First report of a bloodstream infection caused by Trabulsiella odontotermitis in a low-birth-weight newborn undergoing surgery for intestinal obstruction: a fatal case

Introduction

Trabulsiella, belonging to the Enterobacteriaceae family, was first reported by McWhorter et al. in 1991 [1]. In 2007, Trabulsiella odontotermitis, a bacterium specific to termites, was initially isolated from the gut of the termite Odontotermes formosanus Shiraki, in Taiwan Province, China [2]. T. odontotermitis was also found in diverse termite species, including Macrotermes natalensis [3], Odontotermes badius [3], Microtermes sp. [3], Odontotermes obesus [4], Coptotermes formosanus [5], and Heterotermes sp. [6]. There has been limited research conducted on T. odontotermitis, the existing research has particularly emphasized investigation of its metabolic function [3,4,6,7]. To the best of our knowledge, there have been no documented reports of T. odontotermitis causing infections in humans. In this report, we present a case of bloodstream infection caused by this bacterium in a low birth weight newborn.

Case report

A 30-year-old pregnant woman was admitted to the Third Affiliated Hospital of Zhengzhou University (Zhengzhou, China) due to foetal distress in the uterus. Following an immediate caesarean section, a female newborn weighing 2120 grams and with a gestational age of 34 weeks was delivered. The diagnosis and treatment process of the newborn are illustrated in Figure 1(A). The newborn exhibited symptoms of bowel obstruction, groaning breathing, and anaemia after birth. The newborn underwent immediate procedures on the day of birth to address the bowel obstruction, including resection of the affected intestine, repair of a small intestinal fistula, and adhesiolysis of the intestines under general anaesthesia. A blood transfusion was promptly administered to address anaemia. The surgeries were performed successfully, and the patient’s general condition remained stable following the operations. Ventilator therapy was utilized to manage respiratory distress, characterized by audible respiratory sounds from the first to the fifth day after admission. Piperacillin/tazobactam was administered from the second day to the ninth day following admission as a preventive measure against infection. On the 12th day of admission, the newborn presented with a range of symptoms indicative of infection, including a painful facial expression, abdominal distension, irritability, hypotension (blood pressure of 75/40 mmHg), tachypnea (respiratory rate of 60 breaths per minute), tachycardia (heart rate of 180–220 bpm), increased levels of C-reactive protein (CRP, 8.57 mg/L), decreased blood oxygen saturation (85–93%), and decreased white blood cell (WBC) counts (4.12 × 10⁹/L). Simultaneously, the blood culture conducted on the same day yielded a positive result (time to blood culture positivity: 14.9 h), indicating the presence of T. odontotermitis. On the 13th day of admission, the newborn exhibited a variety of symptoms, including skin and mucous membrane bleeding, stomach bleeding, liver failure, renal failure, hypotension (blood pressure of 46/20 mmHg), tachycardia (heart rate of 170–200 bpm), elevated levels of CRP (32.11 mg/L), decreased blood oxygen saturation (90–95%), and reduced WBC counts (8.84 × 10⁹/L). Meanwhile, the blood culture conducted on the same day yielded a positive result (time to blood culture positivity: 31 h), indicating the presence of Microbacterium laevaniformans. Blood transfusion and ventilator therapy were once again employed to address anaemia and respiratory distress from the 13th to the 15th day following admission. During the patient’s admission, clinicians relied on the initial Gram stain results, local epidemiological data, and the patient’s deteriorating condition to prescribe meropenem and fosfomycin from the 13th to the 15th day. In addition, on the 14th to 15th days, vancomycin was introduced. On the 15th day of hospitalization, the newborn experienced a persistent decline in oxygen saturation, elevated heart rate, and disseminated intravascular coagulation (DIC). Despite extensive rescue efforts, the newborn unfortunately succumbed to these complications. The patient’s death was attributed to septic shock, multiple organ failure, DIC, and neonatal intestinal obstruction. The laboratory examination results obtained during hospitalization are shown in Supplementary Table S1.

