, like the seed of a plant, waiting—it may be
years—until proper conditions are present. The spores are protected by
such a thick envelope and have such great potential vitality, that it
is much more difficult to kill them than the developed bacteria.
Certain spores that withstand 212°F. or 100°C., can be killed when
fully developed at 130°F. or 55°C.
+Toxins.+ As bacteria grow, certain poisonous chemical substances appear
about them. These poisons are produced by them directly, or are formed
in the organic matter or tissues in which they live, as the result of
their presence. Some of these substances are alkaloidal and are known
as _ferments_ or _ptomains_. Others are albuminous in nature and are
called _toxalbumins_. The ptomains and toxalbumins are exceedingly
powerful poisons, producing local necrosis, inflammation and even
suppuration, when introduced by themselves and entirely free from
living germs, into the tissues of animals. Pathogenic bacteria
abstract the lymph from the blood. As the lymph contains elements
necessary to the body, such as water, oxygen, albumins, carbohydrates,
etc., their loss brings about body-waste and exhaustion from lack of
nourishment. Again, bacteria produce a vast number of compounds, some
harmless and others highly poisonous.
The symptoms of a microbic disease are largely due to the absorption
of poisonous materials from the area of infection. These poisons may
be formed in the tissues by the action upon them of the bacteria, or
they may be liberated from the bodies of degenerating microbes.
Bacteria secrete and contain ferments like pepsin or trypsin, and as
albumoses are formed in the alimentary canal by the action of the
digestive ferments upon proteids, sugars, and starches, so microbic
albumoses are formed by the action of microbic ferments upon tissues.
The local and general symptoms of these toxins depend upon the
particular toxin employed and a large number of these poisons have
been isolated and studied. Those of the surgically important
pathogenic germs, produce inflammation locally, with general symptoms
of fever, chills, cardiac depression, irritation of the kidneys and
bowels and cerebral symptoms, such as delirium and coma. The
toxalbumins also appear to have the effect of destroying the bacteria
to which they owe their origin when they have been produced in large
quantity.
+Cultivation.+ Bacteria are cultivated for study in the laboratory in
meat extracts, in gelatine, or agar agar (a sort of vegetable
gelatine), or raw potato, in blood serum and in other materials. The
simplest method of cultivation is in bouillon, sterilized in flasks,
with cotton plugs. Another method of studying bacteria is by the
inoculation of animals.
+Infection.+ Bacteria gain admission to the living tissues under natural
conditions, by penetrating any of the mucous membranes which they can
reach, or by entering open wounds. It may be said in general that an
intact epidermis is almost a complete protection against infection,
and that an intact mucous membrane is a good protection. This
difference in vulnerability between the mucous membrane and the skin
is important, and is probably due to the cornifaction of the
epithelial cells, and to their numerous layers, as well as to the
protection afforded by the thick corium. The single layer of soft
mucous cells is much more easily penetrated.
Typhoid bacilli and other hostile germs have been actually observed in
the urine, in the bile, in the intestinal secretions and in the
saliva. The bacteria of typhoid fever and tuberculosis have been found
in the milk of nursing mothers.
The local phenomena of inflammation usually follow the introduction of
living bacteria into the tissues, and general symptoms of poisoning
follow later, when the bacteria, toxins, or ptomains, have entered the
circulation. Some bacteria, however, excite no local reaction, but
enter the circulation at once. The pyogenic variety, it should be
noted, cause the production of pus.
+Elimination.+ Bacteria can be eliminated from the blood in several
ways; the kidneys, however, are the organs which carry the burden of
most frequently relieving the body of them. Even the sweat glands are
supposed to eliminate both bacterial toxins and bacteria.
+Resistance Offered by Tissues.+ The tissues have considerable power of
resistance under ordinary circumstances, although the exact sources of
this power are not well under stood. _Phagocytosis_—the power of
destruction and removal of bacteria supposedly possessed by the
leucocytes emigrating from the blood vessels—explains it in part. It
is also accounted for by the germicidal properties of the blood serum.
The resistance of the tissues may in some cases be due to the absence
from them of some particular element necessary to the growth of a
particular microorganism. This refractoriness varies in every species
of animal in its relation to every form of germ. Different individuals
of one species also vary in their susceptibility, and even different
parts of the body vary in the same individual. The lower animals offer
a greater resistance to pyogenic bacteria than do human beings.
Any cause that lowers the vitality by depressing the system, reduces
the resistance to bacteria and is therefore apt to favor their growth.
Exhausting diseases such as anemia, obesity, alcoholism, diabetes,
fatigue, or even exposure to cold, are instances. Germ growth is also
favored by the presence of dead, or injured tissues, of blood clots,
of foreign substances, and above all, by the presence of some of the
substances in which the germ has already been growing at the time of
its inoculation, and containing some of its toxins.
