The gram negative bacteria of medical importance
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The Gram-Negative Bacteria of Medical Importance. Chapter 20. Gram Negative Bacteria. Cocci. Family Neisseriaceae. Gram-negative cocci Residents of mucous membranes of warm-blooded animals Genera include Neisseria , Moraxella , Acinetobacter 2 primary human pathogens

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Family neisseriaceae
Family Neisseriaceae

  • Gram-negative cocci

  • Residents of mucous membranes of warm-blooded animals

  • Genera include Neisseria, Moraxella, Acinetobacter

  • 2 primary human pathogens

    • Neisseriagonorrhoeae

    • Neisseriameningitidis


  • Gram-negative, bean-shaped, diplococci

  • No flagella or spores

  • capsules on pathogens

  • pili

  • Strict parasites, do not survive long outside of the host

  • Aerobic or microaerophilic

  • Pathogenic species require enriched complex media and CO2

Neisseria gonorrhoeae

  • Causes gonorrhea, an STD

  • Virulence factors: pili, other surface molecules, IgA protease

  • Strictly a human infection

  • In top 5 STDs

  • Does not survive more than 1-2 hours on fomites

  • Infection is asymptomatic in 10% of males and 50% of females

Neisseria gonorrhoeae1


  • Males – urethritis, yellowish discharge, scarring & infertility

  • Females – vaginitis, urethritis, salpingitis (PID), common cause of sterility & ectopic tubal pregnancies

  • Extragenital infections – anal, pharygeal, conjunctivitis, septicemia, arthritis


Potential scar tissue blockage infertility


Potential for PID (pelvic inflammatory disease)

Gonorrhea in newborns
Gonorrhea in newborns

  • Infected as they pass through birth canal

  • Eye inflammation, blindness

  • Prevented by prophylaxis after birth

Neisseria meningitidis

  • Virulence factors – capsule, pili, IgA protease

  • Many strains exist

  • Prevalent cause of meningitis

  • Disease begins when bacteria enter bloodstream, pass into cranial circulation, multiply in meninges; very rapid onset; endotoxin causes hemorrhage and shock; can be fatal

  • Treated with penicillin, chloramphenicol

  • Vaccines exist

Neisseria meningitidis1

Spread of bacteria from a nasopharyngeal infection to blood and CSF

Septic shock endotoxic shock
Septic Shock-Endotoxic shock

  • LPS (lipopolysacchardide) Component of Gram negative cell wall is a potent immune stimulant.

  • May lead to circulatory failure, tissue damage and death

Release of LPS as bacteria breaks apart

Aerobic gram negative bacilli
Aerobic Gram-Negative Bacilli

  • Pseudomonas – an opportunistic pathogen

  • Brucella & Francisella – zoonotic pathogens

  • Bordetella & Legionella – mainly human pathogens

  • Alcaligenes – opportunistic pathogen


  • small gram-negative rods with a single polar flagellum, produce oxidase & catalase

  • highly versatile metabolism

Pseudomonas aeruginosa
Pseudomonas aeruginosa

Single polar flagellum

Pseudomonas aeruginosa1
Pseudomonas aeruginosa

  • common inhabitant of soil & water (ubiquitous-wide spread)

  • intestinal resident in 10% normal people

  • grapelike odor

  • greenish-blue pigment (pyocyanin)

  • resistant to soaps, dyes, quaternary ammonium disinfectants, drugs, drying

  • frequent contaminant of ventilators, IV solutions, anesthesia equipment

  • opportunistic pathogen

Pseudomonas aeruginosa2
Pseudomonas aeruginosa

  • common cause of nosocomial infections in hosts with burns, neoplastic disease, cystic fibrosis

  • Can cause: pneumonia, UTI, abscesses

  • Septicemia can lead to: endocarditis, meningitis, bronchopneumonia

  • Corneal ulcers from contaminated lens solutions

  • Ear infections (Otitis) “swimmer’s ear”

  • Skin rash (contaminated hot tubs, saunas, swimming pools)

  • multidrug resistant

Pseudomonas aeruginosa3
Pseudomonas aeruginosa

Skin rash/eruption

Pseudomonas aeruginosa4
Pseudomonas aeruginosa

Multiple drug resistance

Staphylococcus aureus

Pseudomonas aeruginosa


  • tiny gram-negative coccobacilli

  • 2 species

    • Brucellaabortus (cattle)

    • Brucellasuis (pigs)

  • Brucellosis (synonyms=malta fever, undulant fever, & Bang disease) – a zoonosis transmitted to humans from infected animals

