To date, there have been no reports of culturing vagococcus fluvialis from human urine specimens, and there are very few reports of human infections caused by vagococcus fluvialis: In 1997, Teixeira[3] reported the isolation of 4 strains of riverine vagococcus fluvialis from human clinical specimens, most of which were initially classified as unidentified enterococci. Teixeira confirmed them as vagococcus fluvialis through the study of phenotypic and genotypic characteristics of the isolates, providing the molecular characteristics of vagococcus fluvialis and the first evidence of their possible association with human infections. In 2008[4], Ali Al-Ahmad isolated vagococcus fluvialis from filled teeth with periapical lesions. In 2019[9], Jadhav reported a case of vagococcus fluvialis infective endocarditis. In 2019[11], Zhou reported the isolation of vagococcus fluvialis from postoperative infection puncture fluid in the lower segment of the left femur in humans. In 2020[12], Kucuk reported a case of vagococcus fluvialis isolated from ascites in a patient with liver cirrhosis. In 2023[15], Wang first reported the isolation and identification of vagococcus fluvialis from gallbladder puncture fluid in patients with chronic cholecystitis. Vagococcus fluvialis can also be isolated from various injuries in pigs, cows, cats, tonsils, and the tonsils of horses[20]. It is a Gram-stain positive, catalase-negative cocci. Most of the strains isolated from injury cases were obtained from animals with conditions unrelated to vagococcus infections. Only a portion of vagococcus fluvialis strains are motile. Many strains produce positive reactions in the V-P test, alkaline phosphatase, and leucine arylamidase test, or ferment lactose and D-tagatose to produce acid. It has been reported that this bacterium causes severe damage to rainbow trout in fish farming at low water temperatures[22]. Given that vagococcus fluvialis can cause infections in both humans and animals, and can be isolated from clinical specimens, it is often misidentified or overlooked in clinical laboratories due to diagnostic challenges. Therefore, when isolating suspected vagococcus fluvialis-like bacteria from various specimens, it is important to differentiate them from relevant bacterial species and perform accurate identification. Meanwhile, we also discovered some advanced materials for precise detection of bacteria, as well as the latest nanomedical approaches for treating bacterial infections, which have propelled new strategies for accurate diagnosis and treatment[23][24][25].
Although vagococcus fluvialis infections are currently extremely rare, these research reports indicate that if timely and appropriate antimicrobial treatment is not given in clinical practice, it can lead to bloodstream infections, and in severe cases, it can be life-threatening. Studies have shown that vagococcus fluvialis express a large number of proteins related to known Gram-stain positive bacterial pathogenic and virulence factors, among which enolase and phosphoglycerate kinase are highly expressed, providing further directions for the study of the pathogenic mechanisms of vagococcus fluvialis[1].
Many literature reports indicate that the main pathogens causing urinary tract infections are Escherichia coli, followed by Staphylococcus spp., Pseudomonas aeruginosa, Klebsiella spp., and Proteus spp. However, cases of vagococcus fluvialis causing infections are extremely rare. In this study, preliminary verification of the pathogenic bacteria belonging to the rare genus of vagococcus fluvialis was conducted through colony morphology observations after blood agar plate cultivation, Gram-stain microscopic analysis, automated microbiological detection instrument bioassays. To ensure accurate identification of the pathogenic bacteria, in combination with relevant literature reports, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used, which has significant advantages in identifying rare bacterial species[10][21]. In this study, MALDI-TOF MS technology was also utilized for identification and the results once again confirmed it to be vagococcus fluvialis (with a confidence level of 99.9%).
So far, there is no standard method or criteria for drug sensitivity testing of vagococcus fluvialis. In this study, the drug sensitivity test of enterococci was used as a reference, which suggests the need for more clinical research to standardize drug sensitivity testing for this bacterium. The patient in this case received cephalosporin treatment for infection upon admission, and based on the patient's condition and the results of various infection indicators such as blood routine, C-reactive protein, cytokines, and procalcitonin, it was considered that the patient's infection was still manageable. Postoperative re-examination of urine culture showed no bacterial or fungal growth, and other infection indicators were within normal range. The patient improved and was discharged one week after surgery.
One of the principles of using antimicrobial drugs is that they should not be changed or discontinued arbitrarily. Generally, antimicrobial drugs need to be taken for 2–3 days to reach a certain drug concentration in the body before they take effect. Changing drugs at will is not conducive to the effectiveness of the drugs. The use of antimicrobial drugs should pay attention to the correct drug level. However, not all diseases require high-level drugs. As long as the selected drugs are appropriate, even low-level drugs can exert sufficient effects. Excessive use of high-level drugs can lead to bacterial resistance and affect the efficacy of treatment for severe infections. The selection of appropriate antimicrobial drugs should be based on the characteristics and severity of the infection, and the effects and effectiveness of antimicrobial drugs on pathogenic bacteria are closely related to the characteristics and severity of the disease. Therefore, this case has certain clinical value for diagnose and the rational use of antimicrobial drugs in patients with vagococcus fluvialis infections.