Antibacterial Agents & Conditions. Stijn van der Veen

Transcription

1 Antibacterial Agents & Conditions Stijn van der Veen

2 Antibacterial agents & conditions Antibacterial agents Disinfectants: Non-selective antimicrobial substances that kill a wide range of bacteria. Only applied on non-living surfaces. Antiseptics: Antimicrobial substances that are applied on living tissue to prevent infection. Antibiotics: Antibacterial substances that are applied within the body to treat or prevent a bacterial infection. Antibacterial conditions Heat: Moist or dry heat Radiation: Ultraviolet radiation, ionizing radiation

3 Sterilization To completely kill or remove all microbes by physical or chemical methods. Effective in removing endospores. Sterilants: Substances or method used to remove or kill all microbes.

4 Physical sterilants Heat Denaturing of proteins / macromolecules Moist heat: 121 C or 132 C for various time intervals Dry heat: 1 hr at 171 C, 2hr at 160 C or 16hr at 121 C Not good for heat-sensitive, toxic or volatile substances Radiation Damage to DNA / proteins / macromolecules Ultraviolet radiation: Variable exposure to ultraviolet light Ionizing radiation: Variable exposure to microwave or gamma radiation

5 Physical sterilants Filtration Physical removal Pore size μm HEPA (High-Efficiency Particular Air) filters most commonly used Unable to remove some small bacteria (Microplasma) and viruses.

6 Gas vapor sterilants Ethylene oxide Alkylation of DNA / proteins mg/l at C for 2-5hr Most common, but flammable, explosive, and carcinogenic Formaldehyde vapor Alkylation of DNA / proteins 2-5% at C Carcinogenic

7 Gas vapor sterilants Hydrogen peroxide (H 2 O 2 ) vapor Oxidation of DNA / proteins 30% at C Plasma gas Oxidation of DNA / proteins Highly ionized hydrogen peroxide (H 2 O 2 ) gas No toxic byproducts Not good for materials absorbing or reacting with H 2 O 2 Chlorine dioxide gas Oxidation of DNA / proteins Variable conditions

8 Liquid sterilants Peracetic acid Oxidation of DNA / proteins 0.2% Oxidizing agent with good activity No toxic byproducts Glutaraldehyde Alkylation / crosslinking of DNA / proteins 2% Toxic and highly irritant

9 Disinfection To kill most microbes except some highly resistant ones. Not effective in removing bacterial endospores. Used for surfaces or items that do not withstand sterilization, e.g. endoscopes, surgical instruments, etc. Disinfectant: Substance or method used to kill microbes

10 Effectiveness of disinfection Disinfection is influenced by: Nature of the item to be disinfected Number and resilience of the microbes Presence of organic material Type and concentration of disinfectant Duration and condition of exposure

11 Disinfectants Moist heat C for 30 min Glutaraldehyde Up to 2% Hydrogen peroxide 3-25% Formaldehyde 3-8% Chlorine dioxide Variable Peracetic acid Variable Chlorine compounds ppm

12 Disinfectants Alcohol Denature proteins 70-95% Phenolic compounds Denature proteins, disrupt cell membrane 0.4-5% Iodophore compounds Oxidize proteins / DNA ppm Quaternary ammonium compounds Disrupt cell membrane %

13 Antisepsis Use of chemical agents on living tissue to kill or inhibit microbes. Antiseptic agents are selected based on a combination of safety and efficiency. Antiseptic agents Alcohol 70-90% Iodophors 1-2 mg free iodine/l Chlorhexidine (disruption cell membrane) 0.5-4% Parachlormetaxylenol (disruption cell membrane) % Triclosan (disruption cell membrane) 0.3-2%

14 Antibiotics Antibacterial substances that can be used inside the host that selectively inhibit or kill bacteria without causing serious harm to the host.

15 Effectiveness antibiotics The effectiveness of antibiotics is dependent on: The required dose (should be low), i.e. concentration that exhibits antibacterial activity. The degree of selective toxicity for bacteria (should be high), i.e. selectively killing or inhibiting bacteria without causing damage to the host. Selective toxicity of antibiotics is dependent on the differences in structure and metabolism between bacteria and host cells.

16 Origin of antibiotics Natural products of microbes. Bacilli Streptomycetaceae Fungi Semisynthetic Chemically modified forms of natural antibiotics. Synthetic

17 Origin of antibiotics Antibiotics are part of microbial self protection against other microbes. Microorganisms that produce these substances have molecular mechanisms to control production and prevent self-destruction. Naturally produced antibiotics are generally products of secondary metabolic pathways.

18 Antibiotic spectrum Antibiotic spectrum is dependent on the target of the antibiotic. Broad spectrum antibiotics are effective against many types of bacteria. Narrow spectrum antibiotics are effective against one or a few types of bacteria.

19 Antibiotic activity Bacteriostatic antibiotics inhibit growth but do not kill the bacteria. These antibiotics are dependent on the host immune system to clear the infection. Bactericidal antibiotics kill the bacteria.

