Disinfectant- modify proteins, interact with RNA, DNA...several of different mechanism
How do quaternary ammoniums act as antimicrobial agent?
Interact with phospholipids of cytoplasmic membrane
How do alkylating agents act as antimicrobial agents?
Disinfectant/Sterilant- Ethylene gas, formaldehyde, glutaraldehyde. Very toxic
How are antimicrobial drugs classified?
Mechanism of action
Spectrum of antimicrobial activity
What are the properties of a good antimicrobial drug?
NO side effects, must be far more toxic for bacteria than mammalian cells
Broad spectrum of activity to facilitate rapid medical intervention
Appropriate bioavailability and pharmacokinetic (must reach the site of infection)
Low cost to develop and manufacture
What is selective toxicity?
The ability to inhibit or kill a pathogen without affecting the host
What is salvarsan?
One of the first antimicrobial drugs, use to treat syphilis (treponema pallidum)
What are growth factor analogs?
Structurally similar to growth factors but do not function in the cell
Analogs similar to vitamins, amino acids, and other compounds
What are Sulfa drugs?
Discovered by Gerhard Domagk in the 1930s
Sulfanilamide is an analogue of p-aminobenzoid acid
What is isoniazid?
A growth analog effective only against Mycobacterium
Interferes wwith synthesis of mycolic acid
What are Nucleic acid base analogs?
Have been formed by the addition of bromine or fluorine
Stop DNA replication, translation
What are quinolones?
Antibacterial compounds that interfere with DNA gyrase
What are antibiotics?
Antibiotics are antimicrobial agents naturally produced by a variety of bacteria and fungi to inhibit or kill other microorganisms
Why do gram-positive and gram-negative bacteria very in their sensitivity to antibiotics?
The cell wall is a major factor
What are beta-Lactam antibiotics?
One of the most important groups of antibiotics of all time
Include penicillins, cephalosporins, and cephamycins
What are Penicillins?
Discovered by Alexander Flemin, isolated from Penicillium chrysogenum (mold)
Primarily effective against gram-positive bacteria
Some synthetic forms are effective against some gram-negative bacteria
Inhibit cell wall synthesis
What are Cephalosporins?
Produced by fungus Cephalosporium
Same mode of action as the penicillins
Commonly used to treat gonorrhea (Neisseria gonorrhea)
What are Aminoglycosides?
Kanamycin, neomycin, amikacin, streptomycin
Target 30S subunit of ribosome, cause misreading of mRNA
What is Chloramphenicol?
Bind to 23S rRNA and block peptide elongation
What are Macrolides?
Broad-spectrum antibiotic that targets the 50S subunit of ribosome, block protein synthesis
What are Tetracyclines?
Broad-spectrum inhibition of protein synthesis, bacteriostatic
Inhibits functioning of 30S ribosomal subunit, block protein synthesis
What is Daptomycin?
Also produced by Streptomyces
Used to treat gram-positive bacterial infections
Forms pores in cytoplasmic membrane
What is Platensimycin?
New structural class of antibiotic
Broad-spectrum, effective against MRSA and vancomycin-resistant enterococci
What is antimicrobial drug resistance?
The acquired ability of a microorganism to resist the effects of a chemotherapeutic agent to which it is normally sensitive
What is producer tolerance?
Lack target sites (no peptidoglycan)
Modify target sites
Lack of uptake mechanism
What is resistance mechanism?
Destroy or modify the antibiotic (beta-lactamase)
Modify the target site
Modify uptake mechanism
Efflux pumps: reduce intracellular
How does one acquire resistance?
Mutation of target sites
What is an example of a pathogen that has developed resistance to all known antimicrobial agents?
Methicillin-resistant S. Aureus (MRSA)
How can resistance be minimized?
Resistance can be minimized by using antibiotics correctly and only when needed (reduce selection)
How do antiviral drugs work?
Most antiviral drugs also target host structures, resulting in toxicity (viruses use host cell machinery)
Risk to the host may not justify the use of antiviral
What are the most successful and commonly used antivirals?
Most successful and commonly used antivirals are the nucleoside analogs (eg AZT): block reverse transcriptase and production of viral DNA (RNA viruses)
What are protease inhibitors?
