Bioinformatics and Functional Assessment of Toxin-Antitoxin Systems in Staphylococcus aureus

Genome-wide comparative analysis of CC1 Staphylococcus aureus between colonization and infection

BACKGROUND

Staphylococcus aureus is one of the most important bacteria in human colonization and infection. Clonal complex1 (CC1) is one of the largest and most important S. aureus CCs, and it is a predominant clone in S. aureus colonization and can cause a series of S. aureus infections including bloodstream infections. No studies on the relationship of CC1 S. aureus between colonization and infection have been published.

METHODS

To figure out if there are some significant factors in CC1 S. aureus help its colonization or infection, 15 CC1 S. aureus isolates including ten from colonization and five from bloodstream infections were enrolled in this study. Whole-genome sequencing and bioinformatics analysis were performed.

RESULTS

Virulence factor regulators XdrA, YSIRK signal peptide, CPBP family and OmpR family specifically found in infection isolates can promote virulence factors and enhance the pathogenicity of S. aureus. In addition, some significant differences in metabolism and human diseases were discovered between colonization and infection. Fst family of type I toxin-antitoxin system that mainly maintains stable inheritance was specifically found in CC1 S. aureus colonization isolates and might help S. aureus survive for colonization. No significant differences in genomic evolutionary relationship were found among CC1 S. aureus isolates between colonization and infection.

CONCLUSIONS

Virulence factor regulators and metabolic state can promote CC1 S. aureus pathogenic process compared with colonization, and it seems that the strains of colonization origin cannot have pathogenic potential. Experimental confirmation and a bigger number of CC1 S. aureus strains are necessary for further study about the details and mechanism between colonization and infection.

Mechanism of action of sprG1-encoded type I toxins in Staphylococcus aureus: from membrane alterations to mesosome-like structures formation and bacterial lysis

sprG1/SprF1 is a type I toxin-antitoxin system located on Staphylococcus aureus prophage. It has previously been shown that the two toxins, SprG131 and SprG144, encoded by the sprG1 gene, are two membrane-associated peptides structured in a single α-helix. Overexpression of these two peptides leads to growth inhibition and even S. aureus death. In this study, we investigated the involvement of each peptide in this toxicity, the sequence requirements necessary for SprG131 toxicity, and the mechanism of action of these two peptides. Our findings show that both peptides, when expressed individually, are able to stop growth, with higher toxicity observed for SprG131. The combination of a hydrophobic domain and a charged domain located only at the C-terminus is necessary for this toxicity, likely to retain the orientation of the transmembrane domain. A net cationic charge for SprG131 is not essential to induce a growth defect in S. aureus. Furthermore, we established a chronology of toxic events following overexpression to gain insights into the mode of action of SprG144 and SprG131. We demonstrated that mesosome-like structures are already formed when membrane is depolarized, about 20 min after peptides induction. This membrane depolarization occurs concomitantly with a depletion of intracellular ATP, leading to S. aureus growth arrest. Moreover, we hypothesized that SprG144 and SprG131 do not form large pores in the S. aureus membrane, as ATP is not excreted into the extracellular medium, and membrane permeabilization is delayed relative to membrane depolarization. The next challenge is to identify the conditions under which SprG144 and SprG131 are naturally expressed, and to uncover their potential roles during staphylococcal growth, colonization, and infection.

The functional repertoire of AmpR in the AmpC β-lactamase high expression and decreasing β-lactam and aminoglycosides resistance in ESBL Citrobacter freundii

Citrobacter freundii is characterized by AmpC β-lactamases that develop resistance to β-lactam antibiotics. The production of extended-spectrum β-lactamase (ESBL) is substantially high in Escherichia coli, C. freundii, Enterobacter cloacae, and Serratia marcescens, but infrequently explored in C. freundii. The present investigation characterized the ESBL C. freundii and delineated the genes involved in decrease in antibiotics resistance. We used the VITEK-2 system and Analytical Profile Index (API) kit to characterize and identify the Citrobacter isolates. The mRNA level of AmpC and AmpR was determined by RT-qPCR, and gel-shift assay was performed to evaluate protein-DNA binding. Here, a total of 26 Citrobacter strains were isolated from COVID-19 patients that showed varying degrees of antibiotic resistance. We examined and characterized the multidrug resistant C. freundii that showed ESBL production. The RT-qPCR analysis revealed that the AmpC mRNA expression is significantly high followed by a high level of AmpR. We sequenced the AmpC and AmpR genes that revealed the AmpR has four novel mutations in comparison to the reference genome namely; Thr64Ile, Arg86Ser, Asp135Val, and Ile183Leu while AmpC remained intact. The ΔAmpR mutant analysis revealed that the AmpR positively regulates oxidative stress response and decreases β-lactam and aminoglycosides resistance. The AmpC and AmpR high expression was associated with resistance to tazobactam, ampicillin, gentamicin, nitrofurantoin, and cephalosporins whereas AmpR deletion reduced β-lactam and aminoglycosides resistance. We conclude that AmpR is a positive regulator of AmpC that stimulates β-lactamases which inactivate multiple antibiotics.

