bohomolets microbiology lecture #7
DESCRIPTION
By Ms. Kostiuk from Microbiology departmentTRANSCRIPT
Antimicrobial medicines
Principles of chemotherapyAntibiotics
Disinfection
is the process that reduces the number of potential pathogens on a material until they no longer represent a hazard.
Asepsis
asepsis refers to any practice that prevents the entry of infectious agents onto sterile tissues and thus prevent infection
Antisepsis
is the complex of procedures of growth inhibition and reproduction potential pathogenic microorganisms on skin of mucous membrane
Categories antimicrobial agents based on their appsication
Term Description Examples
Disinfec-tant
Agent that kills microorganisms on inanimate objects
Hypochlorite, formaldehyde
Antiseptic Agent that kills of prevents the growth of microorganisms on lining tissues
Soap, hydrogen peroxide, iodine, ethanol
Sanitizer A disinfectant that is used to reduce numbers of bacteria to levels judged safe by public health officials
Ethanol
Preserva-tive
Agents that prevents microbial growth: often added to products such as foods and cosmetics to prevent microbial growth
Lactic acid, benzoic acid, sodium chloride
Antibiotic Agent produced by microorganisms that inhibits or kills other microorganisms
Penicillin, tetracycline
The action of antimicrobial agents
Term Action Examples
Bactericide Agent that kills bacteria Chlorhexidine, ethanol
Biocide Agent that kills living organisms
Hypochlorite
Fungicide Agent that kills fungi Ethanol
Germicide (microbicide)
Chemical agent that specifically kills pathogenic microorganisms
Formaldehyde, silver, mercury
Sporicide Agent that kills bacterial endospores
Glutaraldehyde
Virucide Inactivates viruses so that they lose the ability to replicate
Cationic detergents
Antimicrobial agents
Disinfectants and antiseptics
Can kill or inhibit growth and development majority of microorganisms in space around patient, and microorganisms that are on human body surface
Chemotherapeutic medicines
Can kill or inhibit reproduction of agents of disease in the patient organism. Have selective influence upon microorganisms.
Classification of disinfectants based on their mode of action
Mode of action Type of disinfectant
Coagulate proteins Formaldehyde, glutaraldehyde, alcohols, dyes, mercurials, acids
Oxidize proteins Halogens: iodine, iodophors, chlorine, chlorine compoynds
Destroys cell membrane
Phenolics, quaternary ammonium compounds (surface-active agents)
Chemotherapy
is a method of therapy of infectious disease and cancer with chemical agents – chemotherapeutic medicines
Chemotherapeutic index
Maximal tolerated dose is the most quantity of drug that not cause harmful effect in a patient.
Minimal curative dose is the least dose of drug that kill of inhibit reproduction of microorganisms
Maximal tolerated dose
Minimal curative dose> 3
Paul Ehrlich’s principles of chemotherapy
Receptor interaction of drug and microorganism Changing of chemical structure of drug causes change of its activity Changing of drug structure can occur in microorganism’s cell, therapeutic effect can slacken or intensify during it Microbes can develop drug resistance to medicine The drug can be used only if its chemotherapeutic index is not less three.
