📖 General Microbiology
Enzymes
General MicrobiologyEnzymes:
Serum lysozyme:
Provides innate & nonspecific immunity
Lysozyme is a hydrolytic enzyme capable of digesting bacterial cell walls containing peptidoglycan
• In the process of cell death, lysosomal NZs fxn mainly to aulolyse necrotic cells (NOT “mediate cell degradation”)
• Attacks bacterial cells by breaking the bond between NAG and NAM.
• Peptidoglycan – the rigid component of cell walls in most bacteria – not found in archaebacteria or eukaryotic cells
• Lysozyme is found in serum, tears, saliva, egg whites & phagocytic cells protecting the host nonspecifically from microorganisms
Superoxide dismutase: catalyzes the destruction of O2 free radicals protecting O2-metabolizing cells against harmful effects
Catalase:
- catalyzes the decomposition of H2O2 into H2O & O2
- Aerobic bacteria and facultative anaerobic w/ catalase are able to resist the effects of H2O2
- Anaerobic bacteria w/o catalase are sensitive to H2O2 (Peroxide), like Strep
- Anaerobic bacteria (obligate anaerobes) lack superoxide dismutase or catalase
- Staph makes catalase, where Strep does not have enough staff to make it
Coagulase
- Converts Fibronogen to fibrin
• Coagulase test is the prime criterion for classifying a bug as Staph aureus – from other Staph species
• Coagulase is important to the pathogenicity of S. aureus because it helps to establish the typical abscess lesion
• Coagulase also coats the surface w/ fibrin upon contact w/ blood, making it harder to phagocytize
Complement Fixation Test (CFT)
General MicrobiologyComplement Fixation Test (CFT)
This test is based upon two properties of the complement viz:
a. Complent combines with all antigen-antibody complexes whether or not it is required for that reaction
b. Complement is needed in immunolytic reaction.
Test system
It contains an antigen and a serum suspected to be having antibody to that antigen. The serum is heat treated prior to the test to destroy its complement. Complement Is added in measured quantity to this system. This complement is the form of guinea pig serum which is considered a rich source of complement. The test system is incubated.
Indicator system
To test system, after incubation, is added the indicator system which consists of sheep
RBCs and antibody to sheep RBCs (haemolysin) and another incubation is allowed.
If there is specific antibody in the test system, it will bind to antigen and to this complex the complement will also get fixed. Hence, no complement will be available to combine with indicator system which though contains RBCs and their specific antibody, cannot undergo haemolysis unless complement gets attached. Absence of haemolysis shall indicated positive test or presence of specific antibody in the serum which has been added in the test system. Erythrocytes lysis is obtained in negative test.
Bacteria
General MicrobiologyBacteria
A bacterial cell has a nuclear apparatus which is a loose arrangement of DNA This is surrounded cytoplasm which contains ribosomes, mesosomes and inclusion granules. The cytoplasm is enclosed within a cytoplasmic membrane. Bacterium has a rigid cell wall Fimbriae and flagella are the surface adherents. Some bacteria may have a capsule (or loose slime) around the cell wall.
Shape and Size of Bacteria
The bacteria can be spheroidal (coccus), rod or cylindrical (bacillus) and spirillar (spirochaete). Very short bacilli are called as coccobacilli Some of the bacilli may be curved or comma shaped (Vibrio cholerae).
Arrangement of Bacterial Cells
Streptococci are present in chains; staphylococci in grape-like clusters Cocci in pairs (diplococci) are suggestive of pneumococci, gonococci or menigococci.
Bacilli do not exhibit typical arrangement pattern except the Chinese letter arrangement shown by Corynebacterium diphtheriae
Surface Adherents and Appendages
CAPSULE The gels formed by the capsule adhere to the cell Capsule can be detected by negative staining ,with specific antiserum and observing the capsular swelling phenomenon called as Quellung reaction
Usually weakly antigenic Capsule production is better in vivo as compared to in vitro environment.
Eg. Capsules seen in Pneumococci, Klebsiella, Escherichia coli, Haemophilus influenzae
Flagella : provide motility to the bacterium.
Motile organisms: vibrios, pseudomonas, Esch.coli, salmonellae, spirochaetes and spirilla.
Pathogenic cocci are nomotile.
Flagella measure in length from 3 to 20 µm and in diameter from 0.01 to 0.0 13 µm.
Arrangement
Bacteria with one polar flagellum are known as monotrichous;
Tuft of several polar flagellae is known as lophotrichous
Presence of Flagellae at both the ends of organism is amphitrichous
Flagellae distributed all over the surface of the bacterium, it is called peritrichous.
• Filament is composed of a protein-flagellin. The flagellar antigen is called as H (Hauch) antigen in contrast to somatic antigen which is called as O (Ohne haunch)
PILI (fimbriae) : hair like structures help in attachment also called sex pilli, transfers genetic material through conjugation , Present in Certain Gram negative bacteria. Only Composed of protein pilin
Gram positive bacterium that has pili is Cornebacterium renale
The Cell Wall
The cell wall of bacteria is multilayered structure. The external surface of cell wall is smooth in Gram positive bacteria Gram negative bacteria have convoluted cell surfaces. The average thickness of cell wall is 0.15 to 0.50 .µm. Chemically composed of mucopeptide scaffolding formed by N acetyl glucosamine and N acetyl muramic acid
The cell wall is a three layered structure in Gram negative bacteria: outer membrane middle layer and plasma membrane. The outer membrane consists of lipoprotein and 1ipoppolysaccaride component
Functions of bacterial cell wall
Provides shape , Gives rigidity , Protection, Surface has receptor sites for phages, Site of antibody action, Provides attachment to complement, Contains components toxic to host
Cytoplasmic Structures
The Plasma Membrane: This delicate membrane separates rigid cell wall from cytoplasm. It accounts for 30% of total cell weight. Chemically, it is 60% protein, 20-30% lipids and remaining carbohydrates.
Mesosomes:
Principal sites of respiratory enzyme , Seen well in Gram positive bacteria as compared to Gram negative batcteria. Attachement of mesosomes to both DNA chromatin and membrane have been noticed thus help in cell division
Ribosomes:
sites of protein synthesis. These are composed of RNA and proteins and constitute upto 4 of total cell protein and 90% of total cellular RNA.
Cytoplasmic Granules: Glycogen : Enteric bacteria
Poly-beta & hydroxy Butyrate : Bacillus & Pseudomonas
Babes-Ernst :Corynebacterium & Yersinia pestis
Nuclear Apparatus
Bacterial DNA represents 2-3% of the cell weight and 10% of the volume of bacterium. Nucleous can be demonstrated by staining it with DNA specific Fuelgen stain .Consists of a single molecule of double stranded DNA arranged in a circular form. Bacterial chromosome is haploid and replicates by binary fission, the bacteria may have plasmid an extrachromosomal genetic material.
Types of microscopy used in bacteriology
General MicrobiologyTypes of microscopy used in bacteriology
Light microscopy
Phase contrast microscopy
Fluorescence microscopy
Darkfield microscopy
Transmission electron microscopy
Scanning electron microscopy
Fluorescent microscopy in which ultraviolet rays are used to examine cells after treatment with fluorescent days.
Phase contrast microscope enhances the refractive index differences of the cell components. This microscopy can be used to reveal details of the internal structures as well as capsules, endospores and motility
Electron microscope The resolving power is more than 200 times that of light microscope.