Evaluation of toxin-antitoxin genes, antibiotic resistance, and virulence genes in Pseudomonas aeruginosa isolates

OBJECTIVE

Toxin-antitoxin genes RelBE and HigBA are known to be involved in the formation of biofilm, which is an important virulence factor for Pseudomonas aeruginosa. The purpose of this study was to determine the presence of toxin-antitoxin genes and exoenzyme S and exotoxin A virulence genes in P. aeruginosa isolates and whether there is a relationship between toxin-antitoxin genes and virulence genes as well as antibiotic resistance.

METHODS

Identification of the isolates and antibiotic susceptibilities was determined by a VITEK 2 (bioMérieux, France) automated system. The presence of toxin-antitoxin genes, virulence genes, and transcription levels were detected by real-time polymerase chain reaction.

RESULTS

RelBE and HigBA genes were detected in 94.3% (82/87) of P. aeruginosa isolates, and exoenzyme S and exotoxin A genes were detected in all of the isolates (n=87). All of the isolates that harbor the toxin-antitoxin and virulence genes were transcribed. There was a significant increase in the RelBE gene transcription level in imipenem- and meropenem-sensitive isolates and in the HigBA gene transcription level in amikacin-sensitive isolates (p<0.05). There was a significant correlation between RelBE and exoenzyme S (p=0.001).

CONCLUSION

The findings suggest that antibiotic resistance may be linked to toxin-antitoxin genes. Furthermore, the relationship between RelBE and exoenzyme S indicates that toxin-antitoxin genes in P. aeruginosa isolates are not only related to antibiotic resistance but also play an influential role in bacterial virulence. Larger collections of comprehensive studies on this subject are required. These studies should contribute significantly to the solution of the antibiotic resistance problem.

Mechanism and treatment of α-amanitin poisoning

Amanita poisoning has a high mortality rate. The α-amanitin toxin in Amanita is the main lethal toxin. There is no specific detoxification drug for α-amanitin, and the clinical treatment mainly focuses on symptomatic and supportive therapy. The pathogenesis of α-amanitin mainly includes: α-amanitin can inhibit the activity of RNA polymeraseII in the nucleus, including the inhibition of the largest subunit of RNA polymeraseII, RNApb1, bridge helix, and trigger loop. In addition, α-amanitin acts in vivo through the enterohepatic circulation and transport system. α-Amanitin can cause the cell death. The existing mechanisms of cell damage mainly focus on apoptosis, oxidative stress, and autophagy. In addition to the pathogenic mechanism, α-amanitin also has a role in cancer treatment, which is the focus of current research. The mechanism of action of α-amanitin on the body is still being explored.

Pathophysiology of Methicillin-Resistant Staphylococcus aureus Superinfection in COVID-19 Patients