Inhibit the processing of large viral proteins into individual components
What are fusion inhibitors?
Prevent viruses from successfully fusing with the host cell
Why do fungi pose special problems for chemotherapy?
Fungi pose special problems for chemotherapy because they are eukaryotic: much of the cellular machinery is the same as that of animals and humans
What are a few drugs that target unique metabolic processes not found in mammals?
Ergosterol synthesis (nystatin, fluconazole)
Cell wall synthesis (inhibitor of chitin synthesis)
What is the decimal reduction time?
The time required to reduce the population by a factor of 10.
What is the thermal death time?
Thermal death time is the time needed to kill all cells at a given temperature
What is thermal death time dependent on?
Thermal death time is dependent on the population size of the microorganism tested. Need to standardize the starting number of ells to be able to compare the sensitivity of different microorganisms
What is Minimum Lethal Concentration (MLC)?
The lowest concentration of an agent that kills a test organism
The four W’s
Hospital-acquired infections spread by:
• Wind-placement of contaminated ventilators-pneumonia
• Water-urethral catheters-UTI
• Wires-IV lines
Heat Methods of Antimicrobial Control:
The killing or removal of all viable organisms within a growth medium
Effectively limiting microbial growth
The treatment of an object to make it safe to handle
Directly targets the removal of all pathogens, not necessarily all microorganisms.
What is the most widely used method of controlling microbial growth?
Heat sterilization. High temperatures denature macromolecules.
Structural change in macromolecules.
What can survive heat
• Sealed device thqt uses steam under pressure
• Allows temps to exceed 100C.
• It is the heat that kills things, not the pressure
• Process of using precisely controlled to reduce the icrobial load in heat-sensitive liquids
• Does not kill all organisms, so it is different than sterilization.
Radiation sterilization Methods:
• Gamma rays
Mechanisms of UV Radiation:
• Sufficient energy to cause modifications and breaks in DNA
• Useful for decon of surface
• Generates thymine dimers
Abnormally chemically bonded adjacent thymine bases in DNA, caused by UV light.
Sources of Radiation Sterlization
• Cathode ray
• Radioactive Nucleotides
Ionizing Radiation Sterilization
• Electromagnetic radiation that produces ions and other reactive molecules
• Generates electrons, hydroxyl radiacals, and hydride radicals
• Some microorganisms are more resistant to radiation than others.
Uses of radiation Sterilization
Medical field and food industry.
Approved by the WHO for decon of foods susceptible to contamination:
• Depth filters (HEPA)
• Membrane filter-like a sieve
• Membrane filter- can be accomplished by syringe, pump or vacuum
• A type of membrane filter is the nucleation track (nucleopore) filter
Nuclepore® polycarbonate track-etched membranes are made from high quality polycarbonate film and have sharply defined pore sizes, high flow rates and excellent chemical and thermal resistance.
Chemical Antimicrobial Agent Classifications
• Bacteriostatic-inhibits growth of bacteria
• Bactericidal-kills bacteria
• Bacteriolytic-kills and destroys bacteria
Minimum Inhibitory Concentration (MIC)
Smallest amount of an agentneeded to inhibit growth of a microorganism.
Varies with the organism used, , inoculum size, temp, pH, etc.
Disc diffusion assay
• Antimicrobial agent added to filter paper discMIC is reached at some distance
Zone of inhibition
Area of no growth around disc
Small paper discs are added to culture tray
Chemical agents that kill or inhibit growth and are safe enough to be applied to living tissue
• Alcohol-lipid solvent and protein denaturant
• Quat disrupts phospholipid bilayer
• H202 Oxidizing agents remove electrons
• Betadine replaces hydrogen to inactivate molecules
Destroy most forms of microbial life where heat or radiation cannot be used.
Folic Acid metabolism Antibacterial drugs:
Cell Wall Synthesis Inhibitors
• Beta-lactam drugs are the most widely used
• Primarily effective against gram-positive bacteria
Protein Synthesis inhibitors
• Macrolide Antibiotics
• Erythromycin binds to 50s RNA subunit
• Tetracycline prevents tRNA binding
• Clindamycin obstructs peptide bond formation
Antimicrobial Drug Resistance Mechanisms
Role of pharmaceutical sales reps
Results in symptomology treatment instead of lab tests to determine actual bug.
