Alistipes is a genus of strictly anaerobic Gram-negative bacilli that is made up of 13 species, from which A. finegoldii was initially isolated in 1997 from an appendiceal sample1 and it was described in 2003 from unidentified bacteria from appendiceal samples2. This microorganism is part of the gastrointestinal tract microbiota and has recently been implicated in inflammation, cancer and mental health disorders3. We present a case of bacteraemia due to A. finegoldii in an elderly female patient diagnosed with intestinal perforation.
The patient was a 77-year-old woman, with no notable medical history, treated for hypogastric pain and abdominal distension coursing for 72 h, associated with nausea, vomiting and constipation. The physical examination highlighted the presence of signs of generalised peritonism, as well as fever of 38 °C. Laboratory tests on admission showed an increase in C-reactive protein (300 mg/dl), procalcitonin (20.3 ng/mL) and leukocytes (17,000/mm3). A CT scan of the abdomen showed signs of perforation with generalised faecaloid peritonitis. Two blood cultures were taken and sent to the microbiology laboratory and incubated in the BACTEC FX™ 40 (Becton Dickinson, Franklin Lakes, NY) system. Empiric antibiotic treatment was started with piperacillin-tazobactam (4 g/IV in extended infusion) and metronidazole (500 mg/8 h/IV). An exploratory laparotomy with sigmoidectomy and end colostomy was performed. On the second day of incubation, the two anaerobic vials were positive and were subcultured on blood agar (incubated at 37 °C both in aerobic and anaerobic atmosphere) (BD Columbia Agar with 5% Sheep Blood, Becton Dickinson, Franklin Lakes, NY). The AnaeroGen Compact system (Oxoid Ltd, Wade Road, Basingstoke, UK) was used for the anaerobic atmosphere. Fine Gram-negative bacilli were observed in the blood culture Gram stain. On the third day of incubation, growth in pure culture of abundant raised, circular and opaque colonies was observed only on the blood agar plate incubated in an anaerobic atmosphere (Fig. 1). MALDI-TOF MS (version 9, 8468 msp) was performed (Bruker Biotyper, Billerica, MA) and the isolate was identified as A. finegoldii (log score 2.25). The strain was sent to the Centro de Genómica e Investigación Oncológica [Centre for Genomics and Oncology Research] (GENYO) in Granada, Spain, for analysis of the 16S rRNA gene by means of sequencing4 A 1335 bp fragment was obtained, providing 99.45% similarity to the Gene Bank sequence strain JCM 16770 (accession number: NR 113150.1) from A. finegoldii. The 16S sequence was sent to the Gene Bank (accession number: OM900033).
The evaluation of antimicrobial susceptibility was performed by E-test®, applying EUCAST 20225 criteria. The MIC values were: benzylpenicillin >32 mg/l, piperacillin-tazobactam 2 mg/l, meropenem 0.75 mg/l, vancomycin 48 mg/l, clindamycin 1 mg/l and metronidazole 0.032 mg/l. The patient remained afebrile after the treatment applied and was discharged one month after admission.
A. finegoldii has rarely been implicated in infectious pathology in humans. To date, only three cases of infection by this anaerobe have been published, two of them in separate bacteraemias in patients with colon cancer and another in a patient on peritoneal dialysis with peritonitis6,7. In our case, the bacteraemia occurred as a consequence of peritonitis due to intestinal perforation, so the source of infection could possibly be due to intestinal alteration. The presence of this microorganism has been implicated in certain diseases, such as tumour pathology3,6. However, larger studies are needed to confirm this relationship.
The routine use of MALDI-TOF MS in clinical microbiology laboratories has greatly improved the identification of microorganisms, especially anaerobes. In addition, it is enabling the identification of new species which hitherto have not been related to human pathology, since phenotypic identification of them is difficult8. Species identification is highly likely when the log score is ≥2.08, but it must be confirmed when it falls below that cut-off by means of other techniques, such as 16S rRNA gene sequencing. Moreover, it is advisable when the microorganism identified rarely produces infectious pathology, as in our case.
Regarding treatment, the need to apply antibiotic bitherapy with piperacillin-tazobactam and metronidazole to avoid treatment failures due to the production of β-lactamases by some Gram-negative anaerobes should be highlighted, as well as adequate control of the focus of surgical infection to avoid sequelae and complications.
In conclusion, this is the third isolation of A. finegoldii as a cause of isolated bacteraemia in pure culture, and it indicates that this pathogen may be responsible for serious infections.
FundingNo.
Conflicts of interestThe authors have no conflicts of interest to declare.
