Discussion and Conclusions
Yersinia regensburg belongs to the Enterobacteriaceae family. Yersinia regensburg is mainly distributed in well water and also exists in insect intestinal flora. It can infect humans and has been isolated from human respiratory tract, wounds, blood, urine and feces. This bacterium is described as a gram-negative enterobacteria, without endospores, and possessing peripheral flagellar movement. [1-3] There are biochemical similarities between Y. regensburgei and H. alvei, which can easily be misidentified by automated systems. It has been found that Y. regensburgei has its own unique characteristics. It cannot produce hydroxyproline amidase, tripeptidase or proline deaminase due to its weak catalase positive. Stoke et al. used a series of parameter tests to distinguish between Y. regensburgei and H. alvei. These parameters include hydroxyproline amidase, maltosidase, tripeptidase, proline deaminase, and catalase. Reaction, Voges-Proskauer test and fermentation test of glycerol, melibiose and inositol [4]. According to reports, the Phoenix instrument can accurately identify Regensburg yeast through key tests of citrate utilization and melibiose fermentation. [6] But the detection rate of Yersinia Regensburg did not increase as expected, partly because of different commercial systems. [5,8]
The development of sequencing omics provided a new and powerful method for identifying bacterial species. 16S rRNA gene sequencing is also very useful in bacterial classification. Based on whole genome sequencing analysis, Desiree J et al. obtained more detailed structure and function information of Y. regensburgei. [18] By combining data, the advantages of these technologies can be used to improve the accuracy of identification.
However, due to the high similarity, many researchers have encountered resolution problems at the genus and/or species level in Enterobacteriaceae through 16s rRNA sequencing. [11] MALDI-TOF MS is based on the analysis of protein profiles and has been used in the identification and separation of strains in clinical microbiology laboratories. Its accuracy rate is higher than that of conventional bacterial culture methods. [10] The technique matrix-assisted laser desorption ionization–time-of-flight mass spectrometry is considered to be a promising alternative to the expensive and time-consuming 16s rRNA sequencing method, which has high resolution capability for bacterial strains that are difficult to distinguish. We reported for the first time a case of Yersinia regensburgh infection with no underlying disease and an immunocompetent host, and reviewed the relevant literature. The main details described in these reports are summarized in Table 2. This bacteria can be cultured using standard culture methods. [6-8,12-15], most Yersinia regensburg infections occur in patients with comorbidities such as chronic kidney disease [13] -15], high-dose steroids [6,15] , Liver disease [6,12] and diabetes. [14-15] Patients without underlying diseases are rarely infected with Yersinia regensburg. [16] Almost all cases occurred in hot and humid areas, and our report is no exception. At the same time, cases of Yersinia regensburgh infection were relatively rare, and fewer infected hosts were immunocompetent. At present, only one case Y. regensburgei infected was an immunocompetent host, and the infection after craniotomy causes postoperative secondary osteomyelitis [20]. In general, Y. regensburgei causes life-threatening infections in immunocompromised individuals, especially those infected with human immunodeficiency virus (HIV), immunosuppressive therapy, and organ transplant recipients. [6-8] Other possible risk factors include alcohol abuse. [12] In this case, the laboratory indicators HbA1c, RF negative, ESR, and IgG levels proved that the patient was an immunocompetent host. Stock and colleagues [4] proved that Y. regensburgei possesses the amp C gene and highly inducible β-lactamase, and is inherently resistant to azithromycin and some β-lactam antibiotics. AmpC β-lactamase gene (blaYOC-1) and a conjugating plasmid (pYRW13-125) are present in Y. regensburgei W13. These plasmids confer resistance to multiple antibiotics, including tetracycline, ampicillin (chloramphenicol and florfenicol), and streptomycin. [19] While cefoperazone/sulbactam and levofloxacin still have ability to kill Y. regensburgei, the patient in this study were successfully treated with these antibiotics.
However, there is not enough information to fully understand the pathogenesis and resistance mechanisms of Yersinia regensburg. Although Y. regensburgei can infect immunocompromised hosts, it was worth noting that these immunocompromised hosts suffered tissue damages. When the body’s immune system is involved in the repair of tissue damage, its antibacterial immune response may be weakened [21]. Therefore, the prerequisite for Y. regensburgei infection may be still immune abnormality.
In summary, in this case, this patient had no underlying diseases and no systemic symptoms such as fever and chills. Agricultural activities and stab wounds may be related to Yersinia Regensburg infection. The main cause of chronic non-healing wounds was deep wood thorns. Wound healing is also closely related to immediate debridement, abscess drainage and wound care. Cooperation between clinical microbiology laboratories and surgeons is essential for early diagnosis of Yersinia regensburg, antibiotic selection, and surgical debridement.