Antimicrobial susceptibility testing challenges Linda Joyce St Vincent s Hospital Melbourne
Bacteria/antimicrobials without breakpoints (B.A.W.B.S.)
Enterobacteriacae Pseudomonas aeruginosa, Acinetobacter spp, Burkholderia cepacia, Stenotrophomonas maltophilia, Other Non- Enterobacteriacae Staphylococcus spp Enterococcus spp Haemophilus influenzae and parainfluenzae Neisseria gonorrhoeae Streptococcus pneumoniae Streptococcus spp beta haemolytic group, viridans group Neisseria meningitidis Anaerobes
Abiotrophia /Granulicatella spp Aeromonas/Plesiomonas spp Bacillus spp (not B.anthracis) Campylobacter jejuni/coli Corynebacterium spp Erysipelothrix rhusiopathiae HACEK group Helicobacter pylori Lactobacillus spp Leuconostoc spp Listeria monocytogenes Moraxella catarrhalis Pasteurella spp Pediococcus spp Vibrio spp including Vibrio cholera Potential agents of bioterrorism includes Arcanobacterium, Brevibacterium, Cellulomonas,Dermacter,Leifsonia,Microbacterium, Oerksovia,Rothia and Turicella Aggregatibacter, Actinobacillus, Cardiobacterium, Eikenella, Kingella spp B.anthracis, Y.pestis, B.mallei, B.pseudomallei, F.tularensis and Brucella spp
Challenges in developing breakpoints for uncommon organisms Relatively few strains available Resistant strains may be rare No clinical trials Most clinical data from case reports Laboratory data from centres doing surveys and studies CLSI M45-A2 guidelines for breakpoints cannot be as stringent as standards for common species
Unusual urine isolates Actinobaculum schaalii (4) Actinomyces neuii (3) Actinomyces turiscensis (1) Aerococcus urinae (5) Aerococcus sanguiicola (8) Other Aerococcus spp (5) Arthrobacter spp (1)
Option 1- don t test just add a comment Aerococcus urinae is usually susceptible to a wide range of antibiotics including beta lactams Actinobaculum schaalii is usually susceptible to beta lactam antibiotics but resistant to trimethoprim and ciprofloxacin Actinomyces turicensis is usually sensitive to penicillin. Augmentin is the drug of choice.
Option 2 Provide an MIC If necessary, a dilution method is usually the most appropriate testing method Physicians should be informed of the limitations of the results and advised to interpret with caution
Examples of Bacteria/antibiotics without breakpoints Moraxella nonliquefaciens Streptococcus pneumoniae/ Ciprofloxacin Propionibacterium spp/ Vancomycin Rifampicin Enterobacteriacae/ Colistin Enterobacteriacae (not E.coli) /Fosfomycin Burkholderia cepacia/ Piperacillin Tazobactam, Tigecycline, Moxifloxacin Capnocytophaga spp Aerobic Actinomycetes including Nocardia, Gordonia, Tsukamurella and Rhodococcus Salmonella spp/ Azithromycin
Reporting 1. Discuss with clinician PK/PD breakpoints EUCAST website MIC distributions Published case studies 2. Report the MIC only
SUMMARY If there are no breakpoints, review the literature for clinical reports of MIC and treatment. Either report with comment only OR If the isolate is clinically significant and MIC specifically requested for the management of the patient, use broth micro dilution method or E tests, following documented methods and QC Report MIC only Always discuss with clinician or add a qualifying comment
Questions
PK/PD (Non-species related) breakpoints EUCAST Clinical Breakpoint Table v. 4.0, valid from 2014-01-01 These breakpoints should not be used when there are species specific breakpoints, such as values or "-" in the tables. Penicillins MIC breakpoint (mg/l) S R > PK/PD (Non-species related) breakpoints are based on the following dosages (See section 8 in Rationale Documents) Benzylpenicillin 0.25 2 The non-species related S/I and I/R breakpoints are based on 600 mg x 4 (2.4 g/day) and 2.4 g x 6 (14.4 g/day) doses respectively. Ampicillin 2 8 The non-species related breakpoints are based on doses of at least 0.5 g x 3-4 (1.5-2 g/day). Ampicillin-sulbactam 2 8 Amoxicillin 2 8 The non-species related breakpoints are based on doses of at least 0.5 g x 3-4 (1.5-2 g/day). Amoxicillin-clavulanate 2 8 Piperacillin 4 16 Breakpoints apply to piperacillin-tazobactam dosage of 4 g x 3. Piperacillin-tazobactam 4 16 Breakpoints apply to piperacillin-tazobactam dosage of 4 g x 3. Ticarcillin 8 16 Ticarcillin-clavulanate 8 16