Figure 1. (A) Timeline to summarize the case history of patient’s admission, treatment, and isolate collection. The colonial morphology of TBY01 was observed using various agar media, including Columbia blood agar (B1), chocolate agar (B2), eosin methylene blue (EMB) agar (B3), Salmonella-Shigella (SS) agar (B4), and Mueller-Hinton (MH) agar (B5). Additionally, Gram staining was performed to further characterize the isolate’s morphology (B6). (C) Whole-genome phylogenetic analysis of the T. odontotermitis isolates in the NCBI database. In addition to TBY01 in this study, there were seven T. odontotermitis strains available in the NCBI database (1 August 2023), including TbO1.1 (GenBank accession no. GCA_001297845.1), TbOT1.10 (GCA_001297775.1), TbOT1.3 (GCA_001297785.1), TbO2.3 (GCA_001297765.1), 01 (GCA_001188485.1), TbO2.7 (GCF_001297855.1), and 12 (GCA_001188495.2). Conserved marker genes in the eight T. odontotermitis genomes were extracted and aligned using GTDB-Tk (v2.1.1) [8]. Phylogenetic analysis was conducted with IQTree2 (v2.2.2.3; -m MFP) [9] based on these marker genes from GTDB, and the phylogenetic tree was visualized in iTOL (https://itol.embl.de/). The fill colour of the rectangle represents a specific geographic location, while the stroke colour represents the host.

Discussion

T. odontotermitis and M. laevaniformans were detected in the blood cultures on the 12th and 13th days of admission, respectively. The survival rates of Galleria mellonella larvae injected with the M. laevaniformans isolate (100% survival at 24 h and 90% survival at 72 h; data not shown) were not significantly different from those injected with the T. odontotermitis isolate (TBY01), E. coli ATCC 25922 or phosphate-buffered saline (PBS) (Supplementary Figure S2A). This result suggests that both the M. laevaniformans isolate and TBY01 exhibit comparable and relatively low levels of virulence. Given the compromised physical condition and weakened immune system of the newborn, along with symptoms indicative of infection such as a painful facial expression, abdominal distension, irritability, and increased levels of CRP, it is possible that the newborn developed a postoperative bloodstream infection caused by multiple bacteria. M. laevaniformans strains isolated from blood have been described previously [10,11]; thus, this report specifically focuses on T. odontotermitis isolated from blood. TBY01 was initially identified as Escherichia fergusonii using the Vitek 2 automated system and Enterobacter hormaechei using MALDI-TOF MS. However, subsequent 16S rRNA sequencing and whole genome sequencing confirmed its true identity as T. odontotermitis. Similarly, the M. laevaniformans isolate was initially identified as Microbacterium flavum using MALDI-TOF MS. However, 16S rRNA sequencing and assessment of phenotypic characteristics (yellow-white colonies and growth at 37 °C) [12] verified its true identity as M. laevaniformans. For rare bacteria, the accuracy of identification using Vitek 2 and MALDI-TOF MS may be compromised, making molecular identification a more reliable approach.

TBY01 is a gram-negative bacillus with pink pigmentation (Figure 1(B6)). Its colonies are characterized by their large size, thickness, greyish white colour, moisture, smoothness, and opacity (Figure 1(B1–5)). Through biochemical tests, the isolate exhibited positive utilization of D-glucose, D-maltose, and D-mannitol, while showing negative results for oxidase activity, H₂S generation, and urease activity (Supplementary Table S2). TBY01 was subjected to drug susceptibility testing (Supplementary material). According to the CLSI M100 32nd edition Enterobacterales breakpoints, the isolate showed susceptibility to the following antibiotics: amikacin, gentamicin, tobramycin, ampicillin, ampicillin/sulbactam, piperacillin/tazobactam, cefotetan, ceftazidime, ceftriaxone, cefepime, aztreonam, ertapenem, imipenem, meropenem, and trimethoprim/sulfamethoxazole (Supplementary Table S3). Clinicians decided to administer meropenem, along with fosfomycin and vancomycin, for the treatment of the infection. Unfortunately, the patient’s condition seriously deteriorated, possibly due to her severely compromised physical condition. Additionally, the source of TBY01 bloodstream infection remains unclear. The 30-year-old pregnant woman underwent a caesarean section due to foetal distress. There were no signs of infection during her hospitalization, and she was discharged three days after giving birth. Based on the newborn’s history of intestinal surgery and the documented presence of T. odontotermitis in the human gut microbiota [13], there is speculation that this bacterium, known to be associated with bloodstream infections, may originate from the intestine. Regrettably, faecal culture was not conducted in this case.

