Function of Burkholderia pseudomallei RpoS and RpoN2 in bacterial invasion, intracellular survival, and multinucleated giant cell formation in mouse macrophage cell line

Melioidosis, a human infectious disease with a high mortality rate in many tropical countries, is caused by the pathogen Burkholderia pseudomallei (B. pseudomallei). The function of the B. pseudomallei sigma S (RpoS) transcription factor in survival during the stationary growth phase and conditions of oxidative stress is well documented. Besides the rpoS, bioinformatics analysis of B. pseudomallei genome showed the existence of two rpoN genes, named rpoN1 and rpoN2. In this study, by using the mouse macrophage cell line RAW264.7 as a model of infection, the involvement of B. pseudomallei RpoS and RpoN2 in the invasion, intracellular survival leading to the reduction in multinucleated giant cell (MNGC) formation of RAW264.7 cell line were illustrated. We have demonstrated that the MNGC formation of RAW264.7 cell was dependent on a certain number of intracellular bacteria (at least 5 × 104). In addition, the same MNGC formation (15%) observed in RAW264.7 cells infected with either B. pseudomallei wild type with multiplicity of infection (MOI) 2 or RpoN2 mutant (∆rpoN2) with MOI 10 or RpoS mutant (∆rpoS) with MOI 100. The role of B. pseudomallei RpoS and RpoN2 in the regulation of type III secretion system on bipB-bipC gene expression was also illustrated in this study.

The clinical features and genomic epidemiology of carbapenem-resistant Acinetobacter baumannii infections at a tertiary hospital in Vietnam

OBJECTIVES

To characterise the clinical features of A. baumannii infections and investigate the phylogenetic structure and transmission dynamics of A. baumannii in Vietnam.

METHODS

Between 2019 and 2020, a surveillance of A. baumannii (AB) infections was conducted at a tertiary hospital in Ho Chi Minh City, Vietnam. Risk factors for in-hospital mortality were analyzed using logistic regressions. Whole-genome sequence data were used to characterise genomic species, sequence types (STs), antimicrobial resistance genes, surface antigens and phylogenetic relatedness of AB isolates.

RESULTS

Eighty-four patients with AB infections were enrolled in the study, 96% of whom were hospital-acquired. Half of the AB isolates were identified from ICU-admitted patients while the remaining isolates were from non-ICU patients. The overall in-hospital mortality was 56%, with associated risk factors including advanced age, ICU stay, exposure to mechanical ventilation/central venous catheterization, pneumonia as source of AB infection, prior use of linezolid/aminoglycosides, and AB treatment with colistin-based therapy. Nearly 91% of isolates were carbapenem-resistant; 92% were multidrug-resistant and 6% were colistin-resistant. ST2, ST571 and ST16 were the three dominant CRAB genotypes, exhibiting distinct AMR gene profiles. Phylogenetic analysis of CRAB ST2 isolates together with previously published ST2 collection provided evidence of intra- and inter-hospital transmission of this clone.

CONCLUSIONS

Our study highlights a high prevalence of carbapenem resistance and multidrug resistance in A. baumannii and elucidates the spread of CRAB within and between hospitals. Strengthening infection control measures and routine genomic surveillance are crucial to reducing the spread of CRAB and timely detecting novel pan drug-resistant variants.