Genomic context as well as sequence of both psr and penicillin-binding protein 5 contributes to β-lactam resistance in Enterococcus faecium

Penicillin-binding protein 5 (PBP5) of Enterococcus faecium (Efm) is vital for ampicillin resistance (AMP-R). We previously designated three forms of PBP5, namely, PBP5-S in Efm clade B strains [ampicillin susceptible (AMP-S)], PBP5-S/R (AMP-S or R), and PBP5-R (AMP-R) in clade A strains. Here, pbp5 deletion resulted in a marked reduction in AMP minimum inhibitory concentrations (MICs) to 0.01-0.09 µg/mL for clade B and 0.12-0.19 µg/mL for clade A strains; in situ complementation restored parental AMP MICs. Using D344SRF (lacking ftsW/psr/pbp5), constructs with ftsWA/psrA (from a clade A1 strain) cloned upstream of pbp5-S and pbp5-S/R alleles resulted in modest increases in MICs to 3-8 µg/mL, while high MICs (>64 µg/mL) were seen using pbp5 from A1 strains. Next, using ftsW ± psr from clade B and clade A/B and B/A hybrid constructs, the presence of psrB, even alone or in trans, resulted in much lower AMP MICs (3-8 µg/mL) than when psrA was present (MICs >64 µg/mL). qRT PCR showed relatively greater pbp5 expression (P = 0.007) with pbp5 cloned downstream of clade A1 ftsW/psr (MIC >128 µg/mL) vs when cloned downstream of clade B ftsW/psr (MIC 4-16 µg/mL), consistent with results in western blots. In conclusion, we report the effect of clade A vs B psr on AMP MICs as well as the impact of pbp5 alleles from different clades. While previously, Psr was not thought to contribute to AMP MICs in Efm, our results showed that the presence of psrB resulted in a major decrease in Efm AMP MICs.

IMPORTANCE

The findings of this study shed light on ampicillin resistance in Enterococcus faecium clade A strains. They underscore the significance of alterations in the amino acid sequence of penicillin-binding protein 5 (PBP5) and the pivotal role of the psr region in PBP5 expression and ampicillin resistance. Notably, the presence of a full-length psrB leads to reduced PBP5 expression and lower minimum inhibitory concentrations (MICs) of ampicillin compared to the presence of a shorter psrA, regardless of the pbp5 allele involved. Additionally, clade B E. faecium strains exhibit lower AMP MICs when both psr alleles from clades A and B are present, although it is important to consider other distinctions between clade A and B strains that may contribute to this effect. It is intriguing to note that the divergence between clade A and clade B E. faecium and the subsequent evolution of heightened AMP MICs in hospital-associated strains appear to coincide with changes in Pbp5 and psr. These changes in psr may have resulted in an inactive Psr, facilitating increased PBP5 expression and greater ampicillin resistance. These results raise the possibility that a mimicker of PsrB, if one could be designed, might be able to lower MICs of ampicillin-resistant E. faecium, thus potentially resorting ampicillin to our therapeutic armamentarium for this species.

Comparative analysis of proteomic adaptations in Enterococcus faecalis and Enterococcus faecium after long term bile acid exposure

BACKGROUND

All gastrointestinal pathogens, including Enterococcus faecalis and Enterococcus faecium, undergo adaptation processes during colonization and infection. In this study, we investigated by data-independent acquisition mass spectrometry (DIA-MS) two crucial adaptations of these two Enterococcus species at the proteome level. Firstly, we examined the adjustments to cope with bile acid concentrations at 0.05% that the pathogens encounter during a potential gallbladder infection. Therefore, we chose the primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA) as well as the secondary bile acid deoxycholic acid (DCA), as these are the most prominent bile acids. Secondly, we investigated the adaptations from an aerobic to a microaerophilic environment, as encountered after oral-fecal infection, in the absence and presence of deoxycholic acid (DCA).

