Introduction to Microbiology , Microbes are every where , understand them so you can live with them . I hope you like this presentation my colleagues . it is useful to students and Infection control practitioners . ! Enjoy
• Microbiology is the study of micro-organisms, or microbes,
which are terms used to describe any living organism that is too
small to be seen by the naked eye.
• BACTERIA, VIRUSES, FUNGI AND PROTOZOA.
• An understanding of the ways they behave and their effects
enables the application of the principles of safe patient care.
• Only a small proportion of the micro-organisms that abound in nature
are disease-producing or ‘pathogenic’ for Humans.
• Most areas of the body have a natural flora or ‘commensal’
population of microbes.
• Commensals are harmless in the area where they normally live
but if transmitted to other parts of the body may cause infection.
• Some organisms will only cause an infection when the body’s
defense system is impaired. These are referred to as
Classification of micro-organisms
• Prokaryotic or Eukaryotic cells.
• Prokaryotic cells have a simple structure and the nuclear material is free
in the cytoplasm; they include bacteria.( Viruses)
• Eukaryotic cells have their DNA enclosed within a nuclear membrane and
a clear nucleus can be seen under the microscope. ( protozoa, fungi and
some algae )
• The shape of the bacterium is maintained by a rigid cell wall. There may
be additional layers of material and a protective coat or capsule outside
the cell wall.
• Reproduction is by binary fission, during which the cell divides, the DNA
replicates and the daughter chromosomes are drawn apart.
• microscopic organisms that range from 0.3 to 14 microns in length and therefore
need a microscope to observe them.
• classified according to three main properties: Gram stain, shape (morphology), and
• Gram staining
bacteria are small colorless organisms when seen under the microscope.
To make them more easily visible they can be stained with a dye, usually crystal
• Gram-positive organisms retain this dye following decolourization with acetone
and appear deep violet in color.
• Gram-negative organisms lose the violet stain in the decolourization process
but take up a red counterstain and appear pink.
• Staphylococcus aureus, which can cause skin infections, is a
typical Gram-positive organism.
• Escherichia coli, part of the normal flora of the bowel and a
common cause of urinary tract infection, is a typical Gram-
Bacteria are classified into four main groups by
1. Cocci – which are round
2. Bacilli – which are rod-shaped
3. Coccobacilli – which are very short rods and may
4.Spirochaetes – which are spiral.
Some bacteria require oxygen in their
environment in order to grow. These
are classified as obligate aerobes.
Others cannot tolerate the presence of
oxygen and these are classified as
obligate anaerobes. Some, facultative
anaerobes, are able to grow with or
is an important pathogen causing superficial and deep infections e.g. boils, impetigo and surgical
wound infections. It is found in approximately 20–30% of healthy individuals.
normal skin flora and rarely causes infections although it may cause opportunistic infections at
the sites of prostheses and intravascular cannula, particularly in people who are
inhabit the mucous membranes of man and animals including the mouth, upper respiratory tract
and the intestinal tract.
• Streptococcus viridans
• Streptococcus pneumoniae
• Clostridium tetani
Contamination of a wound with soil or manure.
• Clostridium perfringens
Contamination of a wound with soil or manure.
• Clostridium difficile
Present in normal feces, result in a severe bowel infection
• Corynebacterium diphtheriae : cause diphtheria.
• Listeria monocytogenes : causing food poisoning.
• It may also cause meningitis and septicaemia in neonates and in the immunosuppressed.
are found in the mucous membranes of the upper respiratory
and genital tract.
• Neisseria meningitides : is often carried in the upper respiratory
tract of healthy people but can become pathogenic and cause meningitis.
• Neisseria gonorrhoeae: transmitted by sexual intercourse and
causes urethritis and cervicitis.
Gram-negative aerobic bacilli
• Pseudomonas aeruginosa
can colonize the lower intestinal tract of hospitalized patients. Because it may cause an infection
when the host’s defense mechanisms are impaired.
Gram-negative bacilli which may inhabit the human intestine.
• Salmonellae are important intestinal pathogens causing gastroenteritis. Inadequately cooked poultry
is often the source of these organisms.
• Shigellae cause mild dysentery infections and outbreaks are common amongst children.
• Klebsiellae are non-motile Gram-negative bacilli often carried in the intestine and are capable of
causing urinary tract, chest and wound infections.
• Escherichia coli is a normal inhabitant of the human intestine. It is the most frequent cause of urinary
• Proteus and Serratia are common in the hospital environment and are capable of causing urinary
tract and wound infections.
Gram-negative anaerobic bacilli
• Bacteroides is a non- sporing Gram-negative anaerobe found in the gut.
• Bacteroides fragilis can cause abdominal and gynaecological infections.
• Fusobacteria colonizes the mouth and may cause oral infections including acute gingivitis.
• Acid-fast bacilli
Mycobacterium bovis and Mycobacterium tuberculosis both cause
human infection, the former being acquired from ingestion of infected milk.
may be aerobic or facultatively aerobic.
They lack a cell wall so have no fixed shape.
A few species cause disease, for example Mycoplasma pneumoniae.
Gram-negative anaerobic bacilli
• Rickettsia and Chlamydia
prokaryotic cells that are unable to grow outside a host cell.
fragile and not viable when removed from the host cell (with the exception of the organism that
causes Q fever) and transfer to humans often involves arthropods, such as ticks.
• Chlamydia trachomatis
sexually transmitted disease such as non-specific urethritis and pelvic inflammatory disease.
Chlamydia psittaci and Chlamydia pneumoniae can cause chest infections.
• include mushrooms, yeasts and moulds, are eukaryotic cells and are
more complex than bacteria.
1. Yeasts – round/oval cells which reproduce by budding, for example Cryptococcus neoformans.
2. Yeast-like fungi – most of these will reproduce by budding but some form filaments, e.g.
3. Filamentous fungi – these fungi grow as filaments (hyphae) which interweave into a mesh
(mycelium), e.g. ringworm
4. Dimorphic fungi – grow in two forms according to their situation: as yeasts in the body or as
mycelia in the environment or in culture, for example Blastomyces and Histoplasma.
• Protozoa may cause human disease, including
1. Plasmodium spp. (causing malaria)
2. Entamoeba histolytica (amoebic dysentery)
3. Giardia lamblia and Cryptosporidium parvum (diarrhoeal diseases)
4. Toxoplasma gondii (congenital infection)
5. Pneumocystis carinii (opportunistic lung infection).
• Obligate, intracellular parasites and differ from other micro-organisms in several important ways.
• Growing only within living cells.
• Virus particles consist of a core of nucleic acid (DNA or RNA) surrounded by a protein coat (capsid).
• Viruses are everywhere: many cause us no harm but, like bacteria, they are responsible for a wide
range of diseases. These include influenza, colds, polio, herpes, glandular fever, gastro-enteritis,
many childhood infections such as measles and chickenpox, several types of hepatitis and the
more recently discovered acquired immune deficiency syndrome (AIDS), caused by human
immunodeficiency virus (HIV).
it is very hard to me to list all names of viruses
present in nature, so I think this is the end of the
presentation , thanks for reading this terrible