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Biology of Microorganisms
Presented by
فطاني. مان جي محمد احمد آصف د) عبدالعزيز ) الملك جامعة والجراحة الطب بكاالوريوس
) مانشستر ) جامعة والجزيئية الطبية الدقيقة الكائنات ماجستير) بريطانيا ) – مانشستر جامعة الطبية الدقيقة الكائنات دكتوراه
Dr Asif Jiman-Fatani, MB ChB, MSc, PhD (UK)
Assistant Professor in Medical Microbiology,Faculty of Medicine, King Abdulaziz University
Consultant MicrobiologistHead, Clinical Microbiology Laboratories
King Abdulaziz University Hospital1431 H – 2010 G
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Learning objectives At the end of the lecture you should be able to:
1. Outline the main groups of microorganisms
2. Describe their important structural features
3. Know the medically significant microorganisms
4. Discuss the structural features that are important medically and for identification
5. Discuss how the metabolism and growth of microorganisms affect their infectivity and their control
6. Describe the indigenous flora of the human body, the areas colonized and the potential for infection
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Classifying Microorganisms
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Naming Microorganisms For each organism 2 names (2 parts):
Genus الجنس noun, always capitalized -إسم Species الفصيلة أو النوع adjective, lowercase - إسم
Both italicized or underlined
First letter may be used in an abbreviated version. Staphylococcus aureus (S. aureus) Bacillus anthracis (B. anthracis) Escherichia coli (E. coli)
A common name is derived from historical use, e.g. pneumococcus for Streptococcus pneumoniae.
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Major categories of microorganism
The main groups of microorganisms are:
Bacteria √ Fungi √ Helminths Protozoa Viruses √
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(1). Bacteria
Single-celled organisms )prokaryotes بدائية ، النواة أولية)النواة
Have a cell wall Contain both DNA and RNA Have no defined nucleus. May possess surface features
such as pili )fimbriae(, flagella or capsules.
Do not have mitochondria or other organelles
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Bacteria
Staining Reactions
The Gram stain Many species can be defined
as;
1. Gram-positive, e.g. streptococci, or
2. Gram-negative, e.g. Neisseria spp.
Some organisms stain poorly with Gram stain but can be stained with other stains as mycobacteria (Ziehl-Neelsen stain).
Gram NegativeGram NegativeGram PositiveGram Positive
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Bacteria
Shape & Arrangement
Three shapes are seen:
1. Spherical (coccus) مكورة2. Straight rod (bacillus) عصوية3. Curved or spiral ملتوية
There is diversity within these groups;
For example, cocci may be arranged in:
1. Clusters )staphylococci(,
2. Chains )streptococci(, or
3. Pairs )pneumococci(.
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Bacteria
Shapes (cont.) Cocci المكورات
o Gram-positive, e.g. staphylococci, streptococcio Gram-negative, e.g. Neisseria spp.
Bacilli العصوياتo Gram-positive, e.g. clostridia - Bacillus spp.,o Gram-negative, e.g. Escherichia coli -
Pseudomonas spp.o Acid-fast, e.g. mycobacteria )Mycobacterium
tuberculosis(
Spiral or curved rods e.g. vibrios, spirochaetes
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(2). Fungi الفطريات
Fungi possess DNA and RNA, a defined nucleus and a cell wall.
There are two major types: Yeasts: Small, round,
unicellular. Moulds: grow as filaments
)hyphae( that may form mass )mycelium(.
Dimorphic fungi exist in both forms, e.g. Histoplasma.
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Fungal reproduction Asexual reproduction –
spores are formed through budding or in conidia.
Sexual reproduction – spores are formed following fusion of male & female strains.
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(3). Viruses الفيروسات
They grow inside a living cell (obligate intracellular parasites).
Composed of a nucleic acid, either DNA or RNA, and a coat of protein subunits (capsomeres).
A lipid envelope is found in some species.
Viral particles have helical, icosahedral or no regular symmetry.
