The Association of the mazEF Toxin-antitoxin System and Vancomycin Resistance in Clinical Isolates of Vancomycin Resistant Enterococcus faecalis

Vancomycin resistant enterococci are challenging bacteria as they are difficult to be eradicated. Toxin-antitoxin (TA) systems are genetic elements located in most prokaryotic genomes. The mazEF TA system is harbored by a plasmid among Enterococcus faecalis (E. faecalis). To explore the relation between the existence of mazEF TA system and vancomycin resistance among clinical isolates of E. faecalis. Samples were collected from patients showing clinical picture of infection. Isolates of E. faecalis were identified by standard microbiological methods and their antimicrobial susceptibility patterns were detected by disk diffusion method. In addition, the E-test was used to confirm vancomycin resistant isolates. All the E. faecalis isolates were screened for the mazEF TA system by PCR. A total of 180 E. faecalis strains were identified with a vancomycin resistance rate of 30.6%. Vancomycin resistance was significantly associated with prolonged hospital stay (P= 0.04) and ICU setting (P= 0.001). The mazEF TA system was detected among 100% of vancomycin resistant isolates, while only 33.6% of the vancomycin sensitive isolates carried the system with a significant difference (P= 0.002). In addition, there was a significant association between the mazEF TA system-positive strains and the ICU setting (P= 0.02). A significant association was found between vancomycin resistance and the presence of the mazEF TA system among E. faecalis isolates. This association supports the current efforts to utilize the mazEF TA system as a possible target for novel antibacterial agents; however, further studies on a wider scale are necessary.

Toxin-antitoxin systems and their medical applications: current status and future perspective

Almost all bacteria synthesize two types of toxins-one for its survival by regulating different cellular processes and another as a strategy to interact with host cells for pathogenesis. Usually, "bacterial toxins" are contemplated as virulence factors that harm the host organism. However, toxins produced by bacteria, as a survival strategy against the host, also hamper its cellular processes. To overcome this, the bacteria have evolved with the production of a molecule, referred to as antitoxin, to negate the deleterious effect of the toxin against itself. The toxin and antitoxins are encoded by a two-component toxin-antitoxin (TA) system. The antitoxin, a protein or RNA, sequesters the toxins of the TA system for neutralization within the bacterial cell. In this review, we have described different TA systems of bacteria and their potential medical and biotechnological applications. It is of interest to note that while bacterial toxin-antitoxin systems have been well studied, the TA system in unicellular eukaryotes, though predicted by the investigators, have never been paid the desired attention. In the present review, we have also touched upon the TA system of eukaryotes identified to date. KEY POINTS: Bacterial toxins harm the host and also affect the bacterial cellular processes. The antitoxin produced by bacteria protect it from the toxin's harmful effects. The toxin-antitoxin systems can be targeted for various medical applications.

Toxin-Antitoxin Systems: A Tool for Taxonomic Analysis of Human Intestinal Microbiota

The human gastrointestinal microbiota (HGM) is known for its rich diversity of bacterial species and strains. Yet many studies stop at characterizing the HGM at the family level. This is mainly due to lack of adequate methods for a high-resolution profiling of the HGM. One way to characterize the strain diversity of the HGM is to look for strain-specific functional markers. Here, we propose using type II toxin-antitoxin systems (TAS). To identify TAS systems in the HGM, we previously developed the software TAGMA. This software was designed to detect the TAS systems, MazEF and RelBE, in lactobacilli and bifidobacteria. In this study, we updated the gene catalog created previously and used it to test our software anew on 1346 strains of bacteria, which belonged to 489 species and 49 genera. We also sequenced the genomes of 20 fecal samples and analyzed the results with TAGMA. Although some differences were detected at the strain level, the results showed no particular difference in the bacterial species between our method and other classic analysis software. These results support the use of the updated catalog of genes encoding type II TAS as a useful tool for computer-assisted species and strain characterization of the HGM.

Employing toxin-antitoxin genome markers for identification of Bifidobacterium and Lactobacillus strains in human metagenomes

Recent research has indicated that in addition to the unique genotype each individual may also have a unique microbiota composition. Difference in microbiota composition may emerge from both its species and strain constituents. It is important to know the precise composition especially for the gut microbiota (GM), since it can contribute to the health assessment, personalized treatment, and disease prevention for individuals and groups (cohorts). The existing methods for species and strain composition in microbiota are not always precise and usually not so easy to use. Probiotic bacteria of the genus Bifidobacterium and Lactobacillus make an essential component of human GM. Previously we have shown that in certain Bifidobacterium and Lactobacillus species the RelBE and MazEF superfamily of toxin-antitoxin (TA) systems may be used as functional biomarkers to differentiate these groups of bacteria at the species and strain levels. We have composed a database of TA genes of these superfamily specific for all lactobacilli and bifidobacteria species with complete genome sequence and confirmed that in all Lactobacillus and Bifidobacterium species TA gene composition is species and strain specific. To analyze composition of species and strains of two bacteria genera, Bifidobacterium and Lactobacillus, in human GM we developed TAGMA (toxin antitoxin genes for metagenomes analyses) software based on polymorphism in TA genes. TAGMA was tested on gut metagenomic samples. The results of our analysis have shown that TAGMA can be used to characterize species and strains of Lactobacillus and Bifidobacterium in metagenomes.