1. Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010 Chapter 9: The clinical significance of bacterial anatomy

2.  This chapter details the structures of microorganisms that are involved with infectious disease.  Bacterial structures play a significant role in the five steps required for infection.  Understanding bacterial structure and function opens the way for new antibiotic treatment and vaccines.

5.  The bacterial cell wall is a protective barrier against: ◦ Osmotic pressure changes ◦ Other environmental stresses  The cell wall is a complex meshwork structure composed of several parts.  The key structure is peptidoglycan.  The cell wall is different in Gram-positive and Gram-negative bacteria.

6.  Composed of repeating sugar molecules. ◦ N-acetyl glucosamine (NAG) ◦ N-acetyl muramic acid (NAM)  Cross-linked by 4 amino acids via NAM ◦ In gram positives sometimes additional glycine pentapeptide bridge

8.  The linking together of NAG and NAM subunits is facilitated by several enzymes.  Cell wall construction mechanisms are targets for antibiotics.  There are three phases of peptidoglycan assembly of a new wall which can be inhibited by antibiotics ◦ Cytoplasmic phase: build precursor subunits (fosfomycin, vancomycin) ◦ Membrane-associated phase: transport precursors to the extracellular space (nisin) ◦ Extra-cytoplasmic phase: Cross-link the precursors via transpeptidases (penicillin)

9.  Gram-positive bacteria ◦ Have thick peptidoglycan with many layers of teichoic acids and lipoteichoic acids interweaved.  Gram-negative ◦ have only a very thin peptidoglycan with few layers but they have additional layer, an outer membrane which contains lipopolysaccharide and is attached to the peptidoglycan via Braun’s lipoprotein.

10. periplasmic space

11.  Mycolic acids ◦ Long chain fatty acids  Very hard to penetrate  Special antibiotics that are called antimycobaterial drugs, tuberculostatic  Require special disinfectants

12.  Primary component of the outer membrane  Only found in gram negative bacteria  Composed of lipids and polysaccharides  Pyrogen ◦ Monocytes and macrophages detect LPS and respond with secretion of proinflammatory cytokines that mediate fever and acute phase response by action on liver cells  C-reactive protein (CRP) levels rapidly increase

13.  Highly variable O- polysaccharide side chains ◦ Immunogenic ◦ Serotyping: E. coli O157: H7 is designated by O polysaccharide 157.  Core sugars  Conserved lipid A (toxic)  Endotoxin  Fever inducing

14.  It contains specialized proteins called porin proteins: ◦ These form a channel through the outer layer. ◦ This channel is responsible for passage of molecules and ions into and out of the Gram-negative cell. ◦ Porin proteins exclude large molecules.

16.  Structures involved primarily with adherence (staying in) ◦ Glycocalyx (sugars)  Slime layer  Capsule (more organized) ◦ Fimbriae (protein) ◦ Pili (protein)  Can also mediate motility: twitching or gliding motility  Structures involved primarily with motility ◦ Flagella  Axial filament

17. Panel a: © Dr Immo Rantala / Science Photo Library; Panel b: © CDC; Panel c: © Professor William Costerton, University of Southern California

18.  Both are involved in adherence.  Both appear as sticky projections which are shorter than flagella.  They are found on Gram-negative organisms.  Both are composed of pilin protein subunits.  Genes for these can be transferred from one organism to another via specialized sex pili ◦ Transfer also antibiotic resistance genes and virulence factors  High mutation rates in mucosal pathogens ◦ Vaccines do not work

19. flagella

20.  Flagella are used only for motility.  They are long structures that extend far beyond the cell wall and even beyond the glycocalyx.  Composed of protein  A flagella consists of the following three parts: ◦ Filament ◦ Hook ◦ Basal body

21.  Made of flagellin subunits  Immunogenic  Used in serotyping  “H” designation

22.  Monotrichous – one flagellum located at the end of the cell  Amphitrichous – two flagella, one at each end of the cell  Lophotrichous – two or more flagella located at the same end of the cell  Peritrichous – flagella surround the entire cell.

23.  Propeller like (unlike eukaryotic flagella)  100,000 rpm  20 cell lengths per second (~ 80 miles per hour for a 6 ft human)  ATP driven

24.  Axial filaments are flagellum-like structures that are found on spirochetes.  They wrap around the bacterial cell and are confined to the space between the plasma membrane and cell wall.  They are used for motility and cause the entire organism to rotate like a corkscrew.  Well suited for movement through viscous fluid and tissue. ◦ Treponema pallidum spreads throughout the entire body

26.  Plasma membrane  Nucleoid  Plasmids  Ribosomes  Inclusion bodies  Endospores

27.  Lipid double layer ◦ No cholesterol  It surrounds the internal cellular matrix and organelles.  It provides a barrier between the inside and the outside of the cell.  It is involved in: ◦ DNA replication ◦ Generation of energy: electron transport chain ◦ Transport and secretion

28. membrane proteins (peripheral and integral)

29.  The plasma membrane regulates what enters the cell cytoplasm and what does not.  There are three types of membrane transport: ◦ Osmosis ◦ Passive transport ◦ Active transport

30.  In osmosis, water chases the concentration of solutes. ◦ If the solute concentration is greater inside the cell:  It allows water to enter the cell and results in osmotic lysis (cell bursts). ◦ If the solute concentration is greater outside the cell:  It allows water to leave the cell and results in plasmolysis (cell shrinks)

31. Osmotic lysisPlasmolysis

32.  There are two types of passive transport ◦ Simple diffusion ◦ Facilitated diffusion

33.  Simple diffusion does not require ATP.  It is based on the development of concentration gradients.  Solutes move from regions of higher concentration to regions of lower concentration.  The higher the concentration gradient between two regions, the faster diffusion occurs.  Diffusion slows down as equilibrium is reached.  Simple diffusion only occurs with: ◦ Lipid soluble molecules ◦ Molecules small enough to pass through the membrane.

