Foundations in Microbiology

Sixth Edition

Chapter 20The Gram-Negative Bacilli of Medical

Importance

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• Large, diverse group of non-spore-forming bacteria

• Wide range of habitats – large intestines (enteric), zoonotic, respiratory, soil, water

• Most are not medically important; some are true pathogens, some are opportunists.

• All have a lipopolysaccharide outer membrane of cell wall – endotoxin.

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Aerobic Gram-Negative Nonenteric Bacilli

• Pseudomonas and Burkholderia – an opportunistic pathogen

• Brucella and Francisella – zoonotic pathogens

• Bordetella and Legionella – mainly human pathogens

• Alcaligenes – opportunistic pathogen

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Pseudomonas: The Pseudomonads

• Small Gram-negative rods with a single polar flagellum

• Free living– primarily in soil, sea water, and fresh water; also colonize

plants and animals

• Important decomposers and bioremediators• Frequent contaminants in homes and clinical settings• Use aerobic respiration; do not ferment carbohydrates • Produce oxidase and catalase• Many produce water soluble pigments.

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Pseudomonas aeruginosa

• Common inhabitant of soil and water

• Intestinal resident in 10% normal people

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

• Frequent contaminant of ventilators, IV solutions, anesthesia equipment

• Opportunistic pathogen

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Pseudomonas aeruginosa

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

• Complications include pneumonia, UTI, abscesses, otitis, and corneal disease

• Endocarditis, meningitis, bronchopneumonia• Grapelike odor• Greenish-blue pigment (pyocyanin)• Multidrug resistant• Cephalosporins, aminoglycosides, carbenicillin,

polymixin, quinolones, and monobactams

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Other Gram-Negative Aerobic Rods

• Genera Burkholderia, Acinetobacter,

Stenotrophomonas• Similar to pseudomonads• Wide variety of habitats in soil, water, and related

environments• Obligate aerobes; do not ferment sugars• Motile, oxidase positive• Opportunistic

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Burkholderia

• Burkholderia cepacia – active in biodegradation of a variety of substances; opportunistic agent in respiratory tract, urinary tract, and occasionally skin infections; drug resistant

• B. pseudomallei – generally acquired through penetrating injury or inhalation from environmental reservoir; wound infections, bronchitis and pneumonia, septicemia

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Acinetobacter and Stenotrophomonas

• Acinetobacter baumanii – nosocomial and community acquired infections; wounds, lungs, urinary tract, burns, blood; extremely resistant – treatment with combination antimicrobials

• Stenotrophomonas maltophilia – forms biofilms; contaminant of disinfectants dialysis equipment, respiratory equipment, water dispensers, and catheters; clinical isolate in respiratory soft tissue, blood ,CSF; high resistance to multidrugs

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Brucella and Brucellosis• Tiny Gram-negative coccobacilli• 2 species:

– Brucella abortus (cattle)– Brucella suis (pigs)

• Brucellosis, malta fever, undulant fever, and Bang disease – a zoonosis transmitted to humans from infected animals

• Fluctuating pattern of fever –weeks to a year• Combination of tetracycline and rifampin or

streptomycin• Animal vaccine available• Potential bioweapon

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Francisella tularensis and Tularemia• Causes tularemia, a zoonotic disease of mammals

endemic to the northern hemisphere, particularly rabbits

• Transmitted by contact with infected animals, water and dust or bites by vectors

• Headache, backache, fever, chills, malaise and weakness

• 10% death rate in systemic and pulmonic forms• Intracellular persistence can lead to relapse• gentamicin or tetracycline• Attenuated vaccine• Potential bioterrorism agent

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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

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Bordetella pertussis

• Virulence factors– receptors that recognize and bind to ciliated

respiratory epithelial cells– toxins that destroy and dislodge ciliated cells

• Loss of ciliary mechanism leads to buildup of mucus and blockage of the airways.

• Vaccine – DTaP- acellular vaccine contains toxoid and other Ags

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Alcaligenes

• Live primarily in soil and water

• May become normal flora

• A. faecalis – most common clinical species– isolated from feces, sputum, and urine– occasionally associated with opportunistic

infections – pneumonia, septicemia, and meningitis

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Legionella pneumophila and Legionellosis

• Widely distributed in water• Live in close association with amebas• 1976 epidemic of pneumonia afflicted 200 American

Legion members attending a convention in Philadelphia and killed 29

• Legionnaires disease and Pontiac fever• Prevalent in males over 50• Nosocomial disease in elderly patients• Fever, cough, diarrhea, abdominal pain, pneumonia

fatality rate of 3-30%• Azithromycin

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Enterobacteriaceae Family• Enterics• Large family of small, non-spore-forming

Gram-negative rods• Many members inhabit soil, water, decaying

matter, and are common occupants of large bowel of animals including humans.

• Most frequent cause of diarrhea through enterotoxins

• Enterics, along with Pseudomonas sp., account for almost 50% of nosocomial infections.

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• Facultative anaerobes, grow best in air• All ferment glucose, reduce nitrates to nitrites,

oxidase negative, and catalase positive.• Divided into coliforms (lactose fermenters) and

non-coliforms (non-lactose fermenters)• Enrichment, selective and differential media

utilized for screening samples for pathogens

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Antigenic Structures and Virulence Factors

Complex surface antigens contribute to pathogenicity and trigger immune response:

• H – flagellar Ag

• K – capsule and/or fimbrial Ag

• O – somatic or cell wall Ag – all have

• Endotoxin

• Exotoxins

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Coliform Organisms and Diseases

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Escherichia coli: The Most Prevalent Enteric Bacillus

• Most common aerobic and non-fastidious bacterium in gut

• 150 strains

• Some have developed virulence through plasmid transfer, others are opportunists.

