The patient in this case report had polycystic kidney disease combined with polycystic liver. When she was referred to our hospital, she had end-stage renal disease for which she was on regular hemodialysis treatment, and her blood culture was positive for E. casseliflavus, a rare pathogen. Continuous antibiotic treatment and monitoring indicated that she had a cystic infection in the liver. Five days before her hospitalization, she had intestinal symptoms. Thus, the intestinal bacteria could have entered the bloodstream and then disseminated through blood to result in secondary liver cyst infection.
Diagnosis and treatment of polycystic liver cyst infection are challenging due to the lack of clear laboratory test results and the difficulty in detecting intracystic infection through imaging examinations. The contents of the cyst, such as pus or tissue, appear similar to those of hematoma [5], and its enhancement is manifested as residual renal parenchyma [6–7]. In this case, PET-CT proved to be a promising method for detecting infection, and MRI helped determine the location of the infected cyst for interventional treatment.
There are no clear recommendations or guidelines for the treatment of polycystic liver and its comorbidities, and empirical treatments are mostly applied at various centers [9–11]. Once multiple cystic liver infection or a suspicious infection is diagnosed, antibiotics should be used first to treat the infection. Because the infection occurs in the capsule, quinolones with strong lipid solubility are preferred. If the symptoms are not relieved within 72 h, third-generation anti-infection treatment with ceftrian should be added to the regimen and the antibiotic regimen should be adjusted according to drug sensitivity and culture results. Accordingly, in the present case, the laboratory parameters were regularly monitored and the antibiotic regimen was adjusted based on the laboratory data. If the infection cannot be controlled with anti-infection treatment, timely surgical intervention is necessary [12]. The surgical treatment of polycystic liver infection generally includes percutaneous liver cyst drainage, laparoscopic decompression of the liver cyst, laparoscopic liver resection, and liver transplantation. If the cyst is large (> 5 cm) and the clinical manifestations are caused by individual larger cysts, early percutaneous drainage is recommended. If the number of cysts is large and it is difficult to control the symptoms of infection by puncture drainage, laparoscopic cyst clipping decompression or partial hepatectomy can be used according to the number, size, and distribution of cysts [3, 12, 13]. In the present case, it was difficult to control the infection in the early stage of antibiotic treatment. Therefore, the cyst was punctured and drained under ultrasound guidance. At the first drainage, 160 mL of dark brown liquid was drawn. Following this, the patient’s body temperature reduced. Because of the separation of the cyst observed on an MR scan, cyst puncture and drainage were performed at two sites. Later, because of cyst infection, moxifloxacin was used for anti-infection treatment.
In this case, the blood culture before admission showed a positive result for E. casseliflavus, and the culture of the aspirated cyst fluid also confirmed the presence of E. casseliflavus. This indicates that the patient had both bacteremia and a liver cyst infection caused by this bacterium. In the United States, vancomycin-resistant Enterococcus has gradually become an important cause of invasive infections [14, 15]. A study evaluating cases of bacteremia caused by E. casseliflavus and E. gallinarum showed that malignancy (70.0%) and diabetes mellitus (20.0%) were the most common complications in these bacteremia cases, suggesting that E. casseliflavus bacteremia is more likely to occur in immunocompromised hosts [16]. During the patient's hospitalization, tumor markers CA125 and CA199 were elevated, but no solid tumors were identified. Long-term dialysis was also identified as a risk factor for colonization by E. casseliflavus [17–18]. In a survey conducted in the United States, the 30-day all-cause mortality rate of E. casseliflavus patients was found to be 10.4%, and the comprehensive treatment failure rate was 39.6% [19].
E. casseliflavus carries the VanC gene intrinsically and exhibits moderate resistance to vancomycin (VCM). Due to this moderate resistance, the Clinical and Laboratory Standards Institute (CLSI) considers VCM concentrations below 4 mg/dL to be susceptible for Enterococcus species, and therefore, the drug is not actively recommended for the treatment of E. casseliflavus [20–21]. In fact, the minimum inhibitory concentration (MIC) of VCM demonstrated in this case was 4 mg/dL. It is important to note that even if microbiological tests show that this microorganism is susceptible to VCM, the actual therapeutic effect of VCM is likely to be low [20–21]. However, most strains of E. casseliflavus are sensitive to penicillin and ampicillin. Therefore, combination therapy with ampicillin and aminoglycoside drugs such as gentamicin or streptomycin is considered the standard treatment [22]. Since most E. casseliflavus strains are negative for β-lactamase, meropenem does not have a better effect than ampicillin in the treatment of enterococcal infections. Thus, in the reported cases, there is no clear indication for combination therapy with meropenem and β-lactamase inhibitors [23]. In this case, the patient was treated with meropenem and β-lactamase inhibitors, but the infection remained difficult to control. This may be explained by the deep location of the infection site within the hepatic cyst.
The difficulty in treating E. casseliflavus infection in polycystic liver disease may be attributed to several factors. Firstly, the lesions in polycystic liver disease are typically located deep within the liver, making it challenging for antibiotics to effectively penetrate the infection site. Secondly, E. casseliflavus exhibits intrinsic resistance to vancomycin under natural conditions, rendering conventional treatment with vancomycin ineffective. Additionally, the multidrug resistance and spread of resistant genes in E. casseliflavus contribute to the difficulty in treating the infection. Promising outcomes were achieved after full puncture and drainage in this case. The patient is currently undergoing regular dialysis treatment, and the levels of inflammation markers, albumin, and other nutritional indicators have returned to normal. Therefore, in cases of difficult-to-control polycystic liver infection, immediate PET-CT examination is recommended to exclude the possibility of intracystic infection and promptly perform puncture drainage as an interventional treatment.