The Gram-Negative Bacilli of Medical Importance 1/2

1. The Gram-Negative Bacilli of Medical Importance 1/2 Professor Sudheer Kher

2. Learning Objectives • Enlist medically important GNBs • Explain the basis of classification of GNBs • General properties of enterobacteriaceae • Discuss the role of toxins and other virulence factors in pathogenesis • Describe the mechanism of action of various toxins6. • List pathogenicity Resources - Ananthnarayan

3. 1. Gram-negative rods a. Family Enterobacteriaceae Medically important species Escherichia coli, Salmonella enterica, Shigella, Klebsiella spp, Proteus spp b. Pseudomonas spp related Organisms c. Bordetella pertussis d. Haemophilus spp 2. Curved rods • Vibrio spp • Campylobacter spp • Helicobacter spp 3.Miscellaneous Legionella spp Chlamydia spp Rickeettsia Representative Gram-negative Bacilli

4. 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

6. Aerobic Gram-Negative Bacilli • Pseudomonas – an opportunistic pathogen • Brucella & Francisella – zoonotic pathogens • Bordetella & Legionella – mainly human pathogens

7. Pseudomonas • small gram-negative rods with a single polar flagellum, produce oxidase & catalase • highly versatile metabolism

8. 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

9. 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

10. Brucella • tiny gram-negative coccobacilli • 2 species • Brucella abortus (cattle) • Brucella suis (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

11. Brucellosis Undulating fever

12. 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

13. 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

14. Bordetella pertussis • 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

15. Time course

16. Legionella pneumophilia

17. Legionella pneumophila • widely distributed in water • live in close association with amebas • 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

18. Enterobacteriaceae Family • Large family of gram-negative non sporing rods, motile / non motile • Reduce nitrates to nitrites • Catalase positive • Oxidase negative • Do not produce pigments. • many members inhabit soil, water, & decaying matter & common occupants of large bowel of humans & animals • facultative anaerobes, grow best in air • Cause diarrhea through enterotoxins • Divided into coliforms (lactose fermenters) and non-coliforms (non lactose fermenters)

19. 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

20. Nosocomial Infections Nosocomial infections from Gram negative enterics

21. 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)

22. Escherichia coli • most common aerobic & non-fastidious bacterium in gut • enterotoxigenic E. coli causes severe diarrhea due to heat-labile toxin & heat-stable toxin – stimulate secretion & fluid loss; also has fimbrae • enteroinvasive E. coli causes inflammatory disease of the large intestine • enteropathogenic E. coli linked to wasting form infantile diarrhea; O157:H7 strain causes hemorrhagic syndrome & kidney damage

23. 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

24. E. coli O157:H7 • 70,000 cases annually • Bloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome • Displaces normal, harmless strains in Intestines • Produces shiga-like toxin (kills host cells)

25. Other coliforms • Klebsiella pneumoniae– 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

26. Capsule of Klebsiella pneumoniare

27. Noncoliform lactose-negative enterics • Proteus • Salmonella & Shigella

28. Proteus • Swarm on surface of moist agar in a concentric pattern • Cause UTI, wound infections, pneumonia, septicemia, & infant diarrhea

29. Salmonella • S. typhi & S. paratyphi A, B, C – 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

30. Phases of Typhoid Fever Invasion Septicemia

31. Typhoid Mary

32. Shigella • 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 & in complicated cases ciprofloxacin & sulfa-trimethoprim Patches of mucus and blood