Laboratory proficiency test results on use of selective media for isolating Pseudomonas cepacia from simulated sputum specimens of patients with cystic fibrosis

Abstract

Pseudomonas cepacia colonization of or infection in patients with cystic fibrosis (CF) has been associated with increased morbidity and premature death. However, current data on national incidence may be biased because of interlaboratory differences in the methods of culturing sputa of patients with CF. We conducted three tests to evaluate the proficiency of microbiology laboratories at CF centers in identifying and isolating P. cepacia and to assess the value of using selective media for P. cepacia (P. cepacia agar and oxidation-fermentation polymyxin-bacitracin-lactose medium [OFPBL]) to recover P. cepacia from specimens simulating sputa of patients with CF. In test 1, we evaluated the proficiency of laboratories in identifying P. cepacia. Of 111 laboratories tested, 105 (95%) correctly identified P. cepacia. In test 2, we evaluated the proficiency of laboratories in isolating P. cepacia from stimulated CF sputum specimens. Only 36 (32%) of 115 laboratories detected P. cepacia. Recovery of the microorganism was associated with the use of P cepacia agar or OFPBL; 14 (95%) of 15 laboratories using P. cepacia agar or OFPBL (or both) versus 22 (22%) of 100 laboratories not using either medium recovered P. cepacia (P < 0.0001, Fisher exact test, one tailed). Laboratories failing test 2 were requested to use a selective medium for P. cepacia in a repeat test; 73 (97%) of 75 laboratories using P. cepacia agar or OFPBL (or both) versus 0 of 4 laboratories not using either medium detected P. cepacia (P < 0.0001, Fisher exact test, one tailed). Our studies show that (i) microbiology laboratories at CF centers are proficient in identifying P. cepacia, and (ii) the use of selective media for P. cepacia enhances recovery of the microorganism in simulated sputum specimens. Therefore, we recommend the use of selective media for P. cepacia in laboratories processing sputa of patients with CF.