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