Structure and function of microorganisms

why should we study microbiology? 3

• microbes cause most common dental diseases

• we need to understand infection to enable effective treatment options and preventions

• by understanding the basic processes of microbes we can develop future treatments

what common dental infections are caused by microorganisms?

caries and periodontal diseases

what is the definition of microbiology?

the biology of organisms that are too small to be seen by the naked eye

what are some examples of microbes? 4

1. • TSEs “scrapie-like” agents (Transmissable Spongiform Encephalopathies.

2. Viruses.

3. Bacteria.

4. Eukaryotic microbes: fungi and protozoa.

are protozoa eukaryotic or prokaryotic?

eukaryotic

what are TSEs?

• TSEs “scrapie-like” agents (Transmissable Spongiform Encephalopathies)

• ‘infective’ proteins

• Examples – Kuru, Scrapie, Creutzfeld-Jacob, Scrapie

• Cause sponge-like lesions in the brain - by modulating the conformation of a particular protein - normal conformation vs misfolded proteins - eg amyloid plaques - may become insoluble - causes destruction of cells - abnormally folded protein

• this may cause a further rection which causes normally folded proteins into abnormally folded proteins - infective nature

bacteria

• bacteria come in a wide variety of forms / shapes/ sizes

• they are all much smaller than a mammalian cell - some examples but BNL very small

viruses

even smaller than a bacteria - similar ratio that bacteria have with animal cells

differentiation between microbes?

which microbes are visible in a light microscope?

bacteria and eukaryotes

which microbes are capable of free growth? - can grow on their own

eukaryotes and some bacteria

ALL viruses need other cells to grow in - obligate intracellular paracites

cell division makes new cells?

both bacteria and eukaryotes

viruses don’t

which microbes are metabolically active?

bacteria and eukaryotes - viruses AREN’T (reliant on host)

which microbes have genes separated from cytoplasm via a membrane?

only eukaryotes - compartmentalisation , n/a for viruses

different genomes in different microbes

bacteria have DNA, eukaryotic have DNA and viruses have DNA/RNA

What are viruses?

1. infect bacteria, plants and animals

2. small - only “visible” in electron microscope

3. 10 to 200 nm

are they alive????

Viral structure

nucleic acid packaged in protein- nuclear capsid : icosohedral - geometic or helical

genome - DNA/RNA

nuclear capsid can be naked or enveloped (by host cell membrane/protein)

Viral replication

virus comes into contact with the animal cell

entry into the cell - recognition b/w virus and surface of the cell, triggers a fusion event + gains entry

after gaining entry, the virus will then uncoated - releases its genome into the nucleoplasm but mainly cytoplasm

uses host cells machinery to replicate its genome via RNA or DNA -

at the same time it will transcribe its genome to start producing viral proteins - nuclear capsules or immunosuppresant molecules - or shifting machinery down a different route

all proteins assemble and package new viruses - bud off cell or explodes

mechanisms of viral replication - reverse transcription

viral genome - RNA is converted to DNA

mechanisms of viral replication - integration

reverse transcribed DNA can insert itself into hosts genome

viral genome examples

all have capsids

bacterial structure

living organisms - metabolically active, reproduce , binary fission

plasmids code for a variety of things - antimicrobial resistance, virulence factors

some proteins that are produced become membrane associated proteins

bacterial cell walls

can be quite complex - gram negative bacteria

simple - gram positive bacteria

structural support

naming bacteria

• genus and species are in italics

• genus is in capitals, species in lowercase

• genus can be shortened , say original first

• plural of the genus - all lowercase and plural suffix

• named after famous microbiologists

Identification and Taxonomy

• Range of complexity: from groups of bacteria to individual isolates

• shape and size

• arrangement of growing bacteria

• Gram stain

• culture requirements - acidogenic or aciduric

• biochemical reactions

• antigenic structure

• nucleic acid technologies

typing

Shape and arrangement

arrangement - streptococci (lines) vs staphylococci (clusters)