The global spread of the coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has infected humans in all age groups, deteriorated host immune responses, and caused millions of deaths. The reasons for individuals succumbing to COVID-19 were not only the SARS-CoV-2 infection but also associated bacterial infections. Antibiotics were largely used to prevent bacterial infections during COVID-19 illness, and many bacteria became resistant to conventional antibiotics. Although COVID-19 was considered the main culprit behind the millions of deaths, bacterial coinfections and superinfections were the major factors that increased the mortality rate in hospitalized patients. In the present study, we assessed the pathophysiology of methicillin-resistant Staphylococcus aureus (MRSA) superinfection in COVID-19 patients in Pakistan. A total of 3492 COVID-19 hospitalized patients were screened among which 224 strain were resistant to methicillin; 110 strains were tazobactam-resistant; 53 strains were ciprofloxacin-resistant; 23 strains were gentamicin-resistant; 11 strains were azithromycin-resistant; 3 strains were vancomycin-resistant. A high frequency of MRSA was detected in patients aged ≥50 with a prevalence of 7.33%, followed by patients aged >65 with a prevalence of 5.48% and a 5.10% prevalence in patients aged <50. In addition, pneumonia was detected in the COVID-19-associated MRSA (COVID-MRSA) that showed decreased levels of lymphocytes and albumin and increased the mortality rate from 2.3% to 25.23%. Collectively, an MRSA superinfection was associated with increased mortality in COVID-19 after 12 to 18 days of hospitalization. The study assessed the prevalence of MRSA, mortality rate, pneumonia, and the emergence of antibiotic resistance as the main outcomes. The study summarized that COVID-MRSA aggravated the treatment and recovery of patients and suggested testing MRSA as critical for hospitalized patients.

Are Bacterial Persisters Dormant Cells Only?

Bacterial persisters are a sub-population of phenotypic variants that tolerate high concentrations of antibiotics within the genetically homogeneous cells. They resume division upon the removal of drugs. Bacterial persistence is one of major causes of antibiotic treatment failure and recurrent infection. Cell dormancy, triggered by toxin/antitoxin pair, (p)ppGpp, SOS response and ATP levels, is known to be the mechanistic basis for persistence. However, recent studies have demonstrated that bacteria with active metabolism can maintain persistence by lowering intracellular antibiotic concentration via an efflux pump. Additionally, others and our work have showed that cell wall deficient bacteria (CWDB), including both L-form and spheroplasts that produced by β-lactam antibiotics, are associated with antibiotic persistence. They are not dormant cells as their cell walls have been completely damaged. In this review, we discuss the various types of persisters and highlight the contribution of non-walled bacteria on bacterial persistence.

Functional characterization of HigBA toxin-antitoxin system in an Arctic bacterium, Bosea sp. PAMC 26642

Toxin-antitoxin (TA) systems are growth-controlling genetic elements consisting of an intracellular toxin protein and its cognate antitoxin. TA systems have been spread among microbial genomes through horizontal gene transfer and are now prevalent in most bacterial and archaeal genomes. Under normal growth conditions, antitoxins tightly counteract the activity of the toxins. Upon stresses, antitoxins are inactivated, releasing activated toxins, which induce growth arrest or cell death. In this study, among nine functional TA modules in Bosea sp. PAMC 26642 living in Arctic lichen, we investigated the functionality of BoHigBA2. BohigBA2 is located close to a genomic island and adjacent to flagellar gene clusters. The expression of BohigB2 induced the inhibition of E. coli growth at 37°C, which was more manifest at 18°C, and this growth defect was reversed when BohigA2 was co-expressed, suggesting that this BoHigBA2 module might be an active TA module in Bosea sp. PAMC 26642. Live/dead staining and viable count analyses revealed that the BoHigB2 toxin had a bactericidal effect, causing cell death. Furthermore, we demonstrated that BoHigB2 possessed mRNA-specific ribonuclease activity on various mRNAs and cleaved only mRNAs being translated, which might impede overall translation and consequently lead to cell death. Our study provides the insight to understand the cold adaptation of Bosea sp. PAMC 26642 living in the Arctic.

Identification and characterization of VapBC toxin-antitoxin system in Bosea sp. PAMC 26642 isolated from Arctic lichens

Toxin-antitoxin (TA) systems are genetic modules composed of a toxin interfering with cellular processes and its cognate antitoxin, which counteracts the activity of the toxin. TA modules are widespread in bacterial and archaeal genomes. It has been suggested that TA modules participate in the adaptation of prokaryotes to unfavorable conditions. The Bosea sp. PAMC 26642 used in this study was isolated from the Arctic lichen Stereocaulon sp. There are 12 putative type II TA loci in the genome of Bosea sp. PAMC 26642. Of these, nine functional TA systems have been shown to be toxic in Escherichia coli The toxin inhibits growth, but this inhibition is reversed when the cognate antitoxin genes are coexpressed, indicating that these putative TA loci were bona fide TA modules. Only the BoVapC1 (AXW83_01405) toxin, a homolog of VapC, showed growth inhibition specific to low temperatures, which was recovered by the coexpression of BoVapB1 (AXW83_01400). Microscopic observation and growth monitoring revealed that the BoVapC1 toxin had bacteriostatic effects on the growth of E. coli and induced morphological changes. Quantitative real time polymerase chain reaction and northern blotting analyses showed that the BoVapC1 toxin had a ribonuclease activity on the initiator tRNA^fMet, implying that degradation of tRNA^fMet might trigger growth arrest in E. coli Furthermore, the BoVapBC1 system was found to contribute to survival against prolonged exposure at 4°C. This is the first study to identify the function of TA systems in cold adaptation.

