Questions and Answers
What is the requirement for viral growth?
Heat, cold, pH, and stabilization by salts
Viruses are obligatory ______________________ parasites that grow in living cells.
intracellular
What is the effect of radiation on viruses?
What is the purpose of embryonated eggs in virus cultivation?
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Non-ionic detergents denature proteins of the capsid.
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The type of tissue culture derived from tumor cells is known as ______________________ cell lines.
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What is the purpose of the neutralization test?
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What is the step of virus replication where the virus enters the host cell?
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What is the role of receptors in virus attachment?
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Prions are highly resistant to heat, formaldehyde, and U.V.
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What is the difference between local and systemic virus infections?
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Study Notes
Introduction to Microbiology
- Microbiology is the study of very small living organisms (microorganisms) that are viewed with the help of a microscope.
- Microorganisms include bacteria, viruses, fungi, algae, parasites, and protozoa.
Branches of Microbiology
- Medical microbiology: studies pathogens, their pathogenicity, and body defenses against microbes.
- Subdivided into medical bacteriology and medical virology.
- Food microbiology: concerned with microbes in soil, air, water, sewage, and food.
- Industrial microbiology: uses microbes to produce beer, wine, antibiotics, and vitamins.
- Sanitary microbiology: deals with processing and disposal of garbage and sewage wastes.
Milestones of Microbiology
- Robert Hooke (1665): proposed the Cell Theory.
- Anton van Leeuwenhoek (1667): described bacteria using a simple microscope.
- Louis Pasteur (1822-1895): developed the germ theory of disease, proposed aseptic techniques, and developed vaccines.
- Joseph Lister (1867): used phenol to disinfect wounds.
- Robert Koch (1876): postulated the Germ Theory, identified microbes that cause diseases, and developed microbiological media.
Eukaryotic and Prokaryotic Cells
- Eukaryotic cells: have a true nucleus and nuclear membrane.
- Prokaryotic cells: lack a true nucleus and nuclear membrane, are smaller than eukaryotic cells.
Structure of the Bacterial Cell
- Bacterial cells are small, prokaryotic, and unicellular.
- Shapes of bacteria: bacilli, cocci, and spirals.
- Bacterial cell wall: protects the cell, maintains shape, and expresses receptors.
- Gram-positive and gram-negative bacteria: differ in cell wall composition.
Bacterial Growth and Metabolism
- Bacterial reproduction: occurs through binary fission.
- Bacterial growth curve: includes lag, logarithmic, stationary, and decline phases.
- Bacterial metabolism: involves breakdown of organic compounds to produce energy.
- Catabolism: breaks down organic compounds to produce energy.
- Anabolism: uses energy to synthesize protoplasmic material.
Classification of Bacteria
- Based on phenotypic, genotypic, and medical characteristics.
- Phenotypic classification: includes shape, staining reaction, ways of respiration, arrangement, biochemical reactions, motility, presence of capsule, and spore production.
Bacterial Sporulation
- Process by which bacteria produce spores to survive unfavorable conditions.
- Steps: DNA division, separation of DNA and cytoplasm, formation of cortex and protein coat, and release of endospore.### Antigenic Structure of Bacteria
- Most bacteria are antigenic, meaning they can stimulate a host's immune response to produce antibodies.
- Antigenic determinants are the parts of the bacteria that stimulate the immune response.
Classification of Bacteria
- Bacteria can be classified according to the place of existence:
- Extracellular bacteria: live outside the host cell
- Intracellular bacteria: live inside the host cell
- Medical classification of bacteria:
- According to the mode of transmission:
- Airborne infection
- Food and waterborne infection
- Sexually transmitted infection
- Through animal bites infection
- Direct contact infection
- According to the site of pathogenesis:
- Bacteria infecting the urinary system
- Bacteria infecting the digestive system
- Bacteria infecting the nervous system
- Bacteria infecting the genital system
- Bacteria infecting the respiratory system
- Bacteria infecting the cardiovascular system
- Bacteria infecting the musculoskeletal system
- Bacteria infecting the blood and lymph
- Bacteria infecting the skin
- According to the mode of transmission:
- Genotypic classification of bacteria:
- Based on the analysis and sequencing of bacterial DNA
Virulence Factors of Bacteria
- Virulence is the degree of pathogenicity of an organism, or the ability of an organism to cause disease.
