Abstract：
The present study aimed to explore the genotypic and phenotypic characteristics of biofilm formation in Bulgarian nosocomial Stenotrophomonas maltophilia isolates (n = 221) during the period 2011-2022, by screening for the presence of biofilm-associated genes (BAG) (spgM, rmlA and rpfF), their mutational variability, and assessment of the adherent growth on a polystyrene surface. The methodology included: PCR amplification, whole-genome sequencing (WGS) and crystal violet microtiter plate assay for biofilm quantification. The overall incidence of BAG was: spgM 98.6%, rmlA 86%, and rpfF 66.5%. The most prevalent genotype was spgM+/rmlA+/rpfF+ (56.1%), followed by spgM+/rmlA+/rpfF- (28.5%), and spgM+/rmlA-/rpfF+ (9.5%), with their significant predominance in lower respiratory tract isolates compared to those with other origin (P < 0.001). All strains examined were characterized as strong biofilm producers (OD550 from 0.224 ± 0.049 to 2.065 ± 0.023) with a single exception that showed a weak biofilm-forming ability (0.177 ± 0.024). No significant differences were observed in the biofilm formation according to the isolation source, as well as among COVID-19 and non-COVID-19 isolates (1.256 ± 0.028 vs. 1.348 ± 0.128, respectively). Also, no correlation was found between the biofilm amounts and the corresponding genotypes. WGS showed that the rmlA accumulated a larger number of variants (0.0086 per base) compared to the other BAG, suggesting no critical role of its product to the biofilm formation. Additionally, two of the isolates were found to harbour class 1 integrons (7-kb and 2.6-kb sized, respectively) containing sul1 in their 3\' conservative ends, which confers sulfonamide resistance. To the best of our knowledge, this is the first study on S. maltophilia biofilm formation in Bulgaria, which also identifies novel sequence types (ST819, ST820 and ST826). It demonstrates the complex nature of this adaptive mechanism in the multifactorial pathogenesis of biofilm-associated infections.
摘要：
本研究旨在通过筛选生物膜相关基因（BAG）（spgM，rmlA和rpfF)，它们的突变变异性，并评估聚苯乙烯表面的粘附生长。方法包括：PCR扩增，全基因组测序（WGS）和结晶紫微量滴定板测定用于生物膜定量。BAG的总发生率为:spgM98.6%,rmlA86%，和rpfF66.5%。最普遍的基因型是spgM+/rmlA+/rpfF+(56.1%),其次是spgM+/rmlA+/rpfF-(28.5%)，和spgM+/rmlA-/rpfF+(9.5%)，与其他来源的分离株相比，它们在下呼吸道分离株中占显著优势(P<0.001)。所有检查的菌株均被表征为强生物膜生产者（OD550从0.224±0.049到2.065±0.023），只有一个例外显示出弱的生物膜形成能力（0.177±0.024）。根据分离来源，生物膜形成没有观察到显著差异，以及COVID-19和非COVID-19分离株(1.256±0.028vs.分别为1.348±0.128）。此外，生物膜数量与相应基因型之间未发现相关性.WGS显示，与其他BAG相比，rmlA积累了更多的变体（每个碱基0.0086），表明其产品对生物膜形成没有关键作用。此外,发现其中两个分离株含有1类整合子(大小为7kb和2.6kb，分别)在其3个保守端含有sul1，赋予磺酰胺抗性。据我们所知,这是保加利亚第一个关于嗜麦芽窄食链球菌生物膜形成的研究，其还识别新的序列类型(ST819、ST820和ST826)。它证明了这种适应性机制在生物膜相关感染的多因素发病机理中的复杂性质。