Expression of type II toxin-antitoxin systems and ClpP protease of methicillin-resistant Staphylococcus aureus under thermal and oxidative stress conditions

Background and Objectives:

Staphylococcus aureus is a main human pathogen that causes a variety of chronic to persistent infections. Across the diverse factors of pathogenesis in bacteria, Toxin-Antitoxin (TA) systems can be considered as an anti-bacterial target due to their involvement in cellular physiology counting stress responses. Here, the expression of TA system genes and ClpP protease was investigated under the thermal and oxidative conditions in S. aureus strains.

Materials and Methods:

The colony-forming unit (CFU) was used to determine the effects of thermal and oxidative stresses on bacterial survival. Moreover, the expressions of TA system genes in S. aureus strains were evaluated 30 min and 1 h after thermal and oxidative stresses, respectively, by quantitative reverse transcriptase real-time PCR (qRT-PCR).

Results:

The cell viability was constant across thermal stress while oxidative stress induction showed a significantly decrease in the growth of Methicillin-Resistant S. aureus (MRSA) strain. Based on the qRT-PCR results, the expression of mazF gene increased under both thermal and oxidative stresses in the MRSA strain.

Conclusion:

A putative TA system (namely immA/irrA) most likely has a role under the stress condition of S. aureus. The MRSA strain responds to stress by shifting the expression level of TA genes that has diverse effects on the survival of the pathogen due to the stress conditions. The TA systems may be introduced as potential targets for antibacterial treatment.

The Mesorhizobium huakuii transcriptional regulator AbiEi plays a critical role in nodulation and is important for bacterial stress response

Background

Bacterial abortive infection (Abi) systems are type IV toxin–antitoxin (TA) system, which could elicit programmed cell death and constitute a native survival strategy of pathogenic bacteria under various stress conditions. However, no rhizobial AbiE family TA system has been reported so far. Here, a M. huakuii AbiE TA system was identified and characterized.

Results

A mutation in M. huakuii abiEi gene, encoding an adjacent GntR-type transcriptional regulator, was generated by homologous recombination. The abiEi mutant strain grew less well in rich TY medium, and displayed increased antioxidative capacity and enhanced gentamicin resistance, indicating the abiEi operon was negatively regulated by the antitoxin AbiEi in response to the oxidative stress and a particular antibiotic. The mRNA expression of abiEi gene was significantly up-regulated during Astragalus sinicus nodule development. The abiEi mutant was severely impaired in its competitive ability in rhizosphere colonization, and was defective in nodulation with 97% reduction in nitrogen-fixing capacity. The mutant infected nodule cells contained vacuolation and a small number of abnormal bacteroids with senescence character. RNA-seq experiment revealed it had 5 up-regulated and 111 down-regulated genes relative to wild type. Of these down-regulated genes, 21 are related to symbiosis nitrogen fixation and nitrogen mechanism, 16 are involved in the electron transport chain and antioxidant responses, and 12 belong to type VI secretion system (T6SS).

Conclusions

M. huakuii AbiEi behaves as a key transcriptional regulator mediating root nodule symbiosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02304-0.

Impacts of the Type I Toxin-Antitoxin System, SprG1/SprF1, on Staphylococcus aureus Gene Expression

Type I toxin-antitoxin (TA) systems are widespread genetic modules in bacterial genomes. They express toxic peptides whose overexpression leads to growth arrest or cell death, whereas antitoxins regulate the expression of toxins, acting as labile antisense RNAs. The Staphylococcus aureus (S. aureus) genome contains and expresses several functional type I TA systems, but their biological functions remain unclear. Here, we addressed and challenged experimentally, by proteomics, if the type I TA system, the SprG1/SprF1 pair, influences the overall gene expression in S. aureus. Deleted and complemented S. aureus strains were analyzed for their proteomes, both intracellular and extracellular, during growth. Comparison of intracellular proteomes among the strains points to the SprF1 antitoxin as moderately downregulating protein expression. In the strain naturally expressing the SprG1 toxin, cytoplasmic proteins are excreted into the medium, but this is not due to unspecific cell leakages. Such a toxin-driven release of the cytoplasmic proteins may modulate the host inflammatory response that, in turn, could amplify the S. aureus infection spread.