RESULTS

Our findings showed similarities, but also species-specific variations in the response to the different bile acids. Both Enterococcus species showed an IC50 in the range of 0.01- 0.023% for DCA and CDCA in growth experiments and both species were resistant towards 0.05% CA. DCA and CDCA had a strong effect on down-expression of proteins involved in translation, transcription and replication in E. faecalis (424 down-expressed proteins with DCA, 376 down-expressed proteins with CDCA) and in E. faecium (362 down-expressed proteins with DCA, 391 down-expressed proteins with CDCA). Proteins commonly significantly altered in their expression in all bile acid treated samples were identified for both species and represent a "general bile acid response". Among these, various subunits of a V-type ATPase, different ABC-transporters, multi-drug transporters and proteins related to cell wall biogenesis were up-expressed in both species and thus seem to play an essential role in bile acid resistance. Most of the differentially expressed proteins were also identified when E. faecalis was incubated with low levels of DCA at microaerophilic conditions instead of aerobic conditions, indicating that adaptations to bile acids and to a microaerophilic atmosphere can occur simultaneously.

CONCLUSIONS

Overall, these findings provide a detailed insight into the proteomic stress response of two Enterococcus species and help to understand the resistance potential and the stress-coping mechanisms of these important gastrointestinal bacteria.

Deciphering the role of Enterococcus faecium cytidine deaminase in gemcitabine resistance of gallbladder cancer

Gemcitabine-based chemotherapy is a cornerstone of standard care for gallbladder cancer (GBC) treatment. Still, drug resistance remains a significant challenge, influenced by factors such as tumor-associated microbiota impacting drug concentrations within tumors. Enterococcus faecium, a member of tumor-associated microbiota, was notably enriched in the GBC patient cluster. In this study, we investigated the biochemical characteristics, catalytic activity, and kinetics of the cytidine deaminase of E. faecium (EfCDA). EfCDA showed the ability to convert gemcitabine to its metabolite 2',2'-difluorodeoxyuridine. Both EfCDA and E. faecium can induce gemcitabine resistance in GBC cells. Moreover, we determined the crystal structure of EfCDA, in its apo form and in complex with 2', 2'-difluorodeoxyuridine at high resolution. Mutation of key residues abolished the catalytic activity of EfCDA and reduced the gemcitabine resistance in GBC cells. Our findings provide structural insights into the molecular basis for recognizing gemcitabine metabolite by a bacteria CDA protein and may provide potential strategies to combat cancer drug resistance and improve the efficacy of gemcitabine-based chemotherapy in GBC treatment.

C-terminal deletion of RelA protein is suggested as a possible cause of infective endocarditis recurrence with Enterococcus faecium

Infective endocarditis (IE) caused by Enterococcus spp. represents the third most common cause of IE, with high rates of relapse compared with other bacteria. Interestingly, late relapses (>6 months) have only been described in Enterococcus faecalis, but here we describe the first reported IE relapse with Enterococcus faecium more than a year (17 months) after the initial endocarditis episode. Firstly, by multi locus sequence typing (MLST), we demonstrated that both isolates (EF646 and EF641) belong to the same sequence type (ST117). Considering that EF641 was able to overcome starvation and antibiotic treatment conditions surviving for a long period of time, we performed bioinformatic analysis in identifying potential genes involved in virulence and stringent response. Our results showed a 13-nucleotide duplication (positions 1638-1650) in the gene relA, resulting in a premature stop codon, with a loss of 167 amino acids from the C-terminal domains of the RelA enzyme. RelA mediates the stringent response in bacteria, modulating levels of the alarmone guanosine tetraphosphate (ppGpp). The relA mutant (EF641) was associated with lower growth capacity, the presence of small colony variants, and higher capacity to produce biofilms (compared with the strain EF646), but without differences in antimicrobial susceptibility patterns according to standard procedures during planktonic growth. Instead, EF641 demonstrated tolerance to high doses of teicoplanin when growing in a biofilm. We conclude that all these events would be closely related to the long-term survival of the E. faecium and the late relapse of the IE. These data represent the first clinical evidence of mutations in the stringent response (relA gene) related with E. faecium IE relapse.

Study of an Enterococcus faecium strain isolated from an artisanal Mexican cheese, whole-genome sequencing, comparative genomics, and bacteriocin expression

Enterococci are ubiquitous microorganisms in almost all environments, from the soil we step on to the food we eat. They are frequently found in naturally fermented foods, contributing to ripening through protein, lipid, and sugar metabolism. On the other hand, these organisms are also leading the current antibiotic resistance crisis. In this study, we performed whole-genome sequencing and comparative genomics of an Enterococcus faecium strain isolated from an artisanal Mexican Cotija cheese, namely QD-2. We found clear genomic differences between commensal and pathogenic strains, particularly in their carbohydrate metabolic pathways, resistance to vancomycin and other antibiotics, bacteriocin production, and bacteriophage and CRISPR content. Furthermore, a bacteriocin transcription analysis performed by RT-qPCR revealed that, at the end of the log phase, besides enterocins A and X, two putative bacteriocins not reported previously are also transcribed as a bicistronic operon in E. faecium QD-2, and are expressed 1.5 times higher than enterocin A when cultured in MRS broth.

