Spiroplasma, a genus of bacteria in the phylum Mycoplasmatota, is characterized by cell structures with no cell walls (1). Spiroplasma isolates have been primarily reported from plants, guts of insects, tick triturates, and crustaceans (2), although a few cases of Spiroplasma infection in humans have also been reported, causing cataracts and uveitis in infants and systemic infections in immunocompromised patients (3–6). We describe a rare Spiroplasma bloodstream infection in a patient after surgery for type A aortic dissection in China.

The case-patient, a 68-year-old man, underwent surgery to repair his aorta on June 3, 2022, and he developed a severe respiratory infection afterward while still hospitalized. Fibrobronchoscopy revealed extensive and severe airway erosion, with yellow and thick sputum adhering to the airway walls. A biopsy of a bronchial embolism was taken and sent for examination (Appendix Figure, panel A), and microscopic observation revealed a layered arrangement of thrombi mixed with neutrophils (Appendix Figure, panel B). On June 9, 2022, the patient’s health began to deteriorate (Appendix Table). The patient was diagnosed with pulmonary infection, acute respiratory distress syndrome, sepsis, and septic shock.

Medical staff performed multiple tests on the patient to identify an infectious etiology to explain the patient’s acute illness (Table). Candida tropicalis was cultured in bronchoalveolar lavage fluid (BALF) samples. Seven of 12 blood cultures tested positive (Bactec FX; Becton Dickinson, https://www.bd.com/en-us) for a microorganism that was isolated as rare colonies under conditions of 35°C and a 5% CO₂ atmosphere. Subcultures on Columbia blood agar showed pinpoint-size zones of hemolysis with no macroscopic colony growth at 4 days of incubation; however, Gram stain and Giemsa-Wright stain of the blood could not detect the presence of bacteria. Finally, metagenomic next-generation sequencing was performed on both the blood and BALF samples. Unique reads of Spiroplasma eriocheiris (n = 1,577 in BALF, n = 2,344 in blood), human alphaherpesvirus 1 (n = 66,185 in BALF, n = 1,942 in blood), and Aspergillus fumigatus (n = 7 in BALF, n = 12 in blood) were detected (Table). We have uploaded raw data to the National Center for Biotechnology Information Sequence Read Archive (BioProject no. PRJNA1021328).

Figure

Figure. Neighbor-joining phylogenetic tree based on 16S rRNA gene sequences from a postsurgery patient with a blood infection, China, 2022. Tree shows the phylogenetic relationship among the strain DGKH1 from this...

We characterized the cultivated microorganism, designated DGKH1, by 16S rRNA gene sequencing and whole-genome sequencing analysis. Results of 16S rRNA gene phylogeny show DGKH1 is closely related to S. eriocheiris CCTCC M 207170^T (Figure). However, the average nucleotide identity value between the genomes of the 2 isolates was 94%, and the average digital DNA–DNA hybridization value between them was 56%, both of which were lower than the threshold values (95%–96% average nucleotide identity and 70% digital DNA–DNA hybridization) used for delineating prokaryotic species (7). Therefore, DGKH1 is represented as an unclassified species that is phylogenetically related to S. eriocheiris. The 16S rRNA gene sequence (accession no. OQ955597) and genomic DNA sequence (accession no. JASTWG000000000) were deposited into GenBank.

Results of serum galactomannan testing were negative, and the patient did not respond clinically to voriconazole and caspofungin treatment. We theorize that C. tropicalis and A. fumigatus played an unlikely role in the patient’s infection, and their detection may reflect colonization or contamination. We postulate that Spiroplasma species and human alphaherpesvirus 1 were the main causes of pulmonary infection, acute respiratory distress syndrome, sepsis, and septic shock in this case. Human alphaherpesvirus 1 (previously known as herpes simplex virus 1) is a potential cause of multiorgan failure and septic shock (8). Although Spiroplasma infection is much less common, the related bacteria Metamycoplasma hominis (previously known as Mycoplasma hominis and Mycoplasmoides pneumoniae) can cause bloodstream infection, pneumonia, and septic shock (9). Unfortunately, even with the addition of acyclovir and doxycycline in the therapy, the patient developed multiple organ failure and died on June 23, 2022.

In conclusion, we report a rare case of Spiroplasma sp. blood infection in a patient after surgery for type A aortic dissection. Spiroplasma is an arthropod-infecting bacterium that may be part of the commensal microbiome of the human gut; there are 13 pieces of relevant information deposited into the gutMEGA database (http://gutmega.omicsbio.info) (10). Spiroplasma detection is challenging, and the discovery and diagnosis of emerging pathogens, such as the one we have described, can be aided by new technologies such as 16S rRNA gene sequencing and metagenomic next-generation sequencing.

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