We performed whole-genome sequencing of TBY01 to reveal its genomic characteristics (Supplementary material). TBY01 contained a 4.7-Mb genome, including a 4.65-Mb chromosome and a 51.5-kb plasmid (pTBY01). The TBY01 chromosome and pTBY01 plasmid sequences were deposited under GenBank accession numbers CP125781 and CP125782, respectively. The genome was found to contain genes encoding enzymes that may be involved in 80 different metabolic processes according to Gene Ontology (GO) such as carbohydrate, glutathione, lipid, nitrogen compound, amino acid, nucleobase-containing compound, formate, and organic phosphonate metabolism (Supplementary Table S4). As of 8 August 2023, the NCBI Assembly database contained a total of eight T. odontotermitis genomes. Seven strains were isolated from termite species (five from Heterotermes sp. in Mexico and two from Macrotermes natalensis in South Africa), while one strain (TBY01) was isolated from humans (Figure 1(C)). The strains can be classified into three distinct branches in the phylogenetic tree based on their respective hosts or geographic locations, with a closer genetic relationship observed between TBY01 and the two strains from Macrotermes natalensis in South Africa. Additionally, the plasmid pTBY01, belonging to the incompatibility group IncN, harbours the fluoroquinolone resistance gene qnrS1 and the trimethoprim resistance gene ΔdfrA14 (Supplementary Figure S1). The best hit was with the plasmid “unnamed3” (CP061973.1; identity of 99.84%, coverage 92%) available on the NCBI nucleotide collection (nr/nt) database (4 August 2023; supplemental material).

In addition, we evaluated the virulence of TBY01 by performing survival analysis, melanization analysis, and hemocyte counting in infected G. mellonella larvae (Supplementary material; Supplementary Figure S2). As shown in Supplementary Figure S2A, the survival rates of G. mellonella larvae injected with TBY01 (90% survival at 24 h and 80% survival at 72 h) were not significantly different from those injected with E. coli ATCC 25922 (90% survival at 24 h and 80% survival at 72 h) or PBS. This indicates that the virulence of TBY01 is low. In accordance with the results, no virulence genes were detected in the whole genome sequencing data (data not shown). The number of melanized larvae was essentially equal to the number of larval mortalities at each time point (24, 48, and 72 h) (Supplementary Figure S2B; data for 24 and 72 h not shown). However, injection of TBY01 into G. mellonella larvae resulted in a significant decrease in haemocyte density when compared to larvae that were uninfected or infected with E. coli ATCC 25922 (P < 0.01; Supplementary Figure S2C). This suggests that TBY01 may lead to increased haemocyte cell death.

In conclusion, the first report of T. odontotermitis causing human infection is presented in this study. Significantly, TBY01 does not exhibit high virulence or widespread resistance, and it may also cause rapid disease progression in individuals with severely compromised immune systems. TBY01 isolated from bloodstream infections is speculated to have originated from the intestine. T. odontotermitis strains tend to cluster based on their respective hosts or geographic locations, which may be related to the fact that there are very few sequenced strains. Additionally, clinicians and microbiologists should remain vigilant regarding the presence of rare bacteria and utilize sequencing techniques for accurate identification.

Ethics statement

The study was approved by the Ethics Committee of the Third Affiliated Hospital of Zhengzhou University.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the Medical Science and Technology Planning Project of Henan Province, China (grant number LHGJ20200457) and PhD research startup foundation of the Third Affiliated Hospital of Zhengzhou University (grant number 2021077).