Introduction to the Microbial World 1

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Introduction to the Microbial World 1
Welcome to CMID !

• Professor A G Duse
• Chief Specialist and Head (Chair) CMID
• NHLS and Wits School of Pathology
• Room 3T11, Level 3, WMS
• Tel [phone]

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Lecture Objectives

1. Briefly describe the evolutionary relationships
   of living organisms
2. List the main distinguishing features of
   prokaryotic versus eukaryotic cells
3. Provide a simple classification of the different
   forms of microbial life
4. Understanding the underlying principles of
   microbial taxonomy
5. Understand the concept of microbial morphology
   and its importance in clinical microbiology
6. Draw an annotated diagram of a typical bacterial
   cell

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Molecular Phylogeny

• Cyanobacteria (3.6 billion years old) earliest
  evidence of unicellular life
• Molecular phylogeny tool that enables us to
  understand the complexity of life recognize the
  relationships of living forms
• Determined by comparing difference in homologous
  genes encoding ribosomal RNA (16S r RNA genes
  from PROKARYOTIC cells 18S rRNA from eukaryotic
  cells)
• Computer analysis of rRNA gene sequences gt life
  has evolved along 3 major lineages
• Bacteria
• Archae not clinically significant (solely
  microbial composed of only unicellular
  organisms), and
• Eukaryotes (more complex, multi-cellular
  organisms)
• Hence, prokaryotes eukaryotes both ancient
  derived from a common UNIVERSAL ancestor!
• Homo sapiens other species either live in
  harmony (colonization) or are diseased (infected
  with manifest symptoms and signs to cause
  PATHOLOGY) with both prokaryotic and eukaryotic
  organisms!

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Differences Between Prokaryotic and Eukaryotic
Cells

• EUKARYOTES
• nucleus
• present
• diploid
• mitotic division
• present
• present
• 80S ribosomes
• more complex

• PROKARYOTES
• nucleoid
• no nuclear membrane
• haploid chromosome
• no mitotic division (replicate by binary fission)
• no mitochondria
• no Golgi apparatus, microtubules
• 70S ribosomes
• motile by flagella

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Classification of Microbes
DNA or RNA
Protozoa Trematodes Cestodes Nematodes
Yeasts Dimorphic Moulds
Cocci Bacilli Spiral
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Nomenclature (Taxonomy) of Bacteria

• FAMILY
• The Enterobacteriaceae
• GENUS
• Salmonella
• Escherichia
• SPECIES
• typhi (S typhi OR S typhi)
• coli (E coli OR E coli)

Binomial classification Genus and species
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Bacterial Morphology

• SIZE microns
• SHAPE
• ARRANGEMENT
• e.g. cocci in chains
• e.g. cocci in clusters
• ULTRASTRUCTURAL FEATURES capsules, flagella,
  fimbriae / pili spores

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Bacterial Cell Structure
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Introduction to the Microbial World 2
Welcome to CMID !

• Professor A G Duse
• Chief Specialist and Head (Chair) CMID
• NHLS and Wits School of Pathology
• Room 3T11, Level 3, WMS
• Tel [phone]

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Lecture Objectives

• Using a bacterial cell as an example, describe
  the ultra-structural features of bacteria
  discuss both their laboratory clinical
  relevance
• Discuss the role of bacterial cell components in
  disease causation (pathogenesis)
• Classify bacteria according to their morphology,
  aero-tolerance, and staining reactions with
  particular emphasis on Gram and acid-fast stains

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Bacterial Cell Components
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Bacterial Cell Components

• Capsule (mostly polysaccharide) antiphagocytic
  antigenic/ immunogenic
• Flagella (proteinaceous) locomotion antigenic
  ? Immune evasion
• Fimbriae/pili adherence
• Cell wall (cytoskeleton peptidoglycan)
  rigidity shape protection against osmotic
  pressure - prevention of lysis antigenic
• Cytoplasmic membrane cell respiration cell
  precursor synthesis
• Intracytoplasmic inclusions DNA ribosomes
• Spores protect species of genera Bacillus and
  Clostridium from unfavourable conditions

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Construction of the Cell Walls of Gram-positive
and Gram-negative Bacteria
LIPOPOLYSACCHARIDE
(ENDOTOXIN)
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Bacterial Morphology

• STAINING REACTIONS
• Gram staining
• Gram-positive (dark-blue/purple)
• Gram-negative (pink)
• Acid-fast
• stains poorly with Gram stain e.g. Mycobacterium
  tuberculosis
• Ziehl-Neelsen stain Kinyoun stain auramine
  stain

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Morphology-based bacterial classification
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Man versus Microbes
Welcome to CMID !