Effects of Enterococcus faecium (R8a) on nonspecific immune gene expression, immunity and intestinal flora of giant tiger shrimp (Penaeus monodon)

In this study, Penaeus monodon were gave basic feed supplemented with three levels of Enterococcus faecium. Then, the expression of non-specific immunity-related genes, and the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), malondialdehyde (MDA), acid phosphatase (ACP), alkaline phosphatase (AKP), phenol oxidase (PO) were evaluated. Meanwhile, the disease resistance test and intestinal flora determination were conducted. The results showed that the MDA levels of 2% and 5% E. faecium groups were significantly lower than that of the control group (P < 0.05). While the SOD and T-AOC and ACP and AKP of experimental groups were significantly higher (P < 0.05), the PO of experimental groups were significantly lower than that of the control group (P < 0.05). In addition, the expressions of immunity-related genes (tlr22, dorsal, lysozyme, crustin, imd, and relish) in the 2% and 5% E. faecalis groups were significantly greater than those in the control group (P < 0.05). After P. monodon was challenged with Vibrio parahaemolyticus for 7 days, the average cumulative mortality of P. monodon in the 2% and 5% groups were significantly lower than that in the 0% group (P < 0.05). With the increase of feeding time, the number of effective OTUs in each group showed a downward trend. At the 14th d, Proteobacteria, Bacteroidetes and Firmicutes, the dominant flora in the intestinal tract of P. monodon. In summary, supplied with E. faecium could increase the expression of non-specific immunity-related genes, enhance the immune capacity of P. monodon.

Cultivated Enterococcus faecium B6 from children with obesity promotes nonalcoholic fatty liver disease by the bioactive metabolite tyramine

Gut microbiota plays an essential role in nonalcoholic fatty liver disease (NAFLD). However, the contribution of individual bacterial strains and their metabolites to childhood NAFLD pathogenesis remains poorly understood. Herein, the critical bacteria in children with obesity accompanied by NAFLD were identified by microbiome analysis. Bacteria abundant in the NAFLD group were systematically assessed for their lipogenic effects. The underlying mechanisms and microbial-derived metabolites in NAFLD pathogenesis were investigated using multi-omics and LC-MS/MS analysis. The roles of the crucial metabolite in NAFLD were validated in vitro and in vivo as well as in an additional cohort. The results showed that Enterococcus spp. was enriched in children with obesity and NAFLD. The patient-derived Enterococcus faecium B6 (E. faecium B6) significantly contributed to NAFLD symptoms in mice. E. faecium B6 produced a crucial bioactive metabolite, tyramine, which probably activated PPAR-γ, leading to lipid accumulation, inflammation, and fibrosis in the liver. Moreover, these findings were successfully validated in an additional cohort. This pioneering study elucidated the important functions of cultivated E. faecium B6 and its bioactive metabolite (tyramine) in exacerbating NAFLD. These findings advance the comprehensive understanding of NAFLD pathogenesis and provide new insights for the development of microbe/metabolite-based therapeutic strategies.

Flow cytometric detection of vancomycin-resistant Enterococcus faecium in urine using fluorescently labelled enterocin K1

A urinary tract infection (UTI) occurs when bacteria enter and multiply in the urinary system. The infection is most often caused by enteric bacteria that normally live in the gut, which include Enterococcus faecium. Without antibiotic treatment, UTIs can progress to life-threatening septic shock. Early diagnosis and identification of the pathogen will reduce antibiotic use and improve patient outcomes. In this work, we develop and optimize a cost-effective and rapid (< 40 min) method for detecting E. faecium in urine. The method uses a fluorescently labelled bacteriocin enterocin K1 (FITC-EntK1) that binds specifically to E. faecium and is then detected using a conventional flow cytometer. Using this detection assay, urine containing E. faecium was identified by an increase in the fluorescent signals by 25-73-fold (median fluorescence intensity) compared to control samples containing Escherichia coli or Staphylococcus aureus. The method presented in this work is a proof of concept showing the potential of bacteriocins to act as specific probes for the detection of specific bacteria, such as pathogens, in biological samples.

