| Anaerobic gram-positive bacilli are more
well known than some of their aerobic counterparts; everybody in the known
world has heard of the Clostridia. There were only a few genera of them so we
decided to begin with them.|
Actinomyces sp. Filamentous gram positive
obligate anaerobic rods cause actinomycosis. The most common species is A.
Infection is usually the result of trauma. Pus and fluid at the
site of infection have characteristic sulfur granules. DOC: penicillin or
Two images from Bristol Biomedical Image Archive:
|Bifidobacterium are bone shaped
gram positive obligate anaerobic opportunistic pathogens which are normal
inhabitants of the gut. The ends of the rods show characteristic splitting on
gram stain and the organism shows branching filaments as well. B.
dentium is the most common species.
of Wisconsin online Textbook of Microbiology has an excellent section on the
clostridia. In fact, there is an excellent gram stain image of pus from a mixed
anaerobic infection. Gram stains are the, "real world of clinical
microbiology," and represent the routine view of what clinicians actually see
of bacterial organisms. In contrast EM images are more popularly viewed by
laypersons. The following quote lists the general characteistics of
"The clostridia are relatively large, Gram-positive, rod-shaped
bacteria. All species form endospores and have a strictly fermentative mode of
metabolism. Most clostridia will not grow under aerobic conditions and
vegetative cells are killed by exposure to O2, but their spores are able to
survive long periods of exposure to air. The clostridia are ancient organisms
that live in virtually all of the anaerobic habitats of nature where organic
compounds are present, including soils, aquatic sediments and the intestinal
tracts of animals."
|Clostridium botulinum Everybody
knows that you have to be careful when canning meat, fish, fruits and veggies
so that you don't get botulism. Didn't your grandmother ever tell you that
botulism is the world's worst poison, so you have to be very careful? Well,
guess what? It is. Don't even taste foods suspected to be spoiled by
clostridium botulinum. But just to get your ducks in a row; botulinum is
the name. Botulism is the condition. Botulin is the poison itself. People who
work in clinical bacteriology are very unlikely to see this bacterium
1) You work in a bacteria bank where they keep lyophilized specimens
of every strain of bacteria.
2) You are doing epidemiology work for the CDC
and are trying to locate the source of an outbreak of botulism poisoning.
You are doing research work involving gene sequencing of C botulinum
According to the CDC, "In the United States an average of 110 cases
of botulism are reported each year. Of these, approximately 25% are foodborne,
72% are infant botulism, and the rest are wound botulism. Outbreaks of
foodborne botulism involving two or more persons occur most years and usually
caused by eating contaminated home-canned foods."
these cases of botulism usually involve the toxin instead of the organism
|Clostridium difficile They
probably named them, "difficile," because they are difficult. Or possibly
because of the difficulty in remebering that it causes, "pseudomembranous
colitis." Probably some people have known of someone who had strong
antimicrobial therapy to clean out their intestines for one reason or another
who ended up with a nasty form of enteritis caused by C. difficile which
wasn't killed off by the antibiotics on the first go around. The doctor didn't
even have to do a culture, he knew what had happened, didn't he? When he
performed an endoscopy even the patient could see all those big white spots. He
zapped those bugs on the second go around though. What a relief. It's like
hitting yourself on the head with a hammer. It feels so good when it stops.
This little difficulty with Clostridium difficile occurs in Americans,
Europeans and Japanese. C. difficile is an equally opportunistic
|Clostridium perfringens is an
invasive pathogen which posesses a, "huge array of invasins and toxins,"
wound and surgical infections and also severe uterine infections, especially
when coat hangers are used for abortions. Old timers remember someone who got
gas gangrene while living in the trenches in WWl. Some called it foot rot, or
boot rot. The foot and leg swell up due to the gas produced and if you press
down on it, the gas bubbles out. It smells really fetid like the putrid smell
of rotted meat. Guess what? It is rottet meat. Your rotted meat.
The Clostridia which includes C. perfringens are at the bottom of the
food chain. They live in soil and they breakdown not only the proteins but, the
amino acids. When they break down lysine and arginine, the straight chain
amines putrecine and cadaverine are produced. These small volatile molecules
float through the air and when they reach the receptors in the nostrils, they
elicit an electrical impulse which travels along a special pathway to a
particular part of the brain. Over millions of years humans who have reacted to
the resulting sensation of a, "stinky," smell by assiduously avoiding its
source have survived by not being breakfast for these organisms.
biomedical image archive:
gangrene," gram stain.
|Clostridium tetani Everybody knows
that if you cut yourself with a metal object or get dirt in a cut, you have to
get a nasty tetanus shot. A lot of people know that Clostridia form spores but,
they can't remember which Clostridia form which kind of spores. Here's a hint,
"T" is for terminal and also tetani, get it? It's a little demonic mnemonic to
help you remember on your medical micro proficiency exam.
