Introduction to
Microbiology
H. GEE. MD, FRCOG
Hon. Assoc. Clinical Professor
University of Warwick
Peter Gayo Munthali
Consultant Microbiologist
UHCW
What is Microbiology
• The study of micro-organisms
– Bacteria (Bacteriology)
– Viruses (Virology)
– Parasites (Parasitology)
– Fungi (Mycology)
• Human, Animals, Plants
Aim
To introduce general principles in microbiology
with an emphasis on bacteria and viruses
Objectives
• By the end of the session you should be
able to;
– Distinguish between gram-positive and gramnegative bacteria
– Describe bacteria by their shape as either cocci or
rods
– Name some common bacterial and viral diseases
linked to their causative organisms
– Describe in broad terms, how antibiotics work on
bacteria
– Describe the difference between bacteria and
viruses.
Some definitions
Infection
‘the establishment of a microorganism
within a host’
Pathogen
‘any microorganism that has the
capacity to cause disease’
Virulence
‘ quantitative measure of the
likelihood of causing disease’
Opportunistic
• Principle pathogens regularly cause disease
• Opportunistic pathogens require a defect in
the immune defence
– Eg Pseudomonas
Bacteria
Bacteria
Description
• Unicellular
• Prokaryotic
– Primitive nucleus
• No nucleus membrane
• Genome
• Single circular molecule double stranded DNA
• Can harbour independent small circular DNA molecules
called plasmids
• Structure
• Rigid wall which determines their shape
Prokaryote
Eukaryote
Prokaryote vs Eukaryote
Overall structure of bacterial cell walls
Gram –ve cell wall
Gram +ve cell wall
Bacteria Classification
• Cell wall classification by gram stain
• Gram positive
– thicker cell wall
• Gram negative
– thinner cell wall
• Classification by shape
– Spherical
• Cocci
– Cylindrical
• Rods/bacilli
Gram-Positives
Gram Stain
Gram-positive cocci in clusters (Staphylococci)
Gram-negatives
Gram-negative rods
Gram-positive rods
Gram-positive Cocci in
chains (Streptococci)
Gram-negative cocci
Gram Stain - Importance
• First stage of identification
– (Culture)
• Indicator for treatment
– (Sensitivity)
Gram Stain
• +ve cocci, clustered
• +ve cocci, paired or chains
• +ve bacilli (large + spores)
• -ve cocci (intra-cellular)
• -ve rods, coliform
• -ve rods
S. Aureus (coag -ve)
Strep.
Enterococci
Clostridium
Gonorrhoea
E. Coli/Coliforms
Pseudomonas
Anaerobes
Haemophilus spp
Culture & Sensitivity
• Culture
– Aerobic/Anaerobic
– Haemolytic
– Others (type of media)
• Sensitivity
– Antibiotics
Bacterial Cell Division
Super coiled DNA
DNA relaxation
and duplication
Duplication of the DNA
Enzymatic Cleavage
bacterial chromosome replicates leading
to two identical chromosomes
Division
Identical Daughter cells
Genetic variability
Lateral gene transfer
Virulence
‘ quantitative measure of
pathogenicity or the likelihood of
causing disease’
Virulence factors
1. Aid colonisation
1. Adhesion proteins
2. Entry into cells
2. Aid survival
1. Immune avoidance eg. antiphagocytic
2. Immunosuppression
3. Damage host
1. Toxins
4. Obtain nutrition from host
Obligatory steps for infection
Attachment +/- Evade natural protection
and cleansing mechanisms
Entry into body
Local or general spread
Evade immediate local defences
Multiplication
Evasion of host defences
Evade immune and other defences for
growth in the host
to be completed
Shedding from body Leave body
at a site and on a scale that ensures
spread to fresh host- transmission
Relationship with humans
• We are sterile in utero
• Shortly after birth colonised
• Of 100000000 bacterial only 1000 are
successful
– Suggests highly evolved
Microbiome
Vaginal Flora
• Lactobacilli (Gram -ve)
• Gram +ve
–
–
Atopobium spp.
Peptostrep. spp.
– Staph. Spp.
– Strep. Spp.
– Bacteroides
–
Fusobacterium spp.
– Gardnerella Vaginalis
–
–
Mobiluncus
Prenotella spp.
• Gram -ve
–E. Coli
• Others
– Candida albicans
– Mycoplasma
– Ureaplasma
Biofilms
Any Questions?
Size Matters
1nm
10nm
100nm
1 µm
10 µm
100µm
1mm
Light microscope
Electron Microscope
Proteins
Viruses
Small molecules
Plant and animal cells
Bacteria
Bacteria Classification
Bacteria and Human body
• Bacteria >10x than human cells in the body
(10¹ versus 10¹³)
– Skin surface and in deep layers
– Saliva and oral mucosa
– Gastrointestinal tracts
– Genital tract
• Normal microbiota or microflora
– Beneficial to human health
– Opportunistic infections
• < 10% culturable
• Others not part of normal microbiota
– Pathogenic
– Opportunistic pathogens