Microbe-host interactions. Nov 15, 2006 Ch. 21 Science 307: , 2005.

Transcription

1 Microbe-host interactions Nov 15, 2006 Ch. 21 Science 307: , 2005.

2 Antimicrobial drug resistance Acquired ability to resist effects of a chemotherapeutic to which it is normally susceptible Common mechanisms 1. Lack structure drug targets 2. May be impermeable to drug 3. Organism may be able to modify drug to an inactive form 4. Organism may modify the target itself 5. Organism may develop a new pathway 6. Organism may be able to pump out the drug

3 R factors Most drug resistant bacteria isolated from patients contain drug resistance genes on plasmids Many of these plasmids encode enzymes that inactivate drugs Multi-drug resistance plasmids predate medical use of antibiotics Widespread emergence of multi-drug resistance

4 Resistance to all known drugs Gram-negative Gram-positive Gram-positive/acid-fast Other gram-negative rods Staphylococcus aureus Salmonella sp. Shigella dysenteriae Shigella sp. Salmonella typhi Haemophilus influenzae Neisseria gonorrhoeae Pseudomonas aeruginosa Acinetobacter sp. Enterococcus faecalis Streptococcus pneumoniae Mycobacterium tuberculosis Haemophilus ducreyi Methicillin- resistant Staphylococcus aureus (MRSA) Vancomycinresistant Enterococcus (VRE) Figure by MIT OCW.

5 Healthcare-associated infections Healthcare-associated infections (HAIs) are infections that patients acquire during the course of receiving treatment for other conditions In hospitals alone, HAIs account for an estimated 2 million infections, 90,000 deaths, and $4.5 billion in excess health care costs annually

6 Changing patterns for HAIs 1950s to 1960s gram positive bacteria were a major problem (Streptococcus pyogenes and Staphylococcus aureus) 1970s and 1980s gram negative bacteria became a major problem (E. coli and Pseudomonas spp.) Currently, gram positive bacteria are again emerging as a major problem (S. aureus and Enterococcus spp.)

7 Methicillin-resistant Staphylococcus aureus N315 Image removed due to copyright restrictions. Hiramatsu et al. Trends Microbiol 9:486, 2001

8 Terminology Normal microbial flora or microflora Better term is microbiota Commensal (at the same table) Pathogen Infection versus disease Virulence Opportunistic pathogen

9 Indigenous microbiota Microorganisms that inhabit body sites in which surfaces and cavities are open to the environment Skin, oral cavity, upper respiratory tract, gastrointestinal (GI) tract, and vagina Each habitat can be considered a separate ecosystem For every cell in human body (10 13 ) there are 10 viable indigenous bacteria in the GI tract The GI tract (10 14 ) harbors 100-fold more bacteria than the skin (10 12 )

10 Major bacteria present Prevotella Streptococcus Veillonella Helicobacter Esophagus Anus Duodenum Organ Esophagus Stomach Major physiological processess Secretion of acid (HCI) Digestion of macromolecules ph 2 Enterococci Lactobacilli Small Continued digestion Jejumum Bacteroides intestine Absorption of monosaccharides, Bifidobacterium amino acids, fatty acids, water Clostridium Ileum ph 4-5 Enterobacteria Enterococcus Escherichia Large Absoption of bile acids, Colon Eubacterium intestine vitamin B 12 Klebsiella ph 7 Lactobacillus Peptococcus Peptostreptococcus Proteus Ruminococcus Staphylococcus Streptococcus Figure by MIT OCW.

11 Defining the GI microbiota Autochthonous microbiota Present during the evolution of an animal and therefore present in every member of a species Normal microbiota Common and perhaps even present in every individual in a given geographic area/community, but not in every member of the species True pathogens Acquired accidentally and therefore not normally present in all members of a community of an animal species Dubos et al. J Exp Med 122:67-76, 1965

12 Ecological principles In a stable GI ecosystem, all available habitats are occupied by indigenous microbiota Transient species derived from food, water, or even another part of the GI tract or the skin will not establish (colonize) Habitats are physical spaces in the GI tract normally occupied by a climax community of indigenous microbiota Population levels and species composition are stable and not easily disrupted

13 Succession & climax populations Lactic acid bacteria and coliforms predominate in infant human and animal GI tracts During weaning the microbiota changes drastically and obligate anaerobic bacteria become predominant The indigenous GI microbiota of adults consists of climax communities that are remarkably stable Each region of the GI tract has a characteristic population of microbes, in terms of complexity and population density

14 Model systems Germ free animals Delivered by Cesarean section into sterile plasticfilm isolators Maintained free of all bacteria, fungi, protozoa, viruses, and other detectible life forms Introducing microorganisms is called association or colonization Contamination is accidental introduction of unwanted microorganisms Germ free animals can be monoassociated with a singe species or poly associated with multiple species

