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Bacteriology Study Notes
Bacteriology Study Notes
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Bacteriology Study Notes...
Bacteriology Study Notes
BACTERIOLOGY:
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Bacteriology is the study of bacteria. Of primary interest is medical bacteriology, which deals with the bacteria that causes disease in man. Bacteria are prokaryotic microorganisms of the kingdom Protista. They reproduce asexually.
Bacteria are classified according to their (1) disease-producing ability, (2) growth requirements, (3) morphologic characteristics, (4) colonial morphology, (5) biochemical activity, (6) toxins, and (7) Gram's stain reaction.
Disease producing ability is termed as either pathogenic or nonpathogenic. Pathogens are bacteria that cause diseases and nonpathogens are the harmless bacteria.
The four growth requirements are:
1. temperature
2. oxygen
3. nutrition
4. moisture
Temperature requirements are divided into three categories:
1. Psychrophilic --- those that reproduce best at 15 to 20 degrees Centigrade
2. Mesophilic --- those that reproduce best at 20 to 45 degrees Centigrade
3. Thermophilic --- those that reproduce best at 50 to 55 degrees Centigrade
Aerobes are those organisms that reproduce in the presence of oxygen. Obligate aerobes are those that grow only in the presence of free oxygen. Anaerobes are organisms that do not reproduce in the presence of oxygen, and obligated anaerobes are those that grow only in the absence of free oxygen and are killed if exposed to free oxygen. Facultative organisms are those that grow both in the presence of free oxygen and in an oxygen-free atmosphere. Microaerophilic organisms are those that grow only in reduced amounts of oxygen.
Autotrophic bacteria are self nourishing and heterotrophic bacteria are not self-sustaining.
Morphologic characteristics are based on three distinct shapes or categories:
1. Coccus (pl. cocci) --- spherical, appearing singly, in pairs, chains, or clusters
2. Bacillus (pl. bacilli) --- rod-shaped, appearing singly, in chains, or in palisades
3. Spirillum (pl. spirilla) --- spiral shaped, corkscrew-shaped, or comma-shaped, appearing singly only.
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COMMON BACTERIA:
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Three special structures assist in the classification of bacteria. The capsule is a gummy gelatinous, or mucoid structure surrounding certain bacteria. The spore is an inactive, resting, and resistant form produced within the organism, usually as a result of unfavorable environmental conditions. The third and final special structure is the flagellum, which is a hair like structure that provides motility.
Gram-positive reactions will stain dark blue-black and gram-negative reactions will stain deep pink or reddish.
Cocci
Gram-positive cocci stain dark blue with Gram's stain.
1. Streptococcus pneumoniae --- causes pneumonia
2. Streptoccoccus pyogenes ( Beta Streptococci Group A) --- causes strep throat
3. Staphylococcus aureus --- most common cause of boils, furuncles, impetigo, septicemia
Gram-negative cocci stain dark pink with Gram's stain.
Bacilli
Gram-positive bacilli
1. Corynebacterium diphtheria --- causes diphtheria
2. Clostridium (all are anaerobic and spore formers)
a. C. perfringens (welchii) --- causes gas gangrene
b. C. septicum --- causes gas gangrene
c. C. tetani ---causes tetanus or lockjaw
d. C. botulinum --- causes food poisoning (botulism)
Gram-negative bacilli
1. Yersinia (Pasteurella) pestis --- causes bubonic or pneumonic plague
2. Brucella abortus --- causes undulant fever (brucellosis)
3. Bordetella pertussis --- causes whooping cough
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BACTERIOLOGIC METHODS:
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Intestinal (Enteric) Gram-Negative Bacilli
Salmonella
1. S. typhi --- causes typhoid fever
2. S. paratyphi A & B ---- causes paratyphoid fever
3. S. newport (S. enteritidis) --- causes gastroenteritis
Shigella -- all of these cause bacillary dysentery (shigellosis).
1. S. dysenteriae (group A)
2. S. flexneri (group B)
3. S. boydii (group C)
4. S. sonnei (group D)
Vibrio cholerae (comma) --- causes cholera
Escherichia coli --- normally a nonpathogenic organism in the intestine, but can cause peritonitis. E. coli also been known to cause urinary tract infections and diarrhea.
SMEARS
Can be made of almost all body discharges, lesions, or sediments.