RNA antitoxin SprF1 binds ribosomes to attenuate translation and promote persister cell formation in Staphylococcus aureus

Persister cells are a subpopulation of transiently antibiotic-tolerant bacteria associated with chronic infection and antibiotic treatment failure. Toxin-antitoxin systems have been linked to persister cell formation but the molecular mechanisms leading to bacterial persistence are mostly unknown. Here, we show that SprF1, a type I antitoxin, associates with translating ribosomes from the major human pathogen Staphylococcus aureus to reduce the pathogen's overall protein synthesis during growth. Under hyperosmotic stress, SprF1 levels increase due to enhanced stability, accumulate on polysomes and attenuate protein synthesis. Using an internal 6-nucleotide sequence on its 5'-end, SprF1 binds ribosomes and interferes with initiator transfer RNA binding, thus reducing translation initiation. An excess of messenger RNA displaces the ribosome-bound antitoxin, freeing the ribosomes for new translation cycles; however, this RNA antitoxin can also displace ribosome-bound mRNA. This translation attenuation mechanism, mediated by an RNA antitoxin, promotes antibiotic persister cell formation. The untranslated SprF1 is a dual-function RNA antitoxin that represses toxin expression by its 3'-end and fine-tunes overall bacterial translation via its 5'-end. These findings demonstrate a general function for a bacterial RNA antitoxin beyond protection from toxicity. They also highlight an RNA-guided molecular process that influences antibiotic persister cell formation.

Targeting Type II Toxin-Antitoxin Systems as Antibacterial Strategies

The identification of novel targets for antimicrobial agents is crucial for combating infectious diseases caused by evolving bacterial pathogens. Components of bacterial toxin–antitoxin (TA) systems have been recognized as promising therapeutic targets. These widespread genetic modules are usually composed of two genes that encode a toxic protein targeting an essential cellular process and an antitoxin that counteracts the activity of the toxin. Uncontrolled toxin expression may elicit a bactericidal effect, so they may be considered “intracellular molecular bombs” that can lead to elimination of their host cells. Based on the molecular nature of antitoxins and their mode of interaction with toxins, TA systems have been classified into six groups. The most prevalent are type II TA systems. Due to their ubiquity among clinical isolates of pathogenic bacteria and the essential processes targeted, they are promising candidates for the development of novel antimicrobial strategies. In this review, we describe the distribution of type II TA systems in clinically relevant human pathogens, examine how these systems could be developed as the targets for novel antibacterials, and discuss possible undesirable effects of such therapeutic intervention, such as the induction of persister cells, biofilm formation and toxicity to eukaryotic cells.

Cross-Regulations between Bacterial Toxin-Antitoxin Systems: Evidence of an Interconnected Regulatory Network?

Toxin-antitoxin (TA) systems are ubiquitous among bacteria and include stable toxins whose toxicity can be counteracted by RNA or protein antitoxins. They are involved in multiple functions that range from stability maintenance for mobile genetic elements to stress adaptation. Bacterial chromosomes frequently have multiple homologues of TA system loci, and it is unclear why there are so many of them. In this review we focus on cross-regulations between TA systems, which occur between both homologous and nonhomologous systems, from similar or distinct types, whether encoded from plasmids or chromosomes. In addition to being able to modulate RNA expression levels, cross-regulations between these systems can also influence their toxicity. This suggests the idea that they are involved in an interconnected regulatory network.

Small-Molecule Acetylation by GCN5-Related N-Acetyltransferases in Bacteria

Acetylation is a conserved modification used to regulate a variety of cellular pathways, such as gene expression, protein synthesis, detoxification, and virulence. Acetyltransferase enzymes transfer an acetyl moiety, usually from acetyl coenzyme A (AcCoA), onto a target substrate, thereby modulating activity or stability. Members of the GCN5- N -acetyltransferase (GNAT) protein superfamily are found in all domains of life and are characterized by a core structural domain architecture. These enzymes can modify primary amines of small molecules or of lysyl residues of proteins. From the initial discovery of antibiotic acetylation, GNATs have been shown to modify a myriad of small-molecule substrates, including tRNAs, polyamines, cell wall components, and other toxins. This review focuses on the literature on small-molecule substrates of GNATs in bacteria, including structural examples, to understand ligand binding and catalysis. Understanding the plethora and versatility of substrates helps frame the role of acetylation within the larger context of bacterial cellular physiology.

