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.