ABSTRACT
SUMMARY 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.
ABSTRACT
RESUMEN Los persistentes bacterianos son variantes transitorias de una población genéticamente homogénea, generada por exposición al estrés, como el que ocurre durante el tratamiento antibiótico. Es un fenómeno epigenético o un fenotipo no heredado, que puede ser llamado primera línea de defensa antes de que se adquiera la resistencia antimicrobiana. A pesar de su descubrimiento hace más de 70 años, su definición, mecanismos de formación, clasificación y morfologías adoptadas de implicancia clínica son temas de investigación actual. En el presente estudio se describe la relación de persistentes con infecciones crónicas y formación de biopelículas como factores importantes en la recaída, recidivas y mayor virulencia en las infecciones. Así mismo, se hace una revisión breve de los diversos mecanismos implicados en la persistencia bacteriana y su eliminación ineficaz por tolerancia antibiótica para terminar con la presentación de posibles estrategias de tratamiento. En conjunto, se cree que la persistencia impone una carga significativa de atención en salud pública, que se estima, provocará hasta 10 millones de víctimas al año para el 2050. Una mejor comprensión de este fenotipo es fundamental en la lucha contra las bacterias patógenas con la finalidad de obtener una mejor perspectiva en las terapias futuras.
ABSTRACT Persistent bacteria are the transient variants of a genetically homogeneous population generated by exposure to stress as in antibiotic treatment. They are an epigenetic phenomenon or a non-inherited phenotype, which may be considered as the first line of defense before developing antimicrobial resistance. Despite their discovery more than 70 years ago, their definition, mechanisms of formation, classification and morphologies of clinical implication are still current research topics. In the present research, we describe the relationship between chronic persistent infections and the formation of biofilms as important factors in recurrences, relapses and greater virulence in infections. Likewise, a brief review of the various mechanisms involved in bacterial persistence, their ineffective elimination due to antibiotic tolerance and possible treatment strategies is provided. Overall, it is believed that persistence poses a significant burden of public health care. It is estimated that up to 10 million people will be yearly affected by 2050. Thus, a better comprehension of this bacterial phenotype is essential to fight against pathogenic bacteria and improve therapeutic results in the future.
ABSTRACT
Objective: To explore the molecular mechanism of mazG gene involved in regulating mazEF toxin-antitoxin system(TAs)mediated bacterial growth inhibition and programmed death, and to clarify the true physiological function of MazG protein. Methods: The Escherichia coli (E.coli)strain MC4100 was used as a prototype and the relA gene was recovered to obtain the relA wildtype strain MC4200. E. coli mazG, mazEF, mazEFG and other series of gene knockout strains were constructed to test the effects of mazG gene overexpression in different genetic background strains on the survival rate of bacteria. Rifampicin, H2O2 and nalidixic acid and other stress conditions were used to treat the bacteria and study growth curve and survival rate of mazG gene and mazEFG operondeleted strains. The E.coli mazG gene and mutant were cloned into an inducible overexpression to construct pET28a-mazG and pET28amazG E38A. Then the protein was overexpressed in BL21 strain and purified using Ni-NTA resin. The dephosphatase activity of MazG protein was verified by enzyme experiments and the effect of mutant overexpression on bacterial survival was tested. Results: The overexpression of mazG had no significant effect on the growth of E.coli MC4200, but had a significant inhibitory effect on the mazEFG gene knockout strain. The cytotoxicity of MazG depended on its NTP-PPase enzyme activity. The presence of mazEF significantly inhibited the phenotype of mazG;Knockout of the mazEF/mazG/mazEFG genes did not affect the growth curve of E.coli under normal envi- ronment. Under stress conditions, the survival rate of the mazG knockout strain was basically the same as that of the mazEFG knockout strain, which was significantly higher than that of the wild type. Conclusion: The mazG gene is involved in the regulation of bacterial programmed cell death induced by mazEF and has an important role in bacterial growth inhibition. This study provides a new perspective for the study of TAs and further understanding of its role in the regulation of bacterial growth and death.
ABSTRACT
Although analysis of toxin-antitoxin (TA) systems can be instructive, to date, there is no information on the prevalence and identity of TA systems based on a large panel of Acinetobacter baumannii clinical isolates. The aim of the current study was to screen for functional TA systems among clinical isolates of A. baumannii and to identify the systems’ locations. For this purpose, we screened 85 A. baumannii isolates collected from different clinical sources for the presence of the mazEF, relBE and higBA TA genes. The results revealed that the genes coding for the mazEF TA system were commonly present in all clinical isolates of A. baumannii. Reverse transcriptase-polymerase chain reaction analysis showed that transcripts were produced in the clinical isolates. Our findings showed that TA genes are prevalent, harboured by chromosomes and transcribed within A. baumannii. Hence, activation of the toxin proteins in the mazEF TA system should be investigated further as an effective antibacterial strategy against this bacterium.