pathogenic gram-negative bacteria pathogenic gram-negative bacteria baldwin toye m.d., frcpc...
TRANSCRIPT
PathogenicGram-Negative
Bacteria
PathogenicGram-Negative
Bacteria
Baldwin Toye M.D., FRCPCDivision of Microbiology
Division of Infectious Diseases Children’s Hospital of Eastern Ontario
The Ottawa HospitalUniversity of Ottawa
Baldwin Toye M.D., FRCPCDivision of Microbiology
Division of Infectious Diseases Children’s Hospital of Eastern Ontario
The Ottawa HospitalUniversity of Ottawa
Objectives• Give a general classification for medically important
Gram negative bacteria. • List which gram negative organisms are part of the
normal human microbiome (colonization, carrier, etc.).
• Recognize medically important Gram negative pathogens in common infectious diseases.
• Identify important virulence factors among Gram negative bacteria (using Escherichia coli and Pseudomonas aeruginosa as examples).
Nature 511, 108–111 (03 July 2014) doi:10.1038/nature13484
O antigens
3-deoxy-D-mannooctulosonic Acid (KDO, keto-deoxyoctulosonate)
Clinically Important Gram Negative Bacteria
Gram-Negative Bacilli Gram-Negative Cocci
H. influenzae
Enterobacteriaceae(glucose fermenters)
Non-glucose Fermenters
Haemophilus
• Pseudomonas• Acinetobacter etc.
Neisseria
N. meningitidisN. gonorrhoeae
Enterobacteriaceae on MacConkey Agar
ProteusMorganellaSalmonellaShigella
Escherichia coli EnterobacterSerratiaCitrobacter
Klebsiella
Natural Habitat - Enterobacteriaceae• GI tract (“coliforms”)
– Normal human microbiota– e.g., E. coli, Klebsiella, Citrobacter, etc.
• Hospital environment• Water, sewage, soil, plants, animals
Case
24 yr old, otherwise healthy, woman1-2 day history of urinary frequency, urgency, dysuriaNo feverUrine culture grew E. coli
Dx of urinary tract infection
What can Enterobacteriaceae cause?
• Urinary tract infection• Bacteremia (bloodstream infection)• Pneumonia (usually hospital-acquired)• Skin & soft tissue infection
Virulence Factors
• Adherence factors (e.g., fimbriae)• Capsule (antiphagocytic)
e.g., Klebsiella, Enterobacter• LPS (endotoxin)• Exotoxins
What can Enterobacteriaceae cause?• Urinary tract infection• Bacteremia (bloodstream infection)• Pneumonia (usually hospital-acquired)• Skin & soft tissue infection• Gastroenteritis
E. coli Salmonella Shigella Yersinia
ingestion of contaminated food or water
Case35 yr old male vacationing in Mexico5 days into vacation, developed watery non-bloody diarrhea (5-6 x/day)Associated with abdominal cramps & nausea but no fever
What is the diagnosis?
Traveler’s diarrhea likely due to enterotoxigenic E. coli
Case11 yr old girl, 2 day history of watery diarrhea that became increasingly bloodyAssociated with fever, headache, lower abdominal painNo history of travelHad eaten a hamburger at a picnic 3 days prior1 week after onset of diarrhea, developed reduced urine output and had elevated serum creatinine
What is the diagnosis?
E. coli Diarrhea - Mechanisms
Pathotype Adhesin Toxin Other Virulence Factors
Enterotoxigenic (ETEC)
CFA (colonization factor antigens)
LT (heat labile enterotoxin)ST (heat stable enterotoxin)
Enteropathogenic (EPEC) Bfp (bundle forming pili)
Intimin
Shiga toxin producing E. coli (STEC) Enterohemorrhagic (EHEC)
Lpf(long polar fimbria)
STx (shiga toxin) Intimin
Enteroinvasive (EIEC) none invasiveness
Enteroaggregative (EAEC) AAF(aggregative adherence fimbriae)
EAST (enteroaggregative ST)
Diffusely adherent E. coli (DAEC)
Afa/Dr adhesins(afimbrial & fimbrial)
E. coli Diarrhea - Mechanisms
Pathotype Adhesin Toxin Other Virulence Factors
Enterotoxigenic (ETEC)
CFA (colonization factor antigens)
LT (heat labile enterotoxin)ST (heat stable enterotoxin)
Enteropathogenic (EPEC) Bfp (bundle forming pili)
Intimin
Shiga toxin producing E. coli (STEC) Enterohemorrhagic (EHEC)
Lpf(long polar fimbria)
STx (shiga toxin) Intimin
Enteroinvasive (EIEC) none invasiveness
Enteroaggregative (EAEC) AAF(aggregative adherence fimbriae)
EAST (enteroaggregative ST)
Diffusely adherent E. coli (DAEC)
Afa/Dr adhesins(afimbrial & fimbrial)
Nature Reviews Microbiology 2010; 8:26-38
Enterotoxigenic E. coli (ETEC)
• Most common cause of Travelers’ diarrhea
• Usually self-limited• CFA (fimbriae)• LT binds to GM1
– ADP ribosyl transferase, cleaves NAD
– Activates adenyl cyclase → ↑cAMP → phosphorylates CFTR → ↑ Cl- secretion
• ST binds to guanylin receptor → ↑cGMP → phosphorylates CFTR → ↑ Cl- secretion
Prevention of Travelers’ Diarrhea• Hand hygiene• Avoid undercooked or raw meats/seafood,
unpasteurized eggs/dairy products.• Avoid foods cooked earlier in day and not sufficiently
reheated• Avoid vegetables difficult to clean• Avoid fruits you have not peeled yourself• Drink bottled water with intact seals or boiled water• Antibiotics only in select patients• Vaccine (Dukoral®)?
