Vibrio splendidus persister cells induced by host coelomic fluids show a similar phenotype to antibiotic-induced counterparts

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.

Isolation, characterization and application of a lytic phage vB_VspM_VS1 against Vibrio splendidus biofilm

Vibrio splendidus is a common pathogen in the ocean that infects Apostichopus japonicus, Atlantic salmon and Crassostrea gigas, leading to a variety of diseases. In this study, a virulent phage vB_VspM_VS1, which infects V. splendidus, was isolated from aquaculture ponds in Dalian, China, and it belongs to the family Straboviridae in the order Caudoviricetes. vB_VspM_VS1 had an adsorption rate of 96% in 15 min, a latent period of 65 min, and a burst size of 140 ± 6 PFU/cell. The complete genome of phage vB_VspM_VS1 consists of a linear double-stranded DNA that is 248,270 bp in length with an average G + C content of 42.5% and 389 putative protein-coding genes; 116 genes have known functions. There are 4 tail fiber genes in the positive and negative strands of the phage vB_VspM_VS1 genome. The protein domain of the phage vB_VspM_VS1 tail fibers was obtained from the Protein Data Bank and the SMART (http://smart.embl.de) database. Bacterial challenge tests revealed that the growth of V. splendidus HS0 was apparently inhibited (OD600 < 0.01) in 12 h at an MOI of 10. In against biofilms, we also showed that the OD570 value of the vB_VspM_VS1-treated group (MOI = 1) decreased significantly to 0.04 ± 0.01 compared with that of the control group (0.48 ± 0.08) at 24 h. This study characterizes the genome of the phage vB_VspM_VS1 that infects the pathogenic bacterium V. splendidus of A. japonicus.

Exogenous adenosine and/or guanosine enhances tetracycline sensitivity of persister cells

Vibrio splendidus is an opportunistic pathogen, its pathogenicity continues to be a major aquaculture disease infection problem in many parts of the world. Bacteria can form dormant and persister cells, which may be responsible for the difficulty in treating latent infections. Bacterial persister cells are a small subpopulation with high phenotypic heterogeneity that have the ability to persist in response to high concentrations of antibiotics. In our previous work, we have confirmed tetracycline could induce V. splendidus AJ01 persister cells formation. Here, we show that exogenous adenosine and/or guanosine supply restores susceptibility of AJ01 persister cells to tetracycline, leading to effective killing of this persist subpopulation upon wake-up. Mechanistically, exogenous adenosine and/or guanosine promotes the intracellular ATP level, reduces percentage of cells with protein aggresomes, and destroys membrane stability. In addition, when cells were exposed to tetracycline, we found that cells with small nucleocytoplasmic ratio is easy to survive. Overall, our results support that exogenous adenosine or guanosine could be an effective strategy for treating infections with antibiotic-persist bacteria via regulating persisters cells formation.

Purine metabolism regulates Vibrio splendidus persistence associated with protein aggresome formation and intracellular tetracycline efflux

A small subpopulation of Vibrio splendidus AJ01 that was exposed to tetracycline at 10 times the minimal inhibitory concentration (MIC) still survived, named tetracycline-induced persister cells in our previous work. However, the formation mechanisms of persister is largely unknown. Here, we investigated tetracycline-induced AJ01 persister cells by transcriptome analysis and found that the purine metabolism pathway was significantly downregulated, which was consistent with lower levels of ATP, purine, and purine derivatives in our metabolome analysis. Inhibition of the purine metabolism pathway by 6-mercaptopurine (6-MP, inhibits ATP production), increased persister cell formation and accompanied with the decreasing intracellular ATP levels and increasing cells with protein aggresome. On the other hand, the persister cells had reduced intracellular tetracycline concentrations and higher membrane potential after 6-MP treatment. Inhibition of the membrane potential by carbonyl cyanide m-chlorophenyl hydrazone reversed 6-MP-induced persistence and resulted in higher levels of intracellular tetracycline accumulation. Meanwhile, cells with 6-MP treatment increased the membrane potential by dissipating the transmembrane proton pH gradient, which activated efflux to decrease the intracellular tetracycline concentration. Together, our findings show that reduction of purine metabolism regulates AJ01 persistence and is associated with protein aggresome formation and intracellular tetracycline efflux.