  • fluctuating pattern of fever –weeks to a year

  • combination of tetracycline & rifampin or streptomycin

  • animal vaccine available (efforts underway to eradicate from cattle herds and swine)

  • potential bioweapon


Undulating fever

Francisella tularensis

  • causes tularemia, a zoonotic disease of mammals endemic to the northern hemisphere, particularly rabbits

  • transmitted by contact with infected animals, water & dust or bites by vectors

  • headache, backache, fever, chills, malaise & weakness

  • 10% death rate in systemic & pulmonic forms

  • intracellular persistence can lead to relapse

  • gentamicin or tetracycline

  • attenuated vaccine available

  • potential bioterrorism agent

Bordetella pertussis

  • minute, encapsulated coccobacillus

  • causes pertussis or whooping cough, a communicable childhood affliction

  • acute respiratory syndrome

  • often severe, life-threatening complications in babies

  • reservoir – apparently healthy carriers

  • transmission by direct contact or inhalation of aerosols

  • May be relatively common in adults (as chronic cough) and be misdiagnosed as a cold or the flu

Bordetella pertussis1

  • virulence factors

    • receptors that recognize & bind to ciliated respiratory epithelial cells

    • toxins that destroy & dislodge ciliated cells

  • loss of ciliary mechanism leads to buildup of mucus & blockage of the airways

  • Hacking coughs followed by abrupt deep inhalation (whoop)

  • Vaccine does not give long-term immunity so adults and older children can have a recurrence


Prevalence increasing due to decrease in vaccination rate in children as a result of concern over its publicised vaccine side effects


  • live primarily in soil & water

  • may become normal flora

  • A. faecalis – most common clinical species

    • isolated from feces, sputum, & urine

    • occasionally associated with opportunistic infections – pneumonia, septicemia, & meningitis

Legionella pneumophilia

Legionella pneumophila

  • widely distributed in water

  • 1976 epidemic of pneumonia afflicted 200 American Legion members attending a convention in Philadelphia & killed 29 (source was a contaminated air-conditioning system) Legionnaires disease

  • Most prevalent in males over 50

  • nosocomial disease in elderly patients

  • Symptoms: fever, cough, diarrhea, abdominal pain, pneumonia fatality rate of 3-30%

  • azithromycin

Enterobacteriaceae family
Enterobacteriaceae Family

  • enterics

  • large family of gram-negative bacteria

  • many members inhabit soil, water, & decaying matter & common occupants of large bowel of humans & animals

  • all members are small, non-sporing rods

  • facultative anaerobes, grow best in air

  • cause diarrhea through enterotoxins

  • divided into coliforms (lactose fermenters) and non-coliforms (non lactose fermenters)

Dichotomous key for the enterobacteriaceae
Dichotomous Key for the Enterobacteriaceae

Diarrheal disease
Diarrheal Disease

  • Two Mechanisms

    • Toxigenic

      • Organism itself does not invade the tissue

      • Enterotoxins released which cause cells to increase secretion secretory diarrhea

    • Invasive

      • Microbes breakdown epithelial cells and form ulcerations. May see bleeding

  • Fluid and electrolyte loss may result in dehydration…death.

  • Diarrheal disease = 40% of infectious diseases

    • 18% of death worldwide

Nosocomial Infections

Nosocomial infections from Gram negative enterics

Coliforms- Ferment lactose. (normal enteric flora but may cause infections)

Noncoliforms- Do not ferment lactose. (some are normal enteric flora others are true pathogens…Salmonella, Shigella)

Escherichia coli
Escherichia coli

  • most common aerobic & non-fastidious bacterium in gut

  • enterotoxigenicE. coli causes severe diarrhea due to heat-labile toxin & heat-stable toxin – stimulate secretion & fluid loss; also has fimbrae

  • enteroinvasiveE. coli causes inflammatory disease of the large intestine

  • enteropathogenicE. coli linked to wasting from infantile diarrhea; O157:H7 strain causes hemorrhagic syndrome & kidney damage

Escherichia coli1
Escherichia coli

  • pathogenic strains frequent agents of infantile diarrhea – greatest cause of mortality among babies

  • causes ~70% of traveler’s diarrhea

  • causes 50-80% UTI

  • indicator of fecal contamination in water

Escherichia coli o157 h7
Escherichia coli O157:H7

The Ready-To-Eat Spinach outbreak of ‘06

E coli 0157 h7 outbreak
E. Coli 0157:H7 outbreak

  • September 28, 2006 : 187 people infected in 26 states (97 hospitalized…29 developed HUS)

