Controlling antibiotic-resistant pathogens

Antibiotics once revolutionized the therapy of bacterial infections and succeeded in making them fall behind cardiovascular diseases and cancer as main causes of death. This success, however, has been endangered for quite some time: multi-resistant pathogens are making more and more headlines. Treatment with hitherto effective antibiotic agents now fails to destroy these pathogens: currently, about 700,000 people per year worldwide die from infections with resistant pathogens. In view of the explosive increase in such resistances that is observed at present, experts reckon that we are heading towards a “post-antibiotic era” in which bacterial infections could once again take the lead with a death toll of up to 10 million per year [1].

On the one hand, bacteria develop different mechanisms by means of spontaneous gene mutations, enabling them to survive antibiotic treatment. Examples are enzymes that cleave and thereby inactivate antibiotic agents, transporter pumps which simply push antibiotics out of the microbial cell, and gene mutations causing elimination of the cell target which the antibiotic attacks. During antibiotic treatment, pathogens which happen to be resistant to this treatment through one of these mechanisms have an increased chance of survival. While all susceptible pathogens are killed by the antibiotic agent, resistant germs survive and multiply. These pathogens are able to transfer their resistance to other bacteria and thus to further propagate this trait – the antibiotic is then no longer effective in these germs.

On the other hand, pathogens frequently form biofilms. Biofilms are aggregates of bacteria embedded within a self-produced extracellular matrix that acts as a protective cover against attacks by the host’s immune system or antibiotic treatment. And what is more: the micromilieu in the biofilm causes a change in bacterial behavior. In particular inside the biofilm, probably as a result of the limited supply of oxygen and nutrients, the bacteria enter a “dormant” state in which they are less susceptible to antibiotic treatment, as many antibiotics kill only dividing bacteria. Consequently, antibiotic treatment frequently eliminates only microorganisms in the outer area of a biofilm, while the bacteria embedded in the interior survive, become resistant, and start growing again.

Effective new strategies for the fight against resistant pathogens are, therefore, urgently needed – in particular for treating lung infections, which according to the World Health Organization are among the leading causes of death [2]. This problem has now been addressed by Fraunhofer ITEM scientists, who have set out to join the fight against multiresistant bacteria and help develop novel antimicrobial medications and inhalable antibiotics.

1. Review on Antimicrobial Resistance. Antimicrobial Resistance: Tackling a Crisis for the Health and Wealth of Nations. 2014
2. WHO Fact sheet N°310

Inhaled antibiotic therapy is the treatment of choice for patients with lung infections: it delivers the therapeutic agent directly to the site of infection, thus enabling higher doses with reduced systemic impact on the body. In the development of inhaled therapeutics, it is mandatory to verify whether the active ingredients are still active after nebulization and what formulation is most effective.

To this end, the Working Group on Infection, Inflammation and Allergy is developing biofilm models based on Pseudomonas aeruginosa as an example, aimed at enabling preclinical testing of novel therapeutic strategies.  

To enable reliable prediction of the efficacy of inhaled antibiotic agents against biofilm-associated infections at an early stage of drug development, Fraunhofer ITEM scientists have established an in-vitro system for exposing bacterial biofilms to inhalable antibiotics. For this purpose, biofilms of the bacterium Pseudomonas aeruginosa, a typical “problematic pathogen” in the context of lung infections, are grown in vitro and can be exposed to drug candidates. As a biofilm, these bacteria display a substantially increased resistance to antibiotics, enabling much better prediction of efficacy for biofilm-associated infections than with traditional microbiological tests.

By using an exposure system developed at Fraunhofer ITEM, therapeutic substances can be nebulized for treatment of biofilms, allowing determination of the effective dose. In the future, this system can be used for comparative testing of novel inhaled formulations or carrier systems, to enable prediction of what combination of active agents is most effective in breaking through the protective cover of biofilms and in killing the pathogens.

Our findings about how human mucus affects biofilm and its susceptibility to antibiotic treatment have been published in the “Journal of Antimicrobial Chemotherapy”.