Nosocomial bacteremia due to Cupriavidus pauculus in a patient with ulcerative colitis

Cupriavidus spp. are non-fermenting, environmental Gram-negative bacilli of low virulence, which can cause infections related to intravascular catheters or other devices in immunocompromised patients or patients subject to invasive procedures, with Cupriavidus pauculus being the species involved most frequently.

In August 2017, a 27-year-old male, diagnosed in September 2012 with ulcerative colitis, attended the Emergency Department due to presenting with diarrhoea, rectal bleeding, abdominal pain and fever. After being diagnosed with a severe outbreak of ulcerative colitis, he was admitted to the Gastroenterology Department, and immunosuppressive therapy was started. Due to the presence of fever upon admission, it was proceeded to rule out bacterial infection, with the urine culture and blood culture coming back negative. On day 18 of his admission, following another episode of fever, two batches of blood cultures (four vials) were drawn, which were incubated in the Bactec FX® system (Becton Dickinson). Following a time-to-positivity of 26 h in the two aerobic vials, growth of Gram-negative, oxidase- and catalase-positive bacilli was observed, subsequently identified, by means of mass spectrometry (MALDI-TOF®, Bruker), as C. pauculus. The identification was confirmed in the Instituto de Salud Carlos III [Carlos III Health Institute] by means of the amplification and sequencing of a fragment of 1.353 bp of 16S rRNA: a 99.8% similarity was obtained with C. pauculus GenBank sequence (AB109753). C. pauculus was not identified in other samples from the patient, or in other patients of the Gastroenterology Department in the 30 days prior and subsequent to this isolation. The patient did not have a central venous catheter inserted and had never been admitted to the Intensive Care Unit. Environmental cultures were not performed either and the origin of this infection was not identified.

Antimicrobial susceptibility was performed by broth microdilution using the MicroScan WalkAway® system (Siemens Healthcare Diagnostics). The criteria of the European Committee on Antimicrobial Susceptibility Testing (EUCAST), defined for the susceptibility of Pseudomonas spp., were applied. It was susceptible to ceftazidime, ciprofloxacin, imipenem, co-trimoxazole and piperacillin-tazobactam and resistant to colistin, meropenem and aminoglycosides. After determining the identification and antibiotic susceptibility, antibiotherapy was started with imipenem, which was later de-escalated to ciprofloxacin. Given the patient's clinical improvement and with the follow-up blood cultures coming back negative, he was discharged definitively.

Cupriavidus spp. are ubiquitous environmental organisms which are found mainly in soil, water and plants.¹ They are motile aerobic, non-spore-forming Gram-negative bacilli, which are catalase- and oxidase-positive, oxidise glucose, use citrate and are urease-positive.^1,2 They grow well in blood agar, where they are not haemolytic, and in MacConkey agar with colourless colonies, as they do not ferment lactose.¹ It was in 2004 when bacteria of the genus Wautersia were grouped along with Cupriavidus necator and it formed the genus Cupriavidus¹, which currently consists of more than 13 different species.³ The species which is isolated most frequently in clinical samples is C. pauculus. This bacterium, initially known as CDC group IVc-2 and subsequently as Ralstonia paucula,¹ has been recognised as an opportunistic pathogen described in various serious infections, fundamentally of nosocomial origin, in immunosuppressed patients, treated by invasive procedures or that require multiple antibiotherapy procedures and that affects both children and adults.^4,5 It has been isolated with greatest frequency in bacteraemia of diverse foci, abscesses, peritonitis, tenosynovitis, respiratory infections^6,7 and septic shock.³ It has also been isolated in tap water, swimming pools, underground water and bottled water.^1,4

Although there are no recommended procedures for studying its antimicrobial susceptibility, in our experience the microorganism grew well in commercial microdilution panels. As previously indicated, we applied the EUCAST criteria for Pseudomonas spp. for the determination of its antimicrobial susceptibility. These criteria are more restrictive than Clinical and Laboratory Standards Institute (CLSI) criteria for different antibiotics (beta-lactams, colistin, fluoroquinolones, aminoglycosides). However, this is not the case for imipenem and meropenem, which is why this circumstance has to be considered when comparing susceptibility/resistance with other publications. The strain isolated from our patient presented the same susceptibility as that described in various previous publications^2,6,7 and in a recent case of septic shock,³ in which the EUCAST criteria were also applied.

In summary, we described the first case of bacteraemia due to C. pauculus in our setting, an ubiquitous, aerobic Gram-negative bacillus which is usually resistant to meropenem, aminoglycosides and colistin. There is limited clinical experience in the treatment of serious infections caused by this microorganism, but, in view of its isolation in a sterile sample, imipenem could be used as empirical therapy until its antimicrobial susceptibility is known.