A taxonomic study of the Burkholderia cepacia complex : an analysis of genotypic, phenotypic and susceptibility characteristics

Abstract

The development of novel molecular tools has provided the scientific community with quick, easy, and scientifically sound ways of identifying individual strains belonging to the Burkholderia cepacia complex (Bcc). Bcc strains isolated from the sputum of 44 patients attending the Freeman Hospital Cardiopulmonary Transplant Unit were genotyped using recA PCR-RFLP analysis, and a clonality study performed using PFGE analysis. It was found that B. cenocepacia and B. multivorans were the predominant colonizing strains in these patients, and that infection with the ET-12 epidemic clone was the most prevalent strain amongst B. cenocepacia- infected patients. It was also found that pre-transplant strains remained responsible for post-transplant infections. Phenotypic methods for the identification of Bcc strains and closely related organisms have been difficult to develop. A collection of 493 strains including Burkholderia cepacia (genomovars I- IX), Pseudomonas aeruginosa, and other closely related organisms, were investigated for their abilities to produce a wide range of peptidases, glycosidases, esterases and other miscellaneous enzymes using both chromogenic and fluorogenic substrates. The 312 Bcc strains within the collection were also screened for their capacity to oxidise a number of carbohydrates. The heterogeneous nature of all nine Bcc species was confirmed by this study, as was the close phenotypic relationship of B. cepacia and B. cenocepacia. Some substrates, however, were shown to have some taxonomic utility for the differentiation of species within the Bcc and also for closely related organisms. Metabolic activities that showed diagnostic potential included production of 13-ribosidase, 13-xylosidase and 13-glucosidase, as well as oxidation of cellobiose, maltose and trehalose. Screening for palmitate esterase and a or 13-trypsin production was useful for the differentiation of Pandoraea sp. and Ralstonia picketti respectively. CF infections caused by P. aeruginosa and Bcc strains, are most successfully treated using two or three drug combinations. A number of cell wall-acting antibiotics were tested in combination with the phosphonopeptide alafosfalin for synergistic effects against Bcc and P. aeruginosa strains. Alafosfalin was most effective in combination with ceftazidime against Bcc strains, and in combination with tobramycin and ceftazidime as a triple combination against P. aeruginosa.

Date of Award	23 Jun 2004
Original language	English
Awarding Institution	Northumbria University
Supervisor	Gary Black (Supervisor)