Cystic fibrosis (CF) is an autosomal recessive hereditary disease which is characterized by the production of abnormally thickened, viscous mucus and a disturbance in electrolyte transport across epithelial membranes, mainly in respiratory tract and the pancreas.1 Chronic microbial colonization of the respiratory tract, leading to exacerbations of pulmonary infection, is the major cause of disease and death in patients with CF. Pseudomonas aeruginosa, Staphylococcus aureus, Haemophilus influenzae and Burkholderia cepacia complex are typical pathogens.2,3 However, other Gram-negative glucose nonfermenters are also occasionally recovered from respiratory samples from CF patients, but their pathogenic importance remains to be clarified.2,3 In this way, we report the first Inquilinus limosus isolated in a CF patient from Spain.
A 23-year-old girl who has compound homozygote with ΔF508 genetic mutations since 1990. She presents an intermittent colonization of the respiratory tract since childhood with S. aureus and P. aeruginosa. For more than 2 years, a mucoid Gram-negative glucose nonfermenter bacterium appears together with P. aeruginosa and/or Aspergillus fumigatus from at least ten sputum samples. The patient was clinically stable at the time of isolates, nevertheless she received a chronic treatment with azithromycine, levofloxacin and/or tobramycin.
All respiratory samples were cultured on sheep blood agar, PVX agar, SMRA, MacConkey agar, B. cepacia complex selective agar. Plates were incubated at 37°C and 5% CO2 atmosphere for 48h; moreover the B. cepacia complex selective agar was incubated for another 5 days at room temperature. We observed a Gram-negative glucose nonfermenter bacterium which grew very slowly with non-pigmented colonies and showed an extremely mucoid morphotype on sheep blood agar and B. cepacia complex selective agar culture media. The bacterium failed to grow on MacConkey agar. All isolates showed the same antimicrobial susceptibility. They were fully resistant to penicillins and cephalosporins, tobramycin, colistin and co-trimoxazole and susceptible to carbapenems, ciproloxacin and amikacin. The API 20 NE strip (BioMerieux) classified the clinical isolates as Sphingomonas paucimobilis or Rhizobium radiobacter with a questionable biochemical profile. The Vitek 2 GN identified the clinical isolates as Roseomonas gilardii. Although the mucoid Gram-negative glucose nonfermenter bacterium was isolated from ten sputum samples over 2 years, the 16S rRNA sequencing was only realized to the last six isolates because of technician problems. The isolate was identified by means of 16S rRNA sequencing fragment of 1405bp by using a previously reported method.4 The six sequences obtained showed a homology of 99.3% with I. limosus (GenBank accession numbers AY043375, AF085496 and others) by using the BLAST algorithm.
I. limosus was described in 19995 and was characterized in 2002.6 This bacterium has been documented mainly in CF patients and was sometimes accompanied with exacerbation or respiratory decline.5–9 The pathogenic potential, the impact on respiratory function and the risk of patient-to-patient transmission of I. limosus are still unclear, and the environmental habitat of this bacterium is unknown. Previously, it has been isolated only in USA, Germany, France and UK.5–9 To our knowledge, isolation of I. limosus from clinical samples has not been described in Spain.
Correct identification of CF pathogens is important, since it underlies effective infection control measures and therapeutic intervention.10 The prevalence of this multi-resistant bacterium may be underestimated because of its slow growth on selective media, its absence in the databases of commercial identification kits and the need for molecular methods for its identification. Some of these strains can be identified as mucoid P. aeruginosa. However, these isolates do not grow on MacConkey agar and are often resistant to colistin. Nevertheless, additional studies including more isolates will be needed to increase our knowledge of Inquilinus spp.
We thank Sistemas Genómicos, especially Dra. Celia Buades Gomis and Laura Cano Bermudez for the sequencing.
