Framing an Appropriate Research Question 6b9b26d93da94caf993c038d9efcdedb.pdf
Medical Microbiology Laboratory (pathogenic bacteria classification)
1. Medical Microbiology Laboratory
(Pathogenic Bacteria Classification)
Hussein A. Abid
Medical Laboratory Scientist
Member at American Society of Microbiology
Chairman of Iraqi Medical Laboratory Association
Teacher at Middle Technical University
2. 2
BACTERIA
Bacteria are living organisms that are classified as
prokaryotes.
They lack membrane-enclosed nuclei and organelles,
i.e., mitochondria, Golgi complexes, endoplasmic
reticulum.
They could be classified according:
1) Morphological properties 2) Anatomical properties 3) Staining reaction
4) Environmental factors 5) Pathogenicity 6) Nutrition
7) Relationship between host and organism
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MORPHOLOGICAL PROPERTIES
Morphological properties include (cell shape, size, structure,
and arrangements).
Bacteria can be classified into six groups according to their
morphological properties:
1. True bacteria: divided into two groups cocci and bacilli
2. Actinomycetes
3. Spirochetes
4. Mycoplasmas
5. Rickettsiae
6. Chlamydia
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MORPHOLOGICAL PROPERTIES
Actinomycetes:
o These are rigid organisms like true bacteria
but they resemble fungi in that they exhibit
branching and tend to form filaments.
o They are termed such because of their
resemblance to sun rays when seen in
tissue sections.
Spirochetes:
o These are relatively longer, slender, non-
branched microorganisms of spiral shape
having several coils.
Leptospira interrogans
Actinomycetes (Nocardioforms)
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MORPHOLOGICAL PROPERTIES
Mycoplasmas:
o These bacteria lack in rigid cell wall (cell
wall lacking) and are highly pleomorphic
and of indefinite shape.
o They occur in round or oval bodies and in
interlacing filaments.
Rickettsiae and chlamydia:
o These are very small, obligate parasites, and at one time were
considered closely related to the viruses. Now, these are regarded
as bacteria.
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ANATOMICAL FEATURES
Morphological properties include
(capsule, flagella, and spores).
According to capsule
1. Capsulated (Streptococcus pneumoniae)
2. Non-capsulated (Viridans streptococci)
According to flagella
1. Flagellate (Monotrichous, Lopho-trichous,
Amphi-trichous and peritrichous)
2. Afflagellate (e.g. Shigella spp.)
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STAINING REACTIONS
Gram’s stain reaction:
1. Gram positive (+ve) bacteria: after gram staining
procedure, the bacteria appear blue to purple in color.
2. Gram negative (-ve) bacteria: after gram staining
procedure, the bacteria appear red to pink in color.
Acid-Fast stain reaction:
1. Acid-fast bacteria: after Ziehl-Neelsen staining procedure,
the bacteria will appear pink in color.
2. Non-acid-fast bacteria: Ziehl-Neelsen staining procedure,
the bacteria will appear blue in color.
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PATHOGENICITY
Pathogenic bacteria: Are able to cause disease (e.g.
Salmonella typhi).
Non-pathogenic bacteria: Do not cause a disease (e.g.
lactobacilli)
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RELATIONSHIP BETWEEN HOST
AND ORGANISM
Saprophytes: free living microbes on dead animals or
decaying things, that can be found in soil and water and play
important role in degradation of organic matter.
Parasites: that establish themselves and multiply in hosts.
Commensals: microbes that live in complete live with
harmony, but they can produce disease when host
resistance is lowered. (e.g. normal flora organism).
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NUTRITION
Autotroph: organism that produces complex organic
compounds (such as carbohydrates, fats, and proteins) from
simple substances present in its surroundings.
Heterotroph: organism that cannot produce its own food,
relying instead on the intake of nutrition from other sources
of organic carbon, mainly plant or animal matter.
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TEMPERATURE
Psychrophiles (15-20 ºC): Pseudomonas fluorescens
Mesophiles (20-40 ºC): Escherichia coli, Staphylococcus
aureus
Thermophiles (50-60 ºC)
Extremely thermophiles (as high as 250 ºC)
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pH
Acidophiles
Alkaliphiles (e.g.Vibrio spp.)
Neutralophiles, pH 6-8, majority of the medically
important bacteria grow best at neutral or slightly alkaline
media (pH 7.2-7.6).
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OXYGEN REQUIREMENTS
Aerobes: grow in ambient temperature, which contains 21%
O2 and a small amount of CO2, 0.03%
Obligate aerobes: Strictly require O2 for their growth
(Pseudomonas aeruginosa)
Microaerophilic: grow under reduced O2, 5- 10% and
increased CO2, 8-10%; (e.g. Campylobacter jejuni,
Helicobacter pylori).
Obligate anaerobes: doesn't need O2 for growth, may be
inhibited by oxygen.
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OTHER WAYS FOR CLASSIFICATION
Motility: motile/non-motile
Antibiotic sensitivity: sensitive/resistant
Fermentation: fermenter/non-fermenter