Here's a scanning electron micrograph of Clostridium tetani
at a magnification of x11,200. Both vegetative and spore stages are shown. The
spore forms are the ones with the big bulges. There are faint blue strands
which are flagella on the vegetative cells.
beautiful examples of electron microscopy come from THE master of the art,
Dennis Kunkel, at a University in Hawaii. Some guys have the luck. Clicking the
thumbnail will take you to the website where you can see electron micrographs
of all types of life forms. He calls bacteria prokaryotes. You might not find
that unusual. Heck you might even call bacteria prokaryotes. Twenty five
years. He's been doing electron microscopy for twenty five years. He's recieved
a few awards.
|Aerobic gram-positive bacilli, in
|Bacillus anthracis , a real bad
boy. Does B anthracis sporm fores? Ok who hasn't heard all about
anthrax? Raise your hands. Right. You'll want to visit:
where you can view both a gram stain and the original light micrographs taken
by Dr Robert Koch of the anthrax bacillus which was the very first bacterium
shown to be the agent of a disease in 1877. The gram stain image is superb in
clarity and detail. Long chains and spores can be seen.
You will also want
to visit the CDC. The disease listing of bacterial and mycotic diseases has
anthrax at the top of the alphabetical list;
|Bacillus cereus , causes food
Here's a representative image of Bacillus cereus from
Buckman laboratories of a special staining method, a Schaeffer-Fulton stain
showing chains and spores.http://www.buckman.com/eng/micro101/228a.htm
cereus food poisoning is the general (disease) description, although two
recognized types of illness are caused by two distinct metabolites. The
diarrheal type of illness is caused by a large molecular weight protein, while
the vomiting (emetic) type of illness is believed to be caused by a low
molecular weight, heat-stable peptide."
Bacillus sp. and Streptococcus pneumoniae. SEM
Causes a really nasty skin rash. But since you'll never see it, you can
include it on the next CD backup you burn off. But you can cross it off the
list of things you keep in your active memory directory. "The most common human
infection by E rhusiopathiae is erysipeloid, a well-defined, violet or
wine-colored inflammatory lesion of the skin of the fingers or hand. Itching is
typical. " "This species is transmitted occasionally from infected pigs to
farmers or veterinarians, in whom it causes primarily inflammatory infections
of the skin. Septicemia and endocarditis may develop secondarily."" In contrast
to L monocytogenes, they are nonmotile, nonhemolytic, and catalase negative.
The production of H2S is highly indicative, since very few other Gram-positive
bacteria have this property." "without fever."
you can't forget the nasty picture of an erysipeloid skin rash which you may
have seen in a medical textbook. If you want to use the name of the organism in
conversations with your colleagues or with your friend, you'll have to practise
the pronunciation. Just take it one syllable at a time. This one is not real
difficult. The h is silent in the species name. If it weren't it would sound
really strange like, "er-hoo-zee-ah-pa-thee-ee," with the the th sounded as in
the name theodore and that silly double vowel without elision at the end which
makes the pronunciation of so many latinized species names sound affected if
Lactobacillus sp. Normal flora. Useful for the
dairy industry. "The most common application of Lactobacillus is industrial,
specifically for dairy production. This genus also contains several bacteria
that make up part of the natural flora of the human vagina." There is a gram
stain image at the UTH med center website of Lactobacillus,
It can be opportunistic. It also characteristically produces an acidic
environment which can inhibit growth of other organisms which cause
genitourinary tract infections. What can you say about it. It's another freebie
if you recieve one in your laboratory accreditation test samples. It seems kind
of mean to short change Lactobacillus by not even writing a full
paragraph about it. Umm. Do you want to know about the connection between
lactic acid and the genus name? Oh, you already know that. Well, what about the
latest mention in the MMWR? Oh, right there is none. Ok, well let's go on to
the next gpr.
Listeria monocytogenes , is a
potential pathogen. The CDC lists it as a notifiable disease and as such
statisics are published in the MMWR. For the year 2000, 570 cases of
listeriosis had been cumulative as of November 1, 2000."In the United States,
an estimated 2,500 persons become seriously ill with listeriosis each year. Of
these, 500 die."http://www.cdc.gov/ncidod/dbmd/diseaseinfo/listeriosis_g.htm
The CDC lists the syptoms of listeroisis as, "A
person with listeriosis has fever, muscle aches, and sometimes gastrintestinal
symptoms such as nausea or diarrhea. If infection spreads to the nervous
system, symptoms such as headache, stiff neck, confusion, loss of balance, or
convulsions can occur."
