BACLIB detects antimicrobial susceptibility and resistance two ways:
■ Some forms of antimicrobial resistance are detected as part of the initial, one-hour ID test.
■ MICs (minimum inhibitory concentrations) of antibiotics are provided by a second testing step within six hours of sample collection.
Ultra-rapid antimicrobial resistance testing
Some forms of antimicrobial resistance (AMR) are expressed in microbial membranes. For example, bacteria make their membranes less electrically negative to become resistant to antibiotics including colistin and polymyxins. These membrane changes are expressed even in the absence of antibiotics, and are readily detected by BACLIB, as part of ID testing.
Below, BACLIB spectra from four Gram-negative strains transformed with the mcr-1 plasmid (“Resistant”) are compared to un-transformed strains (“Susceptible”). The mcr-1 plasmid adds a phosphoethanolamine to lipid A molecules, which reduces colistin’s ability to cross the bacterial membrane. This also increases the mass of modified lipid A by 123 Da, which is easily observed by mass spectrometry. Other membrane modifications conferring antimicrobial resistance, such as addition of aminoarabinose, can also be observed in this way.
Antimicrobial resistance of this type is detected automatically by BACLIB at the same time as ID, for Ultra-rapid AMR testing in one hour, direct from specimen.
Rapid antimicrobial susceptibility testing
Membrane-expressed AMR is detected as part of the BACLIB ID test; other forms of AMR are detected in a second step called “BACLIB Rapid AST.” In six hours, direct from specimen, BACLIB Rapid AST determines minimum inhibitory concentrations (MICs).
BACLIB Rapid AST detects microbial growth by adding a small percentage of inexpensive, non-toxic deuterium oxide (D2O) to growth media. The initial inoculum is not labeled with D2O. Any growth in labeled media will increase the mass of lipids, which is easily observed by mass spectrometry.
BACLIB Rapid AST works just like traditional AST: samples of a specimen are grown with a range of antibiotic concentrations; the lowest concentration that inhibits growth indicates MIC. The difference is that BALIB Rapid AST determines MICs in six hours, direct from a clinical sample such as a urine specimen –days faster than with traditional AST.
Below, BACLIB Rapid AST spectra are shown for Pseudomonas fluorescens with Kanamycin. The MIC at 50.0 µg/mL is easily observed.
Together, BACLIB ID and BACLIB Rapid AST allow patients to get appropriate therapy in hours, instead of days.
