(P)ppGpp synthetase Rsh participates in rifampicin tolerance of persister cells in Brucella abortus in vitro

(P)ppGpp synthetase Rel facilitates cellulose formation of biofilm by regulating glycosyltransferase in Brucella abortus

Biofilms are complex adhesive structures that establish chronic infection and allow robust protection from external stressors such as antibiotics. Cellulose as one of the compositions of bacteria biofilm which protect bacteria from stress, host immune responses and resistance to antibiotics. Bacterial stress responses are regulated via guanosine pentaphosphate and tetraphosphate (p)ppGpp. This molecule has been a target of research efforts to counteract biofilm formation in pathogenic bacteria. However, a role for (p)ppGpp synthetase Rel influencing in biofilms and its cellulose formation has not been identified in Brucella. Firstly, rel mutant significantly decreased biofilm biomass and rendered biofilms more susceptible to most antibiotics. The rel mutant also showed greatly decreased biofilm architectures including exopolysaccharide, extracellular DNA, and lipid. Remarkably, we found rel mutant significantly decreased biofilm cellulose formation. We further combined proteomic analysis to explore the key proteins involved in cellulose regulation of Rel in Brucella biofilm formation. 287 differentially expressed proteins (DEPs) were identified and enriched in diverse metabolic pathway between WT and Δrel strains including purine and sulfur metabolism, transcription factors and glycosyltransferases which may be related to cellulose formation. The Q-PCR showed that mRNA levels of only glycosyltransferase (WP_006161578.1) of the 12 down-DFPs had significantly upregulated in rel mutant contrast to WT strain and β-galactosidase assay showed a negative regulatory in rel mutant. Furthermore, Rel-dependent biofilms cellulose was also restored and accompanied by an increase in glycosyltransferase (WP_006161578.1) when glucose was added in TSB medium. Overall, this work expands the role of (p)ppGpp synthetase Rel as an important regulator in biofilm and cellulose formation that is tightly linked with pathogenicity and chronic persistent infections in Brucella.

What Is the Impact of Antibiotic Resistance Determinants on the Bacterial Death Rate?

Objectives: Antibiotic-resistant bacteria are widespread, with resistance arising from chromosomal mutations and resistance genes located in the chromosome or in mobile genetic elements. While resistance determinants often reduce bacterial growth rates, their influence on bacterial death under bactericidal antibiotics remains poorly understood. When bacteria are exposed to bactericidal antibiotics to which they are susceptible, they typically undergo a two-phase decline: a fast initial exponentially decaying phase, followed by a persistent slow-decaying phase. This study examined how resistance determinants affect death rates during both phases. Methods: We analyzed the death rates of ampicillin-exposed Escherichia coli populations of strains sensitive to ampicillin but resistant to nalidixic acid, rifampicin, or both, and bacteria carrying the conjugative plasmids RN3 or R702. Results: Single mutants resistant to nalidixic acid or rifampicin decayed faster than sensitive cells during the early phase, whereas the double-resistant mutant exhibited prolonged survival. These contrasting impacts suggest epistatic interactions between both chromosomal mutations. Persistent-phase death rates for chromosomal mutants did not differ significantly from wild-type cells. In contrast, plasmid-carrying bacteria displayed distinct dynamics: R702 plasmid-bearing cells showed higher persistent-phase death rates than plasmid-free cells, while RN3 plasmid-bearing cells exhibited lower rates. Conclusions: Bactericidal antibiotics may kill bacteria resistant to other antibiotics more effectively than wild-type cells. Moreover, epistasis may occur when different resistance determinants occur in the same cell, impacting the bactericidal potential of the antibiotic of choice. These results have significant implications for optimizing bacterial eradication protocols in clinical settings, as well as in animal health and industrial food safety management.

Serine/threonine protein kinase mediates rifampicin resistance in Brucella melitensis through interacting with ribosomal protein RpsD and affecting antioxidant capacity

Brucellosis, a zoonotic disease, has re-emerged in both humans and animals, causing significant economic losses globally. Recently, an increasing number of rifampicin-resistant Brucella strains have been isolated worldwide without detectable mutations in known antibiotic resistance genes. Here, this study identified the deletion of serine/threonine protein kinase (STPK) gene in B. melitensis as an efficient trigger for rifampicin resistance using bioinformatics predictions, a transposon mutant library, and gene mutation strains. Notably, the absence of the STPK could increase the expression of ribosomal proteins and genes involved in sulfur metabolism and reduced glutathione, and decrease NADPH oxidase activity and NADP+/NADPH ratio, which is associated with the antioxidant capacity of B. melitensis. Moreover, co-immunoprecipitation revealed that STPK could efficiently interact with the ribosomal protein RpsD, possibly altering protein translation and riboswitch expression. These findings demonstrate that the STPK gene mediates resistance by regulating sulfur metabolism to counteract the reactive oxygen species induced by rifampicin. Furthermore, the approaches developed in this study provide a platform for screening new resistance genes in Brucella spp., and the identified STPK or its pathway can serve as a potential target for new drug development against rifampicin-resistant Brucella spp.