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Pathogenic Strains of E. coli

• Enterotoxigenic E. coli causes severe diarrhea due to heat-labile toxin and heat-stable toxin – stimulate secretion and fluid loss; also has fimbriae

• Enteroinvasive E. coli causes inflammatory disease of the large intestine.

• Enteropathogenic E. coli linked to wasting form infantile diarrhea

• Enterohemorrhagic E. coli, O157:H7 strain, causes hemorrhagic syndrome and kidney damage; ID 100 cells

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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

• Coliform count - indicator of fecal contamination in water

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Other Coliforms

Clinically important mainly as opportunists• Klebsiella pneumoniae– normal inhabitant of

respiratory tract, has large capsule, cause of nosocomial pneumonia, meningitis, bacteremia, wound infections and UTIs

• Enterobacter sp. – UTIs, surgical wounds• Serratia marcescens – produces a red pigment;

causes pneumonia, burn and wound infections, septicemia and meningitis

• Citrobacter sp. – opportunistic UTIs and bacteremia

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Noncoliform Lactose-Negative Enterics

• Proteus, Morganella, Providencia

• Salmonella and Shigella

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Opportunists: Proteus and Its Relatives

Proteus, Morganella, Providencia – ordinarily harmless saprobes in soil, manure, sewage, polluted water, commensals of humans and animals– Proteus sp. - swarm on surface of moist agar in a concentric

pattern

– involved in UTI, wound infections, pneumonia, septicemia, and infant diarrhea

– Morganella morganii and Providencia sp. involved in similar infections

• All demonstrate resistance to several antimicrobials.

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Salmonella and Shigella

• Well-developed virulence factors, primary pathogens, not normal human flora

• Salmonelloses and Shigelloses– some gastrointestinal involvement and diarrhea

but often affect other systems

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Typhoid Fever and Other Salmonelloses

• Salmonella typhi – most serious pathogen of the genus; cause of typhoid fever; human host

• S. cholerae-suis – zoonosis of swine• S. enteritidis – includes 1,700 different

serotypes based on variation on O, H, and capsular antigen

• Flagellated; ferments glucose • Resistant to chemicals –bile and dyes

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Typhoid Fever

• Bacillus enters with ingestion of fecally contaminated food or water; occasionally spread by close personal contact; ID 1,000-10,000 cells

• Asymptomatic carriers; some chronic carriers shed bacilli from gallbladder

• Bacilli adhere to small intestine, cause invasive diarrhea that leads to septicemia

• Treat chronic infections with chloramphenicol or sulfa-trimethoprim

• 2 vaccines for temporary protection

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Animal Salmonelloses

• Salmonelloses other than typhoid fever are called enteric fevers, Salmonella food poisoning, and gastroenteritis.

• Usually less severe than typhoid fever but more prevalent

• Caused by one of many serotypes of Salmonella enteritidis; all zoonotic in origin but humans can become carriers– cattle, poultry, rodents, reptiles, animal and dairy

products– fomites contaminated with animal intestinal flora

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Shigella and Bacillary Dysentery

• Shigellosis – incapacitating dysentery• S. dysenteriae, S. sonnei, S. flexneri and S. boydii• Human parasites• Invades villus of large intestine, can perforate

intestine or invade blood• Enters Peyer’s patches instigate inflammatory

response; endotoxin and exotoxins• Treatment – fluid replacement and ciprofloxacin and

sulfa-trimethoprim

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The Enteric Yersinia Pathogens

• Yersinia enterocolitica – domestic and wild animals, fish, fruits, vegetables, and water– bacteria enter small intestinal mucosa, some enter

lymphatic and survive in phagocytes; inflammation of ileum can mimic appendicitis

• Y. pseudotuberculosis – infection similar to

Y. enterocolitica, more lymph node inflammation

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Nonenteric Yersinia pestis and Plague

• Nonenteric

• Tiny, Gram-negative rod, unusual bipolar staining and capsules

• Virulence factors – capsular and envelope proteins protect against phagocytosis and foster intracellular growth– coagulase, endotoxin, murine toxin

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Yersinia pestis

• 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

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Pathology of Plague• ID 3-50 bacilli• Bubonic – bacillus multiplies in flea bite, enters lymph,

causes necrosis and swelling called a bubo in groin or axilla

• Septicemic – progression to massive bacterial growth; virulence factors cause intravascular coagulation subcutaneous hemorrhage and purpura – black plague

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

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• Diagnosis depends on history, symptoms, and lab findings from aspiration of buboes.

• Treatment: streptomycin, tetracycline or chloramphenicol

• Killed or attenuated vaccine available

• Prevention by quarantine and control of rodent population in human habitats

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Oxidase-Positive Nonenteric Pathogens

• Pasteurella multocida

• Haemophilus influenzae

• H. aegyptius

• H. ducreyi

• H. parainfluenzae

• H. aphrophilus

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Pasteruella multocida

• Zoonotic genus; normal flora in animals• Opportunistic infections• Animal bites or scratches cause local

abscess that can spread to joints, bones, and lymph nodes.

• Immunocompromised are at risk for septicemia and complications.

• Treatment: penicillin and tetracycline

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Haemophilus

• Tiny Gram-negative pleomorphic rods• Fastidious, sensitive to drying, temperature

extremes, and disinfectants• None can grow on blood agar without special

techniques – chocolate agar.• Require hemin, NAD or NADP• Some species are normal colonists of upper

respiratory tract or vagina (H. aegyptius, H. parainfluenzae, H ducreyi).

• Others are virulent species responsible for conjunctivitis, childhood meningitis, and chancroid.

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Haemophilus

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

– subunit vaccine Hib

• H. aegyptius –conjunctivitis, pink eye

• H. ducreyi – chancroid STD

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

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