Immune Response Modulation by Pseudomonas aeruginosa Persister Cells

Bacterial persister cells-a metabolically dormant subpopulation tolerant to antimicrobials-contribute to chronic infections and are thought to evade host immunity. In this work, we studied the ability of Pseudomonas aeruginosa persister cells to withstand host innate immunity. We found that persister cells resist MAC-mediated killing by the complement system despite being bound by complement protein C3b at levels similar to regular vegetative cells, in part due to reduced bound C5b, and are engulfed at a lower rate (10- to 100-fold), even following opsonization. Once engulfed, persister cells resist killing and, contrary to regular vegetative cells which induce a M1 favored (CD80⁺/CD86⁺/CD206^-, high levels of CXCL-8, IL-6, and TNF-α) macrophage polarization, they initially induce a M2 favored macrophage polarization (CD80⁺/CD86⁺/CD206⁺, high levels of IL-10, and intermediate levels of CXCL-8, IL-6, and TNF-α), which is skewed toward M1 favored polarization (high levels of CXCL-8 and IL-6, lower levels of IL-10) by 24 h of infection, once persister cells awaken. Overall, our findings further establish the ability of persister cells to evade the innate host response and to contribute chronic infections. IMPORTANCE Bacterial cells have a subpopulation-persister cells-that have a low metabolism. Persister cells survive antimicrobial treatment and can regrow to cause chronic and recurrent infections. Currently little is known as to whether the human immune system recognizes and responds to the presence of persister cells. In this work, we studied the ability of persister cells from Pseudomonas aeruginosa to resist the host defense system (innate immunity). We found that this subpopulation is recognized by the defense system, but it is not killed. The lack of killing likely stems from hindering the immune response regulation, resulting in a failure to distinguish whether a pathogen is present. Findings from this work increase the overall knowledge as to how chronic infections are resilient.

Proteomic analysis of the initial wake up of vibrio splendidus persister cells

Vibrio splendidus is a ubiquitous pathogen that causes various diseases in aquaculture with a wide range of hosts. In our previous studies, we showed that L-glutamic acid was the optimal carbon source that could revive V. splendidus persister cells. In our present study, single cell observation under microscopy showed that V. splendidus could revive using L-glutamic acid as carbon source. A proteomic analysis was carried out to further illustrate the initial wake up of persister cells with L-glutamic acid. To collect the initially revived cells, SDS-PAGE was used to determine the revived time. The total proteins from the persister cells and the revived cells were analyzed using LC‒MS/MS. A total of 106 proteins, including 42 downregulated proteins and 64 upregulated proteins, were identified. GO analysis of the differentially expressed proteins (DEPs) showed that biological processes, including protein complex assembly, protein oligomerization, and arginine metabolism; cellular components, including extracellular membrane, plasma membrane and ribosome; and molecular functions, including the activities of arginine binding and structural constituent of ribosome, were enriched. KEGG analysis showed that lipopolysaccharide biosynthesis, porphyrin and chlorophyll metabolism, and peptidoglycan biosynthesis were upregulated, while the ribosome was downregulated. This is the first time to study the initial wake up of persister cells based on proteomic analysis, and the results revealed the main pathways involved in the early resuscitation of V. splendidus persister cells.

Immune response modulation by Pseudomonas aeruginosa persister cells

Bacterial persister cells - a metabolically dormant subpopulation tolerant to antimicrobials - contribute to chronic infections and are thought to evade host immunity. In this work, we studied the ability of Pseudomonas aeruginosa persister cells to withstand host innate immunity. We found that persister cells resist MAC-mediated killing by the complement system despite being bound by complement protein C3b at levels similar to regular vegetative cells, in part due to reduced bound C5b - and are engulfed at a lower rate (10-100 fold), even following opsonization. Once engulfed, persister cells resist killing and, contrary to regular vegetative cells which induce a M1 favored (CD80+/CD86+/CD206-, high levels of CXCL-8, IL-6, and TNF-α) macrophage polarization, they initially induce a M2 favored macrophage polarization (CD80+/CD86+/CD206+, high levels of IL-10, and intermediate levels of CXCL-8, IL-6, and TNF-α), which is skewed towards M1 favored polarization (high levels of CXCL-8 and IL-6, lower levels of IL-10) by 24 hours of infection, once persister cells awaken. Overall, our findings further establish the ability of persister cells to evade the innate host response and to contribute chronic infections.

Selection of the Amino Acid and Saccharide That Increase the Tetracycline Susceptibility of Vibrio splendidus

Bacterial persister cells are a subpopulation of isogenic bacteria with characteristics of reduced metabolic activity and multidrug antibiotic resistance. Our lab had previously proved that Vibrio splendidus could form persister cells both naturally and after stimulation. However, the conditions for the waking up of V. splendidus persister cells remain marginal. In this study, the carbon sources that could wake up V. splendidus persister cells were selected from 20 amino acids and eight saccharides. The result showed that L-glutamic acid, L-aspartic acid, L-arginine, L-phenylalanine, L-leucine, maltose, D-galactose, sorbitol, mannose, N-acetyl-D-glucosamine, D-glucose, and D-fructose could wake up the V. splendidus persister cells. The chemotaxis activity of both exponential cells and regrown persister cells on plate containing each of the selected carbon source are also high. The existence of the selected carbon source can affect the antibiotic susceptibility of V. splendidus. When L-glutamic acid, L-aspartic acid, L-phenylalanine, and D-glucose were separately added into the cultured V. splendidus simultaneously with tetracycline, V. splendidus could be completely eliminated, while the addition of L-alanine and D-galactose could not. Our study suggested that V. splendidus persister cells could revive in the presence of specific carbon sources, and the addition of these exogenous nutrients could increase the tetracycline susceptibility of V. splendidus.