Resistance of Klebsiella pneumoniae to the innate immune system of African green monkeys

- Hypermucoviscosity phenotype (HMV) is key in Klebsiella pneumoniae virulence.
- The HMV was associated with serotypes K1 and K5, and virulence genes magA and rmpA.
- HMV isolates present resistant to serum-mediated and oxidative killing.
- HMV isolates were found to be highly cytotoxic to non-human primates monocytes.

In recent years, an emergent Klebsiella pneumoniae hypermucoviscosity (HMV) phenotype has been associated with increased invasiveness and pathogenicity in primates. In this project, bacteria recovered from infected African green monkeys (AGM) (Chlorocebus aethiops sabaeus) were screened for HMV phenotype, and were compared to non-HMV isolates in in vitro, serum, and oxidative-mediated killing assays. Complement-mediated killing was assessed utilizing freshly collected serum from healthy AGM. Oxidative-mediated killing was investigated utilizing sodium hypochlorite and hydrogen peroxide. Compared to non-HMV isolates, HMV isolates were more resistant to serum-mediated and oxidative killing (p < 0.05). Phagocytosis resistance was evaluated using AGM peripheral blood monocytes (PBMC), and results indicated that non-HMV isolates associated with the AGM PBMC to a greater extent than HMV isolates (p < 0.001). Measurement of lactate dehydrogenase release showed that HMV isolates were more cytotoxic to AGM PBMC than non-HMV isolates (p < 0.001). Thus, the hypermucoid phenotype appears to be an important virulence factor that promotes evasion of innate immune defenses.