Underlying application of new antimicrobial therapeutics is the need to rapidly identify organisms and determine which antimicrobials therapies will be effective. Therefore, the Laboratory is also actively involved in several projects to refine and improve clinical diagnostics:
1) The Antimicrobial Testing Gap - Application of Ink Jet Printing, Digital Dispensing Technology.
We call the time between when empiric antimicrobial therapy (Rx) is begun, and antimicrobial susceptibility (AST) results are available the "antimicrobial testing gap." Typically this gap may be 2-3 days depending on the time necessary to culture the organisms. Typically antimicrobial susceptibility results are not practically available until the day after bacterial colonies are isolated. With the dramatic emergence of antimicrobial resistance, especially among Gram-negative pathogens, sometimes we perform antimicrobial susceptibility testing (AST) on bacterial isolates, and find that the organisms are resistant to all antimicrobials tested or practically resistant to all antimicrobials if the patient is allergic to or cannot tolerate antibiotics that remain active. We then need to test agents that are more rarely used, for example, colistin, considered one of the agents of last resort for treatment of carbapenem-resistant Enterobacteriaceae. Unfortunately, colistin and a number of other agents that may be useful for treatment of multidrug-resistant infections cannot be tested in hospital-based clinical microbiology laboratories. Therefore, isolates must be sent to a reference laboratory where a reference method called broth microdilution or agar dilution testing is performed. This process delays the availability of AST results for several additional days -- time that patients with multidrug-resistant infections can ill afford.
In collaboration with Tania Konry and Elizabeth Hirsch of Northeastern University, we seek to develop microfluidic, lab-on-a-chip platforms to identify pathogens and determine their susceptibility to antimicrobials directly from patient specimens in under three hours.
3) Improvements in clinical microbiology technology
In clinical laboratories, we isolate bacterial pathogens, grow them in pure culture, and test for the ability of antimicrobials to inhibit growth of organisms. Testing is done using doubling dilutions of antibiotics (e.g., 16, 8, 4, 2, 1, 0.5 mcg/ml). The lowest concentration of antibiotic that visually inhibits bacterial growth is called the "minimal inhibitory concentration" or the MIC. The MIC is used as a surrogate for clinical efficacy. Categorical interpretive breakpoints are applied to the MIC values based on the concentration the drug achieves in tissues and body fluids and observations of clinical response. MIC values above a certain breakpoint are considered "resistant"; below a certain breakpoint are considered sensitive, and in between these breakpoints considered "intermediate". Of course clinically, in many situations, we would like to not only inhibit growth of the organism, but to completely eradicate the organism. Forget inhibition -- we want cell death or bactericidal activity! This is an especially pressing concern in situations when the patient's immune system is compromised or pathogens infect a privileged site where the immune response is typically ineffective (e.g., endocarditis, bone infection). There is increasing evidence of "tolerance" or splay between the concentration it takes to inhibit growth of an organism (MIC) and the concentration needed to kill the organism (MBC). Therefore knowledge of the killing concentration would be really useful
The sticky issue is that minimal bactericidal activity (MBC) testing is so cumbersome to perform that no one ever does it; and because of this difficulty, the clinical correlation data for MBC values is also not reliably available. Traditionally, MBC testing is done through serial dilution, plating, and colony forming unit determination for every growth well where growth of organisms is inhibited. The antimicrobial concentration where growth is inhibited by 99.9% is considered the MBC. The MBC procedure is a LOT of work to do even for a single bug-drug combination, let alone testing against the panel of drugs that we want to examine for each clinical isolate. To address the MBC information gap, we have developed novel technology to rapidly determine both the MIC and MBC, a technology that in principle could be adopted facilely in a clinical microbiology laboratory setting and thereby rapidly provide important data for our clinicians. We are currently exploring the potential of this technology to identify tolerance, especially in multidrug-resistant pathogens, to identify optimal regimens that may remain available.
4) Interface with clinical microbiology laboratory
We have close ties to the BIDMC Clinical Microbiology Laboratory which Dr. Kirby also directs. We constantly seek new ways to apply basic and translation observations to improvement of clinical diagnostics. Projects may also be performed by Clinical Microbiology Fellows or Residents, who spend periods of time in the research laboratory.