15 ASF 361 Lactobacillus animalis Lactobacillus murinus Lactobacillus mali Lactobacillus salivarius ASF 360 Lactobacillus acidophilus Lactobacillus lactis ASF 500 Clostridium propionicum Clostridium neopropionicum ASF 356 Clostridium piliforme Ruminococcus gnavus Eubacterium contortum Roseburia cecicola ASF 502 Catonella morbi Acetitomaculum ruminis ASF 492 Eubacterium plexicaudatum Johnsonella ignava Flexistipes sinusarabic Deferribacter thermophilus Geovibrio ferrireducens Colobus Monkey sp. ASF 457 Rodent sp. 1 Rodent sp. 2 Rodent sp. 3 (Bacteroides) merdae (Bacteroides) distasonis ASF 519 (Bacteroides) forsythus CDC DF-3 Small intestine Esophagus (% Difference) 8 Stomach Figures by MIT OCW Large intestine Cecum

16 ASF356 : spatial distribution Cp of target gene/g 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region ASF361 : spatial distribution Cp of target gene/g 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region ASF457 : spatial distribution Cp of target gene/g 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region Figure by MIT OCW.

17 Continued... ASF492 : spatial distribution Cp of target gene/g 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region ASF500 : spatial distribution Cp of target gene/g 1.E+10 1.E+08 1.E+06 1.E+04 1.E+02 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region ASF519 : spatial distribution Cp of target gene/g 1.E+11 1.E+10 1.E+09 1.E+08 1.E+07 1.E+06 1.E+05 1.E+04 E1 S1 S2 I1 I2 I3 I4 I5 I6 C1 C2 L1 L2 L Gut region Figure by MIT OCW.

18 Human colonic microbiota Highest cell densities recorded for any ecosystem Diversity at the division level is among the lowest Only 8 of the 55 known bacterial divisions have been identified in colonic bacteria to date 2 division dominate Cytophaga-Flavobacterium-Bacteroides (CFB) Firmicutes (genera Clostridium and Eubacterium) Proteobacteria are common, but not dominant Compare to many soil communities, where 20 bacterial division can be present

19 Coprothermobacter Dictyoglomus Guaymas1 SR1 OD1 WS6 Termite Group 1 Synergisters SC4 OP TM7 BD1-5 OP1 OP 11 WS5 Thermotogae EM3 Aquifacae Firmicutes ABY1 SC3 Thermodesulfobacteria Desulfobacteria OP9 to the Archaea Green Non Sulfur Cyanobacteria Fibrobacteres TM6 Deferribacter Spirochaeates Actinobacteria Fusobacteria Marine Group A KSB1 Gemmatimonadetes Chlorobi OP5 Deinococcus-Thermus NKB19 SBR1093 WS2 BRC1 WS3 OP8 OS-K Acidobacteria Plantomycetales Chlamiydiae VadinBE9 7 Nitrospira Verrucomicrobi CFB OP3 Proteobacteria NC10 Bäckhed et al. Science 307: , 2005 Figure by MIT OCW.

20 Diversity 10 4 Strain > 200,000 16S rrna sequence in GenBank 1,822 from human gut 1,689 are uncultured Look at 495 with length > 900 bp ~ 800 species Number of Taxonomic Units Species Genus > 7,000 strains S rrna Sequence Identity (%) Bäckhed et al. Science 307: , 2005 Figure by MIT OCW.

21 Helicobacter pylori HP Photographs of Barry J. Marshall and J. Robin Warren removed due to copyright restrictions.marshall and Warren won the 2005 Nobel prize in medicine for their discovery of Helicobacter pylori and its role in gastritis and peptic ulcer disease. HP+ Gastric Lymphoma Gastric Cancer 1% p.a. Duodenal Ulcer Gastric Ulcer Figure by MIT OCW. Incidence diagram of Helicobacter pylori disease in the world today

22 Gastritis and peptic ulcer H. pylori strain genome (1,667,867 bp) cag pathogenicity island (37,000 bp) HP0524 (VirD4) HP0527 (VirB10) HP0544 (VirB4) caga HP0525 (VirB11) HP0528 (VirB9) The proteins encoded by these genes assemble to form a complex type IV secretion apparatus capable of delivering CagA from the bacterium into host cells Translocation of CagA into gastric epithelial cells Phosphorylation of CagA by host-cell kinases c-src and Lyn Binding to and activation of cellular phosphatase SHP-2 Growth factor-like response in host cell, cytoskeletal rearrangements Figure by MIT OCW.

23 H. pylori and gastritis Images of Helicobacter pylori removed due to copyright restrictions. Helicobacter pylori on gastric epithelial cells (false-color SEM) Suerbaum & Michetti N Eng J Med 2002