"Most human cases occur in patients with
debilitating disease or in prenatal or neonatal infants. Sepsis, meningitis,
and disseminated abscesses occur in infected patients. Meat, vegetables, and
various milk products are the most common sources of infection."
Pregnant women don't want any of these bacteria. Histologic
section micrograph of placental microabcess caused by Listeria
monocytogenes can cause really serious problems especially in CSF,
cerebrospinal fluid. If there are enough organisms in the centrifuged
cerebrospinal fluid specimen so that a few organisms can be seen after viewing
the gram stain slide for five minutes, one can be sure that in the ER or on the
ward a patient will be in a bad condition. Depending on the situation and
timing it may be a very bad condition.
But hey we aren't in the hospital right now so let's lighten
up a little. Can you say listeriosis five times ? Good, now say it really fast.
Lister first identified the organism and it causes monocytes to increase in
number because they eat Listeria monocytogenes for breakfast. So
naturally they called it Listeria monocytogenes.It is found
frequently in test samples to check laboratories for accreditation. In such
cases it's basically a freebie. It's an aerobe. It's not fastidious and grows
easily so it's hard to miss. A few of these are seen each year in patients in
large hospitals. After you've seen a few it loses it's novelty. It becomes just
another gram positive rod.
has a page with links to LM
gram stain images of most, if not all clinically relevant bacteria, including
L monocytogenes which are helpful for the clinician and the technologist
since they will view similar shape, color and size at similar x1,000
magnification in a routine clinical laboratory setting.
You can get a really good idea of the exact shape from
Dennis Kunkel's beautifully artistic electron microscopic imaging. Formerly,
the term, "pleiomorphic gram positive rod," had been applied to
Listeria, Corynebacterium, and Propionibacterium and
attempts were made to lump them together due in part to similarities in
morphology. DNA analysis has subsequently supported classification as three
distinct genera. Some of the rods in the electron micrograph are quite long,
some are short and some are stacked or folded back over one another. At the
magnification of a normal light microscope, the organisms in this electron
micrograph would have the characteristic, "chinese character," or pleiomorphic
shape. The magnification of this SEM is x 29,665.
Definition of Nocardia, "Nocardiosis is defined
as disease resulting from either local or disseminated tissue invasion by
aerobic actinomycetes of the genus Nocardia. Nocardia are aerobic,
Gram-positive branching filamentous bacteria which often appear beaded on
staining. Many strains of Nocardia are weakly acid-fast when stained in tissue
or from primary isolation media, but often lose acid-fast staining on serial
culture." "Since Nocardia are not part of our normal flora and are rarely
laboratory contaminants, any isolate of Nocardia from tissue or normally
sterile body fluids should never be ignored." For diagnosis, "Nocardiosis can
be diagnosed rapidly by examination of sputum or pus with the Gram stain and a
modified acid-fast stain (Ziehl-Neelsen stain decolorized by 1% H2SO4 instead
of acid alcohol). The finding of delicate, filamentous, branching Gram-positive
bacteria which stain with a modified acid-fast stain provide a rapid diagnosis.
Final diagnosis is best confirmed by culture not by serologic testing."
Treatment is described as, "Therapy is usually with sulfonamides or T-S and
requires long term therapy to prevent relapse. Sulfonamide therapy (e.g.
Sulfadiazine 6-10 gm/day given in 3-6 divided doses/day) have been used for
decades. Presently trimethoprim-sulfamethoxazole (T-S) given in doses from
160mg/ 800mg to 320mg/1600mg every 6-8 hours has gained popularity. In severe
cases, CNS disease, or sulfa allergy consider Ceftriaxone 2 gm q 12 hrs. +
Amikacin 400 mg q 12 hrs."http://www.ccm.lsumc.edu/BugBytes/Volume3/Bb-v3n6.htm
Excellent images of Nocardia,
and a description of their morphology, "Nocardia can be described as being
rather short filaments irregularly bent, and displaying "true branching".
Nocardia has cells that are 1.0 µm wide and 1.0-2.0 µm long. The
overall length of a Nocardia filament is between 10-20 µm long." "Once
you have seen Nocardia under the microscope you will never forget the way it
looks. The next time you see it you will readily identify it without the use of
a stain. Nocardia is Gram positive"
Nocardiosis hilights from the CDC, "in the
United States, an estimated 500-1,000 new cases of Nocardia infection
occur annually." "Overall, 80% of cases present as invasive pulmonary
infection, disseminated disease, or brain abscess; 20% present as cellulitis."
"Approximately 10% of cases with uncomplicated pneumonia are fatal.
