Abstract
BackgroundTyphoid fever is an acute systemic infection of humans caused by Salmonella enterica subspecies enterica serovar Typhi (S. Typhi). In chronic carriers, the bacteria survive the harsh environment of the gallbladder by producing biofilm. The phenotype of S. Typhi biofilm cells is significantly different from the free-swimming planktonic cells, and studies have shown that they are associated with antibiotic resistance, immune system evasion, and bacterial persistence. However, the mechanism of this transition and the events leading to biofilm formation are unknown. High throughput sequencing was performed to identify the genes involved in biofilm formation and to postulate the mechanism of action.ResultsPlanktonic S. Typhi cells were cultured using standard nutrient broth whereas biofilm cells were cultured in a stressful environment using high shearing-force and bile to mimic the gallbladder. Sequencing libraries were prepared from S. Typhi planktonic cells and mature biofilm cells using the Illumina HiSeq 2500 platform, and the transcriptome data obtained were processed using Cufflinks bioinformatics suite of programs to investigate differential gene expression between the two phenotypes. A total of 35 up-regulated and 29 down-regulated genes were identified. The identities of the differentially expressed genes were confirmed using NCBI BLAST and their functions were analyzed. The results showed that the genes associated with metabolic processes and biofilm regulations were down-regulated while those associated with the membrane matrix and antibiotic resistance were highly up-regulated.ConclusionsIt is proposed that the biofilm phenotype of S. Typhi allows the bacteria to increase production of the membrane matrix in order to serve as a physical shield and to adhere to surfaces, and enter an energy conservation state in response to the stressful environment. Conversely, the planktonic phenotype allows the bacteria to produce flagella and increase metabolic activity to enable the bacteria to migrate and form new colonies of infection. This data provide a basis for further studies to uncover the mechanism of biofilm formation in S. Typhi and to discover novel genes or pathways associated with the development of the typhoid carrier state.
Highlights
Typhoid fever is an acute systemic infection of humans caused by Salmonella enterica subspecies enterica serovar Typhi
The reads were subjected to Illumina sequencing adapter trimming and base quality (Q ≥ 20) trimming using Fastq-MCF [14] to ensure that only high quality bases derived from the mRNAs were used for subsequent analysis
The planktonic cells appear to have more genes that were expressed within the log10 (FPKM) value of 2 to 3 compared to the biofilm cells that had a lower expression value in the same range
Summary
The bacteria survive the harsh environment of the gallbladder by producing biofilm. High throughput sequencing was performed to identify the genes involved in biofilm formation and to postulate the mechanism of action. The bacteria spread from the intestine via the blood and circulate throughout the body. The bacteria invade various organs, such as the intestinal lymph nodes, liver, gallbladder and the Peyer’s patches, with patients frequently becoming chronic carriers [6]. The bacteria forms a biofilm on either the gallstones or gallbladder epithelium, providing a stable environment for growth and survival of the bacteria, and resulting in increased resistance towards the host’s immune system and antimicrobial agents [7, 8]
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