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Viruses (cont.) Single-stranded DNA viruses, e.g.
parvovirues
Double-stranded DNA viruses, e.g. adenoviruses, herpesviruses, papovaviruses, poxviruses
Single-stranded RNA viruses, e.g. bunyaviruses, coronaviruses, orthomyxoviruses, paramyxoviruses, picornaviruses, retroviruses, rhabdoviruses
Double-stranded RNA viruses, e.g. neoviruses
Segmented RNA viruses, e.g. arenaviruses
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Size smaller Larger
Nucleus - +
Organelles - +
Chromosomes 1 circular Multiple, linear
Ribosomes smaller 70s Larger 80sr
Eukaryotic cellProkaryotic cell
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Morphology and Physiology of
Microorganisms
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The bacterial cell is composed of the following structure
Essential structure: Cell wall. Cytoplasmic membrane. Intracytoplasmic structures :
Nuclear apparatus. Ribosomes
Non-essential structures: Structures outside the cell
wall Capsules Flagella Fimbriae )pili(. Inclusion granulesOther non-essentials: Plasmids
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Essential structure1. Bacterial cell wall
Functions of the bacterial cell wall
Maintains the shape of bacteria. Protects the cell from bursting in hypotonic solutions. Protects the cell from mechanical disruption. Provides a barrier against toxic chemical and biological
agents. Important in determining the cell's reaction to Gram
stain. Contains antigens that stimulate the patient’s antibody
response. Plays an essential role in cell division. With the exception of mycoplasmas, all bacteria possess a cell wall
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GRAM POSITIVEGRAM POSITIVE
GRAM NEGATIVEGRAM NEGATIVE
CytoplasmCytoplasm
CytoplasmCytoplasm
Lipoteichoic acid Peptidoglycan-teichoic acid
Cytoplasmic membrane
Inner )cytoplasmic( membrane
Outer Membrane
Lipopolysaccharide
Porin
Braun lipoprotein
Peri
plas
mic
spa
ce
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Cell Wall The Gram-positive cell wall
contains:
1. Thick layer of peptidoglycan.
2. Teichoic acids.
The Gram-negative cell wall contains:
1. Peptidoglycan is much thinner
2. Lipoproteins.
3. Outer membrane protein
4. Lipopolysaccharides.
5. Periplasmic space.
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2. Cell Membrane
The cell membrane is enclosed by the cell wall Mycoplasmas lack a cell wall and have an exposed cell
membrane.
Functions of the cytoplasmic membrane It plays a role in DNA replication. It is the site of respiration.
It is a permeability barrier and contains proteins involved in selective and active transport of solutes.
Active transport of ions )H+, Na+, K+, etc …( and nutrients into the cell.
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3. Bacterial Chromosomal DNA Single, supercoiled chromosome.
There is no nuclear membrane, no nucleolus, no mitotic apparatus, and no histones
The chromosome carries the genetic information to daughter cells and it is duplicated before cell division.
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4. Ribosomes Made of 60% ribosomal RNA
& 40% protein
Consist of 2 subunits: large & small
Site of protein synthesis
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1. Capsule External to the cell wall.
Confers resistance to phagocytosis.
2. Pili (Fimbriae) Hair-like structures that protrude
from the outer surface of some bacterial species
Assist in adhesion to external surfaces.
Non-essential structures
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3. Flagella Flagella are long thin structures that
protrude from the surface of some bacteria
Organs of locomotion responsible for movement.
4. Inclusions granules Intracellular storage bodies. Examples: glycogen,, gas vesicles for
floating, sulfur and polyphosphate granules
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5. Plasmids5. Plasmids Extra-chromosomal
DNA Coding
pathogenesis and antibiotic resistance factors
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Spores األبواغ Resting, dormant cells. Withstand extremes in heat, drying,
freezing, radiation & chemicals not a means of reproduction
Produced by some G+ genera.
Have a 2-phase life cycle :1. Sporulation -formation of
endospores. It contains contains calcium calcium dipicolinatedipicolinate
2. Germination- return to vegetative growth
Pressurized steam at 120oC for 20-30 minutes will destroy.
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Bacterial Metabolism
Factors that affect the rate of growth are:1. Temperature: Most bacterial species
will grow at 37oC.2. Hydrogen ion concentration (pH):
Most pathogenic species can grow at pH 7.2 – 7.6.
3. Gaseous atmosphere: The gaseous environments used include: Aerobic: oxygen Anaerobic: lacks oxygen Microaerophilic: low oxygen Capnophilic: carbon dioxide.
