Accurate Diagnosis of Pseudomonas luteola in Routine Microbiology Laboratory: On the Occasion of Two Isolates

Abstract

Pseudomonas luteola which was previously known as Chryseomonas luteola; is a gram-negative, nonfermentative, aerobic, motile, non-spore-forming bacillus. It is frequently found as a saprophyte in soil, water and other damp environments and is an opportunistic pathogen in patients with underlying medical disorders or with indwelling catheters. It has been reported as an uncommon cause of bacteremia, sepsis, septic arthritis, meningitis, endocarditis, and peritonitis. Thus, early and accurate identification of this rare species is important for the treatment and also to provide information about the epidemiology of P.luteola infections. This report was aimed to draw attention to the accurate identification of P.luteola in clinical samples, upon the isolation and identification in two cases in the medical microbiology laboratory of a university hospital. In February 2011, a 66-year-old man, with chronic obstructive pulmonary disease, coronary artery disease and aplastic anemia, was admitted to our hospital due to progressive dyspnea. A chest tube was inserted on the 20th day of admission by the reason of recurrent pleural effusion. Staphylococcus aureus and a non-fermentative gram-negative bacillus (NFGNB) with wrinkled, sticky yellow colonies were isolated from the pleural fluid sample obtained on the 9th day following the insertion of the chest tube. In February 2012, a 7-year-old male cystic fibrosis patient who had no signs and symptoms of acute pulmonary exacerbation was admitted to the hospital for a routine control. This patient had chronic colonization with Pseudomonas aeruginosa and S.aureus and his sputum sample obtained at this visit revealed isolation of P.aeruginosa, S.aureus, Aspergillus fumigatus and a wrinkled, sticky yellow NFGNB. Both of these NFGNB were identified as P.luteola by the Phoenix automated microbial identification system (BD Diagnostics, USA). To evaluate the microbiological characteristics of these two isolates, the strains were further analysed by VITEK MS (bioMerieux, France) and Microflex LT mass spectrometer (Bruker Daltonics, Germany). Both of the MALDI-TOF-MS systems identified the isolates as P.luteola and 16S rRNA gene sequencing (ABI PRISM 3100, Applied Biosystems, USA) also confirmed the identification. The strains had wrinkled, sticky yellow colonies which were oxidase-negative, catalasepositive and non-fermentative. The Gram stained smears of the colonies revealed clusters of gramnegative bacilli probably embedded into a biofilm matrix. Since there are no accepted standards for testing the antibiotic susceptibility of P.luteola strains, the standards determined by CLSI for "other nonEnterobacteriaceae" (non-fermentative bacteria excluding P.aeruginosa, Acinetobacter spp., Burkholderia cepacia, B.mallei, B.pseudomallei and Stenotrophomonas maltophilia) were used for the susceptibility testing. Gradient MIC method (E-Test, bioMerieux, France) revealed that the isolates were susceptible to gentamicin, piperacillin-tazobactam, ceftazidime, cefepime, meropenem, colistin and levofloxacin. Accurate and prompt identification of P.luteola which is identified as a rare pathogen in serious cases is of critical importance since it has been suggested that this organism is likely to become more frequent as a nosocomial pathogen since the interventional processes increase in current medical practice. This report supported that Phoenix automated phenotypic identification system (BD Diagnostics, USA) and the two MALDI-TOF-MS based systems (VITEK MS and Bruker Microflex LT mass spectrometer) were successfull in the accurate identification of P.luteola