Case Report: Vibrio Furnissii isolated from a case of acute gastroenteritis in China

Vibrio furnissii , formerly classified as the aerogenic biogroup of Vibro fluvialis , is a motile, Gram-negative, oxidase-positive, halophilic bacteria. It is widely distributed in the marine environment and marine products and was first defined in 1983 by Don J. Brenner. It ia an emerging pathogen can lead to diarrhea, bacteremia, cellulitis, and other manifestations. Whereas, its virulence factors and molecular epidemiological features remain largely unknown. The treatment guideline for V. furnissii infection has not been established. We herein report the first case of gastroenteritis caused by V. furnissii in China and review the relevant literature. Case presentation: A 42-year-old female presented with diarrhea and nausea associated with fever. Microscopic examination of feces displayed 2-4 white blood cells/HPF, 0-1 red blood cells/HPF. The occult blood test was weakly positive. Laboratory tests displayed a high proportion of blood cell neutrophils. A feces culture revealed V. furnissii infection . Conclusion: V. furnissii is a pathogenic bacteria often ignored as a non-cholera Vibrio compared to Vibrio cholerae and Vibrio haemolyticus which are more common in patients. The combination therapy of levo-floxacin, berberine hydrochloride tablets, and paracetamol tablets is an effective treatment of gastroenteritis caused by V. furnissii. More importantly, clinical monitoring of V. furnissii is imperative.


Introduction
V. furnissii is a gram-negative, straight/slightly curved rod that is motile via polar flagella [1]. V. furnissii has frequently been isolated from the estuarine environment [2]. It is one of the 11 non-cholera

Case Report
Vibrio species pathogenic in humans that cause clinical infections such as diarrhea, bacteremia, and cellulitis [2][3][4][5]. The bacterium resembles Aeromonas hydrophila in phenotypical and biochemical properties with the exception that A. hydrophila does not have the ability to grow in 6% NaCl [6]. The virulence factors and molecular epidemiological features of V. furnissii remain largely unknown. The best antimicrobial therapy for V. furnissii infection has not been established yet. There have been only a few cases of reports of gastroenteritis related to V. furnissii, none of which have been reported in China.

Case Presentation
A 42-year-old woman with acute gastroenteritis and fever for two days presented to the emergency department of the Academy of Traditional Chinese Medicine (Jiangsu, China) on 31 August 2022. She had three to four episodes of loose stools per day and nausea. She was not on any medications and had no history of cardiovascular disease, diabetes mellitus, chronic kidney disease, or hypertensive disease.
Her stools were watery, not blood stained, without melena, and non-purulent. Microscopic examination of the feces displayed 2-4 white blood cells/HPF, 0-1 red blood cells/HPF. The occult blood test was weakly positive. On examination, the patient's vital signs were normal and her temperature was 38.7℃.
The patient was started on oral levofloxacin (0.5 g once daily), berberine hydrochloride tablets (0.2 g every eight hours), and paracetamol tablets (0.5 g every 12 hours). The stool specimen from the case was received at the microbiology laboratory attached to the Academy of Traditional Chinese Medicine (Jiangsu, China). The specimen was inoculated on a blood agar plate and alkaline peptone water (pH 8.6) according to the standard procedures. We performed a sub-cultivation from the alkaline peptone water to the vibro chromogenic agar plate after enrichment for six hours as the alkaline peptone water became turbid. The colonies on the blood agar plate were yellow with a clear hemolytic ring and were wathet blue on the vibro chromogenic agar.
The colonies were confirmed as Vibrio furnissii using the Matrix-assisted laser-desorption/ ionization time-of-light mass spectrometry (MALDI-TOF MS; Antu, Zhengzhou, Henan, China). The score value was 9.127. Antibiotic susceptibility testing of the isolates was taken by the standard Kirby-Bauer disc diffusion method following the Clinical and Laboratory Standards Institute (CLSI) guidelines. The strain was resistant (ug per disc) to ampicillin (10), and sensitive (ug per disc) to amoxicillin/clavulanic acid (20/10), ampicillin/sulbactam (10/10), piperacillin (100), piperacillin/tazobactam (100/10), amikacin After treatment, the patient was symptomatically better and the repeat stool culture revealed no intestinal pathogens.

Discussion
V. furnissii is a gram-negative capsular vibrio with no spores. It is 1.5-4 μm long and 0.3-0.8 μm wide.
It is ubiquitously present in aquatic marine environments, is halophilic, and can grow well in 3% and 70% sodium peptone water. It cannot survive without salt [7]. This bacteria causes diarrhea and bromatoxism, but the clinical manifestations are mainly diarrhea and stomach ache accompanied by nausea and emesis.
Members of the genus Vibrio are major causes of human gastroenteritis resulting from the consumption of contaminated marine products. In oue case, the patient ate preserved vegetables rich in salt from a fast food restaurant. This food was likely contaminated by the V. furnissii. The organism then multiplied quickly, causing acute gastroenteritis.
Hemolysin, in addition to other pathogenic Vibrio factors, such as proteases, hemagglutinins, and other hydrolytic exoenzymes, has been suggested to be an important virulence factor in the pathogenesis of many Vibrio species and is the most feared virulence factor involved in the gastrointestinal disorders caused by V. parahaemolyticus [8][9][10]. However, little is known about V. furnissii and its possible production of toxins, which may be important in both pathogenesis and virulence. Flagellum is a virulence factor in Vibrio and several bacteria. V. furnissii culture supernatants lyse erythrocytes, and their lethal effects on epithelial cells are a remarkable feature of pathogenesis [11]. In addition to haemagglutinins and other hydrolytic exoenzymes, hemolysin is also responsible for pathogenesis [12][13][14][15][16]. A functional role of phosphomannomutase in the virulence of V. furnissii was reported [17]. The lipopolysaccharide component also plays an important role in virulence by preventing the formation of the complement membrane attack complex, precluding cell lysis [17].
A literature survey of the PubMed database showed no reports of V. furnissii being isolated from humans in China. There are few bacteremia and gastroenteritis cases reported associated with V. furnissii in other countries (Table 1), and a small number of established in-depth studies have been done on this emerging pathogen to date. In our case, the V. furnissii isolated was resistant to ampicillin and sensitive to amoxicillin/clavulanic acid, ampicillin/sulbactam, piperacillin, piperacillin/tazobactam, amikacin, gentamicin, ciprofloxacin, levofloxacin, chloramphenicol, and trimethoprim/sulfamethoxazole. Other reports revealed the same pattern of antibiotic resistance [3,18]. The mechanism of antimicrobial resistance of V. furnissii may due to posses-sing of drug resistance genes [19]. Treatment with oral levofloxacin coupled with berberine hydrochloride and paracetamol tablets was effective against the gastroenteritis caused by V. furnissii in oue case.