The Gram-Negative Medically Important Bacteria

Chapter 20   


Oxygen requirements: aerobes, facultative anaerobes, obligate anaerobes


ENDOTOXIN - lipopolysaccharide of outer membrane - Lipid A

= macrophages release interleukins, tumor necrosis factor, et al.

Septic shock - bp, reduced circulation to heart brain kidneys, lungs

Nausea, tachycardia, cold clammy skin, weak pulse


I. Aerobic Gram-Negative Nonenteric Bacilli (do not ferment sugars)


Pseudomonas - free-living, soil, seawater, freshwater, plants, animals;

Small gram-negative , single polar flagellum, oxidative, (NO4),

pigments (green, brown, red, yellow)

Metabolically versatile: protease, amylase, pectinase, cellulase, et al.


Pseudomonas aeruginosa -

resist soaps, dyes, quats, drugs, drying, temp = chronic nosocomial pathogen

"opportunistic" pathogen - debilitated, immunocompromised, injury

Characteristic blue green, fluorescent "pyocyancin"

most at risk: burns, tumors, cystic fibrosis

causes: pneumonia, UTI, abscess, ear and eye infections

septicemia: endocarditis, meningitis, bronchopneumoia

usually produces: skin rash, UTI, ear infection, corneal infections w/ contacts

multiple drug resistances

Treatment: 3rd generation cephalosporins, aminoglycosides, carbenicillin, polymixin, quinolones, monobactams


Brucella abortis (cows), Brucella suis (pigs) - zoonosis

Brucellosis = Malta fever, undulant fever, Bang's Disease

 (Europe, Africa, India, Mexico Central & South America)

-cross placenta, cause abortion

-in humans - fever (no abortion) slaughterhouse, handlers, vets enters thru breaks in skin, mucous membranes;

-phagocytes release cells, waves of fever (chills, sweating, headache, muscle pain, weakness, weight loss), focal infections in liver, spleen, bone marrow, kidneys.

Treatment: tetracycline & streptomycin for 3-6 weeks (why?)


Francisella tularensis - Tularensis, Rabbit Fever

Former USSR, Europe, Asia, North America

Rabbits, rodents, wild animals, arthropod vectors - ticks, flies, mites, mosquitoes

Route of entry: skin, eyes, bites, ingestion, inhaled

Infective dose:10-50 cells Incubation time: hours to weeks

Symptoms: headache, backache, fever, chills, weakness

Or skin lesion, swollen glands, conjunctivitis, pharyngitis, GI tract, pneumonia

Treatment: streptomycin, gentamycin, tetracycline


Bordetella pertussis - Whooping Cough, pertussis

Acute respiratory infection, severe in infants <6 months DPT vaccine

Virulence factors: receptors bind to ciliated epitheleum; toxins kill cells

build up mucus and block airways

catarrhal stage - cold-like

paroxysmal stage - coughing fits, inspiration "whoop"

Treatment: erythromycin


Legionella - Legionnaire's diease

200 Legionnaires, Philadelphia, July 1976

Gram-negative motile short rods, to filaments, fastidious - charcoal extract medium

Legionella pneumophila - fresh water, aerosols, nosocomial in debilitated

Symptoms: rising fever, cough, diarrhea, abdominal pain - lung consolidation, impaired respiration, impaired function

Treatment: erythromycin and/or rifampin


II. Enterobacteriacae


Gram-negative, small non-spore-forming rods, aerobic, ferment when no O2 (facultative anaerobes) soil, water, decaying matter, large bowel.

Diarrheal illness (5M/yr), most common cause of death, nosocomial infections, medical devices

Ferment glucose, Nitrates to Nitrites, oxidase negative, catalase +, often motile

Coliforms - ferment lactose quickly

Noncoliforms - non or slow lactose fermenters

Biochemical Characterisitics - lactose,

IMViC = indole, methyl red, Voges-Proskauer and citrate.