Shiga Toxin Producing E. coli (STEC)• Reservoir is GI tract of cattle and other
animals• E. coli O157:H7 most common cause• Linked to consumption of undercooked
ground beef & other contaminated food• Ability to induce attaching and effacing effect
(similar to EPEC) via multiple genes including intimin
Attaching & Effacing
Shiga Toxin Producing E. coli (STEC)• Production of shiga toxins (Stx)
– Binds to GB3 (globotriaosylceramide) • Intestinal mucosa• Kidney epithelial cells• Endothelial cells
– Cleaves adenine from 28S rRNA → inhibits protein synthesis, cell death
• Complications include hemolytic uremic syndrome (HUS)
Virulence Factors
• Adherence factors (e.g., fimbriae)• Capsule (antiphagocytic)• LPS (endotoxin) • Exotoxins
Case• 16 yr old male, previously healthy• Felt unwell & lethargic yesterday, didn’t go to
school• Over next few hours, fever, headache, nausea• Unresponsive, brought to ED• On exam: T-39.5oC, BP 80/50, P 125/min not rousable skin rash
Lancet Infect Dis 2003;3:565. Lancet 2007;2196-2210
Neisseria meningitidis• Gram-negative diplococci• Natural habitat: nasopharynx (3-25%)• Transmission via droplets, requires close contact• Virulence factors
– Pili (adherence)– Capsule (13 serogroups)– LOS (lipooligosaccaride)
• Invasive Disease– Bacteremia (meningococcemia)– Meningitis
Effect of Endotoxin on Macrophage Release of Inflammatory Mediators
Inflammatory Responses to Sepsis
NEJM 2006; 355:16
Bacterial Pathogenesis 3rd Ed 2011
Pseudomonas aeruginosa• Strict obligate aerobic Gram-negative bacillus• Ubiquitous – soil, water, plants, etc.• Colonies have grape-like odor• Green blue color
– pyoverdin (green)– Pyocyanin (blue)
Pseudomonas aeruginosa
Natural Habitat• Environmental (high moisture, high humidity)
– Hospital (sinks, taps, shower heads, mops, flower vases, etc.)
– Community (whirlpools, hot tubs, spas, swimming pools, humidifiers, etc.)
• Colonizes humans– Hospital acquired– Selected with broad spectrum antibiotic usage
Opportunistic hospital-associated pathogene.g., UTI, pneumonia, bacteremia, etc.
Virulence Factors – P. aeruginosa• Alginate
– Copolymer of mannuronic and gluronic acids– Adherence, antiphagocytic, protection of biofilm from
host immune system and antibiotics, resists opsonic killing– High level production (mutations in regulatory genes)
results in mucoid colonies, seen in CF• Exotoxin A (ExoA)
– ADP-ribosylation of EF-2– Inhibits host cell protein synthesis, results in cell death
• Elastase – elastin, human Ig, complement, some collagens• Quorum-sensing – gene regulating system• Many many others!!!
Cystic Fibrosis
• Genetic disease affecting chloride channels• Thicker mucus in the lungs and airways• Obstruction of airways, interfere with ciliated
cell host-defense• At risk for chronic and recurrent pulmonary
infections
Alginate Biofilm Production
Sherris Medical Microbiology 6th Edition 2014
P. aeruginosa – Antimicrobial Resistance
• Intrinsically resistant to many antibiotics• Many mechanisms of resistance• Often multi-drug resistant• Challenging to treat
Bacterial Pathogenesis1. Adherence2. Entry into body3. Spread4. Cell or tissue damage
direct toxins and other products indirect (inflammation or immune
response) 5. Strategies to counter host defense