Propionibacterium (Propionimicrobium) lymphophilum has undergone several name changes,1,2 and the description of this microorganism has recently been amended.3 This pathogen forms part of human skin and urinary tract microbiota and has been associated with a very small number of infections in humans.4,5 We recently published the first case of bacteremia caused by this bacterium who was isolated in pure culture from an elderly patient,6 and we now report another case obtained from a blood culture that was initially misidentified by MALDI-TOF MS.
An 83-year-old man was admitted to the Trauma-Emergency Department of our hospital with head trauma. Two foci of subarachnoid hemorrhage were observed on cranial CT scan, and severe abdominal pain was reported by the patient, who was transferred to the General Emergency Department. The abdominal CT scan revealed distal ileus perforation with fecaloid peritonitis, and the clinical records showed a history of diabetes mellitus and Parkinson disease. The patient underwent abdominal surgery with resection and anastomosis of the involved small intestine. At admission, blood analysis results were normal but the patient had a fever (38°C). Blood cultures were taken on the same day and at the same hour from each arm and delivered to the hospital microbiology laboratory. At this time, empirical therapy was initiated with meropenem (1g/8h) and linezolid (600mg/12h). The samples were inoculated onto the BACTEC FX 40 (Becton Dickinson, Franklin Lakes, NY) monitorization system for culture. On day 2 of incubation, both anaerobic bottles were found to be positive. The samples were subcultured in aerobic or anaerobic blood agar (BD Columbia Agar with 5% Sheep Blood, Becton Dickinson, Franklin Lakes, NY). All media were incubated at 37°C, and AnaeroGen Compact (Oxoid Ltd., Wide Road, Basingstoke, UK) was used as anaerobic system. Gram staining of the blood cultures exhibited abundant Gram-positive coccobacilli; on the second day of incubation, abundant colonies of these microorganisms were observed in pure culture only in anaerobic blood agar medium. Application of MALDI-TOF MS version 9 (8468 msp) (Bruker Biotyper, Billerica, MA) identified the strain as Peptoniphilus indolicus (score 1.86). Given the relatively low score, the strain was sent to the Center of Genomic and Oncologic Research (GENYO, Granada, Spain) for 16S rRNA gene sequence analysis using a previously reported method.7 A fragment of 1482bp was obtained, yielding 99.3% similarity with the P. lymphophilum type strain JCM 5829 Gene Bank sequence (AB729070). The 16S sequence was also submitted to the GenBank (accession number: MT126739).
The E-test was employed for antimicrobial susceptibility evaluation, applying the 2020 EUCAST criteria8 with the exception of moxifloxacin, for which the 2020 CLSI criteria9 was used. MIC values were penicillin (0.032mg/L), amoxicillin-clavulanate (<0.016mg/L), piperacillin-tazobactam (<0.016mg/L), clindamycin (>256mg/L), meropenem (0.006mg/L), imipenem (0.016mg/L), moxifloxacin (0.38mg/L), and metronidazole (>256mg/L).
Linezolid was withdrawn, and meropenem was changed to piperacillin-tazobactam (1g/12h) for 7 days. The patient became afebrile at 2 days after starting the antimicrobial treatment, and he was discharged one month later.
P. lymphophilum is among the most infrequent anaerobic bacteria associated with human infection, and, to our knowledge, only four cases have been reported in the medical literature to date.4–6 Here, we report a second case of bacteremia due to P. lymphophilum isolated in pure culture. A key issue in relation to this microorganism is whether its isolation corresponds to a true pathogen, which is supported in the present case by its isolation in pure culture in both sets of blood cultures, which were taken using aseptic procedures. In this case, it can be considered a secondary bacteremia from an abdominal source.
MALDI-TOF MS is used for fast routine analyses in clinical laboratories and may be highly useful for the identification of anaerobic microorganisms and for the detection of new species responsible for infection. However, results should be interpreted with caution, and this technique produced the initial misidentification of P. indolicus in the present case. Species identification is highly probable when the score is ≥2.010 but must be confirmed when the score is below this cutoff by employing other diagnostic techniques, such as 16SrRNA gene sequencing. Moreover, a new MALDI software update is recommended in order to improve the scoring.
In conclusion, this is the second report of P. lymphophilum as cause of bacteremia isolated in pure culture and indicates that this pathogen can be responsible for severe infections. This case highlights the need to confirm results when low MALDI-TOF scores are obtained.
FundingSupport for this research was provided by the Ministerio de Agricultura, Alimentación y Medio Ambiente, SAF2015-71714-R (MINECO/FEDER).
Conflict of interestAuthors declare no conflict of interest.
The authors are grateful to Guadalupe Garcia-Medina for technical support.
