Diagnosis of Bacterial InfectionsDiagnosis of Bacterial Infections
الرحيم الرحمن اللة بسمالرحيم الرحمن اللة بسم
Diagnosis of BacterialDiagnosis of Bacterial
TYPES OF SAMPLESTYPES OF SAMPLES
•Animal Tissues – Blood samples
•Foods of animal origin
•Meat and meat products
•Milk and milk products
•Fish and fish products
Steps in diagnostic isolation andSteps in diagnostic isolation and
identification of bacteriaidentification of bacteria
Step 1. Samples of body fluids . blood, urine,Step 1. Samples of body fluids . blood, urine,
cerebrospinal fluid, Abscess)cerebrospinal fluid, Abscess)
streaked on culture platesstreaked on culture plates
isolated colonies of bacteria appear afterisolated colonies of bacteria appear after
incubation for one to several days.incubation for one to several days.
Observation of colonies (size, texture, color, &Observation of colonies (size, texture, color, &
differentiating characteristic- e.g oxygendifferentiating characteristic- e.g oxygen
Colony CharacterColony Character
Stainining ReactionStainining Reaction
Biochemical tests and serological testsBiochemical tests and serological tests
-Commercial kits commonly used, e.g. API20-Commercial kits commonly used, e.g. API20
THE GRAM STAINTHE GRAM STAIN
A colony is dried on a slideA colony is dried on a slide
Step 1. Staining with crystal violet.Step 1. Staining with crystal violet.
Step 2. Fixation with iodine stabilizes crystalStep 2. Fixation with iodine stabilizes crystal
violet staining. All bacteria remain purple orviolet staining. All bacteria remain purple or
Step 3. Extraction with alcohol or other solvent.Step 3. Extraction with alcohol or other solvent.
Decolorizes some bacteria (Gram negative) andDecolorizes some bacteria (Gram negative) and
not others (Gram positive).not others (Gram positive).
Step 4. Counterstaining with safraninStep 4. Counterstaining with safranin
e.g. methyl red
The Gram Stain
Biochemical TestsBiochemical Tests
AerobicAerobic – required oxygen.– required oxygen.
AnaerobicAnaerobic – growing only in the absence of– growing only in the absence of
Antibiotic susceptibility testingAntibiotic susceptibility testing ––
determining the susceptibility ofdetermining the susceptibility of
microorganisms to specific antibiotics.microorganisms to specific antibiotics.
BacillusBacillus – rod-shaped bacterium– rod-shaped bacterium
CoccusCoccus – spherical bacterium– spherical bacterium
ColonyColony - defined mass of bacteria assumed to- defined mass of bacteria assumed to
assumed to have grown form a singleassumed to have grown form a single
CommunicableCommunicable – able to be transmitted– able to be transmitted
directly of indirectly from one individualdirectly of indirectly from one individual
to another.to another.
CultureCulture – growth of microorganisms in a– growth of microorganisms in a
special medium; the process of growingspecial medium; the process of growing
microorganisms in the laboratory.microorganisms in the laboratory.
DNADNA – nucleic acid found primarily in the– nucleic acid found primarily in the
nucleus of all living cells that carriesnucleus of all living cells that carries
genetic information; deoxyribonucleicgenetic information; deoxyribonucleic
Fastidious organismFastidious organism – organism that requires– organism that requires
special nutritional factors to survive.special nutritional factors to survive.
FissionFission – asexual reproduction of a– asexual reproduction of a
FormalinFormalin – solution of formaldehyde used as a– solution of formaldehyde used as a
fixative of preservative.fixative of preservative.
Gram-negativeGram-negative – designation for bacteria that– designation for bacteria that
lose the crystal violet (purple stain) andlose the crystal violet (purple stain) and
retain the safranin (red stain) in the Gramretain the safranin (red stain) in the Gram
stain procedure.stain procedure.
Gram-positiveGram-positive – designation for bacteria that– designation for bacteria that
retain the crystal violet( purple stain) in theretain the crystal violet( purple stain) in the
Gram stain procedure.Gram stain procedure.
Gram stainGram stain – differential stain used to classify– differential stain used to classify
HostHost – organism from which a parasite obtains– organism from which a parasite obtains
nutrients and in which some or part of thenutrients and in which some or part of the
parasites' life cycle is carried.parasites' life cycle is carried.
HyphaeHyphae – filaments of mold that makes up the– filaments of mold that makes up the
Media and CultureMedia and Culture
•Media: Nutrients (agar, pH indicators, proteins
and carbohydrates) used to grow organisms
outside of their natural habitats
•Culture: The propagation of microorganisms
using various media