Candida infections : detection and epidemiology

Abstract

Despite the fact that the yeast Candida is the number 4 cause of bloodstream infections in the United States and ranks number 8 in Europe, adequate detection methods are lacking. Furthermore, relatively little is known about the epidemiology of Candida. Our aim was to improve the detection and identification of Candida infections and to study the epidemiology of Candida infections in Europe. We describe the development of a Nucleic Acid Sequence-Based Amplification (NASBAim) assay for the detection of Candida species in blood and blood cultures. The results were encouraging: when the NASBA assay was used to detect Candida in blood cultures which were negative in the automated blood culture system, the number of positive blood cultures increased with 62%. Furthermore, we demonstrated that a substantial increase in detection rate can already be obtained with a 2 day pre-culture step. Also, Candida RNA was detected in the blood of a patient, whereas no yeast was detected by the automated blood culturing system. In another patient the NASBA assay detected the infection two days earlier than the blood culture system. These results indicate that improved detection of Candida infections (detection rate as well as speed) is possible. Improved detection will lead to a reduced morbidity and mortality. Another study described in this thesis shows that Amplified Fragment Length Polymorphism (AFLPim) analysis is an excellent method for the identification of Candida species. The different species show very distinct clusters. The potential of storing AFLP patterns in general accessible databases will greatly enhance the chances of a correct identification. The second objective of this thesis was to study the epidemiology of Candida albicans infections in Europe. It appeared that a relatively high number of isolates which were involved in pneumonia produced (phospho)lipases, a putative virulence factor. Also, a significantly higher number of these isolates were among the higher producers of this enzyme. A similar trend was observed for the production of proteinases: all isolates obtained from pneumonia were positive in the proteinase assay, and 96% of these isolates were high producers. These results suggest that isolates involved in pneumonia are more virulent than isolates obtained from the other types of infection that were studied. Another interesting epidemiological finding is described. By using AFLP as a fingerprinting method, we typed a large collection of European C. albicans isolates. It was discovered, that isolates from Portugal and Spain all belonged to the same AFLP cluster (cluster 1), whereas isolates from the United Kingdom and all but one isolate from Germany belonged to another cluster (cluster 2). Isolates from France, Italy, Switzerland, and Turkey were represented in both clusters. These results indicate the presence of an Iberian and a Northern European clone. It can be concluded that our first objective, improved detection and identification of Candida infections, was feasible. The second objective, to study the epidemiology of C. albicans infections in Europe, resulted in two interesting discoveries which can be the onset of extensive epidemiological studies