[Association of capsular types with antibiotic resistance and clinical prognosis in Acinetobacter baumannii]

Objective: Analysis of antimicrobial resistance and clinical outcomes in patients infected with different KL types of Acinetobacter baumannii. Methods: This is a cross-sectional study. From 2011 to 2021, 675 non-repetitive A. baumannii strains were isolated from patients with bloodstream infection (BSI, 234 cases), hospital acquired pneumonia (HAP, 423 cases), intra-abdominal infection (IAI, 17 cases) and urinary tract infection (UTI, 1 case) in 10 hospitals across 8 provinces of China. KL types and resistance genes were identified using bioinformatics methods. The minimum inhibitory concentrations of different antibiotics against 675 A.baumannii strains were determined by agar or microbroth dilution method. Ten strains were randomly selected from each KL type using simple random sampling for whole blood survival experiments. Differences in hospitalization duration and clinical outcomes were analyzed among patients infected with different KL types. Results: The 675 patients were aged (59±20) years, including 460 males. The predominant KL types included KL2 (22.0%, 149 strains), KL3 (17.5%, 118 strains), KL210 (7.0%, 47 strains) and KL160 (7.0%, 47 strains), while non-predominant KL types accounted for 314 strains (46.5%). The four predominant KL types showed higher overall resistance rates to most antibiotics compared with non-predominant KL types (all P<0.05). KL2 (92.6%, 113 strains) showed higher resistance to sulfamethoxazole-trimethoprim than KL3 (55.9%, 66 strains) (P<0.05). KL2 (87.2%, 130 strains) and KL210 (91.5%, 43 strains) showed higher resistance to minocycline than KL3 (67.8%, 80 strains) and KL160 (66.0%, 31 strains) (all P<0.05). KL2 exhibited stronger whole blood survival capacity [(58.36±20.33)%] than other KL types (all P<0.05). The fatality rate of KL2-infected patients was 30.9% (46 cases), higher than that of patients infected with KL3 (11.9%, 14 cases) and KL210 (6.4%, 3 cases) (all P<0.05). The hospitalization duration [M(Q₁,Q₃)] of KL2-infected patients was 46.00 (26.50, 74.00) days, longer than that of patients infected with KL3 [30.00 (15.25, 40.75) days], KL210 [27.00 (21.00, 44.00) days], KL160 [27.00 (20.00, 34.00) days] and non-predominant KL types [25.00 (12.00, 40.00) days] (all P<0.05). Conclusions: Different KL types of A.baumannii show variations in antimicrobial resistance and clinical outcomes of infected patients. KL2 demonstrates higher resistance rates and is associated with poorer clinical prognosis.