Microbiology Factors Affecting Viral Survival

Characteristics of Viruses

• Viruses are inactivated by temperatures of 56-60°C for 30 minutes
• pH affects viral survival, with most viruses destroyed at pH below 5 and above 9
• Glycerol affects viruses and bacteria differently, with 50% glycerol surviving most viruses but destroying bacteria
• Bactericidal agents, such as Phenol, are not efficient as viral disinfectants, whereas oxidizing agents are most effective against viruses
• Antibiotics and chemotherapeutic agents, like Sulfonamides, penicillin, streptomycin, and tetracyclines, have little effect on viruses

Reproductive Processes

• Viral reproductive processes differ from bacterial binary fission
• Viruses contain only one kind of nucleic acid, which is covered by a protein coat

Definition of Virology

• Virology is the branch of microbiology that deals with viruses and viral diseases

Nature of Viruses

• Viruses are minute infectious agents that are not resolved in the light microscope
• They lack independent metabolism and replicate only within living host cells
• They have genetic continuity and the possibility of mutation
• They are morphologically heterogeneous, occurring as rod-shaped, spherical, or polyhedral forms
• Viruses are composed of a nucleic acid (the nucleoid), DNA or RNA (but not both), and a protein shell or capsid
• The protein shell contains and protects the nucleic acid
• Viruses are classified according to host specificity, origin, mode of transmission, or the manifestation they produce

Viral Structure

• The individual particle or virion consists of nucleic acid and a protein shell or capsid
• Capsid: a symmetric protein shell that encloses the nucleic acid genome
• Nucleocapsid: the capsid together with enclosed nucleic acid
• A virion lacks certain components essential for its replication and must depend on the host cell for these missing factors
• One component missing from all viruses is an ATP-generating system

Microscopy

• Although most viruses cannot be seen by ordinary microscopic methods, the light microscope has some important applications in virology
• Large viruses of the pox group can be demonstrated by staining procedures
• The fluorescent antibody technique is valuable for demonstrating viral antigens in tissues
• Electron microscopy has brought even the smallest viruses into visible range and is capable of resolving particles with diameters of less than 1 nm

Chemical Composition of Viruses

• Viral Protein: serves to protect the viral genome, participate in attachment to susceptible cells, and determines the antigenic characteristics of the virus
• Virus structural proteins may be very specialized molecules designed to perform specific tasks
• Viral Nucleic Acid: contains a single kind of nucleic acid, either DNA or RNA, that encodes the genetic information necessary for the replication of the virus
• Viral Lipids: some viruses contain lipids as part of their structure

Virus Families

• Poxviridae Family: relatively large, brick-shaped or ovoid viruses containing a double-stranded DNA genome and protein, enveloped by double membranes
• Picornaviridae Family: small, ether-resistant viruses that contain single-stranded RNA
• Reoviridae Family: ether-resistant viruses that contain double-stranded RNA

This quiz assesses your understanding of the factors that affect the survival of viruses, including heat, pH, glycerol, and various disinfectants. Test your knowledge of microbiology and virology concepts.