PLEOMORPHIC GRAM-NEGATIVE ROD, BACTERIA
Bordetella organisms: The most important species in this genus is B. pertussis, the organism which causes
whooping cough. This highly contagious bacterium makes its way into the respiratory tract via inhalation and
subsequently binds to and destroys the ciliated epithelial cells of the trachea and bronchi. It does this through
the use of several toxins: B. parapertussis is a respiratory pathogen that can cause mild pharyngitis. This
bacterium is similar toB. pertussis but lacks some of the toxins which make its sibling so nasty. Bordetella
bronchiseptica is usually a cause of pneumonia, otitis media, and other respiratory infections in animals.
BRUCELLA: The four species of this genus that can infect humans are named for the animal which they are
most commonly found: B. abortus (cattle), B. suis (swine), B. melitensis (goats), B. canis (dogs). Brucella can
enter the body via the skin, respiratory tract, or digestive tract. Once there, this intracellular organism can
enter the blood and the lymphatics where it multiplies inside phagocytes and eventually cause bacteremia
(bacterial blood infiltration).
Haemophilus genus: H. influenzae is the most common cause of bacterial meningitis in children between the
ages of five months and five years. The initial respiratory infection can spread to the blood stream and
eventually the central nervous system. A stiff neck, lethargy, and the absence of the sucking reflex are
common symptoms in infected babies. A vaccine is available, but is not always effective in very young
children. Adult meningitis is much less common and usually only occurs in those predisposed to illness.
H. influenzae is the number one cause of Epiglottitisthis, [a] potentially fatal disease, which may cause airway
obstruction in children between the ages of 2 and 4. Haemophilus infection has also been associated with
chronic bronchitis, pneumonia, bacteremia, conjuctivitis, and a host of other illnesses
Legionella: L. pneumophila is the bacterium associated with Legionnaires' disease and Pontiac fever.
Patients can develop severe pneumonia which is not responsive to penicillins or aminoglycosides.
Legionnaires' disease also has the potential to spread into other organ-systems of the body such as the
gastrointestinal tract and the central nervous system. L. micdadei is the second most commonly isolated
member of Legionella. This bacterium can cause the same flu-like symptoms and pneomonia which
characterize an L. pneumophila infection
PASTEURELLA: P. multocida is the species which most commonly infects humans. Although most members
infect animals, humans can acquire the organism from dog or cat bites. Patients tend to exhibit swelling,
cellulitis, and some bloody drainage at the wound site. Infection may also move to nearby joints where it can
cause swelling and arthritis (not to mention a lot of pain).
MISCELLANEOUS GRAM-NEGATIVE RODS
Campylobacter: C. jejuni, an organism that causes gastrointestinitis. bloody diarrhea indicates that
Campylobacter is an invasive pathogen that infiltrates the lining of the small intestine. Along the way, the
organism excretes toxins that destroy the gut mucosa.
Helicobacter genus : Helicobacter pylori is the leading cause of peptic ulcers and chronic gastritis in America.
VIBRIO: Several species of Vibrio are known to be human pathogens, V. cholerae ([is] the causative agent
of cholera). Another species of Vibrio that causes diarrhea is V. parahaemolyticus. V. vulnificus is also
obtained from eating contaminated seafood. Unlike other Vibrio species, this one is invasive and is able to
enter the blood stream through the epithelium of the gut. Additionally, wound infection may also occur from
contaminated sea water. Cellulitis or ulcer formations may result.