The LiaFSR-LiaX System Mediates Resistance of Enterococcus faecium to Peptide Antibiotics and to Aureocin A53- and Enterocin L50-Like Bacteriocins

Multidrug-resistant Enterococcus faecium strains are currently a leading cause of difficult-to-treat nosocomial infections. The emerging resistance of enterococci to last-resort antibiotics, such as daptomycin, prompts a search for alternative antimicrobials. Aureocin A53- and enterocin L50-like bacteriocins are potent antimicrobial agents that form daptomycin-like cationic complexes and have a similar cell envelope-targeting mechanism of action, suggesting their potential as next-generation antibiotics. However, to ensure their safe use, the mechanisms of resistance to these bacteriocins and cross-resistance to antibiotics need to be well understood. Here, we investigated the genetic basis of E. faecium's resistance to aureocin A53- and enterocin L50-like bacteriocins and compared it with that to antibiotics. First, we selected spontaneous mutants resistant to the bacteriocin BHT-B and identified adaptive mutations in the liaFSR-liaX genes encoding the LiaFSR stress response regulatory system and the daptomycin-sensing protein LiaX, respectively. We then demonstrated that a gain-of-function mutation in liaR increases the expression of liaFSR, liaXYZ, cell wall remodeling-associated genes, and hypothetical genes involved in protection against various antimicrobials. Finally, we showed that adaptive mutations or overexpression of liaSR or liaR alone results in cross-resistance to other aureocin A53- and enterocin L50-like bacteriocins, as well as antibiotics targeting specific components of the cell envelope (daptomycin, ramoplanin, gramicidin) or ribosomes (kanamycin and gentamicin). Based on the obtained results, we concluded that activation of the LiaFSR-mediated stress response confers resistance to peptide antibiotics and bacteriocins via a cascade of reactions, eventually leading to cell envelope remodeling. IMPORTANCE Pathogenic enterococci carry virulence factors and a considerable resistome, which makes them one of the most serious and steadily increasing causes of hospital epidemiological risks. Accordingly, Enterococcus faecium is classified into a top-priority ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) group of six highly virulent and multidrug-resistant (MDR) bacterial pathogens for which novel antimicrobial agents need to be developed urgently. Alternative measures, such as the use of bacteriocins, separately or in combination with other antimicrobial agents (e.g., antibiotics), could be a potential solution, especially since several international health agencies recommend and support the development of such interventions. Nevertheless, in order to exploit their efficacy, more basic research on the mechanisms of cell killing and the development of resistance to bacteriocins is needed. The present study fills some of the knowledge gaps regarding the genetic basis of the development of resistance to potent antienterococcal bacteriocins, pointing out the common and divergent features regarding the cross-resistance to antibiotics.

Enolpyruvate transferase MurAAA149E, identified during adaptation of Enterococcus faecium to daptomycin, increases stability of MurAA-MurG interaction

Daptomycin (DAP) is an antibiotic frequently used as a drug of last resort against vancomycin-resistant enterococci. One of the major challenges when using DAP against vancomycin-resistant enterococci is the emergence of resistance, which is mediated by the cell-envelope stress system LiaFSR. Indeed, inhibition of LiaFSR signaling has been suggested as a strategy to "resensitize" enterococci to DAP. In the absence of LiaFSR, alternative pathways mediating DAP resistance have been identified, including adaptive mutations in the enolpyruvate transferase MurAA (MurAAA149E), which catalyzes the first committed step in peptidoglycan biosynthesis; however, how these mutations confer resistance is unclear. Here, we investigated the biochemical basis for MurAAA149E-mediated adaptation to DAP to determine whether such an alternative pathway would undermine the potential efficacy of therapies that target the LiaFSR pathway. We found cells expressing MurAAA149E had increased susceptibility to glycoside hydrolases, consistent with decreased cell wall integrity. Furthermore, structure-function studies of MurAA and MurAAA149E using X-ray crystallography and biochemical analyses indicated only a modest decrease in MurAAA149E activity, but a 16-fold increase in affinity for MurG, which performs the last intracellular step of peptidoglycan synthesis. Exposure to DAP leads to mislocalization of cell division proteins including MurG. In Bacillus subtilis, MurAA and MurG colocalize at division septa and, thus, we propose MurAAA149E may contribute to DAP nonsusceptibility by increasing the stability of MurAA-MurG interactions to reduce DAP-induced mislocalization of these essential protein complexes.

