Parts of a Thin Blood Film and Blood Smear

Parts of a Thin Blood Film

• A peripheral blood film consists of three parts: Head (portion of blood film near the drop of blood), Body (main part of the blood film), and Tail (tapering end of the blood film)

Features of a Good Blood Smear

• A well-prepared smear covers about three-fourths of the slide and should show a gradual transition from thick to thin
• It should have a smooth appearance, with no holes or ridges, and a feathered edge (about 1.5 cm long) at the thin end of the smear
• When the smear is examined microscopically, the cells should be evenly distributed, with an area at the thin end of the smear where RBCs are not overlapping

Factors Affecting Blood Smear Quality

• The length and thickness of the smear are affected by the size of the drop of blood (medium size), the angle of the spreader slide (30-45 degrees), and the speed at which the smear is made

Fixing of Blood Films

• Before staining, the blood film needs to be fixed with methyl alcohol for 0.5 to 2 minutes to prevent hemolysis

Staining Blood Smears

• There are many types of blood staining, including Giemsa stain, Wright's stain, and Leishman stain

Bacterial Nutrition

Autotrophic Bacteria

• Synthesize all their food from inorganic substances (CO2 and hydrogen donor)
• Include two types: photosynthetic bacteria and chemosynthetic bacteria

Heterotrophic Bacteria

• Obtain their ready-made food from organic substances, living or dead
• Include three types: saprophytic bacteria, parasitic bacteria, and symbiotic bacteria

Oxygen Requirements

• Obligate aerobe: require O2
• Facultative aerobe: O2 not required but better growth when present
• Obligate anaerobe: O2 inhibits bacterial growth

Reaction to the Gram Stain

• Bacteria are divided into two groups according to the reaction with Gram stain
• Gram-positive bacteria: Streptococcus, Staphylococcus, Bacillus, and Clostridium
• Gram-negative bacteria: Escherichia coli, Shigella, Salmonella, etc.

Gram Stain

• Gram-positive: peptidoglycan (cell wall) = blue
• Gram-negative: lipopolysaccharide (cell wall) = red

Laboratory Diagnosis of Bacterial Disease

• It depends on clinical specimens reaching the lab
• Examples of specimens: Blood, Urine, Stool, Sputum, Vaginal swabs, Nose & ear swabs, Cerebral spinal fluid, Food & vomit

Introduction to Microbiology

• Microbiology is the study of microscopic organisms
• Microorganisms (MOs) include protozoa, algae, fungi, bacteria, and viruses
• MOs are present in vast numbers everywhere on the bodies of animals and humans, on plant surfaces, in the air, food, water, dust, soil
• MOs include normal flora, which prevents the spread and growth of fungi and harmful bacteria

Bacteria

• Bacteria (prokaryotes, together with Archaea) share many common features
• Common features: lack of a nuclear membrane, unicellularity, division by binary-fission, and generally small size
• Species can be differentiated through the comparison of several characteristics, allowing their identification and classification

Classification of Bacteria

• Depends on the shape of bacteria
• Examples:
  • Cocci (Spherical): Diplococci, Chain (Cocci), Cluster or Grape like shape
  • Bacilli: Lactobacillus.spp. (rod shaped)
  • Spiral shape: Helicobacter pylori
  • Comma shape: Vibrio cholera

Blood Smear

• A blood smear is a blood test used to look for abnormalities in blood cells
• The test focuses on the number and shape of red cells, white cells, and platelets
• Provides information on the number and shape of these cells, which can help diagnose certain blood disorders or other medical conditions

Why is a Blood Smear Done?

• To diagnose conditions that are causing unexplained jaundice, unexplained anemia, sudden weight loss, severe infection, skin rashes or cuts, bone pain
• A blood film report can provide rapidly and at low cost, useful information about a patient's condition