Septicemic invasive Klebsiella pneumoniae infection in a cynomolgus monkey (Macaca fascicularis) with severe diffused suppurative meningoencephalitis

Abstract

A 2-year-old male cynomolgus monkey (Macaca fascicularis) showed neurological symptoms during quarantine for importation into Japan, and was euthanized due to poor prognosis. Gross anatomical examination revealed a hemorrhagic lesion around the lateral ventricle in the cerebrum. Histologically, severe diffused suppurative meningitis and ventriculitis were detected with numerous Gram-negative bacilli in the cerebrum. Immunohistochemically, the bacilli were positively stained with an antibody against Klebsiella pneumoniae. The bacterium was isolated from the liver, and it was confirmed to be K. pneumoniae by 16S rDNA sequencing. The isolate displayed a hypermucoviscosity phenotype, was positive for the rmpA and k₂A genes, and demonstrated multidrug resistance. These results suggest that invasive K. pneumoniae can cause septicemic infection, characterized by severe diffused suppurative meningoencephalitis in monkeys.

Keywords: invasive Klebsiella pneumoniae; meningoencephalitis; monkey.

Fig. 1.

a. Cerebrum, a cross-section. Hemorrhagic lesion was detected around the lateral ventricle. Bar=1 cm. b. HE staining of the cerebrum showing severe suppurative meningitis. Bar=500 µm. c. HE staining of cerebral ventricle showing severe suppurative ventriculitis with moderate hemorrhage. Bar=500 µm. The inserted figure is Gram staining of parenchyma around the lateral ventricle showing infiltrations of macrophages with numerous Gram-negative bacilli. Bar=20 µm. d. Immunohistochemistry counterstained with hematoxylin of the cerebrum showing that bacilli in the diffused infiltrations react with an antibody against Klebsiella pneumoniae. Bar=50 µm.

Fig. 2.

Positive string test. The HMV phenotype of K. pneumoniae is defined by the test, and mucoviscous string forms greater than 5 mm were determined to be positive results.