Rapid Proteomic Characterization of Bacteriocin-Producing Enterococcus faecium Strains from Foodstuffs

Enterococcus belongs to a group of microorganisms known as lactic acid bacteria (LAB), which constitute a broad heterogeneous group of generally food-grade microorganisms historically used in food preservation. Enterococci live as commensals of the gastrointestinal tract of warm-blooded animals, although they also are present in food of animal origin (milk, cheese, fermented sausages), vegetables, and plant materials because of their ability to survive heat treatments and adverse environmental conditions. The biotechnological traits of enterococci can be applied in the food industry; however, the emergence of enterococci as a cause of nosocomial infections makes their food status uncertain. Recent advances in high-throughput sequencing allow the subtyping of bacterial pathogens, but it cannot reflect the temporal dynamics and functional activities of microbiomes or bacterial isolates. Moreover, genetic analysis is based on sequence homologies, inferring functions from databases. Here, we used an end-to-end proteomic workflow to rapidly characterize two bacteriocin-producing Enterococcus faecium (Efm) strains. The proteome analysis was performed with liquid chromatography coupled to a trapped ion mobility spectrometry-time-of-flight mass spectrometry instrument (TimsTOF) for high-throughput and high-resolution characterization of bacterial proteins. Thus, we identified almost half of the proteins predicted in the bacterial genomes (>1100 unique proteins per isolate), including quantifying proteins conferring resistance to antibiotics, heavy metals, virulence factors, and bacteriocins. The obtained proteomes were annotated according to function, resulting in 22 complete KEGG metabolic pathway modules for both strains. The workflow used here successfully characterized these bacterial isolates and showed great promise for determining and optimizing the bioengineering and biotechnology properties of other LAB strains in the food industry.

Purification, Characterization, Mode of Action, and Application of Jileicin, a Novel Antimicrobial from Paenibacillus jilinensis YPG26

Antimicrobial compounds from the commensal gut microbiota have gained much attention due to their multifunctionality in maintaining good health in the host and killing multidrug-resistant bacteria. Our previous study showed that Paenibacillus jilinensis YPG26 isolated from chicken intestine can antagonize multiple pathogens. Herein, we characterized a bacteriocin-like inhibitory substance, jileicin, purified from P. jilinensis YPG26. Mass spectrometry analysis revealed that jileicin was a protein consisting of 211 amino acids, which showed 88.98% identity to the SIMPL domain-containing protein. The jileicin showed a relatively broad-spectrum antibacterial ability, especially against enterococci. Additionally, the jileicin exhibited good stability after various treatments, no detectable resistance, no significant cytotoxicity, and very low levels of hemolytic activity. The mode of action against Enterococcus faecium demonstrated that jileicin could destroy cell membrane integrity, increase cell membrane permeability, and eventually lead to cell death. Furthermore, jileicin was efficient in controlling the growth of E. faecium in milk. In conclusion, jileicin, as a newly identified antibacterial agent, is expected to be a promising candidate for application in the food, pharmaceutical, and biomedical industries.

Effect of Bacillus subtilis, Enterococcus faecium, and Enterococcus faecalis supernatants on serotonin transporter expression in cells and tissues

BACKGROUND

Bacillus subtilis (B. subtilis), Enterococcus faecium (E. faecium), and Enterococcus faecalis (E. faecalis) are probiotics that are widely used in the clinical treatment of irritable bowel syndrome (IBS). Whether the supernatants of these three probiotics can improve gastrointestinal sensation and movement by regulating the serotonin transporter (SERT) expression needs to be clarified.

AIM

To investigate whether B. subtilis, E. faecium, and E. faecalis supernatants can upregulate SERT expression in vitro and in vivo.

METHODS

Caco-2 and HT-29 cells were stimulated with probiotic culture supernatants for 12 and 24 h, respectively. A male Sprague-Dawley rat model of post-infectious irritable bowel syndrome (PI-IBS) was established and the rats were treated with phosphate-buffered saline (group A) and three probiotics culture supernatants (groups B, C, and D) for 4 wk. The levels of SERT were detected by quantitative PCR and western blotting.

RESULTS

The levels of SERT at post-treatment 12 and 24 h were significantly elevated in Caco-2 cells treated with B. subtilis supernatant compared with those in the control group (^aP < 0.05). Those levels were markedly upregulated in Caco-2 cells stimulated with E. faecium and E. faecalis supernatants at 24 h (^aP < 0.05). In addition, SERT expression in groups B, C, and D was significantly higher than that in group A in the 2nd wk (^aP < 0.05). Increased SERT expression was only found in group D in the 3rd wk (^aP < 0.05). However, there was no significant difference in SERT expression between the groups in the last week (P > 0.05).