Gram stain differentiation

gram positive has a thick peptidoglycan layer

gram negative has a space between the peptidoglycan layer and the cytoplasmic membrane - periplasmic space , thinner pdl layer

both have a glycocalyx exterior structure - slime layer or capsule like layer - support and evading immune responses

gram negative also have an outer membrane and lipoproteins that connect the two layers

gram negative bacteria has a compound called lipopolysaccride on the outer membrane - triggers septic shock - immunogenic

colony characteristics - of bacteria

• haemolysis

• surface texture

• colony morphology

• size indicator dyes

• different nutrients

haemolysis types

agar plate that contains whole blood cells

alpha, beta and gamma haemolysis - breaking down blood cells to release its components

beta haemolysis

clear zone where the bacteria has broken down the red blood cells/haemoglobin

alpha haemolysis

no clear zone but there is a greenish tinge - haemoglobin breakdown a la bile

Biochemical Tests to distinguish bacteria

• sugar fermentation profiles - gas? - acid?

• enzyme profiles eg coagulase

single test not enough - use loads of tests - metabolite profile on a structure - mass spec vs database

Antigenic structure

based on specificity of antibody-protein interactions proteins on bacterial surface unique to that bacterium

antigen is unique to species and even strain

identifying the antibodies via agglutination

mixed with red blood cells coated in antibodies - they agglutinate - large immune complex - clustering effect

Typing - defining it based on a type

• serotyping using antisera - see previous card

• phage typing using phage (bacterial viruses) that recognise surface proteins

• genetic typing using sequence properties of DNA

Genetic typing

All characteristics encoded by DNA

1. plasmid profile – Salmonella

2. sequence and RFLP - fully sequence the organism - restriction enzyme fragment polymorphism - endonuclease

3. probes - match to sequence

4. polymerase chain reaction (PCR)useful for all pathogens

plasma profiling

size separation via electrophoresis

Other analyses

• antimicrobial sensitivity

• serum antibody - ELISA plate

Prokaryotic vs Eukaryotic - general differences

• no internal membranes

• rigid cell wall

• 70s ribosomes

vs

• DNA encased in nucleus

• mitochondria - energy metabolism

• Some have no rigid cell wall

• larger than bacteria

• 80s ribosomes

Fungi and protozoa

fungi: single or multi-cellular digest food with extracellular enzymes some dimorphic such as: Candida albicans – yeast forms or hyphae

protozoa single cellular - may have chloroplast - amoeba

Fungi

Yeasts – Grow as single cells, but can be dimorphic (grow as single cells and as hyphae – e.g. Candida spp, Cryptococcus spp

Moulds – Grow as hyphae - furry (filamentous) only – e.g. Aspergillus spp, Penicillium spp, Fusarium spp

the fungal cell wall

• chitin -

• ergosterol instead of cholesterol

• glucan filaments

• mannoproteins - high degree of mannose sugars

fungal cell wall - continued

glucan layer is thickest

history of microbiology

louis pasteur - germ theory

germ theory - were alive and can cause disease but not all of them

Koch’s Postulates

• The bacteria must be present in every case of the disease.

• The bacteria must be isolated from the host with the disease and grown in pure culture.

• The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.

some nuance in later decades

Microbiology and disease

• pathogenic bacteria – cause diseass

• commensals, normal flora – harmless, “good bacteria”

• competitive exclusion bad stuff, eg Salmonella – nutrient competition – pH – immune system

• synthesis of nutrients

Commensals or opportunistic pathogens

• antibiotics overuse – Salmonella – C. difficile - disrupts microflora

• HIV

– TB

– Candida - in the gut - thrush when HIV positive

trauma – S. aureus - abrasions

opportunistic bacteria

• commensals, normal flora - “good bacteria”

Pathobionts - candida, samonella

pathogenic bacteria •opportunistic bacteria -

Host parasite relationship

disease state is complex and unstable - we can cure diseases

Host parasite relationship

cattle don’t react badly to E-coli