- Virulence factors are the properties or characteristics that enable a microorganism to establish itself on or within a host and enhance its potential to cause disease.
- Types of virulence factors:
- Adhesion factors:
- Flagella (fimbriae): help bacteria adhere to the host cell mucous membrane
- Pili: help bacteria adhere to the urinary tract epithelium
- Glycocalyx: increases the ability of bacteria to adhere to the teeth and mucous membrane
- Protection factors (anti-phagocytic factors):
- M-proteins: help bacteria adhere and act as anti-phagocytic function
- Capsule: protects bacteria from phagocytosis
- Protein A: protects bacteria from phagocytosis
- Invasion factors (extracellular enzymes):
- Coagulase: enables bacteria to clot plasma and persist
- Collagenase and hyaluronidase: help bacteria spread through subcutaneous tissue
- Lecithinase: breaks down lecithin
- Streptokinase: breaks down fibrin clot
- Immunoglobulin A (IgA) protease: breaks down secretory IgA
- Deoxyribonuclease: breaks down DNA
- Adhesion factors:
Bacterial Toxins
- Bacterial toxins are proteins that have a direct harmful effect on tissue cells.
- Types of toxins:
- Endotoxins: integral part of the cell wall of Gram-negative bacteria
- Examples: Escherichia coli, meningococci
- Exotoxins: protein toxins, secreted by living bacteria
- Examples: Clostridium tetani, Clostridium botulinum, salmonella, staphylococcus aureus
- Endotoxins: integral part of the cell wall of Gram-negative bacteria
Infection and Epidemiology
- Pathogen: a microorganism capable of causing disease
- Types of bacteria:
- Saprophytic bacteria: live freely in nature, in soil or water, and on decaying organic matter
- Parasitic bacteria: live in or on a living host
- Normal flora (commensals): live externally or internally on the surface of the body without causing disease
- Opportunistic bacteria: can cause disease under certain conditions
Stages of Bacterial Pathogenesis
- Transmission from an external source into the portal of entry
- Evasion of primary host defenses
- Adherence to mucous membranes
- Colonization by growth of the bacteria
- Disease symptoms caused by toxin production or invasion
- Host responses, both nonspecific and specific immunity
Carriers and Normal Flora
- Carrier: a person who harbors and transmits a pathogen without showing clinical manifestations
- Types of carriers:
- Incubatory carriers
- Convalescent carriers
- Healthy carriers
- Active carriers
- Normal flora (microbial flora):
- Resident flora
- Transient flora
- Opportunistic pathogens
- Functions of resident flora:
- Help in the synthesis of vitamins
- Help in the absorption of nutrients
- Inhibit colonization of microorganisms
- Maintain inhibitory pH in the vagina### Complications of Antibiotics
- Development of drug resistance strains due to:
- Prolonged treatment or usage of inadequate dose
- Inappropriate use of antibiotics
- Inadequate diagnosis
- Super infection due to suppression of normal flora by antibiotics
- Drug toxicity leading to:
- Deafness
- Depression
- Hypersensitivity reactions, where some drugs act as haptens, binding to tissue proteins and stimulating immune responses, leading to tissue damage
- Bone marrow depression caused by certain drugs, such as chloramphenicol
Antimicrobial Drug Resistance
- Definition: ability of microorganisms to grow in the presence of drugs that would normally kill or limit their growth
- Causes of drug resistance:
- Mutation (genetic change or chromosomal mutation)
- Gene transfer (microbes acquiring genes that code for drug resistance)
- Plasmids carrying genes that code for the production of enzymes that convert active drugs to inactive drugs
- Inappropriate use of antibiotics
- Inadequate diagnosis
- Types of multidrug resistance bacteria:
- Methicillin resistance Staphylococcus aureus (MRSA)
- Vancomycin resistance Staphylococcus aureus (VRSA)
- Vancomycin resistance Enterococci
Control of Bacterial Growth
- By sterilization and disinfection:
- Sterilization: complete destruction or elimination of all viable organisms