CONCLUSION

The supernatants of B. subtilis, E. faecium, and E. faecalis can upregulate SERT expression in intestinal epithelial cells and the intestinal tissues in the rat model of PI-IBS.

Enterocin M-Producing Enterococcus faecium CCM 8558 Demonstrating Probiotic Properties in Horses

The effects of non-authochtonous Enterococcus faecium AL41 = CCM 8558, enterocin M-producing and probiotic strain were tested on the microbiota, phagocytic activity, hydrolytic enzymes, biochemical parameters and dry matter in horses based on its previous benefits demonstrated in other animals. E. faecium CCM 8558 sufficiently colonized the digestive tract of horses. At day 14, its counts reached 2.35 ± 0.70 CFU/g (log 10) on average. The identity of CCM 8558 was confirmed by means of PCR after its re-isolation from horse faeces. The inhibition activity of CCM 8558 was demonstrated against Gram-negative aeromonads, counts of which were significantly reduced (P < 0.001). After 14 days application of CCM 8558, a tendency towards increased phagocytic activity (PA) was measured; PA value was 73.13% ± 8.55 on average at day 0/1; at day 14, it was 75.11 ± 8.66%. Cellulolytic, xylanolytic and pectinolytic activity in horse faeces was significantly increased (P < 0.001) at day 14 (after CCM 8558 application) and amylolytic activity as well (P < 0.01) compared to day 0/1. Inulolytic activity increased with mathematical difference 1.378. Dry matter value reached 20.81 ± 2.29% on average at day 0/1; at day 14, it was 20.77 ± 2.59% (P = 0.9725). Biochemical parameters were influenced mostly in the physiological range. These results achieved after application of CCM 8558 in horses are original, giving us further opportunity to continue these studies, to measure additional parameters and to show the benefits of CCM 8558 application in horses.

In vitro evaluation of probiotic potential of Enterococcus faecium strains isolated from Turkish pastırma

This study is aimed at evaluating the probiotic potential of three Enterococcus faecium strains (called 29-P2, 168-P6 and 277-S3) isolated from 'pastırma', a Turkish traditional dry-cured meat product. For this, key probiotic properties and some functional characteristics of strains were tested in vitro. Antimicrobial activity of 3 E. faecium strains was evaluated against 18 indicator microorganisms consisting of 13 foodborne pathogens and 5 lactic acid bacteria and all strains were found as the producer of antimicrobial substance. Especially one strain 168-P6 showed a remarkable activity spectrum and inhibited all of the used foodborne pathogen indicators. Antimicrobial compounds produced by strains were identified by determining the effect of enzyme, pH and temperature on antimicrobial activity. All strains exhibited tolerance to acidic conditions and a simulated gastric environment. Also, strains exhibited high adhesion capacity. The safety of the strains was assessed by determining hemolytic activity and the resistance to 14 different antibiotics. None of the three strains exhibited hemolytic activity, also strains were found reliable in terms of clinically relevant antibiotics, only one strain 29-P2 was found resistant to vancomycin. In addition, metabolic activities of strains including lactic acid, hydrogen peroxide, exopolysaccharide production and proteolytic activity were determined and amounts of all metabolic products were found low. When evaluated all data obtained, it is believed that the strains have enviable characteristics as a probiotic candidate.

Anticancer and antimicrobial potential of enterocin 12a from Enterococcus faecium

BACKGROUND

Increase in the number of infections caused by Gram-negative bacteria in neutropenic cancer patients has prompted the search for novel therapeutic agents having dual anticancer and antimicrobial properties. Bacteriocins are cationic proteins of prokaryotic origin that have emerged as one of the most promising alternative antimicrobial agents with applications as food preservatives and therapeutic agents. Apart from their antimicrobial activities, bacteriocins are also being explored for their anticancer potential.