A novel type I toxin-antitoxin system modulates persister cell formation in Staphylococcus aureus

A plethora of toxin-antitoxin systems exist in bacteria and has multilateral roles in bacterial pathogenesis and virulence. Toxin-antitoxin systems have been involved in persister cell formation in Escherichia coli and Mycobacterium but have not been reported to be associated with Staphylococcus aureus persistence. Persistence is the ability of bacterial cells to tolerate unfavorable conditions and multiple stresses. There are less known and more unknown factors that either alleviate or aggravate bacterial persistence phenomenon. For the first time, we reported a new chromosomally encoded tripartite toxin-antitoxin system and its role in S. aureus persister cell formation. The toxin gene is bacteriostatic in action and counterbalanced by antitoxin RNA that could basepair with the toxin mRNA and formed a duplex. The transcriptional regulator positively regulates the toxin expression under certain stress conditions. The toxin ectopic induction increased S. aureus susceptibility to norfloxacin, ciprofloxacin, and ofloxacin. Whole-genome RNA sequencing revealed that MDR efflux pump norA is significantly down-regulated by toxin ectopic induction. The deletion of norA from S. aureus genome reduced resistance toward ciprofloxacin, norfloxacin, and ofloxacin, as well as resulted in a decrease in minimal inhibitory concentration while complementation of norA successfully restored the phenotypes. The persistence assay of the norA mutant revealed that deletion of norA increased persister cell survival in S. aureus. Altogether, we have provided insight into the first tripartite type-I TA system and revealed the role of MDR NorA in the persister cell formation of S. aureus.

Genome-Wide Screening for Identification of Novel Toxin-Antitoxin Systems in Staphylococcus aureus

Toxin-antitoxin (TA) systems consist of toxin-inhibiting diverse cellular functions (e.g., DNA replication, transcription, and translation) and a noncoding RNA or protein antitoxin. TA systems are associated with various cellular events, such as stress responses, programmed cell death, and bacterial pathogenicity. Recent advances in genome sequencing and bioinformatics research have demonstrated that most bacteria harbor various kinds of TA modules on their chromosomes; however, there is little understanding of chromosomally encoded TA systems in the Gram-positive pathogen Staphylococcus aureus Here, we report on newly discovered S. aureus TA systems, each of which is composed of two proteins. Manual search and gene operon prediction analysis identified eight 2-gene operons as potential candidates for TA systems. Subsequently, using an Escherichia coli host killing and rescue assay, we demonstrated that four of the eight candidates worked as TA systems, designated tsaAT, tsbAT, tscAT, and tsdAT Moreover, the TsaT, TsbT, TscT, and TsdT toxins inhibited S. aureus growth, and the toxicity of TsbT was neutralized by coexpressing the tsbA gene in the native host, S. aureus Further, the bioinformatics analysis of the gene clusters revealed that TsaAT, TsbAT, TscAT, and TsdAT did not exhibit sequence similarity to known bacterial TA systems, and their homologues were present only within Staphylococcus species and not among any other bacteria. Our results further advance not only the understanding of S. aureus TA systems but also the study of unannotated TA systems in various bacterial species.IMPORTANCE Recent advances in genome sequencing and bioinformatics research have demonstrated that most pathogenic bacteria harbor a large number of chromosomally encoded toxin-antitoxin (TA) modules. However, little is known about the TA systems in S. aureus Here, we newly identified four S. aureus TA systems using a combination of manual base-by-base screening and functional analysis in E. coli Moreover, all toxins of the identified TA systems caused growth inhibition in the native host S. aureus Although the newly identified TA systems did not exhibit sequence similarity with known bacterial TA systems, their orthologues were conserved only among other Staphylococcus species, indicating their uniqueness to staphylococci. Our approach opens the possibility for studying unannotated TA systems in various bacterial species.

Staphylococcus aureus Toxins: Armaments for a Significant Pathogen

Staphylococcus species are common inhabitants of humans and other animals [...].