School of Laboratory Medicine, Nanchang Medical College, PR China.
School of Information Engineering, East China Jiaotong University, PR China.
Microb Pathog. 2024 Nov;196:106929. doi: 10.1016/j.micpath.2024.106929. Epub 2024 Sep 11.
Acinetobacter baumannii (A. baumannii) has become a significant nosocomial pathogen globally over the past decade due to the increasing prevalence of antibiotic-resistant isolates. The formation of the mucoid phenotype is a crucial adaptive defense response to external pressure, but the clinical, phenotypic and genotypic characteristics and their relationship with sequence types (ST) and K locus (KL) types remain unclear.
In this study, we screened a total of 736 A. baumannii isolates, from which we identified and characterized 13 mucoid isolates. The study explored the clinical characteristics of patients with mucoid isolates, investigated the mucoid phenotype, performed capsule observation, quantified capsule production, and assessed antimicrobial susceptibility. Subsequently, whole-genome sequencing (WGS) was used to analyze the sequence types (ST), loci for capsular polysaccharide (KL), antibiotic resistance genes, virulence genes, and core-genome single-nucleotide polymorphisms (SNPs). Additionally, the virulence of all mucoid strains was evaluated through serum resistance assay, biofilm-forming assay, and Galleria mellonella survival assay.
All mucoid A. baumannii isolates were found to be encapsulated and extremely drug-resistant. Among patients infected with these isolates, 92.3 % had pulmonary infections, and the 30-day mortality rate was 61.5 %. The analysis revealed that not all strains are highly virulent. Whole-genome sequencing (WGS) identified the sequence types as ST136, ST208, ST381, ST195, and ST281, and the capsular types as KL77, KL7, KL33, KL2, and KL3. The ST208 and KL7 isolates exhibited higher virulence and greater biofilm formation, with KL7 isolates also showing higher capsule production. Despite these differences, no significant variations in virulence genes were observed among the mucoid isolates, except for biofilm-associated and quorum-sensing genes. The highly virulent ST208/KL7 strains (AB276, AB313, and AB552) lacked biofilm-associated genes (csuA/BABCDE), indicating these genes do not directly cause differences in biofilm formation.
The mucoid A. baumannii isolates were extensively drug-resistant, and infections caused by these isolates could lead to higher mortality. However, not all strains had high virulence, with variations likely related to specific sequence types (ST) and K locus (KL) types.
鲍曼不动杆菌（A.baumannii）在过去十年中已成为一种重要的医院获得性病原体，这是由于抗生素耐药分离株的流行率不断增加。粘液表型的形成是对外界压力的重要适应性防御反应，但临床、表型和基因型特征及其与序列型（ST）和 K 基因座（KL）型的关系尚不清楚。
本研究共筛选了 736 株鲍曼不动杆菌分离株，从中鉴定并鉴定了 13 株粘液分离株。研究探讨了粘液分离株患者的临床特征，研究了粘液表型，进行了囊观察，定量了囊的产生，并评估了抗菌药物敏感性。随后，采用全基因组测序（WGS）分析了序列型（ST）、荚膜多糖（KL）基因座、抗生素耐药基因、毒力基因和核心基因组单核苷酸多态性（SNP）。此外，通过血清抗性试验、生物膜形成试验和金龟子幼虫存活试验评估了所有粘液株的毒力。
所有粘液鲍曼不动杆菌分离株均被包裹且具有极强的耐药性。在感染这些分离株的患者中，92.3%患有肺部感染，30 天死亡率为 61.5%。分析表明并非所有菌株都具有高毒力。全基因组测序（WGS）确定了序列型为 ST136、ST208、ST381、ST195 和 ST281，以及荚膜型为 KL77、KL7、KL33、KL2 和 KL3。ST208 和 KL7 分离株表现出更高的毒力和更大的生物膜形成能力，KL7 分离株也表现出更高的囊产量。尽管存在这些差异，但粘液分离株之间并未观察到毒力基因的显著变化，除了与生物膜相关和群体感应基因。高毒力 ST208/KL7 菌株（AB276、AB313 和 AB552）缺乏与生物膜相关的基因（csuA/BABCDE），表明这些基因不会直接导致生物膜形成的差异。
粘液鲍曼不动杆菌分离株广泛耐药，这些分离株引起的感染可能导致更高的死亡率。然而，并非所有菌株都具有高毒力，其差异可能与特定的序列型（ST）和 K 基因座（KL）型有关。