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Bacterial growth Bacterial growth follows
recognisable stages.
1. Lag phase: no increase in cell number
2. Log phase: maximum increase in cell number
3. Stationary phase: no net increase in cell number as a result of substrate limitation or inhibition by metabolite accumulation
4. Death phase: decrease in cell number owing to toxic metabolites or substrate deprivation.
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Binary Fission
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The Microbial Environment
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Air Outdoor air contains bacteria, moulds and spores. Depend on the
soil type, climate and population. Indoor air contains organisms that are found in dust, droplets and
droplet.
Water Water acts as a vehicle for microorganisms that cause diseases,
such as diarrhea, dysentery, enteric fever, cholera, hepatitis, etc
Soil Soil exposure is important cases of tetanus, gas gangrene Bacteria are found in highest numbers in the layer penetrated by
plant roots.
Animals Some organisms are animal pathogens but can cause diseases
in humans )Zoonotic disease) e.g. Brucella abortus )brucellosis in humans, septic abortion in domestic animals(
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The indigenous human flora
These organisms are normally found in harmless, close association with human body surfaces.
The tissues, blood and internal body fluids of humans are normally sterile.
Under certain circumstances, they can cause infection, e.g.
Lowered host mechanisms e.g. immunosuppressed, diabetics, leukaemic patients.
Alteration of the host tissues, e.g. Viridans streptococci may cause endocarditis after tooth extraction if the host has a predisposing heart lesion.
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Skin Exposed areas are suitable for the growth of Staphylococcus
epidermidis, coryneform bacilli, micrococci and low numbers of S. aureus.
Numbers of bacteria are higher around hair shafts.
Anaerobic bacteria (e.g. Propionibacterium acnes) are only found in anaerobic conditions of the sebaceous glands.
An alteration in skin conditions that increases hydration or damages the surface (e.g. occlusion, high humidity, or chronic inflammatory conditions such as eczema and psoriasis) increases colonisation by organisms like Staphylococcus aureus.
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Respiratory tract
In the anterior nares, the species found are similar to those on the skin of the face.
Staphylococcus aureus is present in up to 25-30% of adults.
The nasopharynx contains streptococci, Non-pathogenic Neisseria spp., Streptococcus pneumoniae and Haemophilus influenzae
Few microorganisms can be found below the larynx.
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Gastrointestinal tract1. Mouth Both α-haemolytic streptococci and non-pathogenic Neisseria are
found on many surfaces. Streptococcus sanguis (important in the formation of dental caries)
is present shortly after teeth eruption. Gingival crevice support the growth of Bacteroides spp., fusiform
bacteria and actinomycetes.
2. Stomach: Low pH and pepsin prevent the growth of most bacteria.
3. Small intestine: Motility keeps low numbers of organisms.
4. Large intestine: Anaerobic bacteria: Bacteroides fragilis Facultative bacteria: Escherichia coli and Enterococcus faecalis Other species present: staphylococci, clostridia, pseudomonads
and yeasts.
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Vagina
In childhood, the organisms are aerobic bacteria such as Enterobacteriaceae, staphylococci and yeasts.
At puberty (oestrogen) encourages the growth of lactobacilli; they create a low-pH Group B β-haemolytic streptococci may be found colonising
the adult vagina.
At the menopause: Flora similar to that found before puberty, with an increase in Enterobacteriaceae.
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Acquisition of the indigenous flora
The baby’s colon is usually colonised within about 6-12 hours of birth.
If the baby is breast-fed, this is mainly with bifidobacteria, and if bottle-fed, mainly with Enterobacteriaceae.
Once an indigenous flora has been established, it is more difficult for new species to become established in the mouth or lower gastrointestinal tract.
This has been called ‘colonisation resistance’.
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Medical importance of the indigenous flora
By definition, members of the indigenous human flora are not harmful in their normal habitat.
However, under certain circumstances, they can cause infection, e.g.
Colonic flora: urinary tract infection
Skin flora: surgical wound infection
Oral flora: dental caries, infective endocarditis
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Medical importance of the indigenous flora (cont.)
The alterations in indigenous flora seen when antibiotics are used can cause adverse effects in the patient such as:
diarrhoea, colitis
selection of antibiotic resistance
secondary infection, e.g. candidiasis
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