Antigens: flagellar (H), capsule +/or fimbri (K), somatic=cell wall=LPS (O)

Serotype HKO

Endotoxins, overcome host defenses and multiply

Virulence factors: endotoxin, enterotoxins, capsules, hemolysins, fimbrae (colonize)




Escherichia coli - most common, non-fastidious

Enterotoxigenic - heat-labile (LT), heat-stabile (ST). fimbrae to attach

Enteroinvasive - invasion and ulceration of mucosa

Enteropathogenic - wasting disease of newborns

Diseases: Infantile diarrhea,

Traveler's Diarrhea - profuse, watery diarrhea, low fever, nausea, vomiting,UTI -

Indicator of fecal contamination (Salmonella spp.)


Other coliforms: Klebsiella pneumoniae: nosocomial prneumonai, meningitis, bacteriemia, wound infections, UTI

Enterobacter and Hafnia, Citrobacter, Serratia


Noncoliform, Lactose-negative enterics


Proteus - ubiqutous, UTI, wounds, pneumonia, septicemia, infant diarrhea, burns


Noncoliform Pathogens


Salmonella typhi - typhoid fever

O, H, and V (capsule)

Motile, ferment glucose with acid and gas, H2S, urease -

Not fastidious, resist bile and dyes, do not loose virulence on cultivation

Typhoid Fever: GI tract, 1k-10k infective dose

Adhere to mucosa of small intestine, progressive invasion -> septicemia

Lymph nodes -> liver and spleen, bacteremia

Fever, diarrhea, abdominal pain

Mesenteric lymph nodes ulcerate, perforate, peritonitis

Treatment: Chloramphenicol and ampicilin

Chronic carrier - remove gall bladder

Vaccine - killed whole cells (why?)


Other: S. enteriditis, S. paratyphi, S.schottmulleri, S. hiirschfield, S. typhimurium

Zoonoses - cattle, poultry, rodents, reptiles, Chickens, eggs, milk

Enteric fevers, gastroenteritis (N/V/D), asymptomatic infections

Treatment: Chlroamphenicol, ampicilin, electrolyte replacement


Shigella - Bacillary dysentery - Shigellosis

Severe abdominal cramps, watery stool with mucus and blood

Shigella dysentery- invades villi of large intestine

Endotoxin = fever Enterotoxin = inflammation, degenration of villi, bleeding, heavy mucus production

Shiga toxin=heat-labile exotoxin

Non-motile, no capsule, not fastidious,no H2S or urease

Infective dose: 200 cells children most affected

Treatment: replace fluids, ampicillin, sulfa-trimethoprim, (nalidixic acid, cephalosporins)


Nonenteric Yersinia pestis - Plague

100 million people died in 6th century

gram-negative rod, bipolar stain

Virulence factors: capsular and envelope proteins protect against phagocytosis and promote intraceluar growth. Coagulase, endotoxin


Mammals = "endemic reservoir" harbor microbe w/o disease

Spread to "amplifying hosts" which do develop disease

Fleas bite infected mammal, Y. pestis grow in gut and block esopahgus

Consecutive bites transmit Y. pestis


Infective dose: 3-50 cells

Bubonic - bite to lymph node - inflammation = bubo

Incubation time - 2-8 days - fever. Chills, headache, nausea, weakness, tender bubo

Septicemic - coagulate blood in vessels, subcutaneous hemmorage, purpura to necrosis to gangrene

Pneumonic - lungs, fatal

Treatment: streptomycin, tetracycline, chloramphenicol


Oxidase-postive Nonenteric Pathogens


Pasteurella multocida - zoonose

Chlolera-like in chickens

Hemorrhagic septicemia and pneumonia in cattle

Human - local abscess- joints, bones, lymph nodes

Pulmonary damaged patients risk pneumonia

Treatment: penicillin and tetracycline



Tiny gram-negative, pleomorphic rods

Fastidious, sensitive

Require blood for hemitin (X factor) cytochomes, catalase, peroxidase

V factor Nicotinamide adenine dinucleotide (AND) coenzyme


H. influenzae - acute bacterial meningitis

Treatment: Chloramphenicol and ampicillin

Hib vaccine


H. aegyptius - conjunctivitis = pinkeye

Subconjunctival hemorrhage


H. ducreyi - chancroid - STD - painful necrotic ulcer on genitalia,

Lymph nodes swell like buboes

Treatment: cotrimoxazole