2006 Spinach-associated outbreak




15 +

Newer outbreaks
Newer Outbreaks

  • Nestle Toll House cookie dough (E. coli) June 2009) (72 cases in 30 states)

  • Ground beef (E. coli) ( July 2008) (49 cases in 7 states)

  • Pepperoni pizza (E.coli) (Oct-Nov 2007) (21 cases in 10 states)

Other coliforms
Other coliforms

  • Klebsiellapneumoniae– normal inhabitant of respiratory tract, has large capsule, cause of nosocomial pneumonia, mennigitis, bacteremia, wound infections & UTIs

  • Enterobacter – UTIs, surgical wounds

  • Serratiamarcescens – produces a red pigment; causes pneumonia, burn & wound infections, septicemia & meningitis

  • Citrobacter – opportunistic UTIs & bacteremia

Capsule of Klebsiella pneumoniare

Noncoliform lactose negative enterics
Noncoliform lactose-negative enterics

  • Proteus

  • Salmonella & Shigella


  • Swarm on surface of moist agar in a concentric pattern

  • Cause UTI, wound infections, pneumonia, septicemia, & infant diarrhea


  • S. typhi – typhoid fever – ingested bacilli adhere to small intestine, cause invasive diarrhea that leads to septicemia. Asymptomatic carriers perpetuate and spread the bacteria.

  • S. enteritidis – 1,700 serotypes (varieties)-salmonellosis – can be zoonotic(fecal contamination of food products) (1/3 of all chickens have Salmonella)

    • Food Poisoning-gastroenteritis for 2-5 days

A recent salmonella in peanut butter outbreak late 2008 through 2009
A recent Salmonella in peanut butter outbreak(Late 2008 through 2009)

Phases of Typhoid Fever




  • Shigellosis – bacillary dysentery

  • S. dysenteriae, S. sonnei, S. flexneri & S. boydii

  • Invades large intestine, can perforate intestine or invade blood (septicemia)

  • Virulence factors: endotoxin & exotoxins

  • Treatment – fluid replacement & ciprofloxacin & sulfa-trimethoprim

Patches of mucus and blood

Yersinia pestis

  • Nonenteric…tiny, gram-negative rod

  • virulence factors –

    *capsular & envelope proteins that protect against phagocytosis & foster intracellular growth



Yersinia pestis1

Yersia pestis in blood

Yersinia pestis2

  • humans develop plague through contact with wild animals (sylvatic plague) or domestic or semidomestic animals (urban plague) or infected humans

  • found in 200 species of mammals – rodents without causing disease

  • flea vectors – bacteria replicates in gut, coagulase causes blood clotting that blocks the esophagus; flea becomes ravenous

Yersinia pestis3

Infection cycle

Pathology of plague
Pathology of plague

  • bubonic – bacillus multiplies in flea bite, enters lymph, causes necrosis & swelling called a bubo in groin or axilla

  • septicemic – progression to massive bacterial growth; virulence factors cause intravascular coagulation & subcutaneous hemorrhage. Necrosis and skin blackening occur – black plague

  • pneumonic – infection localized to lungs, highly contagious; fatal without treatment

  • treatment: streptomycin, tetracycline or chloramphenicol

  • Killed or attenuated vaccine that gives a short-term protection exists

Pasteruella multocida
Pasteruella surface)multocida

  • zoonotic genus

  • opportunistic infections

  • animal bites or scratches cause local abscess that can spread to joints, bones, & lymph nodes (septicemia)

  • treatment: penicillin & tetracycline

Hemophilus surface)

  • tiny gram-negative pleomorphic rods

  • Fastidious. can’t grow on blood agar without special techniques.

  • some species are normal colonists of upper respiratory tract or vagina (H. aegyptius, H. parainfluenzae)

  • others are virulent species responsible of conjunctivitis, childhood meningitis, & chancroid

Hemophilus surface)

  • H. influenzae– acute bacterial meningitis, epiglottitis, otitis media, sinusitis, pneumonia, & bronchitis

    • meningitis symptoms: fever, vomiting stiff neck neurological impairment. High fatality is untreated

    • subunit vaccine Hib

  • H. aegyptius–conjunctivitis, pink eye

  • H. ducreyi– chancroid STD

  • H. parainfluenzae & H. aphrophilus– normal oral & nasopharyngeal flora; infective endocarditis

Bacterial meningitis from surface)H. influenzae