IMPORTANCE

New rifampicin resistance gene in Brucella melitensis is identified via bioinformatics predictions and a whole-genome transposon mutant library, new mechanisms of rifampicin resistance in B. melitensis, and new function of serine/threonine protein kinase gene and its interaction proteins.

Type I toxin-antitoxin systems in bacteria: from regulation to biological functions

Toxin-antitoxin systems are ubiquitous in the prokaryotic world and widely distributed among chromosomes and mobile genetic elements. Several different toxin-antitoxin system types exist, but what they all have in common is that toxin activity is prevented by the cognate antitoxin. In type I toxin-antitoxin systems, toxin production is controlled by an RNA antitoxin and by structural features inherent to the toxin messenger RNA. Most type I toxins are small membrane proteins that display a variety of cellular effects. While originally discovered as modules that stabilize plasmids, chromosomal type I toxin-antitoxin systems may also stabilize prophages, or serve important functions upon certain stress conditions and contribute to population-wide survival strategies. Here, we will describe the intricate RNA-based regulation of type I toxin-antitoxin systems and discuss their potential biological functions.

The (p)ppGpp synthetase Rsh promotes rifampicin tolerant persister cell formation in Brucella abortus by regulating the type II toxin-antitoxin module mbcTA

Persister cells are transiently tolerant to antibiotics and are associated with recalcitrant chronic infections due to recolonization of host cells after antibiotic removal. Brucella spp. are facultative pathogens that establish intracellular infection cycles in host cells which results in chronic persistent infections. Brucella abortus forms multi-drug persister cells which are promoted by the (p)ppGpp synthetase Rsh during rifampicin exposure. Here, we confirmed that Rsh promoted persister cells formation in B. abortus stationary phase treated with rifampicin and enrofloxacin. Deletion of the gene for Rsh decreased persister cells level in the presence of these drugs in different growth phases. However, persister cells formation by deletion strain varied in different growth phases in the presence of other antibiotics. Rsh also was involved in persister cells formation during rifampicin treatment under certain stress conditions, including acidic conditions, exposure to PBS, and heat stress. Moreover, Rsh impacted persister cell levels during rifampicin or enrofloxacin treatment in RAW264.7 macrophages. Certain typeIItoxin-antitoxin modules were upregulated under various stress conditions in B. abortus. We established that Rsh positively regulated the type II toxin-antitoxin mbcTA. Moreover, rifampicin-tolerant persister cells formation was elevated and ATP levels were decreased when mbcTA promoter was overexpressed in Rsh deletion background in stationary phase. Our results establish that (p)ppGpp synthetase Rsh plays a key role in B. abortus persistence and may serve as a potent novel target in combination with rifampicin in the development of new therapeutic approaches and prevention strategies to treat chronic infections of Brucella.

Unlocking the enigma of phenotypic drug tolerance: Mechanisms and emerging therapeutic strategies

In the ongoing battle against antimicrobial resistance, phenotypic drug tolerance poses a formidable challenge. This adaptive ability of microorganisms to withstand drug pressure without genetic alterations further complicating global healthcare challenges. Microbial populations employ an array of persistence mechanisms, including dormancy, biofilm formation, adaptation to intracellular environments, and the adoption of L-forms, to develop drug tolerance. Moreover, molecular mechanisms like toxin-antitoxin modules, oxidative stress responses, energy metabolism, and (p)ppGpp signaling contribute to this phenomenon. Understanding these persistence mechanisms is crucial for predicting drug efficacy, developing strategies for chronic bacterial infections, and exploring innovative therapies for refractory infections. In this comprehensive review, we dissect the intricacies of drug tolerance and persister formation, explore their role in acquired drug resistance, and highlight emerging therapeutic approaches to combat phenotypic drug tolerance. Furthermore, we outline the future landscape of interventions for persistent bacterial infections.