Treatment of multi-drug-resistant Gram-negative bacterial infections using capsule depolymerases

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A group of bacteria have recently emerged as a major threat to global human health. These "Gram-negative bacteria (GNB)" exploit the decreased capacity of critically ill patients to ward off infections; they are particularly dangerous as they accumulate genes that confer resistance to front-line antibiotics. Some of these infections are untreatable and morbidity and mortality are common. These bacteria are also becoming more virulent and are beginning cause serious infections outside critical care facilities. They impose a particularly severe burden on healthcare in Thailand: for example, in 2010 in excess of 90,000 hospitalized patients acquired infections with drug resistant GNB, around one third died and these infections resulted in excess of three million days of hospitalization. Because they have evolved so quickly, we do not have sufficient means to control these infections and to treat critically ill patients. Most of the bacteria that cause these infections are protected from the patients' already compromised immune defences by the presence of a sugar-containing capsule; we know that removal of this protective outermost layer from the bacterial cell by capsule-degrading enzymes will enable the host to eliminate the attenuated pathogen. For this proposal, we wish to investigate the capacity of such enzymes ("capsule depolymerases") to strip the capsule from drug resistant strains of two of these bacterial species, Klebsiella pneumoniae and Acinetobacter baumannii. To begin the project, we will collect recent Thai isolates of these bacteria from hospitals in Bangkok and elsewhere in the country and sequence their genomes to enable us to compare them with global populations of similar bacteria. This analysis will inform on the range of capsule types carried by these "local" strains. We will then isolate bacterial viruses ("bacteriophage") that carry capsule depolymerases to enable them to dock onto the surface of their bacterial hosts prior to killing them. Once we have characterised a range of these enzymes, we will purify them and use molecular genetic techniques to engineer proteins in sufficient bulk for experiments in animal models of infection. If we are able to demonstrate that dosing infected rats with engineered enzymes favourably alters the course of infection, we will promote these novel agents as potential therapeutics for the treatment of these devastating infections in the human host.