introduction to microbiology h. gee. md, frcog hon. assoc. clinical professor university of warwick
TRANSCRIPT
Introduction to Microbiology
H. GEE. MD, FRCOG
Hon. Assoc. Clinical Professor University of Warwick
Peter Gayo MunthaliPeter Gayo MunthaliConsultant MicrobiologistConsultant Microbiologist
UHCWUHCW
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 gram-
negative 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
BacteriaDescription
• 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
Gram –ve cell wall Gram +ve cell wall
Overall structure of bacterial cell walls
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 Stain
Gram-positive Cocci in chains (Streptococci)
Gram-positive cocci in clusters (Staphylococci)
Gram-positive rods
Gram-negative cocci
Gram-negative rods
Gram-Positives Gram-negatives
Gram Stain - Importance
• First stage of identification– (Culture)
• Indicator for treatment– (Sensitivity)
Gram Stain
• +ve cocci, clustered S. Aureus (coag -ve)
• +ve cocci, paired or chains Strep.Enterococci
• +ve bacilli (large + spores) Clostridium• -ve cocci (intra-cellular) Gonorrhoea• -ve rods, coliform E. Coli/Coliforms
Pseudomonas• -ve rods Anaerobes
Haemophilus spp
Culture & Sensitivity
• Culture– Aerobic/Anaerobic– Haemolytic– Others (type of media)
• Sensitivity– Antibiotics
Enzymatic Cleavage
Identical Daughter cells
Bacterial Cell Division
Division
bacterial chromosome replicates leading to two identical chromosomes
DNA relaxation and duplication
Super coiled DNA
Duplication of the DNA
Genetic variability
Lateral gene transfer
Virulence
‘ quantitative measure of pathogenicity or the likelihood of
causing disease’
Virulence factors
1. Aid colonisation1. Adhesion proteins2. Entry into cells
2. Aid survival1. Immune avoidance eg.
antiphagocytic2. Immunosuppression
3. Damage host1. Toxins
4. Obtain nutrition from host
Attachment +/- Evade natural protectionand cleansing mechanisms
Entry into body
Local or general spreadEvade immediate local defences
Multiplication
Evasion of host defencesEvade immune and other defences forgrowth in the host to be completed
Shedding from body Leave bodyat a site and on a scale that ensuresspread to fresh host- transmission
Obligatory steps for infection
Relationship with humans
• We are sterile in utero• Shortly after birth colonised• Of 100000000 bacterial only 1000
are successful– Suggests highly evolved
MicrobiomeMicrobiome
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?
1mm100µm10 µm1 µm100nm10nm1nm
Light microscope
Electron Microscope
Plant and animal cellsBacteria
VirusesProteins
Small molecules
Size Matters
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