- Disinfection: procedures that kill most microorganisms, except endospores and viruses
- Decontamination: procedures that reduce pathogenic microorganisms to a safe level
- Antiseptics: microbicidal agents harmless enough to be applied to the skin and mucous membranes
- Examples of antiseptics:
- Alcohols
- Mercurials
- Silver nitrate
- Iodine solution
- Detergents
- Methods of sterilization:
- Sterilization by heat (physical methods)
- Sterilization by radiation:
- Ultraviolet light (UV)
- Ionizing radiation (e.g. gamma rays)
- Sterilization by filtration (mechanical methods)
- Sterilization by gaseous chemicals:
- Ethylene oxide (EO)
- Formaldehyde
- Chemical disinfectants and antiseptics:
- Tincture of iodine (2% of K iodine in ethanol) as a skin antiseptic
- Ethyl alcohol (70% concentration) as a skin antiseptic
- Hydrogen peroxide (H2O2) as an antiseptic to clean wounds
Bacterial Genetics
- Definition: study of the inheritance of different characters that are transmitted from parent to offspring
- Definition of genes: units of heredity, segments of the chromosome (DNA) that carry information for a specific character or structure
- Prokaryotic genomes:
- Bacterial genome: made of DNA, floats freely in the cytoplasm
- Chemically composed of a backbone of phosphate and sugar (deoxyribose) attached to purine and pyrimidine bases
- Genes essential for bacterial growth are carried on the chromosome
- Genes associated with specialized functions are carried on plasmids
- Replication, transcription, and translation:
- Replication: making a copy of the genetic material
- Transcription: process of transferring genetic information from DNA to RNA
- Translation: process of transferring genetic information from RNA to protein
Bacterial Variation
- Phenotypic variation: change in bacterial characters under the influence of the environment, with no genetic change
- Genotypic variation: change in bacterial characters due to changes in the genetic constitution
- Mutation: change in the sequence of bases in the DNA that occur due to:
- Substitution
- Deletion
- Insertion of new bases
- Gene transfer:
- Transformation: transfer of genetic material from one bacterium to another
- Transduction: transfer of genetic material from one bacterium to another through a bacteriophage
- Conjugation: direct transfer of genetic material from one bacterium to another
Nosocomial Infection
- Definition: infection acquired in a medical setting in the course of medical treatment
- Factors that favor nosocomial infection:
- Elderly
- Children
- Underlying illness
- Immunosuppressed patients
- Instrumentation
- Microorganisms involved in nosocomial infection:
- Staphylococcus aureus
- E. coli
- Pseudomonas
- Klebsiella
- Proteus
- Prevention measures:
- Isolation
- Handwashing and gloving
- Education of healthcare workers
- Vaccination
- Proper disposal of infectious hospital waste
Introduction to Virology
- Definition: viruses are the smallest infectious agents that can infect man, animal, insects, plants, and bacteria
- General properties of viruses:
- Small in size
- Contain one kind of nucleic acid (DNA or RNA)
- Obligate intracellular parasites
- Cannot be grown on artificial media
- Depend on the host cell's ribosomes and enzymes for protein synthesis
- Discovery of viruses:
- Dmitri I. Winooski discovered the tobacco mosaic virus (TMV) in 1892
- Virus size and structure:
- Variable in size (10nm to 500nm)
- Can pass through bacterial filters
- Require high speeds for sedimentation
- Structure consists of a protein coat (capsid) and a nucleic acid core (nucleocapsid)
Viral Genome
- Function: carries the genetic information for replication, virulence, and antigenic specificity
- Structure: linear or circular, single-stranded or double-stranded
- Segmented genome: some RNA viruses have a segmented genome, such as Rotavirus and influenza virus
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Description
Learn the basics of microbiology, including the meaning of the term and the study of very small living organisms. This introduction is part of a medical microbiology course.