Transcript a cell wall

Biology of Microorganisms
Presented by
‫ آصف احمد محمد جي مان فطاني‬.‫د‬
)‫بكاالوريوس الطب والجراحة (جامعة الملك عبدالعزيز‬
)‫ماجستير الكائنات الدقيقة الطبية والجزيئية (جامعة مانشستر‬
)‫دكتوراه الكائنات الدقيقة الطبية (جامعة مانشستر – بريطانيا‬
Dr Asif Jiman-Fatani, MB ChB, MSc, PhD (UK)
Assistant Professor in Medical Microbiology,
Faculty of Medicine, King Abdulaziz University
Consultant Microbiologist
Head, Clinical Microbiology Laboratories
King Abdulaziz University Hospital
1431 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

2
Classifying Microorganisms
3
Naming Microorganisms


For each organism 2 names (2 parts):
 Genus ‫إسم الجنس‬- noun, always capitalized
 Species ‫ إسم النوع أو الفصيلة‬- adjective, lowercase
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


1.
2.

The Gram stain
Many species can be defined
as;
Gram-positive, e.g.
streptococci, or
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 Positive
Gram Negative
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Bacteria
Shape & Arrangement

1.
2.
3.


1.
2.
3.
Three shapes are seen:
Spherical (coccus) ‫مكورة‬
Straight rod (bacillus) ‫عصوية‬
Curved or spiral ‫ملتوية‬
There is diversity within these
groups;
For example, cocci may be
arranged in:
Clusters (staphylococci),
Chains (streptococci), or
Pairs (pneumococci).
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Bacteria
Shapes (cont.)

Cocci ‫المكورات‬
oGram-positive, e.g. staphylococci, streptococci
oGram-negative, e.g. Neisseria spp.

Bacilli ‫العصويات‬
oGram-positive, e.g. clostridia - Bacillus spp.,
oGram-negative,
e.g.
Escherichia
coli
Pseudomonas spp.
oAcid-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
icosahedral or no
symmetry.
helical,
regular
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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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
r
Prokaryotic cell
Eukaryotic cell
Size
smaller
Larger
Nucleus
-
+
Organelles
-
+
Chromosomes 1 circular
Multiple, linear
Ribosomes
Larger 80s
smaller 70s
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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 granules
Other non-essentials:
 Plasmids
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Essential structure
1. 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 POSITIVE
Lipoteichoic acid
Peptidoglycan-teichoic acid
Cytoplasmic membrane
Cytoplasm
GRAM NEGATIVE
Lipopolysaccharide
Porin
Outer Membrane
Braun lipoprotein
Inner (cytoplasmic) membrane
Cytoplasm
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Cell Wall

1.
2.

1.
2.
3.
4.
5.
The Gram-positive cell wall
contains:
Thick layer of peptidoglycan.
Teichoic acids.
The Gram-negative cell wall
contains:
Peptidoglycan is much thinner
Lipoproteins.
Outer membrane protein
Lipopolysaccharides.
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
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into the cell.
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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Non-essential structures
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.
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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. 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 :
Sporulation -formation of
endospores. It contains calcium
dipicolinate
Germination- return to vegetative
growth
Pressurized steam at 120oC for
20-30 minutes will destroy.
1.
2.

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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

1.
2.
3.
4.
Bacterial growth follows
recognisable stages.
Lag phase: no increase in cell
number
Log phase: maximum increase
in cell number
Stationary phase: no net
increase in cell number as a
result of substrate limitation or
inhibition
by
metabolite
accumulation
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
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in humans (Zoonotic disease) e.g. Brucella abortus (brucellosis
in
humans, septic abortion in domestic animals)
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
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organisms like Staphylococcus aureus.
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 tract
1. 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
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and yeasts.
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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