Case presentation
In May 2022, a 71-year-old female from China suffered from limited mobility and pain for 2 months after a trauma to her left lower leg, and the symptoms aggravated with redness and swelling for 3 days. Two months ago, she hit a tree while doing farm work. The antero- medial part of the leg was broken and bleeding without appreciable erythema or swelling. The next day, the patient was admitted to local hospital and received wound irrigation and antibiotic treatment. Soon, the wound on leg healed but the patient still felt pain occasionally. Three days prior to her admission, she felt more pain in the wound and fever around the wound. There was no obvious exudation and pus around the wound, which was only covered with some scab.
Her body temperature was 36.4°C, with blood pressure of 171/83, a pulse rate of 67 beats per minute, and oxygen saturation was 98% breathing ambient air. Physical examination on admission was unremarkable, except for her left leg wound as described. There was no history of any major illness in the past, which indicated that she was an immunocompetent host.
Blood examinations revealed anemia with hemoglobin of 90g/liter (reference range, 110 to 160 grams/liter). Her white blood cell count was 6.03 × 109 cells/liter (reference range, 4.0× 109 to 10.0 × 109 cells/liter), differential with 69.50% neutrophilic granulocyte (reference range, 50.0% to 70.0%) and 19.70% lymphocytes (reference range, 20.0% to 40.0%). Blood biochemistry results demonstrated serum creatinine of 58μmol/liter (reference range, 45 to 84 μmol/liter), aspartate amino transferase (AST) 19.1U/liter (reference range, 0 to 32 U/liter), alanine aminotransferase (ALT) 16.0 U/L (reference range, 0 to 33 U/liter), albumin 36.8 g/L (reference range, 35 to 52 g/liter), D-dimer was slightly elevated at 0.83ug/ml (reference range, 0 to 0.55 ug/ml) CRP, ESR, renal function and electrolytes were normal. In addition, HbA1c 4.68%, RF negative, ESR 3mm/h, and IgG levels 11.3g/L, and these lab indicators were within the reference ranges, which demonstrated the patient was an immunocompetent host.
The patient was empirically treated with ceftriaxone for 7 days (1 g intravenous every 24h), but her condition did not improve during treatment. The surgical debridement and abscess drainage were performed by surgeons. Wood thorn inside the wound was removed. The wound after the surgery was shown. (fig.1A) Hematic pus was sent for bacterium cultures and a drug susceptibility test. (fig.1B) A Gram smear of the pus revealed numerous leukocytes. Hematic pus was spread onto blood and MacConkey agar plates (Crmicrobio, China) for bacteria inoculation and then observed morphology of bacterial colony with cultured for 24h at constant 36℃. The colonies were moist, grey-white, semitransparent, regular shaped with slightly elevated and smooth surface. (fig.1C) Gram-negative bacillus can be seen under the microscope. (fig.1D)
In order to identify the species of infected organism, we used the D2Mini semiautomated system (D2Mini, DL Biotech Company, China). The results of a series of biochemical assays revealed it to be Hafnia alve with 99.93% probability. It was positive for glucose, ornithine, lysine, citrate, L-arabinose, raffinose, galactosidase, maltose, cellobiose tests and negative for hydrogen sulfide, urea, arginine, Voges Proskauer, amino acid, malonic, phenylalanine, indole, sucrose, lactose, inositol, melibiose, aesculin, salicin, adonitol, Methylalpha-D- glucopranoside, gelatin, sorbitol tests(DL 96NE, DL Biotech Company, China). Then, it was further exposed again to identification by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF) (Vitek MS, bioMerieux, France). MALDI- TOF analysis identified the colonies as Y. regensburgei. (99.9% confidence interval) Confidence interval of 99.9% is considered acceptable criteria for bacterial identification of gram-negative enteric bacteria.
There were currently no interpretive criteria for susceptibility testing of Yokenella regensburgei. The minimum inhibitory concentrations (MICs) were determined using the agar dilution method following the guidelines of the Clinical and Laboratory Standards Institute (CLSI), and the susceptibility patterns were interpreted according to the CLSI breakpoint criteria of Hafnia alve. The MIC results as shown in Table 1. According to the result for drug sensitivity, antibiotic therapy was switched to cefoperazone/sulbactam and levofloxacin. The patient responded well to the antibiotics and the wounds healed soon(fig.1E). These results also supported that the infected organism was Yokenella regensburgei.