1. Laboratory Training for Field Epidemiologists Antimicrobial resistance and susceptibility testing Antimicrobial resistance May 2007

2. Laboratory Training for Field Epidemiologists Learning objectives At the end of the presentation, participants should: Identify antimicrobial susceptibility testing needs Understand standard antimicrobial susceptibility testing Interpret antimicrobial susceptibility testing

3. Laboratory Training for Field Epidemiologists Leading global infectious diseases S. pneumonia: Up to 55% resistance to penicillin in some regions HIV: Report of resistance to all marketed agents S. dyentariae: 90% resistance to cotrimoxazole S.Typhi: Outbreaks of multi-resistant strains in 11 countries M. tuberculosis: Multi-drug resistant tuberculosis P. falciparum: Chloroquine resistance in 81/92 countries

4. Laboratory Training for Field Epidemiologists Antibiotic resistant infections DiseasesAgentResistances PneumoniaS pneumoniaePenicillin DysenteryS dysenteriaeMultiple resistances TyphoidS typhiMultiple resistances GonorrheaN gonorrhoeaePenicillin and tetracycline TuberculosisM tuberculosisRifampicine and INH Nosocomial infectionsS aureusMethicillin, vancomycin E speciesVancomycin Klebsiella, Pseudomonas Multiple resistances

5. Laboratory Training for Field Epidemiologists Antimicrobial resistance Results from misuse, overuse, under/ inadequate use of antimicrobials Costs money, lives and undermines effectiveness of health delivery programs Threat to global stability and national security WHO Global Strategy for Containment of Antimicrobial Resistance: Intervention framework to slow emergence and reduce the spread of antimicrobial resistant microorganisms

6. Laboratory Training for Field Epidemiologists Natural & acquired resistance Natural resistance Chromosomic genetic support Affect almost all species strains Existed before antibiotic use (Enterobacter sp. - amoxicillin) Acquired resistance (mutation) Chromosomic, plasmidic or transposon genetic support Affects a fraction of strains Increased with antibiotic use (extended spectrum beta-lactamase producing E. coli)

7. Laboratory Training for Field Epidemiologists 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)

8. Laboratory Training for Field Epidemiologists Mechanisms of resistance Prevent antibiotic from reaching its target Impaired cell membrane permeability Efflux phenomenon Prevent the antibiotic from biding to its target Supplementary targets Decreased affinity by target modification Inactivation before reaching the target

9. Laboratory Training for Field Epidemiologists Genetic exchange of antimicrobial resistance genes Enterobacteriaceae Enterococci Staphylococci Pseudomonas Campylobacter Vibrio cholerae Pneumococci Streptococci

10. Laboratory Training for Field Epidemiologists Antimicrobial susceptibility tests Minimum inhibitory concentration [MIC] The smallest concentration of antibiotic that inhibits the growth of organism Liquid media (dilution) allows MIC estimation Solid media (diffusion) Disk diffusion (Kirby-Bauer) E-tests Allows MIC estimation Beta lactamase production: quick screening method

11. Laboratory Training for Field Epidemiologists Dilution in liquid broth Tubes containing increasing antibiotic concentrations Incubation during 18 hr at 37°C Tedious 0 (Control) 0,25 0,50 1 2 4 8 mg/l MIC Bacterial growth Inhibition

12. Laboratory Training for Field Epidemiologists Kirby-Bauer disc testing Antibiotic-impregnated discs placed on an agar plate at the interface between test organism and susceptible control organism Resulting zones of inhibition compared, use of controls Susceptibility is inferred (standard tables)

13. Laboratory Training for Field EpidemiologistsE-test Plastic strips with a predefined gradient of One antibiotic One antifungal Only one manufacturer One strip per antibiotic Wide range of antibiotics Easy to use Storage at -20°C Short shelf life, expensive

14. Laboratory Training for Field Epidemiologists Reading E-tests Susceptible < 1 Resistant > 4 ug/ml Ciprofloxacin for Yersinia pestis Intermediate 1-4 ug/ml Upper reading

15. Laboratory Training for Field Epidemiologists Antimicrobial susceptibility tests Antimicrobial susceptibility testing is expensive (costs include all supplies) Kirby-Bauer 12 discs panel = $1.35 E-test (Performed only in certain situations) One strip = $2.50

16. Laboratory Training for Field Epidemiologists Different standards Use standardized reference National Committee for Clinical Laboratory Standards (USA) Other norms Canadian Chinese National Do not confuse the different tables Choose one for everything

