Antibiotics: Combatting Tolerance To Stop Resistance.

Antibiotic resistance poses an alarming and ever-increasing threat to modern health care. Although the current antibiotic crisis is widely acknowledged, actions taken so far have proved insufficient to slow down the rampant spread of resistant pathogens. Problematically, routine screening methods and strategies to restrict therapy failure almost exclusively focus on genetic resistance, while evidence for dangers posed by other bacterial survival strategies is mounting. Antibiotic tolerance, occurring either population-wide or in a subpopulation of cells, allows bacteria to transiently overcome antibiotic treatment and is overlooked in clinical practice. In addition to prolonging treatment and causing relapsing infections, recent studies have revealed that tolerance also accelerates the emergence of resistance. These critical findings emphasize the need for strategies to combat tolerance, not only to improve treatment of recurrent infections but also to effectively address the problem of antibiotic resistance at the root.

Draft genome sequence of Enterococcus faecium strain LMG 8148.

Enterococcus faecium, traditionally considered a harmless gut commensal, is emerging as an important nosocomial pathogen showing increasing rates of multidrug resistance. We report the draft genome sequence of E. faecium strain LMG 8148, isolated in 1968 from a human in Gothenburg, Sweden. The draft genome has a total length of 2,697,490 bp, a GC-content of 38.3 %, and 2,402 predicted protein-coding sequences. The isolation of this strain predates the emergence of E. faecium as a nosocomial pathogen. Consequently, its genome can be useful in comparative genomic studies investigating the evolution of E. faecium as a pathogen.

Draft genome sequence of Acinetobacter baumannii strain NCTC 13423, a multidrug-resistant clinical isolate.

Acinetobacter baumannii is a pathogen that is becoming increasingly important and causes serious hospital-acquired infections. We sequenced the genome of A. baumannii NCTC 13423, a multidrug-resistant strain belonging to the international clone II group, isolated from a human infection in the United Kingdom in 2003. The 3,937,944 bp draft genome has a GC-content of 39.0 % and a total of 3672 predicted protein-coding sequences. The availability of genome sequences of multidrug-resistant A. baumannii isolates will fuel comparative genomic studies to help understand the worrying spread of multidrug resistance in this pathogen.

Frequency of antibiotic application drives rapid evolutionary adaptation of Escherichia coli persistence.

The evolution of antibiotic resistance is a major threat to society and has been predicted to lead to 10 million casualties annually by 2050(1). Further aggravating the problem, multidrug tolerance in bacteria not only relies on the build-up of resistance mutations, but also on some cells epigenetically switching to a non-growing antibiotic-tolerant 'persister' state(2-6). Yet, despite its importance, we know little of how persistence evolves in the face of antibiotic treatment(7). Our evolution experiments in Escherichia coli demonstrate that extremely high levels of multidrug tolerance (20-100%) are achieved by single point mutations in one of several genes and readily emerge under conditions approximating clinical, once-daily dosing schemes. In contrast, reversion to low persistence in the absence of antibiotic treatment is relatively slow and only partially effective. Moreover, and in support of previous mathematical models(8-10), we show that bacterial persistence quickly adapts to drug treatment frequency and that the observed rates of switching to the persister state can be understood in the context of 'bet-hedging' theory. We conclude that persistence is a major component of the evolutionary response to antibiotics that urgently needs to be considered in both diagnostic testing and treatment design in the battle against multidrug tolerance.

Experimental Evolution of Escherichia coli Persister Levels Using Cyclic Antibiotic Treatments.

Persister cells are difficult to study owing to their transient nature and their usually small number in bacterial populations. In the past, numerous attempts have been made to elucidate persistence mechanisms. However, because of the challenges involved in studying persisters and the clear redundancy in mechanisms underlying their generation, our knowledge of molecular pathways to persistence remains incomplete. Here, we describe how to use experimental evolution with cyclic antibiotic treatments to generate mutants with an increased persister level in stationary phase, ranging from the initial ancestral level up to 100 %. This method will help to unravel molecular pathways to persistence, and opens up a myriad of new possibilities in persister research, such as the convenient study of nearly pure persister cultures and the possibility to investigate the role of time and environmental aspects in the evolution of persistence.