First isolation in Spain of Paracoccus sanguinis in blood cultures

The genus Paracoccus comprises a group of bacteria that includes more than 40 species, the majority of which are recovered from environmental sources such as soil, mud, sludge, or groundwater.¹ To date, only Paracoccus yeeii has been isolated from clinical specimens.² A new species, Paracoccus sanguinis, was recently identified, with the strains being recovered from blood samples.³ Few human infections have been attributed to this microorganism. We describe the isolation of this microorganism in the blood of a premature newborn. To our best knowledge, this is the first report on the isolation of P. sanguinis in Spain.

The mother gave birth at 32 weeks by elective cesarean section due to multiple gestation. After the delivery, the newborn rapidly developed respiratory distress that required intermittent positive pressure ventilation for three minutes, and she was immediately transferred to the neonatal ICU to receive continuous positive airway pressure. The medical history of the mother was only remarkable for a positive Streptococcus agalactiae screening, with no administration of antimicrobial prophylaxis. Physical examination of the newborn was unremarkable, and transfontanellar ultrasound showed no abnormalities. However, chest-X ray revealed a diffuse granular pattern that disappeared on the third day of admission.

At the delivery, blood analysis results were normal except for a high peripheral leucocyte count (19,120/mm³). A pediatric blood culture (BD BACTEC Peds Plus™, Becton Dickinson, Sparks, MD) was drawn and sent to the microbiology laboratory for processing. At this time, empirical therapy was initiated with ampicillin (100 mg/kg/6 h) plus gentamicin (4 mg/kg/day). This treatment was stopped after 48 h, because no clinical signs of infection were observed. The sample was inoculated onto the BACTEC FX 40 (Becton Dickinson, Franklin Lakes, NY) monitorization system for culture. On day 4 of incubation, the blood culture was found to be positive. The sample was subcultured in aerobic blood agar (BD Columbia Agar with 5% Sheep Blood, Becton Dickinson, Franklin Lakes, NY) and chocolate agar (BD Chocolate agar, Becton Dickinson). The plates were incubated at 37 °C in an atmosphere of 5% CO₂. Gram staining of the blood cultures exhibited abundant Gram-negative rods and, on the second day of incubation, abundant circular, convex, moist, pale yellow non-hemolytic colonies were observed in pure culture on both plates. These colonies proved to be catalase- and oxidase-positive. Application of MALDI-TOF MS version 9 (8468 msp) (Bruker Biotyper, Billerica, MA) was not able to identify the strain. Only three Paracoccus species have inputs in its database (P. dentrificans, 1; P. versutus, 2; and P. yeei, 7). No other identification system was applied for this strain, and the isolate was submitted to the National Center of Microbiology (ISCIII, Madrid, Spain) and identified by means of 16S rRNA sequence analysis using a previously reported method.⁴ The obtained fragment of 1382 bp showed 99.93% similarity (1358/1359 nucleotides) with P. sanguinis strain 05503 (GenBank accession number NR_135883.1), with only one discrepant nucleotide (1345A→G). The sequence was deposited in GenBank under accession number MT827286.

Antimicrobial susceptibility testing was performed by Etest®, obtaining the following MIC values: amikacin (0.25 mg/L), cefepime (0.5 mg/L), piperacillin-tazobactam (<0.016 mg/L), ceftazidime (0.75 mg/L), meropenem (0.012 mg/L), ertapenem (0.006 mg/L), gentamicin (0.023 mg/L), tobramycin (0.125 mg/L), ciprofloxacin (0.003 mg/L) and colistin (0.75 mg/L). To date, neither EUCAST nor CLSI have defined breakpoints for this microorganism, but this isolate seemed to be susceptible to all antimicrobials tested when EUCAST breakpoints for Pseudomonas spp. or Acinetobacter spp. were applied.

The clinical course of the newborn was favorable, and she was discharged one month later.

P. sanguinis is a facultative anaerobe Gram-negative rod of 0.5–1 mm that appears in pairs or chains in the Gram stain and, to our knowledge, it has not been associated with human infection to date. We report the first case of bacteremia due to P. sanguinis isolated in pure culture in Spain. A key question related to this case report is whether the isolate corresponds to a true pathogen, given the delayed growth of the bacterium (after 4 days of incubation) and the recovery of the patient in absence of a specific treatment, although the patient previously received ampicillin plus gentamicin, according to the treatment protocol for respiratory distress in premature newborns. The Paracoccus genus is a microorganism of low pathogenicity and mainly causes infections in immunocompromised patients, such as premature newborns.

MALDI-TOF MS can be highly useful for the identification of bacteria and the detection of new species responsible for infections. However, in some circumstances, as in the present case, it yields no results. Frequent updating of MALDI software update is recommended to introduce new inputs and to optimize the diagnosis of new microorganisms that can cause potentially severe infections. In the meantime, species identification must be confirmed using other diagnostic techniques such as 16S rRNA gene sequencing.

In conclusion, this is the first report of P. sanguinis isolated in pure culture as a cause of bacteremia and indicates that this new pathogen could be responsible for human infections. This case highlights the need to confirm results when MALDI-TOF scores are inadequate.

Funding

No funding.

Conflict of interest

Authors declare no conflict of interest.