Systems and methods for performing antimicrobial susceptibility testing
Phenotypic antimicrobial susceptibility testing (AST), the gold-standard diagnostic that indicates whether an antimicrobial will be clinically effective, often suffer the slowest times-to-result for the most resistant pathogens. Here we introduce novel assays to be performed in parallel with standard AST assays that provide additional resistance information and enable rapid, same-shift reporting of AST results for a plurality of pathogens.
1. A method for determining a qualitative susceptibility result of an antimicrobial for a microorganism-comprising sample, the method comprising:
inoculating a plurality of panels comprising a plurality of reservoirs comprising one or more dilution series reservoirs, one or more high microorganism load reservoirs (HMLRs), and one or more control reservoirs, wherein
a microorganism is present at a first concentration C m0 in the one or more dilution series reservoirs comprising an antimicrobial A that extends from a low concentration of antimicrobial (C AL ) that is at or below a susceptible breakpoint to a high concentration of antimicrobial (C AH ) that is at or above a resistant breakpoint;
the microorganism is present at a second concentration≥2×C m0 in the one or more HMLRs comprising the antimicrobial A at a third concentration≥C AL /4; and
the microorganism is not present in one or more control reservoirs comprising the antimicrobial A;
incubating the plurality of panels under conditions promoting microorganism growth;
measuring a relative growth in the one or more dilutions series reservoirs, the one or more HMLRs, and the one or more control reservoirs; and
determining a qualitative susceptibility interpretations from the relative growth measurements.
2. The method of claim 1 , wherein growth in the reservoirs is determined following addition of a metabolic viability probe comprising resazurin and methylene blue, ferrous and ferric potassium salts, or 1-methoxy-5-methlyphenasinum methyl sulfate.
3. The method of claim 2 , wherein growth in the reservoirs is determined by time-resolved fluorescence or time-gated luminescence.
4. The method of claim 2 , wherein growth in the reservoirs is determined following the addition of a probe capable of binding microbial surfaces.
5. The method of claim 1 , wherein the first concentration C m0 is between 1×10 5 and 5×10 6 CFU/mL.
6. The method of claim 1 , wherein the step of determining the qualitative susceptibility interpretations comprises a viability assay where a probe is added following a growth threshold being achieved and a surface area assay following the viability assay, wherein the surface area assay comprises:
incubating a liquid suspension of the microorganism in the presence of the antimicrobial A under conditions that promote growth of the microorganism;
adding a signaling agent configured to bind to a surface of the microorganism;
separating the microorganism bound by the signaling agent from unbound signaling agent; and
measuring one or more signal levels associated with the microorganism as compared to one or more controls, thereby measuring the antimicrobial susceptibility of the microorganism;
wherein the signaling agent comprises a linker group L, and an amplifier group comprising an Europium coordination complex; and wherein,
the linker group L forms a covalent bond to the amplifier group; or
the linker group L forms one or more non-covalent interactions with the amplifier group.
7. The method of claim 1 , wherein the one or more HMLRs comprise the antimicrobial A at a fourth concentration≥C AL .
8. The method of claim 1 , wherein the one or more HMLRs comprise a fourth microorganism concentration≥3×C m0 , ≥4×C m0 , ≥5×C m0 , ≥6×C m0 , ≥7×C m0 , ≥8×C m0 , ≥9×C m0 , ≥10×C m0 , ≥11×C m0 , ≥12×C m0 , ≥13×C m0 , ≥14×C m0 , ≥15×C m0 , ≥16×C m0 , ≥17×C m0 , ≥18×C m0 , ≥19×C m0 , ≥20×C m0 .
9. The method of claim 1 , wherein the antimicrobial A is one or more of, but not limited to, the following: Amikacin, Amikacin-fosfomycin, Amoxicillin, Amoxicillin-clavulanate, Ampicillin, Ampicillin-sulbactam, Azithromycin, Azlocillin, Aztreonam, Aztreonam-avibactam, Besifloxacin, Biapenem, Cadazolid, Carbenicillin, Cefaclor, Cefamandole, Cefazolin, Cefdinir, Cefditoren, Cefepime, Cefepime-tazobactam, Cefetamet, Cefixime, Cefmetazole, Cefonicid, Cefoperazone, Cefotaxime, Cefotetan, Cefoxitin, Ceftolozane-tazobactam, Cefpodoxime, Cefprozil, Ceftaroline, Ceftaroline-avibactam, Ceftazidime, Ceftazidime-avibactam, Ceftazidime-avibactam, Ceftibuten, Ceftizoxime, Ceftobiprole, Ceftolozane-tazobactam, Ceftriaxone, Cefuroxime, Cephalothin, Chloramphenicol, Cinoxacin, Ciprofloxacin, Clarithromycin, Clinafloxacin, Clindamycin, Colistin, Dalbavancin, Daptomycin, Delafloxacin, Dirithromycin, Doripenem, Doxycycline, Enoxacin, Eravacycline, Ertapenem, Erythromycin, Faropenem, Fidaxomicin, Finafloxacin, Fleroxacin, Fosfomycin, Fusidic acid, Garenoxacin, Gatifloxacin, Gemifloxacin, Gentamicin, Gepotidacin, Grepafloxacin, Iclaprim, Imipenem, Imipenem-relebactam, Kanamycin, Lefamulin, Levofloxacin, Levonadifloxacin, Linezolid, Linopristin-flopristin, Lomefloxacin, Loracarbef, Mecillinam, Meropenem, Methicillin, Mezlocillin, Minocycline, Moxalactam, Moxifloxacin, Nafcillin, Nalidixic acid, Netilmicin, Nitrofurantoin, Norfloxacin, Ofloxacin, Omadacycline, Oritavancin, Oxacillin, Penicillin, Piperacillin, Piperacillin-tazobactam, Plazomicin, Polymyxin B, Quinupristin-dalfopristin, Razupenem, Rifampin, Solithromycin, Sparfloxacin, Sulfisoxazole, Sulopenem, Tedizolid, Teicoplanin, Televancin, Telithromycin, Tetracycline, Ticarcillin, Ticarcillin-clavulanate, Tigecycline, Tobramycin, Trimethoprim, Trimethoprim-sulfamethoxazole, Trospectomycin, Vancomycin, Aculeacin A, Amphotericin B, Caspofungin, Clotrimazole, Fluconazole, Flucytosine, 5-Fluorocytosine, Griseofulvin, Itraconazole, Ketoconazole, Nystatin, Sordarin, Terbinafine, Voriconazole and a salt or hydrate form thereof.