• Professor A G Duse
• Chief Specialist and Head (Chair) CMID
• NHLS and Wits School of Pathology
• Room 3T11, Level 3, WMS
• Tel [phone]

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Objectives

• Understand the concept of infectious disease
  causation
• Discuss the interactions between hosts, microbes
  and the environment
• Describe the concepts of true virulence versus
  opportunism
• List, and using appropriate examples, discuss the
  7 major challenges that a microbe must overcome
  to cause infection
• Illustrate all of the above by briefly discussing
  the recent outbreak caused by Rift Valley Fever
  virus in Kenya (Dec 2006-Jan 2007)

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Definitions
X-REF IMMUNOLOGY INNATE/NON-SPECIFIC DEFENCE
MECHANISMS
HOST

• Pathogenesis
• Pathogens true/primary vs. opportunistic
  vs. colonizers
• Carrier state
• Virulence ID 50, LD 50 other

FOCUS OF TODAYS LECTURE
MICROBE
ENVIRONMENT
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Pathogenic BacteriaThe Seven Challenges

• Maintain a reservoir
• Human, animal, environmental
• Gain access to a new host
• Portal of entry mode of transmission
• Adherence non-specific specific mechanisms
• Establishing infection evading host defences
  (X-ref Immunology)
• Mechanisms of disease causation
• Adherence toxins (exotoxins, endotoxin)
  hypersensitivity/autoimmune reactions (X-ref
  Immunology)
• Exiting from one host, entering another

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Portals Of Entry

• Respiratory tract
• Gastrointestinal tract
• Genitourinary tract
• Skin and mucous membranes

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Modes Of Transmission

• By respiratory droplets droplet nuclei
• Airborne (other than above)
• Faecal-oral
• By direct body contact
• By fomites
• Parenteral
• By arthropod vectors

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Remember

• Adherence / -
• Invasion / -
• Toxin production
• Differences between exotoxins endotoxins / -
• Hypersensitivity reactions

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Pathogenic BacteriaThe Seven Challenges

• Maintain a reservoir
• Human, animal, environmental
• Gain access to a new host
• Portal of entry mode of transmission
• Adherence non-specific specific mechanisms
• Establishing infection evading host defences
  (X-ref Immunology)
• Mechanisms of disease causation
• Adherence toxins (exotoxins, endotoxin)
  hypersensitivity/autoimmune reactions (X-ref
  Immunology)
• Exiting from one host, entering another

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Rift Valley Fever
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RVF Kenya Dec 06 - Jan 06
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Natural cycle of RVFV
Infected flood water Aedes Culex sp. oviposit
Eggs with virus dormant
Heavy rains flood
Infectious mosquitoes hatch
Mosquitoes feed on livestock and occasionally
humans
Amplification in vertebrate host
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Ocular RVFV
Macular scarring
Al-Hazmi et al., CID 2003 36245
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Hemorrhagic RVF
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Epizootic cycle of RVFV
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RVFV a worldwide concern

• Many mosquitoes world-wide can be vectors in the
  lab and in the field at blood meal virus
  concentrations found in sheep, cattle, humans
• We know it can cause epidemics when vertebrates
  that develop high viremias are present (sheep,
  cattle, goat)
• Mortality in domestic livestock and subsequent
  trade interruption have severe economic impact
• Humans may visit endemic/epidemic areas and
  return to their homes within an incubation period
  (e.g., tourist with retinopathy)
• Both arthropod and direct transmission from blood
  efficient (concern bioterrorism and aerosols)
• Established epidemics in new territory Egypt,
  Saudi, Yemen

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• THANK YOU !