Preparation of Smear
1. Smear specimen on a glass slide, a thin and evenly spread smear is preferred.
2. Label the smear and circle material to be stained with a diamond point pen for easier identification.
3. Let smear air dry. Forced heat drying will distort bacterial cells and other materials.
4. Fix the smear by passing it through a flame (smear side up) 3 to 4 times.
5. Cool and then stain.
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SEROLOGY:
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GRAM'S STAIN
The most common and useful staining procedure used in bacteriologic work.
Hucker's Modification of Gram's Stain Solution
Crystal violet/ammonium oxalate solution (primary stain), yeast contamination is common and the stain must be filtered before use.
Principle of Gram's Stain
The crystal violet stain is the primary stain, which stains everything in the smear blue. The Gram's iodine acts as a mordant that causes the crystal violet to penetrate and adhere to the gram-positive organisms. The safranine is the counter-stain that stains everything in the smear that has been decolorized: pus cells, mucus, gram negative organisms. The gram-negative organisms will stain a much deeper pink than the pus cells and the mucus cells will stain even lighter pink.
READING AND REPORTING SMEARS
The stained smear reveals only two things: the morphology and the staining characteristics of the bacteria present. Positive identification requires cultures and further studies.
Serology consists of procedures by which antigens and reacting serum globulin antibodies may be measured qualitatively and quantitatively. Serologic tests have been devised to detect either antigens present or antibodies produced in a number of conditions. Most are based on agglutination reactions between an antigen and a specific antibody
Antigen is a substance that, when introduced, may stimulate the individual's cells to produce specific antibodies that react to this substance. The four basic characteristics of an antigen are it must be foreign to the body, it must possess a high molecular weight, it must gain entrance into the body, and it must have a high specificity to stimulate tissues to produce a defensive protein substance called antibody.
Antibodies are the specific defensive proteins produced when an antigen stimulates individual cells. They are produced by the host in response to the presence of an antigen and are capable of reacting with antigens in some detectable way.
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RAPID PLASMA REAGIN (RPR) CARD TEST FOR SYPHILIS
The RPR test is a sensitive, easily done screening test for syphilis. It is performed on unheated plasma or serum.
Principle of the Test
The RPR test is a nontreponemal testing procedure for the serologic detection of syphilis. The RPR card antigen suspension is a carbon particle cardiolipin antigen that detects reagin. When a specimen contains antibody, flocculation occurs with a coagglutination of the carbon particles of the RPR card antigen, which appear as black clumps against the white background of the plastic-coated card. Nonreactive specimens appear to have an even light-gray color.
MONOSTICON SLIDE TEST FOR INFECTIOUS MONONUCLEOSIS
The main reason for including this test is that mononucleosis imitates many diseases so well that diagnosis is confirmed only by selective serologic testing.
Principle of the Test
Absorption of serum with a suspension of a guinea pig or horse kidney antigen removes antisheep agglutinins in the serum of patients with serum diseases. Rapid slide tests for infectious mononucleosis are based on these principles. Suspensions of guinea pig kidney and beef erythrocyte stomata result in satisfactory instant absorption of antibodies and clear differentiation between infectious and noninfectious mononucleosis sera. Infectious mono antibodies may be demonstrated as early as the fourth day of illness and practically always by the twenty-first day. Positive results may continue for several months.
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nontreponemal
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flocculation
mycelia
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POTASSIUM HYDROXIDE (KOH) PREPARATION FOR IDENTIFICATION OF FUNGI
Fungi are seen in clustered round buds with thick wall accompanied by fragments of mycelia. Scrapings from the affected area of the skin are mounted in 10 percent KOH for positive laboratory diagnosis.
Place specimen on slide and add a drop of the 10% KOH. Warm gently over flame, do not boil and do not allow to dry out. Read the preparation, using a high-power objective with subdued light. Fungi in the skin and nails appear as refractile fragments of hyphae. In the hair, fungi appear as dense clouds around the hair stub or as linear rows inside the hair shaft.
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BLOOD GROUPING:
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AGGLUTINATION
The work showing that blood can be classified into four groups was done by random cross matching of the bloods of a large number of people. Two specific antigens were found on the red cells. These were called A and B. One group of red cells contained no A or B antigen and was called O. A fourth group contained both A and B antigens and was called AB.
Blood grouping is accomplished by comparing the effects of agglutination by the antibodies on the corresponding antigens within the red cells.
Rh FACTORS
The most important Rh factor is factor D. Approximately 85 percent of the population is D positive (also called Rh positive), and 15 percent is D negative (also called Rh negative).
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