10. The method of claim 1 , wherein the method further comprises performing one or more first checkpoint assays to determine if microorganism growth has achieved a threshold value; and
(a) if the threshold value is achieved, performing at least one secondary assay to measure a relative growth in the dilution series reservoirs and the one or more HMLRs, and based upon said measuring of the relative growth, determining the qualitative susceptibility result (QSR) and obtaining a minimum inhibitory concentration (MIC); or
(b) if the threshold value is not achieved, performing one or more additional incubation periods under conditions promoting microorganism growth until
(i) the threshold value is achieved, and thereafter performing step (a); or
(ii) a maximum of 18 hours has transpired without the threshold value being achieved and no further assays are performed.
11. The method of claim 10 , wherein the at least one of the one or more first checkpoint assays and the secondary assay is selected from the group consisting of: a metabolic probe assay, a surface-binding probe assay, a chemical probe assay, a biochemical probe assay, an enzymatic biochemical probe assay, an ATP assay, a nucleic acid probe assay, a double-stranded nucleic acid probe assay, an optical density assay, a visual assay, and a pH molecular probe assay, wherein the metabolic probe comprises 7-hydroxy-10-oxidophenoxazin-10-ium-3-one (resazurin).
12. The method of claim 10 , wherein at least one well of the plurality of panels is a second checkpoint assay well comprising a growth indicator during the initial incubation period or the additional incubation period, wherein the growth indicator comprises resazurin.
13. The method of claim 1 , wherein the dilution series comprises at least three reservoirs comprising different antimicrobial concentrations.
14. A method for determining a qualitative susceptibility result of an antimicrobial for a microorganism-comprising sample, the method comprising:
inoculating a plurality of panels comprising a first plurality of reservoirs comprising one or more dilution series reservoirs, one or more high microorganism load reservoirs (HMLRs), and one or more control reservoirs, wherein
a microorganism is present at first concentration C m0 in the dilution series reservoirs of an antimicrobial A that extends from a low concentration of antimicrobial (C AL ) that is at or below a susceptible breakpoint to a high concentration of antimicrobial (C AH ) that is at or above a resistant breakpoint;
the microorganism is present at a second concentration≥2×C m0 in one or more HMLRs comprising antimicrobial A at a third concentration≥C AL /4; and
the microorganism is not present in the one or more control reservoirs comprising the antimicrobial A;
incubating the plurality of panels under conditions promoting microorganism growth;
measuring relative growth in the dilutions series reservoirs, the one or more HMLRs, and the one or more control reservoirs determined by time-resolved fluorescence or time-gated luminescence; and
determining the qualitative susceptibility interpretations from the relative growth measurements.
15. The method of claim 14 , wherein growth in the reservoirs is determined following addition of a metabolic viability probe comprising resazurin and methylene blue, ferrous and ferric potassium salts, or 1-methoxy-5-methlyphenasinum methyl sulfate.
16. The method of claim 14 , wherein growth in the reservoirs is determined following the addition of a probe capable of binding microbial surfaces.
17. The method of claim 14 , wherein the first concentration C m0 is between 1×10 5 and 5×10 6 CFU/mL.
18. The method of claim 14 , wherein the step of determining the qualitative susceptibility interpretations comprises a viability assay where a probe is added following a growth threshold being achieved and a surface area assay following the viability assay, wherein the surface area assay comprises:
incubating a liquid suspension of the microorganism in the presence of the antimicrobial A under conditions that promote growth of the microorganism;
adding a signaling agent that binds to a surface of the microorganism;
separating the microorganism bound by the signaling agent from unbound signaling agent; and
measuring signal levels associated with the microorganism as compared to one or more controls, thereby measuring the antimicrobial susceptibility of the microorganism;
wherein the signaling agent comprises a linker group L, and an amplifier group comprising an Europium coordination complex; and wherein,
the linker group L forms a covalent bond to the amplifier group; or
the linker group L forms one or more non-covalent interactions with the amplifier group.
19. The method of claim 1 , wherein the one or more HMLRs comprises the antimicrobial A at a concentration≥C AL .