Introduction to Microbiology (Micro-organisms)

Bacteria

Size = MICROSCOPIC

Apart from the plasmid, what seem to be the differences between the bacterial cell and a human cell?

Bacterial cells have CELL WALLSBacterial cells don’t have A NUCLEUS

Special Features

Prokaryotic - lacks a clearly differentiated NUCLEUS

Mostly UNICELLULAR

Rigid CELL WALL (protection from bursting)

Some bacteria have a Mucilaginous CAPSULE (protection)

Special Features

Some have FLAGELLA for movement

Where might pseudomonas be found?

PILI help attachment to host

Common examples of bacteria

Clostridium welchii (gas gangrene), Staphylococcus aureus, Streptococcus, Escherichia coli

Streptococcus E.Coli

Classification

Shape:

Coccus Bacillus

VibriosSpirochaetes

Patterns and Staining

Patterns:Staphylococci Streptococci

Diplococci

Staining: e.g. gram positive or gram negative

Growth Requirements: Water and Nourishment

Water is required for chemical reactions and gaseous exchange

Clinical relevance?

Most bacteria are chemotrophs (derive their energy from the oxidation of chemical compounds)

May only need glucose and a few inorganic ions or they may only grow in a living organism.

Clinical relevance?

Growth Requirements: Respiration and pH

Anaerobe - clostridium tetani - grows in the absence of oxygen deep in the body

Aerobe - pseudomonas - needs oxygen

Facultative anaerobes e.g. staph or strep - use oxygen for respiration when it is available

Clinical relevance?

pH

Most pathogenic bacteria prefer slight alkalinity

Clinical relevance?

Growth Requirements: Temperature

Some can form spores - these have very thick walls and they can survive dryness and temperature changes

(E.g. clostridium tetani can form spores)

Clinical

relevance?

Reproduction

Can be cultured in a cell-free medium

Reproduction is mainly Asexual (binary fission)May divide every 20 minutes or so

1 2 ? 8 16 ? 64 ? 256 ?

ReproductionDraw a graph plotting time against population size :

Clinical relevance?

Time

Population

20m 1hr 1.40 2.20 3hr 4hr

500

400

300

200

100

Hospital Acquired Infection

In some species ‘sex’ facilitates biological variation

Most Hospital Acquired Infection (H.A.I.) due to bacteria

LIST EXAMPLES SEEN IN CLINICAL PRACTICE

VIRUSES

Different from other micro-organisms because they consist only of

NUCLEIC ACID (either DNA

or RNA) surrounded by

a protein CAPSULE

Size Smallest infectious agents

Viruses

Possible cause of some CANCERS (oncogenic viruses)

The human papilloma virus (HPV) is a common virus.

HPV types 1, 2 and 4 are associated with the common warts.

Some HPV types can lead to abnormal changes in the cells of the cervix.

Common examples of viruses Hepatitis B, Herpes, Coryza

Classification: Type of nucleic acid (DNA or RNA)Size and shape

Viruses - Growth Requirements and Reproduction

Viruses can only reproduce inside a living cell (intracellular microbe)

Viruses have a poor rate of survival outside living cells although some remain viable in droplets and are spread via air

Viral Replication

Virus fastens to host cell

Nucleic acid injected into cell, protein capsule left on the outside

1 2

Viral Replication

New virus particles are liberated

Viral nucleic acid links up with cell’s genes and the infected host cell manufactures new viruses using the instructions contained in the viral nucleic acid.

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Most community illnesses are due to viruses

FUNGI

Structurally more complicated than bacteria and have a nucleus

Different types Candida albicans, tinea pedis (athlete’s foot)

Do you recognize the condition above?!

Classification of Fungi

Moulds (filamentous) - tinea (ringworm)

True yeastsYeast-like - candida (THRUSH)Dimorphic

Fungi

Growth Requirements

Fungi make spores that can survive drying

Problems

A fungal disease is called a MYCOSIS (superficial or deep mycoses)

Candida albicans is responsible for ‘thrush’ (this is an opportunistic infection especially after patients have received antibiotics)

Other Types of Microorganisms

Protozoa e.g.

Mycoplasms e.g.

Ricketsiae

Chlamydiae

Look up an example of the above (preferably one that you have heard of)

Helminths (worms)

E.g. Roundworm,

Threadworm,

Tapeworms

Terminology

Antiseptic Disinfectants applied to the skin or living tissue

Aseptic Method developed to prevent contamination of wounds (or other susceptible sites) by ensuring only sterile objects or fluids will make contact with these sites and that the risks of airborne contamination are minimized

Bactericidal Bacteria killers

Bacteriostatic Inhibit bacterial growth, but may not kill

Terminology

Carrier Being infected but not having any symptoms

Commensals Found in normal body flora. Benefit host by not allowing pathogens to colonize.

Cause disease if they get in to an abnormal site (e.g. E.coli causing cystitis)

Cross infection Infection acquired from other people - either patients or staff (may be

contact or airborne)

Terminology

Disinfectant Chemical compound which can destroy vegetative micro-organisms

Disinfection Treatment which achieves killing of non-sporing or vegetative micro-organisms

Endogenous Source of infection - organisms that the person carries

Exogenous Source of infection - organisms not normally present in the person, but coming from outside

Incubation Period from arrival of microbe to onset of symptoms

Opportunistic Cause disease in weak or debilitated e.g. pseudomonas

Nosocomial Hospital acquired (from another patient, staff or the environment)

Terminology

Pathogens Will cause disease (depending on host factors such as age, nutrition, immune status, genetics, drug treatment)

Resident organism Not removable by washing

Saprophytes Found in environment (soil for example). Recycle organic compounds. Do not normally cause disease

Terminology

Sepsis Presence of inflammation, pus formation etc

Sterilization Treatment which achieves the complete killing or removal of al

types of micro-organisms, including spores of tetanus and gas gangrene, which are resistant to most disinfectants

Transient organism Can be removed by appropriate hand washing

Virulent Easily able to attack host