Investigation of the virulence characteristics of Klebsiella pneumoniae isolates

Klebsiella pneumoniae, distinguished by its high virulence potential and increasing antibiotic resistance, has emerged as a significant global public health threat, particularly through its hypervirulent pathotypes that cause invasive infections. This study aims to determine the prevalence of hypervirulent Klebsiella pneumoniae in our region, to characterize its molecular and phenotypic features, and to assess their clinical implications. Between March and October 2024, a total of 289 Klebsiella pneumoniae isolates obtained from various clinical specimens were examined for string test positivity, capsular type, presence of the aerobactin gene, antibiotic susceptibility, extended-spectrum beta-lactamase production, and sequence types. A total of 11.8% of the isolates were identified as hypervirulent. The string test was positive in 79.4% (27/34) of hypervirulent isolates. The highest proportions of hypervirulent isolates were detected in empyema (20%), abdominal infections (18.2%), urinary tract infections (13.3%), osteomyelitis (11.1%), bacteremia (10.4%), and pneumonia (6.9%). The K2 capsular type was the most frequently detected among both hypervirulent and classical isolates. In hypervirulent isolates, carbapenem resistance and extended-spectrum beta-lactamase production were observed in 20.6% and 5.9% of cases, respectively, with two isolates exhibiting both mechanisms. Susceptibility rates to the tested antibiotics were generally higher among hypervirulent isolates. The identified sequence types in hypervirulent isolates included ST23 (25%), ST25 (25%), ST147 (25%), ST14 (12.5%), and ST65 (12.5%). Mortality rates were higher among classical strains (56.1%). Our study demonstrates that hypervirulent Klebsiella pneumoniae isolates are circulating in our region and that the K2 capsule type is predominant. The close relationship 80 between hypervirulent isolates identified by the string test suggests that it may be useful in the early identification of hypervirulent strains. In selected cases, antibiotics such as cefixime, trimethoprim-sulfamethoxazole, amikacin, gentamicin, and colistin may be considered for the empirical treatment of hypervirulent infections. The detection of the multidrug-resistant ST23-K1 clone emphasises the need for continuous surveillance programmes to monitor the regional spread of Klebsiella pneumoniae and to identify resistance-virulence interactions at an early stage.