RESULTS

In this study, a broad-spectrum, cell membrane-permeabilizing enterocin with a molecular weight of 65 kDa was purified and characterized from the culture supernatant of vaginal Enterococcus faecium 12a. Enterocin 12a inhibited multidrug-resistant strains of various Gram-negative pathogens such as Salmonella enterica, Shigella flexneri, Vibrio cholerae, Escherichia coli and Gram-positive, Listeria monocytogenes, but had no activities against different strains of gut lactobacilli. The mass spectrometric analysis showed that the enterocin 12a shared partial homology with 4Fe-4S domain-containing redox protein of E. faecalis R712. Further, enterocin 12a selectively inhibited the proliferation of various human cancer cell lines in a dose-dependent manner but not that of normal human peripheral blood mononuclear cells. Enterocin 12a-treated cancer cells showed apoptosis-like morphological changes.

CONCLUSION

Enterocin 12a is a novel bacteriocin that has anticancer properties against human cell lines and negligible activity towards non-malignant cells. Therefore, it should be further evaluated for its anticancer potential in animal models.

A new pharmacodynamic approach to study antibiotic combinations against enterococci in vivo: Application to ampicillin plus ceftriaxone

The combination of ampicillin (AMP) and ceftriaxone (CRO) is considered synergistic against Enterococcus faecalis based on in vitro tests and the rabbit endocarditis model, however, in vitro assays are limited by the use of fixed antibiotic concentrations and the rabbit model by poor bacterial growth, high variability, and the use of point dose-effect estimations, that may lead to inaccurate assessment of antibiotic combinations and hinder optimal translation. Here, we tested AMP+CRO against two strains of E. faecalis and one of E. faecium in an optimized mouse thigh infection model that yields high bacterial growth and allows to define the complete dose-response relationship. By fitting Hill’s sigmoid model and estimating the parameters maximal effect (E_max) and effective dose 50 (ED₅₀), the following interactions were defined: synergism (E_max increase ≥2 log₁₀ CFU/g), antagonism (E_max reduction ≥1 log₁₀ CFU/g) and potentiation (ED₅₀ reduction ≥50% without changes in E_max). AMP monotherapy was effective against the three strains, yielding valid dose-response curves in terms of dose and the index fT_>MIC. CRO monotherapy showed no effect. The combination AMP+CRO against E. faecalis led to potentiation (59–81% ED₅₀ reduction) and not synergism (no changes in E_max). Against E. faecium, the combination was indifferent. The optimized mouse infection model allowed to obtain the complete dose-response curve of AMP+CRO and to define its interaction based on pharmacodynamic parameter changes. Integrating these results with the pharmacokinetics will allow to derive the PK/PD index bound to the activity of the combination, essential for proper translation to the clinic.

Daptomycin treatment impacts resistance in off-target populations of vancomycin-resistant Enterococcus faecium

The antimicrobial resistance crisis has persisted despite broad attempts at intervention. It has been proposed that an important driver of resistance is selection imposed on bacterial populations that are not the intended target of antimicrobial therapy. But to date, there has been limited quantitative measure of the mean and variance of resistance following antibiotic exposure. Here we focus on the important nosocomial pathogen Enterococcus faecium in a hospital system where resistance to daptomycin is evolving despite standard interventions. We hypothesized that the intravenous use of daptomycin generates off-target selection for resistance in transmissible gastrointestinal (carriage) populations of E. faecium. We performed a cohort study in which the daptomycin resistance of E. faecium isolated from rectal swabs from daptomycin-exposed patients was compared to a control group of patients exposed to linezolid, a drug with similar indications. In the daptomycin-exposed group, daptomycin resistance of E. faecium from the off-target population was on average 50% higher than resistance in the control group (n = 428 clones from 22 patients). There was also greater phenotypic diversity in daptomycin resistance within daptomycin-exposed patients. In patients where multiple samples over time were available, a wide variability in temporal dynamics were observed, from long-term maintenance of resistance to rapid return to sensitivity after daptomycin treatment stopped. Sequencing of isolates from a subset of patients supports the argument that selection occurs within patients. Our results demonstrate that off-target gastrointestinal populations rapidly respond to intravenous antibiotic exposure. Focusing on the off-target evolutionary dynamics may offer novel avenues to slow the spread of antibiotic resistance.

