Positive string test in hypervirulent Klebsiella pneumoniae liver abscess.

A 38-year-old diabetic woman presented with fever and jaundice for 4 days. On arrival, she was alert and hemodynamically stable. Physical examination revealed hepatomegaly. An abdominal computed tomography showed a large multiloculated abscess in the right liver lobe without biliary system dilatation (Fig. 1a). There was no evidence of pneumonia, endophthalmitis or central nervous system involvement. Klebsiella pneumoniae was isolated from the blood culture, which was susceptible to amoxicillin-clavulanic acid and ceftriaxone. String tests on colonies from culture media yielded positive results with strings measuring 7 mm in length (Fig. 1b). The diagnosis of hypervirulent K. pneumoniae (HvKP) was established following the detection of iuca, rmpA and peg344 gene.

Figure 1

a Abdominal computed tomography showing a large multiloculated abscess in the right lobe of the liver (segment V/VI/VIII). b Result of string test: formation of a string from stretching of the Klebsiella pneumoniae colonies isolated from the patient’s blood culture.

Hypervirulent strains of K. pneumoniae are more likely to cause severe and disseminated infections than classic K. pneumoniae strains. HvKP are associated with liver abscess, while other manifestations include pneumonia, endophthalmitis, meningitis and necrotizing fasciitis [1, 2]. Colonies grown on an agar plate have a hypermucoviscous appearance. The string test, which is simple to perform in the laboratory, can help in the early diagnosis of HvKP infection. The test is considered positive if a viscous string measuring >5 mm in length is obtained by stretching bacterial colonies on an agar plate with a bacteriology inoculation loop or needle [2]. Detection of HvKP is important due to its high mortality in comparison to multidrug-resistant and classical Klebsiella infections, where coexisting hepatobiliary disease is a potential risk factor for these infections [3].