Identification and Antimicrobial Susceptibility of Alcaligenes xylosoxidans Isolated from Patients with Cystic Fibrosis

Abstract

In the past decade, potential pathogens, including Alcaligenes species, have been increasingly recovered from cystic fibrosis (CF) patients. Accurate identification of multiply antibiotic-resistant gram-negative bacilli is critical to understanding the epidemiology and clinical implications of emerging pathogens in CF. We examined the frequency of correct identification of Alcaligenes spp. by microbiology laboratories affiliated with American CF patient care centers. Selective media, an exotoxin A probe for Pseudomonas aeruginosa, and a commercial identification assay, API 20 NE, were used for identification. The activity of antimicrobial agents against these clinical isolates was determined. A total of 106 strains from 78 patients from 49 CF centers in 22 states were studied. Most (89%) were correctly identified by the referring laboratories as Alcaligenes xylosoxidans. However, 12 (11%) strains were misidentified; these were found to be P. aeruginosa (n ‫؍‬ 10), Stenotrophomonas maltophilia (n ‫؍‬ 1), and Burkholderia cepacia (n ‫؍‬ 1). Minocycline, imipenem, meropenem, piperacillin, and piperacillin-tazobactam were the most active since 51, 59, 51, 50, and 55% of strains, respectively, were inhibited. High concentrations of colistin (100 and 200 g/ml) inhibited 92% of strains. Chloramphenicol paired with minocycline and ciprofloxacin paired with either imipenem or meropenem were the most active combinations and inhibited 40 and 32%, respectively, of strains. Selective media and biochemical identification proved to be useful strategies for distinguishing A. xylosoxidans from other CF pathogens. Standards for processing CF specimens should be developed, and the optimal method for antimicrobial susceptibility testing of A. xylosoxidans should be determined.Cystic fibrosis (CF) is the most common life-shortening disease caused by a recessive autosomal gene in the Caucasian population and afflicts about 60,000 patients worldwide, approximately 30,000 of whom are cared for in the United States (21). While the genetic defect in CF is known, the relationship between abnormal CF transmembrane conductance regulator and chronic pulmonary disease is not yet fully understood (22). Chronic pulmonary disease is characterized by a vicious cycle of inflammation and infection and is the major cause of morbidity and mortality. The pathogens of CF are well characterized and include Staphylococcus aureus, nontypeable Haemophilus influenzae, Pseudomonas aeruginosa, and Burkholderia cepacia (10).During the past decade, several additional potential pathogens have been recovered from CF patients, including nontuberculous mycobacteria (19), Stenotrophomonas maltophilia (3), and Alcaligenes species, particularly Alcaligenes xylosoxidans (29). As reported to the U.S. Cystic Fibrosis Foundation's National Patient Registry in 1996 and 1997, 1.9 and 2.7% of all CF patients harbored Alcaligenes spp. (7,8). As determined by a research laboratory participating in a phase III trial of aerosolized tobramycin in CF patients who were Ն6 years of ...

Survey of Pseudomonas aeruginosa genotypes in colonised cystic fibrosis patients

“…Owing to the diversity of colonial morphologies and biochemical reactivity encountered, misdiagnosis of Gram-negative nonfermenters cultured from CF sputum may occur. In one study, misidentification of 11% of A. xylosoxidans strains was reported [30].…”

Achromobacter xylosoxidans Infection Presenting as a Pulmonary Nodule Mimicking Cancer

“…A. xylosoxidans was misidentified in up to 11% of cases, according to one study (33). When misdiagnosed, A. xylosoxidans is most often falsely identified as nonpigmented strains of Pseudomonas aeruginosa or B. cepacia (34). In light of this propensity for misidentification, sequencing offers a more reliable method of definitive diagnosis (19).…”

“…Pulmonary cases of A. xylosoxidans infection have been associated with a myriad of underlying medical problems, including IgM deficiency (11), hematologic malignancies, including acute myelogenous leukemia (AML) (18,34), solid organ malignancies (20,39), COPD (12), and CF (10, 13, 39, 44) ( Table 1). In one study, A. xylosoxidans was the most common Gram-negative nonfermenter in CF patients, second only to Pseudomonas aeruginosa (13).…”

Shared Genotypes of Achromobacter xylosoxidans Strains Isolated from Patients at a Cystic Fibrosis Rehabilitation Center

“…We found very variable results for ceftazidime, while for only one strain (B other) no large inhibition zone for piperacillin was observed. Also, Saiman et al (20) found piperacillin among the most active antibiotics in vitro. There were no consistent susceptibility characteristics which enabled one to differentiate between the four genotypes, but the susceptibility pattern, i.e., colimycin resistance and combined resistance to aminoglycosides and quinolones, was considered to be helpful in distinguishing this species from P. aeruginosa.…”

“…Due to the diversity of colonial morphologies and biochemical reactivity encountered, misdiagnosis of gram-negative nonfermenters cultured from CF sputum may occur. In one study, misidentification of 11% of A. xylosoxidans strains was reported (20).…”