34.  Facilitated diffusion does not require ATP.  Molecules are brought across the plasma membrane by carrier proteins called permease proteins.  Permeases achieve this by changing their three-dimensional shape.  Molecules too large to fit into a permease are chopped into smaller pieces by enzymes secreted by the cell.

36.  Active transport requires ATP.  Solutes are carried either into or out of a cell against the concentration gradient.  It is the most common form of membrane transport.  There are three types of active transport: ◦ Efflux pumping  Pumps bring in certain molecules and expel others at the same time. ◦ ABC transport systems  Very complex and involve several proteins that grasp the molecule, bring it to the membrane, transport it through and deliver it into cytoplasm ◦ Group translocation  Proteins are chemically modified inside the cell to prevent escape

37.  Confer antibiotic resistance.  Multiple antibiotics can be shuffled out as soon as they enter.  New drugs target efflux pumps.

38.  The plasma membrane is also involved in secretion.  Secretion is the movement of substances out of a cell.  It involves several membrane proteins that act in specific sequence.  There are different types of secretion.  Example: Type III secretion system used in many pathogenic bacteria

39. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.  Injects proteins directly into host cell  “Hypodermic needle” similar to base of flagellum!  Genes on pathogenicity island  Injected proteins cause host to engulf bacterium Salmonella injects over 13 toxins  Alters fusion of vesicles in cell  Causes diarrhea in host

40.  Bacteria have no nucleus.  The region where DNA is located is called the nucleoid.  Bacteria usually have only one circular chromosome which contains all of the genetic information required by the organism.

41.  Plasmids are extra- chromosomal ring structured pieces of DNA that are separate from the main DNA structure.  Some bacteria can carry more than one plasmid.  Plasmids often carry genes for toxins and resistance to antibiotics.  Plasmids can be transferred from one cell to another through pili during conjugation.

42.  Because DNA is the genetic blueprint for the organism, any disruption or damage to it can be a lethal event.  DNA is therefore a primary target for antibiotics ◦ Ciprofloxacin acts on enzymes that are important during replication or transcription  Plasmids carry genes for toxins and antibiotic resistance.

43.  Ribosomes are nonmembrane-enclosed organelles involved in protein synthesis.  More active bacteria contain more active numbers of ribosomes.  Each ribosome is composed of two subunits. ◦ The subunits remain apart till messenger RNA is found.  Ribosomes in prokaryotes (70S) are different to those in eukaryotes (80S). ◦ Many antibiotics target bacterial ribosomes.

44.  Inclusion bodies are membrane-enclosed organelles used to store important materials.  There are several types of inclusion bodies ◦ Those that store glycogen. ◦ Metachromatic granules store phosphates in Corynebacterium species.  Inclusion bodies have no known clinical significance but can be used diagnostic.

45.  Endospores are formed through the process of sporulation.  They form when a bacterium is exposed to great environmental stress.  Well described in a few gram positive bacterial species.  Complex process which leads to a dense packaging of the genetic material with protective substances and formation of a new, highly resistant spore coat.

46. Spore Vegetative Form Sporulation Germination  Terminal  Subterminal  Central

47.  They confer a type of dormancy on the cell.  They are extremely resistant to heat, desiccation, toxic chemicals, UV irradiation, and antibiotics.  Bacteria can survive for extraordinary lengths of time in the endospore state.

48.  Endospores are resistant to almost all disinfectants and antiseptics.  They are also resistant to antibiotics.  They can survive for many years.  They can be easily dissiminated by air.  If a bacterium is pathogenic when it undergoes sporogenesis, it will be pathogenic once it emerges.

49.  Bacillus anthracis  Clostridium perfringens  Clostridium botulinum  Clostridium tetanus

51.  Many of the structures associated with the bacterial cell wall are involved in the infection process.  The cell wall is a meshwork made up of layers of peptidoglycan. There are many layers in Gram-positive organisms and few in Gram-negative organisms.  The cell wall is a primary target for attack by antibiotics.  Gram-negative cells contain an outer layer made up of lipoproteins, lipopolysaccharides (endotoxin), and phospholipids that protect against antibiotics  The five structures found outside the cell wall — capsules, fimbriae, flagella, axial filaments, and pili — are involved in the infection process.

52.  The plasma membrane surrounds the cytoplasm and is the place where the replication of DNA and the production of ATP take place. It is also a target of antibiotics.  Bacteria have no nucleus, and the DNA floats as nucleoid in the cytoplasm.  Plasmids are extrachromosomal structures made of DNA that contain the genes for toxins and antibiotic resistance. These plasmids can be transferred from one bacterial cell to another.  Endospore formation protects bacteria from environmental pressure and also from antibiotics and disinfectants. This structure can have a major role in clinical settings. Chapter 9 key concepts