20 Antibiotic side effects An antibiotic side (adverse) effect is an unwanted reaction that occurs in addition to the desirable therapeutic action of the antibiotic. When used appropriately, antibiotics are relatively safe with very few side effects. Antibiotic side effects can occur and may interfere with the patient s ability to tolerate and finish the course of medication.

21 Common antibiotic side effects Diarrhea Vomiting Nausea Rash Abdominal pain Headache

22 Targets of antibiotics Cell wall biosynthesis DNA & RNA replication Protein biosynthesis Folate metabolism

23 Antibiotic resistance Discovery and use of new antibiotics have gone hand in hand with development of antibiotic resistance. Antibiotic resistance is the ability of bacteria to withstand antibiotic treatments that were originally effective for treatment of infections caused by it.

24 Superbugs Some bacteria have acquired multiple antibiotic resistance and are expected to become untreatable in the near future.

25 Rise & spread of antibiotic resistance Rise and spread of antibiotic resistance poses a serious threat to global public health. Antibiotic resistance is present in all parts of the world. New resistance mechanisms emerge and spread globally.

26 Misuse of antibiotics Development of antibiotic resistance is correlated with the misuse, overuse, or inadequate use of the respective antibiotics. In many countries, antibiotics are widely available and used / prescribed unnecessarily.

27 Antibiotic resistant infections Diseases Agent Resistances Pneumonia S. pneumoniae Penicillin Dysentery S. dysenteriae Multiple resistances Typhoid S. typhi Multiple resistances Gonorrhea N. gonorrhoeae Multiple resistances Tuberculosis M. tuberculosis Rifampicin, Isoniazid Nosocomial infections (ESKAPE) E. species Vancomycin S. aureus Methicillin, Vancomycin K. pneumoniae, A. baumannii, P. aeruginosa Multiple resistances

28 Natural & acquired resistance Natural resistance Genetic origin in the chromosome. Affect almost all strains of a species. Existed before antibiotic use. Acquired resistance Spontaneous mutations Acquirement of specific resistance genes Transformation Transduction Conjugation Affects a fraction of strains. Increases with antibiotic use.

29 Different acquired resistances Acquired to a population of strains in a given species Extremely frequent in nosocomial infections Acquired under treatment; specific strain, specific patient Relatively uncommon except for certain species (e.g., Enterobacter, Pseudomonas, Mycobacterium)

30 Mechanisms of antibiotic resistance

31 Examples of antibiotic resistance

32 Antibiotic susceptibility tests Minimum inhibitory concentration [MIC]. The smallest concentration of antibiotic that inhibits the growth of organism Liquid media (dilution) Solid media (diffusion) Disk diffusion (Kirby-Bauer) E-tests

33 Dilution in liquid broth Tubes containing increasing antibiotic concentrations Incubation during 18 hr at 37 C Tedious Bacterial growth MIC Inhibition 0 (Control) 0,25 0, mg/l

34 Kirby-Bauer disc testing Antibiotic-impregnated discs placed on an agar plate that has been inoculated with a lawn of bacteria. Diameter of resulting zones of inhibition are compared. Use of control organisms and standard tables is required.

35 E-test Plastic strips with a predefined gradient of antibiotic. Only one manufacturer One strip per antibiotic Wide range of antibiotics Easy to use Storage at -20 C Short shelf life, expensive

36 Interpretation of results The main concept is the clinical categorisation. Strains are sorted according to level of Minimal Inhibitory Concentration (MIC) versus reference breakpoints. c and C are the minor and major breakpoints. Susceptible Intermediate Resistant MIC < c MIC < C MIC

37 Breakpoints Breakpoints are the expression of a consensus among the scientific community at a given time in a country. Breakpoints are determined using two approaches Epidemiological concept Pharmacological concept

38 The epidemiological concept The highest MIC within the wild-type MIC distribution has been labeled the epidemiological cut-off (ECOFF). 60 Wild type Inherited resistance mechanism c C MIC ECOFF

39 The pharmacological concept The concentration range tested for an antibiotic and the interpretative criteria for various categories are based on extensive studies that correlate with: Serum achievable levels for each antimicrobial agent Particular resistance mechanisms Successful therapeutic outcome

40 Host factors affecting treatment Antibiotic penetration / diffusion in tissues Serum protein binding Antibiotic interactions Immune system Multiple simultaneous infections Virulence of organism Site and severity of infection

41 Factors to consider when choosing antibiotics Patient's recent antibiotic therapy Hospital flora Presence of underlying diseases Available culture data current AND past Risk for drug resistant pathogens: Receipt of antibiotics within the preceding 90 days Current hospitalization of 5 days Antibiotic resistance in the community Immunosuppressive disease and/or therapy Presence of risk factors for resistance

42 Choosing an antibiotic: Think about Location: Where did the patient become ill? Travel? Exposure? Where did the infection anatomically originate? Where in the body, has or will the infection spread to? Think about the bacteria you are treating:

43 Consider your bacteria

44 Antibiotic of first choice

45 Next lecture Pyogenic cocci (Staph&Strep)