Survey on phenotypic resistance in Enterococcus faecalis: comparison between the expression of biofilm-associated genes in Enterococcus faecalis persister and non-persister cells

Abstract Background Currently, phenotypic resistance is a serious therapeutic challenge, and a definitive remedy has not been discovered yet. Biofilm formation and persister cells are two well-studied phenotypic resistance, leading to the recalcitrance and relapse of different chronic infections. It appears that the presence of persister cells in biofilm is the main factor in the relapse of infections and treatment failure. Thus, we aimed to evaluate the expression of biofilm-associated genes in persister and non-persister E. faecalis isolates. Methods Ninety-five clinical E. faecalis isolates were investigated using microtiter broth dilution (MBD) and microtiter plate (MTP) assay to determine the vancomycin-sensitive isolates and biofilm formation, respectively. To this end, 91 vancomycin-sensitive E. faecalis isolates (biofilm producers) were screened by PCR to determine the presence of biofilm-related genes (gelE, esp, and agg). The vancomycin-tolerant isolates were determined by MTP assay. Bacterial persister assay was performed using an enzymatic lysis assay. Finally, the expression of biofilm-related genes was evaluated in persisters and non-persister isolates of E. faecalis by real-time PCR assay. Results E. faecalis isolates indicated a high (95.8%) sensitivity to vancomycin. PCR assay identified gelE, esp, and agg genes in 91 (100%), 72(79.12), and 74(81.32) of isolates, respectively. All E. faecalis biofilm producers were tolerant to vancomycin, and minimum bactericidal concentration for biofilms (MBCB) was > 2500 µg/ml. Based on enzymatic lysis assay, among 91 isolates, only 3 persister were isolated. The increased expression level of biofilm-related genes was observed in persister than non-persister E. faecalis isolates. Conclusion The expression of biofilm-related genes is higher in persister than non-persister isolates of E. faecalis.

Download Full-text

Molecular Mechanisms оf Persistence оf Bacteria

Journal of microbiology epidemiology immunobiology ◽

10.36233/0372-9311-2020-97-3-10 ◽

2020 ◽

Vol 97 (3) ◽

pp. 271-279

Author(s):

Boris G. Andryukov ◽

Irina N. Lyapun

Keyword(s):

Pathogenic Bacteria ◽

Molecular Mechanisms ◽

Bacterial Resistance ◽

Antimicrobial Agents ◽

Molecular Genetic ◽

Rapid Evolution ◽

Cell Subpopulation ◽

Bacterial Persistence ◽

Persister Cells ◽

Phenotypic Resistance

A significant mortality rate from infectious diseases is largely mediated by the widespread and uncontrolled use of antibiotics, which has led to the emergence of drug-resistant strains of bacteria. The rapid evolution of bacterial resistance to antimicrobials is a serious challenge for modern health care, mediates the need to create new antibiotic agents, as well as to intensify the study of molecular mechanisms underlying the formation of microorganism resistance. One of these mechanisms is bacterial persistence, manifested by the formation of persistent cells in the culture, which are a phenotypic variant of the isogenic population. The persistence of bacteria can occur spontaneously, regardless of exposure to antimicrobials or environmental reasons, such as lack of nutrients, oxidative stress or hypoxia. This small cell subpopulation is able to maintain viability even in the presence of antimicrobial agents at concentrations many times higher than therapeutic. The presence of persistent cells of pathogenic bacteria in the host organism reduces the effectiveness of antibiotic treatment, not due to the genotypic drug resistance of the microorganism, but due to the presence of phenotypic resistance of persister cells. The difference is fundamental, since cell-persisters are insensitive to any antibiotics and the development of fundamentally new antimicrobial strategies is necessary for their eradication. Persister cells are phenotypic variants of the maternal culture of bacteria that are present in all populations of microorganisms, and after the onset of favorable conditions, they are able to reclaim and form a new generation of vegetative bacteria. This review discusses modern concepts of the molecular genetic mechanisms of bacterial persistence with an emphasis on their clinical significance for the occurrence of persistent infections, and discusses innovative technologies for the eradication of resistant cell forms of microorganisms.

Download Full-text