Folic Acid Metabolism Inhibitors
• Folic acid (THF) is a vitamin supplement
• Humans require folic acid for synthesis of nucleic acids
• Bacteria synthesize their own folic acid
• Trimethoprim. Sulfa
• Stephens Johnson symdrome: separation of epidermis and dermis
What are Cell Wall Synthesis Inhibitors?
• Target Cell Wall Synthesis
• Lactam Ring binds to transpeptidase, which make peptide cross-links
Beta lactam from Streptomyces BACTERIA
• DNA gyrase/topoisomerase inhibitors-binds to the enzyme
• Nalidixic Acid
Splits the DNA strand….Un-super coils the build up below the helicase
Koch’s Molecular Postulates
• Used to establish the link between a particular virulence factor and the pathogenicity of that microbe.
• The phenotype or property under investigation should be associated with pathogenic members of a genus or pathogenic strains of a species
• Specific inactivation of the gene(s) associated with the suspected virulence trait should lead to a measurable loss in pathogenicity or virulence, or the genes should be isolated by molecular methods. Specific inactivation or deletion of the genes should lead to loss of function in the clone.
• Reversion or alleic replacement of the mutated gened should lead to restoration of pathogenicity, or the replacement of the modified gene(s) for its alleic counterpart in the strain of origin should lead to loss of function and loss of pathogenicity or virulence. Restoration of pathogenicity should accompany the reintroduction of the wild-type gene/s.
• To assess molecular Koch’s postulates, a system for site-specific genetic manipulation of that microbe is required.
• Genetic Transformation of Borrelia burgdorferi (Lyme disease) with coumarin-resistant gyrB
• First to genetically manipulate the microbe
• Site-directed mutations were successfully introduced using a PCR product
• A PCR product was introduced
Techniques of Genetic Manipulation
• Plasmid Transformation
• Mutagenesis (insertional, replacement)
any deviation from or interruption of the normal structure or function of any body part, organ, or system
Invasion by and multiplication of pathogenic microorganisms in a bodily part or tissue, which may produce subsequent tissue injury and progress to overt disease through a variety of cellular or toxic mechanisms.
Definition: Normal Flora
Bacteria that live in the body, many performing necessary functions
A disease causing organism
Ability of an organism to cause disease
Normal flora that causes an infection when the body’s immunity is lowered
Definition: Frank Pathogen
pathogen-organism that causes disease in the host by direct interactions with the host
the ability of the organism to invade the tissues of the host.
Definition: Lethal dose and LD50
Dose to kill; dosage that kills 50% of a population. There are variables.
Definition: Virulence Factors
the properties (i.e., gene products) that enable a microorganism to establish itself on or within a host of a particular species and enhance its potential to cause disease
Mechanisms of virulence Factors (9):
5. Spreading/invasion factors
6. Lytic toxins
7. Protein synthesis blocking toxins
8. Toxins blocking nerve function
9. Iron Acquisition
• Pili (N. gonorrhea, E. coli)
• Flagella (V. cholerae)
• Cell wall component (S. Pyogenes M-Protein)
Capsule (s. pyogenes)
Cell surface proteins
• Cell surface proteins (invasion of Y. pestis)
• Motility (flagella)
• Endotoxin is a part of cell released on lysis (LPS and septic shock)
• Exotoxin is manufactured and secreted from cell (hemolysins)
Invasion toxins (spreading factors) (5)
• Hyaluronidase (breaks hyaluronic acid, a basement membrane component)
• Streptokinase (clots)
• Proteases (a variety)
• Lecithinase (phospholipase)
• Protein pores (Staph alpha toxin, streptolysin O)
Protein synthesis blocking toxins
• Diptheria toxin, A1-B1, target is elongation factor 2
• Cholera toxin, [cAMP] increase
Toxins blocking nerve function
Clostridium tetani inhibition of glycine release
Iron acquisition ‘toxins’
Siderophores are used to steal Fe from our Lactoferrin and Transferrin
1. Which of the following extracellular enzymes produced by Group A streptococci is called "spreading factor," an enzyme important in skin and soft tissue infection?
