Chapter20 Lecture
Transcript of Chapter20 Lecture
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Foundations in Microbiology
Sixth Edition
Chapter 20The Gram-Negative Bacilli of Medical
Importance
Lecture PowerPoint to accompany
Talaro
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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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 ColiformsClinically 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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