+Immunity.+ To be able to resist the invasion of any species of
bacteria, one is said to be refractory to or immune against that
variety of germs.
Serum therapy is based on the demonstrated fact of immunity, and of
the possibility of producing it by injecting the serum of immunized
animals. In many infectious diseases, one attack protects an
individual for a lifetime and one form of disease may protect against
even a more virulent form, as vaccination protects against smallpox.
It is a fact that if the serum of an animal which has been rendered
immune to a certain disease be injected into a susceptible animal, the
same immunity can be produced temporarily in the second animal. Serum
therapy proves that the injected serum will not only confer immunity
against the infection, but will enable the animal to throw off an
already existing infection.
+Sterilization.+ The question how to destroy microorganisms is one of
the most important in bacteriology. Exactly how chemical antiseptics
act in suspending the growth in living organisms and yet leaving them
capable of restoration, is not understood. The explanation is offered
that the antiseptics enter into combination with the capsule of the
cell and can be freed from it by breaking up this chemical
combination. It has always been evident that very minute quantities of
germicidal substances, and some substances which are not germicidal,
would prevent the growth of bacteria, so that it is not surprising
that chemical disinfectants should act in this prolonged inhibitory
way. It must be remembered that in operative surgical work, germs
which will not develop are, for practical purposes, as good as dead;
therefore such results do not invalidate the present methods of
sterilization for operations. They naturally stimulate interest in the
discovery of better methods of sterilization and especially in the
thorough application of the methods upon which we are now depending,
in order to obtain the best possible results from them. There are
three ways of destroying microorganisms: (1) by deprivation of food
and water, (2) by chemicals (including toxins), (3) by heat.
+Chemical Antiseptics.+ For practical disinfection, chemicals and heat
need only concern us. The power of these substances is greatly
decreased by heat, grease, oil, mucus, and even blood will cover germs
with a coating which prevents chemical germicides from reaching them.
Among the ordinary germicides, bichloride of mercury, iodin, alcohol
and carbolic acid, are of the greatest importance. A source of error
in the direct application of these experiments is the fact that many
of these chemicals are decomposed or rendered inert, by combinations
with the albuminoids of blood and pus, mercuric bichloride being
transformed into an indifferent substance and even carbolic acid being
altered.
+Carbolic Acid+ is a valuable germicide in the strength of from 1 to 40,
to 1 to 20. It is very irritant to tissues and carbolized dressings
may be responsible for the sloughing of a wound. It is inert in fatty
tissues.
Carbolic acid is readily absorbed, and may thus produce toxic
symptoms. One of the early signs of absorption is the appearance of
the urine, which may assume a smoky, greenish or blackish hue.
Examination shows a great diminution or entire absence of sulphates,
when the acidulated urine is heated with chloride of barium. The urine
also contains albumin. The appearance of the urine is an indication
that the use of the drug must be discontinued.
+Kreolin+, a preparation made from coal tar, is a germicide without
irritant or toxic effects. It is less powerful than carbolic acid, but
acts similarly, and is used in emulsion of a strength of from 1 to
15%. It does not irritate the skin like carbolic acid.
+Peroxide of Hydrogen+ is a most admirable agent for the destruction of
pus cocci. It probably destroys the albuminous element upon which the
bacteria live, and starves the fungi.
Peroxide is not fatal to tetanus bacilli.
+Iodoform+ is largely used, but it is not a germicide as bacteria will
grow upon it. It hinders the development of bacteria and directly
antagonizes the toxic products of germ life.
+Silver Nitrate+ is a valuable antiseptic. It exerts an inhibitive
action upon the growth of microorganisms, but irritates the tissues.
+Formaldehyde+ has valuable antiseptic properties. Formalin is a 40%
solution of the gas in water. Solutions of this strength are very
irritant to the tissues, but a 2% solution can be used to disinfect
wounds and instruments.
+Nucleins+, especially protonuclein, possess germicidal powers.
Protonuclein is of value in treating areas of infection, particularly
when sloughing exists. A great many other antiseptics are used.
+Heat+. The surest and quickest method of destroying bacteria is by
heat. Even the spores succumb to it. Anthrax spores are killed in 2
minutes in boiling water, and the various bacilli and cocci in from 2
to 5 seconds.
When a substance to be sterilized by heat will not bear so high a
temperature, the method of fractional sterilization is employed, the
fluid to be sterilized being heated to from 140°F. to 175°F. or to
from 69°C. to 80°C., for from 15 to 30 minutes every 3 days or 7 days.
The theory is that the adult germs are killed by the first heating and
that any spores which develop subsequently are destroyed in their
adult state at the next heating. The fluid, meanwhile, must be kept at
an even temperature which will encourage the development of any spores
it may contain. Even anthrax spores may be killed by 167°F. to 185°F.,
or 75°C. to 80°C., in a one and four-tenths solution of bicarbonate
of soda, in from 8 to 20 minutes. Dry heat is not so efficient as
moist heat.