C. M Protein
D. Deoxyribonuclease C
E. None of the above
3. All of the following statements about the M-protein of Group A Streptococci are correct EXCEPT :
A. The amino terminal portion (distal portion) is variable, accounting for over 80 distinct serotypes.
B. M proteins allow streptococci to resist phagocytosis. C. Antibodies to M protein confer type-specific immunity.
D. M protein is the major virulence factor of Group A streptococci.
E. M protein is the major constituent of the capsule of Group A streptococci.
12. Movement of DNA from one bacteria to another through a tubular bridge or pilus:
38. Specific organisms that are considered strict anaerobes include:
A. E. coli and Streptococcus pneumoniae
B. Bacteroides and Klebsiella
C. Fusobacterium and Clostridium
D. Peptostreptococcus and Nocardia
What bacteria causes 90% of ulcers?
The cell wall component of a bacterium which allows it to adhere to a cell and cause disease.
Example-Gonoccoccus either has pili or not-pili+means disease
Cell Wall components of adhesins
LTA-LipoTeichoic Acid acts as an adhesin
M-Protein(membrane protein) are antiphagocytic. Example: S. pyogenes.
General Antiphagocytic Factors
A. Capsules-are polysaccharides, the are slippery, antiopsionic and decrease phagocytosis. S. pyiogenes if capsule+ is virulent.
B. Invasion-The ability to invade and get to the target site
INVASIN is a little protein that helps to invade i.e. Y. enterococoticia
Flagella help to invade target tissues
What happens if Ampicillin is administered with gram negative septicemia?
Leads to shock and death due to cell wall synthesis inhibiition-endotoxins are released into thebloodstream.
usually a cell wall component of gram -, LPS (lipopolysaccharide)a
One big sx of bugs breakiong up is fever
Low amounts of lps leads to fever, inflammationm
hight amounts of lps leads to shock, intravascular clotting and death
are proteins produced by both gram + and gram-
Exotoxins are released by the bacteria to help dissolve nearby proteins so they can eat.
Example S. aureus has several different toxins associated with different diseases.
Some are localized such as leukocidins (kill WBC)
Some are disseminated (diptheria killls cells indiscriminately)
Invasion toxins AKA:
Hyaluronidase breaks down hyaluronic acid (part of the basement membrane)
Streptokinase breaks up clots--is a spreading factor
Clostridium spreading factors (3):
Collagenases-breks up collagen
Elastases-breaks up fibrous elastin
Proteases-breaks up protein
\Leukocidins have lecithinase (a phospholipase) that puts holes indiscrimately into cells.
RBC attacked means anemia.
S. aureus has A toxin-describe:
similar to complement (the complement cascade that makes holes in cells)
S. pyogenes has what lytic toxin?
Streptolysin O which forms a channel by binding to cholesterol in mammal membranes.
Protein Synthesis blocker toxin
A-B toxins A=activity-does the work, B is the binding molecule
Diphteria toxin how does it work? 4 steps
The A-B toxin is taken into the target cell by endocytosis
The phagosome swallows the toixn
The lysosome and phagosome work together and the acidic pH breaks up the vacualized toxin...(vacuole)
The result is that A part of AB toxin is an Elongation factor #2 which is an mRNA translation blocker
Toxins that block nerve function
Clostridium--C. tetani causes inhibition of glycine release and leads to musculr contraction
C. botuliuum inhibits ACH and results in inability to contract (rubber neck)
Stapholococcus 7 qualities
2nd most common nosocomial intection (E. coli is first)
80% of pus filled lesions are caused by S.a aureus
Opportunistic-always present on skin
Morphology-Gram+, thick cell wall
Forms in 3D clusters like grapes
Looks yellow on plate
Normal flora on the skin and nostrils
Staph infections: 5 items
Abcess small to large-pimple-boil-carbuncle, contained in a wall of fibrin beneath the skin
Wound lesions-sutures, slivers
Scalded skin syndrome-common in nurseries-Toxin exfsolitin causes skin to slough-Scaleded skin syndrome
Food poisoning-Common source is guacamole
Which two pathogens form spores?
Bacillus and Clostridium
Cholera toxin has
cAMP which is responsible for massive rice-water diarrhea of cholera