For studies of antibiotics and how they work, the most-often used measurement of drug efficacy is the MIC. The MIC is the concentration of an antibiotic needed to inhibit bacterial growth.

One major concern in hospitalized patients is infections with pathogens borne on surfaces, patients, and healthcare workers. Fundamental to controlling nosocomial infections is identifying the sources of pathogens, monitoring the processes responsible for their transmission, and evaluating the efficacy of the procedures employed for restricting their transmission. Here we present a method using the bacteriophage Lambda (λ) to achieve these ends. Defined densities of multiple genetically marked λ phages were inoculated at known hotspots for contamination on high-fidelity mannequins. Healthcare workers (HCWs) then entered a pre-sanitized simulated hospital room and performed a series of patient care tasks on the mannequins. Sampling occurred on the scrubs and hands of the HCWs, as well as previously defined high-touch surfaces in hospital rooms. Following sampling, the rooms were decontaminated using procedures designed and demonstrated to be effective. Following the conclusion of the simulation, the samples were tested for the presence, identity, and densities of these Lambda phages. The data generated enabled the determination of the sources and magnitude of contamination caused by the breakdown of established infection prevention practices by HCW. This technique enabled the standardized tracking of multiple contaminants during a single episode of patient care. While our application of these methods focused on nosocomial infections and the role of HCW behaviors in their spread, these methods could be employed for identifying the sources and sites of microbial contamination in other settings.

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Retrons were described in 1984 as DNA sequences that code for a reverse transcriptase and a unique single-stranded DNA/RNA hybrid called multicopy single-stranded DNA (msDNA). It would not be until 2020 that a function was shown for retrons, when compelling evidence was presented that retrons activate an abortive infection pathway in response to bacteriophage (phage) infection. When infected with the virulent mutant of the phage lambda, λVIR, and to a lesser extent, other phages, a retron designated Ec48 is activated, the Escherichia coli bearing this retron element dies, and the infecting phage is lost. With the aid of a mathematical model, we explore the a priori conditions under which retrons will protect bacterial populations from predation by phage and the conditions under which retron-bearing bacteria will evolve in populations without this element. Using isogenic E. coli with and without Ec48 and λVIR, we estimated the parameters of our model and tested the hypotheses generated from our analysis of its properties. Our models and experiments demonstrate that cells expressing a retron-mediated abortive infection system can protect bacterial populations. Our results demonstrate that retron bearing bacteria only have a competitive advantage under a limited set of conditions.