Community interactions
Mutualism
Commensalism
Parasitism
Antagonism (competition)
Synergism
Predation
Antagonism (ammensalism)
Antagonism is a form interaction between organisms when one microorganisms inhibits development of others
Mechanisms of antagonism:
Competition for nutrient substrate (different spread of growth)
Excretion of acids, alcohols, ammonia by microorganisms-antagonist
Excretion antibiotics, bacteriocines by microorganisms-antagonist
Predation
Antibiotic
Chemotherapeutic preparation produced by living organisms or their synthetic analogs that can selectively inhibit disease agents or inhibit growth tumor cells in patient organism
Characteristics of successful antimicrobial drugs
Great activity against microbes Selectively toxic to the microbe but nontoxic to host cells Microbicidal rather than mocrobistatic Relatively soluble and functions even when highly diluted
in body fluids Remains potent long enough to act and is not broken down
or excreted prematurely Not subject to the debelopment of antimicrobial resistance Complements or assists the activities of the host’s
defenses Remains active despite the presence of large volumes of
organic materials It is readily delivered to the site of infection Does not disrupt the host’s health by causing allergies or
predisposing the host to other infections
Classification based on type of antibiotic action
Microbistatic (bacteriostatic, fungistatic) agents prevent the growth of microorganisms (bacteria, fungi)
Microbicidal agent (bactericide, virucide, fungicide) kills microorganisms (bacteria, viruses, fungi)
Categories based on group of organisms that produce of antibiotics
Producers Antibiotics
Bacteria Polmyxyn
Fungi Penicillin, cephalosporin
Actinomycetes Streptomycin, tetracycline
Plants Imanin, salvin,
Animals Lysocim
Classification of antibiotics based on spectrum of action
Narrow-spectrum agents are effective against a limited array of different microbial types (examples: bacitracin inhibit certain gram-
positive bacteria)Broad-spectrum agents are active against a wider range of different microbes (example – tetracycline that affect upon gram-
positive and gram-negative bacteria, rickettsias, mycoplasmas)
Primary sites of action of antimicrobic drugs
Modes of action of antimicrobial medicines
Mechanism of action Drugs Inhibition of cell wall synthesis Penicilins,
cephalosporins
Inhibition of protein synthesis Chloramphenicol, erythromycin
Inhibition of nucleic acid synthesis
Inhibition of nucleotide synthesis Sulfonamides, trimethoprim
Inhibition of DNA synthesis Quinolones
Inhibition of RNA synthesis Rifampin
Alteration of cell membrane function
Antibacterial activity Polymyxin
Antifungal activity Amphotericin B, nystatin
Types of cell wall synthesis inhibition
Inhibit polymerization of peptidoglican Penicillins Cephalosporins Carbapenems Monobactams
Inhibit the synthesis of dipeptide Cycloserine
Inhibit transport of murein components to the assembly place
Bacitracin
Block the formation of precursors subunit (muramic acid, pentapeptide, and slucosamine)
Vancomycin
Inhibition of cell wall synthesis
Mode of action of antibiotics that inhibit protein synthesis
Mode of action of antibiotics that inhibit protein synthesis Riboso-mal subunit
Mode of action Type of action
Example
30 S Blocks functioning of initiation complex and causes misreading of mRNA
Bactericidal Aminogly-cosides
30 S Blocks tRNA binding to ribosome
Bacteriostatic Tetracyc-lines
50 S Blocks peptidyltransferase Both Chloram-phenicol
50 S Blocks translocation Primarily bacteriostatic
Erythro- mycin
50 S Blocks peptide bond formation
Primarily bacteriostatic
Clindami-cin
Alteration of cell membrane function
Polymyxin
Cytoplasm
Membrane
The detergent action of polymyxin
Microbial resistance to drugs
is a possibility of microorganisms to grow and in presence of antibiotic
Specific mechanisms of drug resistance
Synthesis of enzymes that inactivate the drug (a)
Decrease in cell permeability and uptake of the drug Change in the number or affinity of the drug receptor sites
Modification of an essential metabolic pathway (b)
Types of drug resistance
Natural
Acquired Mutation
Recombination
Transferred with plasmids and transposons
Natural selection and drug resistance
Suppression and alteration of the normal microflora by antimicrobics
Method of testing for the drug susceptibility of microorganisms
Qualitative. Diffusion methods
Quantitative. Method of serial dilutions
Diffusion test for investigation of susceptibility of microorganisms to antibiotics
Tube dilution test
Minimal inhibitory dose (MID) is a lowest concentration of drug that inhibits the growth of the microorganisms.
Antiviral therapy
Virus Medication
Cytomegalovirus Ganciclovir, foscarnet
Hepatitis B or C -interferon
Herpes simplex Acyclovir, foscarnet
Human immunodeficiency
Dideoxyinosine, zidovudine
Influenza A Amantadine
Respiratory syncytial
Ribavarin
Modes of action of antiviral medicines
Medicine Mode of action
Amantadine Prevents assembly of the viral core protein
-interferon Inhibits function of viral mRNA or degrades mRNA
Foscarnet Inhibits reverse transcriptase by attaching to its phosphate receptors
Acyclovir, ribavarin, ganciclovir
Inhibit viral DNA synthesis by reacting with DNA polymerases