NEET MDS Lessons
General Microbiology
Variant Forms of Bacteria
Prortoplast ; surface is completely devoid of cell wall component,
Spheroplast : Some residual cell wall component is present
Autoplast: protoplasts which are produced by the action of organisms’ own autolytic enzymes.
L Form: replicate as pleomorphic filtrable elements with defective or no cell wall These are designated as L forms after the Lister Institute where these were discovered by Klineberger-Nobel.
Bacterial Spores: Gram positive bacilli and actinomycetes form highly resistant and dehydrated forms which are called as endospores. The surrounding mother.cell which give rise to them is known as Sporangium. These endospores are capable of survival under adverse conditions
Structure :smooth walled and ovoid or spherical.
In bacilli, spores usually fit into the normal cell diameter except in Clostridium where these may cause a terminal bulge. (drum stick ) or central. , these look like areas of high refractilitv under light microscope.
Germination : This is the process of converting a spore into the vegetative cell. It occurs in less than 2 hours and has three stages:Activation, Germination, Outgrowth
NUTRITION OF BACTERIA
Nutrients
Chemoheterotrophs: nutrient source is organic material
Bacteria also requires a source of minerals.
Oxygen
On this basis bacteria have been divided into four groups.
Obligate Anaerobes: These grow only under conditions of high reducing intensity. These bacteria catalase peroxidase, superoxide dismutase and cytochrome systems
Clostridium and Bacteroides are important examples.
Facultalive Anaerobes. These can grow under both aerobic and anaerobic conditions and include members of family enterobacteriaceae and many other bacteria.
Obligatory Aerobes. These cannot grow unless oxygen is present in the medium. Pseudomonas belong to this group.
Microaerophillic. These organisms can grow under conditions with low oxygen tension. Clostridium tetani is an important example.
The strict anaerobes are unable to grow unless Eh is as low as 0.2 volt
Temperature
• On the basis of temperature requirements, three groups of bacteria are recognised.
• Psychrophilic : Growth in the range of —5 to 30°C with an optimum of 10-20
• Mesophillic : bacteria grow best at 20-40°C with a range of 10-45°C.
• Medically important bacteria belong to this group
• Myco. leprae is one such important example and it can grow only at reduced temperature such as footpad of mouse
• Thermophillic organisms prefer high temperature (25-80°C) for growth and yield maximum growth at 50-60°C
pH : Most pathogenic bacteria require a pH of 7.2-7.6 for their own optimal growth.
Radioimmunoassays (RIA)
It is an extremely sensitive technique in which antibody or antigen is labelled with a radioactive material. The amount of radioactive material in the antigen-antibody complex can be measured with which concentration of antigen or antibody can be assayed. After the reaction ‘free’ and ‘bound’ fractions of antigen are separated and their radioactivity-measured.
Cell Functions:
-> Autolysis
- degradative reactions in cells caused by indigenous intracellular enzymes – usually occurs after cell death
- Irreversible (along with Coagulative necrosis or infarcts) – reversible: fatty degeneration, & hydropic degeneration
-> Autolysin:
• Ab causing cellular lysis in the presence of complement
• Autolytic enzymes produced by the organism degrade the cell’s own cell wall structures
-> In the presence of cephalosporins & penicillins, growing bacterial cells lyse
• W/o functional cell wall structures, the bacterial cell bursts
-> Heterolysis: cellular degradation by enzymes derived from sources extrinsic to the cell (e.g., bacteria)
-> Necrosis: sum of intracellular degradative reactions occurring after individual cell death w/in a living organism
Neutralization Test
These are basically of two types:
• Toxin neutralization
• Virus neutralization
In toxin neutralization homologous anti-bodies prevent the biological effect of toxin as observed in vivo in experimental animals (e.g. detection of toxin of Clostridia and Corynebacterium diphthenae) or by in vitro method (e.g. Nagler’s method).
In virus neutralization test various methods are available by which identity of virus can be established as well as antibody against a virus can be estimated.
NORMAL MICROBIAL FLORA
A. Properties. Normal microbial flora describes the population of microorganisms that usually reside in the body. The microbiological flora can be defined as either
1) Resident flora - A relatively fixed population that will repopulate if disturbed,
2) Transient flora - that are derived from the local environment. These microbes usually reside in the body without invasion and can
even prevent infection by more pathogenic organisms, a phenomenon known as bacterial interference.
The flora have commensal functions such as vitamin K synthesis. However, they may cause invasive disease in immunocompromised hosts or if displaced from their normal area.
B. Location. Microbial flora differ in composition depending on their anatomical locations and microenvironments. The distribution of normal microbial flora.
Application of agglutination reactions
Agglutination reaction Example
Tube agglutination -> Widal test, Weil Felix reaction, Standard tube test for brucellosis
Slide agglutination -> Typing of pneumococci,Diagnosis of Salmonella,Diagnosis of Shigella
Agglutination Absorption test -> Salmonella diagnosis
Coagglutination -> Grouping of streptococci, Identification of gonococci, Detection of Haemophilus, Antigen in CSF
Passive agglutination
Latex agglutination Detection of HBs Ag, ASO, CRP