Case-fatality rate increases with overwhelming infection, disseminated disease,
or brain abscess. Surgical drainage may be indicated and may improve patient
outcome." "The drug of choice is trimethoprim-sulfamethoxazole." "A new
combination drug therapy (sulfonamide, ceftriaxone, and amikacin) has shown
promise for infections difficult to treat. Application of newer molecular
diagnostic and subtyping methods may assist in earlier diagnosis and outbreak
|Streptobacillus Moniliformis, is a
technically a gram negative rod. It stains irregularly and can be mistaken for
gram positive pleiomorphic rods which also exhibit gram-variability. If you
work in a routine clinical bacteriology laboratory, you may as well disabuse
yourself of any hope that you would ever see this organism. It is very rare. It
is very fastidious, i. e., it is difficult to grow. And the clinical
circumstances are unique. This organism must be looked for in order to make a
definitive diagnosis. If rat bite is part of the patient clinical history, a
specimen may be sent to a specialized reference laboratory. If the physician
does not establish a rat bite in the patient's clinical history, a
serendipitous finding of gram variable rods on gram stain which can not be
cultured may or may not result in a specimen being sent to a specialized
reference laboratory, where it may or may not be successfully identified.
Streptobacillus moniliformis, "causes the clinical disease called rat bite
fever. At the site of the rodent bite, an ulcer appears; this may heal
spontaneously. Occasionally, the infection spreads to the regional lymph nodes,
and bacteremia has been observed. General malaise and fever may be present
after a few days. This generalized disease may be fatal. Colonization of
various parts of the body, such as joints or endocardium, may lead to chronic
disease accompanied by local symptoms. Rat bite fever also is caused by
Spirillum minus, a very different bacterium. Streptobacillus
moniliformis is a Gram-negative, nonmotile rod of variable length. The
individual cells are not regularly shaped or stained, and thus pleomorphism is
seen in smears. There is a tendency for spontaneous development of
cell-wall-deficient L-forms. Consequently, growth on artificial media depends
on certain additives, such as serum or ascitic fluid, which are not
always present in common culture media. Growth is best under a CO2
Corynebacterium diptheriae , is a
gram positive pleiomorphic rod. It can exhibit gram variability as well as the
classic, "chinese character," and club shapes. The presence of polyphosphate
inclusions called metachromatic granules may also be demonstrated..
Corynebacterium diptheriae is the causative agent of diptheria, a
condition which in its untreated form can lead to death by suffocation. "CDC
describes diphtheria as "an upper respiratory tract illness characterized by
sore throat, low-grade fever, and an adherent membrane of the tonsil(s),
pharynx, and/or nose". Diphtheria is a rapidly developing, acute, febrile
infection which involves both local and systemic pathology. A local lesion
develops in the upper respiratory tract and involves necrotic injury to
epithelial cells. As a result of this injury, blood plasma leaks into the area
and a fibrin network forms which is interlaced with with rapidly-growing C.
diphtheriae cells. This membranous network covers over the site of the local
lesion and is referred to as the pseudomembrane."
production: "Toxin is synthesized in high yield only after the exogenous supply
of iron has become exhausted ." "Only those strains of Corynebacterium
diphtheriae that that are lysogenized by a specific Beta-phage produce
diphtheria toxin. A phage lytic cycle is not necessary for toxin production or
release. The phage contains the structural gene for the toxin molecule."
The incidence of this disease has reached levels approaching zero due to
vaccination programs. "From 1980-1989, the number of cases in the United States
dropped to 24; two cases were fatal and 18 occurred in persons 20 years of age
or older. Most cases have occurred nonimmunized (or inadequately immunized)
"Because of the high degree of susceptibility of children,
artificial immunization at an early age is universally advocated. Toxoid is
given in 2 or 3 doses (1 month apart) for primary immunization at an age of 3 -
4 months. A booster injection should be given about a year later, and it is
advisable to administer several booster injections during childhood. Usually,
infants in the United States are immunized with a trivalent vaccine containing
diphtheria toxoid, pertussis vaccine, and tetanus toxoid (DPT or DTP
|Propionibacterium acnes This
bacterium can be secondarily involved in the dermatological condition known as
acne. When it is, it is rarely if ever the primary causative agent. It has been
linked to endocarditis, wound infections and abcesses but again, when it is, it
is rarely if ever the primary causative agent. When isolated in culture, it is
frequently disregarded as being a contaminant, particularly in blood cultures.
When the needle used to collect the blood culture specimen penetrates the skin
at the point of a hair follicle where the organism typically resides, a
contamination often results. P. acnes grows best under microaerophilic
or anaerobic conditions. It can stain unevenly on gram stain leading some to
call it a gram-variable rod.
Propionibacterium produces a smelly
acid, propionic acid which gives some French cheeses, toe jam, and Japanese
fermented beans, "natoh," the same stinky smell. Which is why our stomach turns
whenever we are encouraged to eat natoh.
Propionibacterium acnes from a blood