Tamil Nadu HSE Second Year Microbiology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Koch's postulates

Four criteria showing a microorganism causes a disease: present in all cases, isolated in pure culture, causes disease when inoculated, and re-isolated from the infected host.

Three-domain system

Classification by Carl Woese based on 16S rRNA sequences, dividing cellular life into Bacteria, Archaea, and Eukarya.

Peptidoglycan

Polymer of N-acetylglucosamine and N-acetylmuramic acid cross-linked by peptides, forming the rigid bacterial cell wall.

Lipopolysaccharide (LPS)

Outer membrane component of Gram-negative bacteria; lipid A is the endotoxin and the O-antigen is used in serotyping.

Endospore

Highly resistant dormant structure formed by Bacillus and Clostridium, containing calcium dipicolinate and a dehydrated core.

Gram stain principle

Crystal violet-iodine complex is retained by thick Gram-positive peptidoglycan; Gram-negative cells decolourize and take the safranin counterstain.

Ziehl-Neelsen stain

Acid-fast staining using hot carbol fuchsin, acid-alcohol decolourization, and methylene blue counterstain; mycobacteria appear red.

Capsule demonstration

Negative staining with India ink or Anthony's method shows the capsule as a clear halo around the cell.

Generation time

Time required for a population to double during exponential growth; in log phase N = N0 × 2^n where n is the number of generations.

Growth curve phases

Lag, log (exponential), stationary, and death phases describing population changes in a batch culture over time.

Selective vs differential media

Selective media inhibit unwanted organisms; differential media distinguish colonies by biochemical reaction such as haemolysis or lactose fermentation.

Autoclave conditions

Sterilization by moist heat at 121°C and 15 psi (103 kPa) for 15-20 minutes, effective against spores.

Minimum inhibitory concentration

Lowest concentration of an antimicrobial agent that inhibits visible growth of a microorganism in broth or agar dilution tests.

Membrane filtration

Sterilization of heat-labile liquids by passing through a 0.22 µm filter that retains bacteria.

Conjugation

Transfer of DNA through a sex pilus from an F+ donor to an F− recipient; Hfr strains transfer chromosomal DNA at high frequency.

Transduction

Bacteriophage-mediated transfer of bacterial DNA; generalized transfers any gene, specialized transfers specific genes.

Ames test

Assay using his− Salmonella to detect mutagens by reversion to histidine prototrophy.

PCR steps

Denaturation at 94-95°C, primer annealing at 50-60°C, and extension at 72°C by Taq polymerase.

Antibody classes

IgG is most abundant and crosses the placenta; IgM is the primary-response antibody; IgA is secreted; IgE mediates allergy; IgD is a B-cell receptor.

Primary vs secondary response

Primary response is slow and dominated by IgM; secondary response is rapid and dominated by high-affinity IgG from memory cells.

Hypersensitivity types

Type I IgE-mediated anaphylaxis, type II cytotoxic, type III immune complex, and type IV delayed T-cell mediated reactions.

Vaccine types

Live attenuated, killed, toxoid, subunit or conjugate, and mRNA vaccines, each with different immunogenicity and safety profiles.

Mycobacterium tuberculosis

Acid-fast bacillus stained by Ziehl-Neelsen and cultured on Lowenstein-Jensen medium; the causative agent of tuberculosis.

Vibrio cholerae

Comma-shaped Gram-negative bacillus transmitted by contaminated water, causing rice-water diarrhoea treated with oral rehydration.

HIV diagnosis

Screening by ELISA for antibodies, confirmed by Western blot or nucleic acid testing; the virus targets CD4+ T cells.

Nitrogen cycle

Fixation by Rhizobium and Azotobacter, nitrification by Nitrosomonas and Nitrobacter, and denitrification by Pseudomonas.

BOD

Biochemical oxygen demand measures oxygen consumed by microbes decomposing organic matter; high BOD indicates organic pollution.

Coliform indicator organisms

Faecal coliforms such as E. coli indicate water contamination; their density is estimated by the MPN test.

Citric acid fermentation

Industrial production using Aspergillus niger in submerged fermentation, a major organic acid product.

Food-borne pathogens

Salmonella, Staphylococcus aureus, Clostridium botulinum, Listeria monocytogenes, and E. coli O157:H7 are common causes of food poisoning.

Biosafety levels

BSL-1 low risk, BSL-2 moderate risk, BSL-3 serious risk, and BSL-4 dangerous agents, each requiring specific containment practices.

Autoclave biological indicator

Spores of Geobacillus stearothermophilus are used to verify that an autoclave cycle achieves sterilization.