Salmonella is one of the most important foodborne zoonotic pathogens, and becoming multidrug-resistant (MDR), which represents a serious public health concern worldwide. This study aimed to identify the circulating MDR strains of Salmonella through cutting edge molecular techniques including gene specific PCR, RAPD-PCR, ribosomal gene sequencing, and multilocus sequence types (MLST) in the poultry industry of Bangladesh. Two hundred Salmonella isolates were retrieved from 154 samples comprising droppings (n = 60), cloacal swabs (n = 60), feeds (n = 14), feeding water (n = 14), and handler’s swab (n = 6) from 14 commercial layer farms of Bangladesh. The isolates were confirmed as Salmonella through invA gene specific PCR, and further genotyping was done by RAPD-PCR, and 16S rRNA sequencing. The isolates were distributed into 18 different genotypes according to RAPD typing. The phylogenetic analysis identified three diverging phylogroups such as S. enterica Litchfield, S. enterica Enteritidis and S. enterica Kentucky with 11, 8, and 6 strains, respectively. The in vitro antibiogram profiling the Salmonella isolates through disc diffusion method using 13 commercially available antibiotics revealed highest resistance against doxycycline (91.5%) followed by tetracycline and ampicillin (86.0%, in each), and 72.0% isolates as MDR, being resistant to ≥ 5 antibiotics. The MLST typing was carried out based on the PCR amplification of seven housekeeping genes (aroC, hisD, hemD, purE, secA, thrA, and dnaN). MLST typing also revealed three sequence types (STs) such as ST11, ST198, and ST214 in these isolates, and eBURST analysis showed ST11 as the founder genotype. The three STs were highly resistant to tetracyclines and quinolone group of antibiotics, and all of the isolates harboring S. enterica Litchfield showed the highest resistance. Circulating common MLSTs with MDR properties in different farms confirmed the possibility of a common route of intra-farm transmission. We report for the first time of the association serovar Litchfield (ST11) in avian salmonellosis with MDR properties which is an urgent public health concern in Bangladesh.

沙门氏菌是最重要的食源性人畜共患病病原体之一，并且正在成为耐多药（MDR），这代表着全球严重的公共卫生问题。本研究旨在通过包括基因特异性 PCR、RAPD-PCR、核糖体基因测序和孟加拉国家禽业中的多位点序列类型 (MLST) 在内的尖端分子技术鉴定沙门氏菌的循环 MDR 菌株。从 154 个样本中分离出 200 株沙门氏菌，包括粪便 ( n = 60  )、泄殖腔拭子 ( n  = 60)、饲料 ( n  = 14)、喂食水 ( n  = 14) 和操作员拭子 ( n = 6) 来自孟加拉国的 14 个商业蛋鸡养殖场。通过inv A基因特异性PCR确认分离物为沙门氏菌，并通过RAPD-PCR和16S rRNA测序进一步进行基因分型。根据RAPD分型，将分离物分为18个不同的基因型。系统发育分析确定了三个不同的系统群，例如S. enterica Litchfield、S. enterica Enteritidis 和S. enterica Kentucky，分别有 11、8 和 6 个菌株。沙门氏菌的体外抗菌谱分析使用 13 种市售抗生素通过圆盘扩散法分离菌株显示对多西环素的耐药性最高（91.5%），其次是四环素和氨苄青霉素（各为 86.0%），72.0% 的菌株为 MDR，对≥5 种抗生素耐药。MLST 分型是基于 7 个管家基因（aro C、his D、hem D、pur E、sec A、thr A 和dna ）的 PCR 扩增进行的。N)。MLST 分型还揭示了这些分离株中的三种序列类型 (ST)，例如 ST11、ST198 和 ST214，并且 eBURST 分析显示 ST11 是创始人基因型。3株ST对四环素类和喹诺酮类抗生素均具有高度耐药性，所有携带S. enterica Litchfield的菌株均表现出最高的耐药性。在不同农场循环使用具有 MDR 特性的普通 MLST，证实了农场内传播的共同途径的可能性。我们首次报道了具有 MDR 特性的禽沙门氏菌血清型 Litchfield (ST11) 关联，这是孟加拉国紧迫的公共卫生问题。