17. Laboratory Training for Field Epidemiologists Critical points in quality assurance 1. Culture media: Muller-Hinton 2. Reagents: disks 3. Size of the inoculums 4. Incubation condition 5. Control with reference strains 6. Reading inhibition diameters (accurate measurement) 7. Knowledge of staff

18. Laboratory Training for Field Epidemiologists Standard strains for quality assurance Precision and accuracy ensured through control strains Known susceptibility to antimicrobial agents Standard strains include Staplylococcus aureus ATCC 25923 Escherichia coli ATCC 25922 Pseudomonas aeruginosa ATCC 27853

19. Laboratory Training for Field Epidemiologists 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 SusceptibleIntermediateResistant MIC <c≤ MIC < C≤ MICInterpretation

20. Laboratory Training for Field Epidemiologists Understanding breakpoints Words of laboratory specialists It is not possible to work alone Breakpoints are the expression of a consensus among the scientific community at a given time in a country Breakpoints are determined using two approaches Pharmacological concept Epidemiological concept

21. Laboratory Training for Field Epidemiologists MIC c Wild type Inherited resistance mechanism C The epidemiological concept for breakpoints

22. Laboratory Training for Field Epidemiologists The pharmacological concept for breakpoints The concentration range tested for a drug 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 In practice situations the entire range may not be used for decision making and therefore the concept of breakpoint concentration

23. Laboratory Training for Field Epidemiologists From breakpoints to interpretation Measuring antimicrobial sensitivity of a strain isolated from a patient, to determine its status as S, I or R is an individual problem Defining the status of a bacterial species or genus is an epidemiological problem distributed across time and space that requires monitoring MIC ≤ c Sensitive strain MIC > C Intermediate strain c < MIC ≤ C Resistant strain

24. Laboratory Training for Field Epidemiologists Host factors affecting treatment Diffusion in tissues Serum protein binding Drug interactions Immune system Multiple simultaneous infections Virulence of organism Site and severity of infection

25. Laboratory Training for Field Epidemiologists Interpreting intermediate resistance Sometime the agent can still be used Higher doses required to ensure efficacy Agent may be efficacious if concentrated in vivo in an infected body fluid (e.g., urine) Sometimes there is uncertainty Intermediate resistance may represent a “buffer” zone that prevents strains with borderline susceptibility from being incorrectly categorized as resistant

26. Laboratory Training for Field Epidemiologists Common interpretation problems Results depends on the technique used Many factors influence results Lack of standardization of the inoculums Thickness and quality of the culture media Quality and conservation of the disks Wuality control with standardized strains Condition and duration of incubation

27. Laboratory Training for Field Epidemiologists An agar gel that is too thick leads to smaller zones Common interpretation problems Source: http://www.who.int/csr/resources/publications/drugresist/WHO_CDS_CSR_RMD_2003_6/en/

28. Laboratory Training for Field Epidemiologists Common interpretation problems Problem with the size of the inoculums Solution: Use McFarland 0.5 photometer Scale -> same tubes

29. Laboratory Training for Field Epidemiologists Common interpretation problems Contamination with another organism

30. Laboratory Training for Field Epidemiologists Common interpretation problems Bad manipulation Inoculation of the Muller Hinton Swabbing Not by flooding

31. Laboratory Training for Field Epidemiologists Problems with E-test reading Common interpretation problems

32. Laboratory Training for Field Epidemiologists Cost of anti-microbial resistance Cheap antimicrobials become ineffective Individual treatment failure Prolonged illness, hospitalization Need to switch to more expensive, complex drugs that are often not even available in resource-poor settings Need to develop new antimicrobials Good antimicrobial susceptibility testing saves lives and money

33. Laboratory Training for Field Epidemiologists WHO Global Principles For The Containment of Antimicrobial Resistance In Animals Intended for Food Department for Communicable Diseases Surveillance and Response World Health Organization Report of a WHO Consultation with the participation of the Food and Agriulture Organization and the Office International des Epizooties Geneva, Switzerland 5 – 9 June 2000 WHO/CDS/CSR/APH/2000.4 Distr. : General English only

34. Laboratory Training for Field Epidemiologists Developed by the Department of Epidemic and Pandemic Alert and Response of the World Health Organization with assistance from: European Program for Intervention Epidemiology Training Canadian Field Epidemiology Program Thailand Ministry of Health Institut Pasteur Antimicrobial resistance

35. Laboratory Training for Field EpidemiologistsReferences Manual for the laboratory Identification and Antimicrobial Susceptibility Testing of Bacterial Pathogens of Public Health Importance in the Developing World WHO/CDS/CSR/RMD/2003.6 http://www.who.int/csr/resources/publications/drugres ist/WHO_CDS_CSR_RMD_2003_6/en/