The following are the more important bacteria we meet in surgical
conditions:
_Staphylococcus pyogenes aureus_—a microorganism producing
yellow pus.
_Staphylococcus pyogenes citreus_—a microorganism producing
lemon-colored pus.
_Staphylococcus pyogenes albus_—a microorganism producing
white pus.
_Streptococcus pyogenes_—a streptococcus producing pus.
(Erysipelas for example).
_Micrococcus gonorrhea_—bacillus of Neisser, or gonococcus.
_Bacillus pyocyaneous_—producing a green pus.
_Bacillus coli communis_—producing intestinal conditions.
(Appendicitis for example).
_Bacillus typhosis_—Eberth’s bacillus; producing typhoid
fever.
_Bacillus tuberculosis_—Koch’s bacillus; producing
tuberculosis.
_Bacillus tetani_—Nicolaier’s bacillus; causing tetanus.
_Treponema pallidum_, or _spirochaeta pallida_ of Hoffman and
Schaudin—a protoza causing syphilis.
The first six are known as _pyogenic bacteria_, as they all produce
pus; in addition to the above there are many more microorganisms, but
from a surgical standpoint those mentioned are the most important.
The _staphylococcus pyogenes_ is a spherical coccus of somewhat
variable size but averaging about 8 microns; when properly stained it
can often be seen to be formed of two separate hemispheres. In pus it
is generally found in small heaps containing from two to ten members,
but it also occurs singly and in pairs, and even in short chains like
the streptococcus, thus rendering diagnosis difficult with the
microscope alone. Its cultures are of a yellowish tinge. The aureus
type is the most usual cause of abscesses (circumscribed suppurations)
and 77% of acute abscesses are due to the staphylococci.
The _staphylococcus pyogenes aureus_ is a facultative anaerobic
parasite which is widely distributed in nature, and is found in the
soil, in the dust of air, in water, in the alimentary canal, under the
nails, and in the superficial layers of the skin. It forms the
characteristic color only when it grows in air. It is killed in ten
minutes by a moist temperature of 58°C. and is instantly killed by
boiling water. Carbolic acid (1 to 40) and bichloride of mercury (1 to
2000) are quickly fatal to these cocci.
_Staphylococcus pyogenes citreus_, the lemon-colored coccus, is found
occasionally in acute circumscribed suppurations, but far more rarely
than the other two forms. Its pyogenic power is even weaker than that
of the albus.
_Staphylococcus pyogenes albus_, the white coccus, acts like the
aureus, but is more feeble in power. When this organism is found upon
and in the skin, it is called _staphylococcus epidermis albus_, an
organism which is the cause of stitch abscesses.
_Streptococcus pyogenes_ is found in spreading suppurations and in
very acute abscesses. About 16% of acute abscesses contain
streptococci. It is easily killed by boiling, and can be destroyed by
carbolic acid and by corrosive sublimate. The streptococcus of
erysipelas is thought to be identical with the streptococcus pyogenes,
but their difference in action is believed to be due to difference in
virulence induced by external conditions and by the state of the
tissues of the host. The coccus of erysipelas is larger than the
ordinary form of streptococcus pyogenes, and infection takes place
through a wound, often a very trivial one, or through a mucous
membrane. The organism multiplies in the small lymph channels. The
streptococcus may cause suppuration in erysipelas, mixed infection not
being necessary to cause pus to form.
The _gonococcus_ of Neisser is found both inside and outside of pus
cells and mucous cells. The gonococci cannot be cultivated upon
ordinary media, but grow best upon human-blood serum. Gonococci stain
easily and are readily decolorized by Gram’s method.
The _bacillus coli communis_, or the bacillus of Escherich, is
invariably found in the fæces. It is believed by many observers to be
the cause of appendicitis, peritonitis, and abscesses about the
intestine. In cases of appendicitis we can rarely get a pure culture
of Escherich’s bacillus, but usually find also streptococci and
staphylococci.
The _bacillus of typhoid fever_ (Eberth’s bacillus) is responsible for
some cases of gangrene, for some of embolism and for not a few bone
and joint diseases.
The _bacillus tuberculosis_ (Koch’s bacillus), the cause of all
tubercular processes, is met with especially in dusty air which
contains the dried sputum of victims of tuberculosis. This infected
air is the chief means of its transmission, though it may be conveyed
by the milk of tubercular cows and by the meat of tubercular animals.
Wounds may open a gateway for infection.
The _bacillus tetani_ (Nicolaier’s bacillus), an aerobic organism, is
found especially in the soil of gardens, in the dust of old buildings,
in street dirt, and in the sweepings of stables. Spores develop at the
ends of these bacilli. This organism is capable of producing toxins of
deadly power. Its spores are hard to kill.