A retrospective study of probiotics for the treatment of children with antibiotic-associated diarrhea

This retrospective study aimed to explore the benefits and safety of probiotics (live combined Bacillus subtilis and Enterococcus faecium granules with multivitamines) for the treatment of children with antibiotic-associated diarrhea (AAD).A total of 72 children with AAD were analyzed in this study. Of these, 36 children received routine treatment plus probiotics, and were assigned to a treatment group. The other 36 children underwent routine treatment alone, and were assigned to a control group. Patients in both groups were treated for a total of 7 days. The efficacy and safety were evaluated by duration of diarrhea (days), number of dressings needed daily, abdominal pain intensity, stool consistency (as assessed by Bristol Stool Scale (BSS)), and any adverse events.After treatment, probiotics showed encouraging benefits in decreasing duration of diarrhea (days) (P < .01), number of dressings needed every day (P < .01), abdominal pain intensity (P < .01), and stool consistency (BSS (3-5), P < .01; BSS (6-7), P < .01). In addition, no adverse events were documented in this study.The findings of this study demonstrated that probiotics may provide promising benefit for children with AAD. Further studies are still needed to warrant theses findings.

Merulinic acid C overcomes gentamicin resistance in Enterococcus faecium

Enterococci are gram-positive, widespread nosocomial pathogens that in recent years have developed resistance to various commonly employed antibiotics. Since finding new infection-control agents based on secondary metabolites from organisms has proved successful for decades, natural products are potentially useful sources of compounds with activity against enterococci. Herein are reported the results of a natural product library screening based on a whole-cell assay against a gram-positive model organism, which led to the isolation of a series of anacardic acids identified by analysis of their spectroscopic data and by chemical derivatizations. Merulinic acid C was identified as the most active anacardic acid derivative obtained against antibiotic-resistant enterococci. Fluorescence microscopy analyses showed that merulinic acid C targets the bacterial membrane without affecting the peptidoglycan and causes rapid cellular ATP leakage from cells. Merulinic acid C was shown to be synergistic with gentamicin against Enterococcus faecium, indicating that this compound could inspire the development of new antibiotic combinations effective against drug-resistant pathogens.

Biofilm synthesis and other virulence factors in multidrug-resistant uropathogenic enterococci isolated in Northern India

Purpose

Enterococci express high degree of resistance towards wide range of antibiotics. Production of biofilm and many virulence factors along with drug resistance makes it difficult to eradicate the infection from urinary tract. The present study detected the expression of such factors including biofilm production by multidrug-resistant (MDR) enterococci.

Materials and Methods

Drug susceptibility of 103 uropathogenic enterococci was performed followed by estimation of minimum inhibitory concentration of high-level gentamicin and vancomycin by microbroth dilution method. Vancomycin-resistant genes were detected by multiplex polymerase chain reaction. Production of virulence factors such as haemagglutination, caseinase, lipase, gelatinase, haemolysin and β-lactamase was detected by phenotypic methods in MDR strains. Biofilm production was detected by calcofluor-white fluorescence staining and semi-quantitative adherence assay.

Results

45% and 18.4% of the isolates were high-level gentamicin-resistant and vancomycin-resistant enterococci (VRE), respectively. vanA gene was detected in 14 and vanB gene in 5 strains. Biofilm, caseinase and gelatinase were the most expressed virulence factor. Expression of caseinase, gelatinase and lipase was significantly higher in Enterococcus faecalis (P < 0.05). Expression of haemagglutination, gelatinase and haemolysin among the vancomycin-resistant isolates was significantly higher (P < 0.05).

Conclusion

VanA and vanB are the prevalent genotypes responsible for vancomycin resistance. The high prevalence of MDR enterococcal strains producing biofilm and virulence determinants raises concern. asa1, hyl, esp, gelE, cyl and other genes are known to express these factors and contribute to biofilm formation. Most uropathogenic enterococci expressed biofilm at moderate level and can be detected effectively by calcofluor-white staining. No correlation was noted between vancomycin resistance and biofilm production.

Diversity of volatile organic compound production from leucine and citrate in Enterococcus faecium

Enterococcus faecium is frequently isolated from fermented food; in particular, they positively contribute to the aroma compound generation in traditional cheese. Citrate fermentation is a desirable property in these bacteria, but this feature is not uniformly distributed among E. faecium strains. In the present study, three selected E. faecium strains, IQ110 (cit^-), GM70 (cit⁺ type I), and Com12 (cit⁺ type II), were analyzed in their production of aroma compounds in milk. End products and volatile organic compounds (VOCs) were determined by solid-phase micro-extraction combined with gas chromatography mass spectrometry (SPME-GC-MS). Principal component analysis (PCA) of aroma compound profiles revealed a different VOC composition for the three strains. In addition, resting cell experiments of E. faecium performed in the presence of leucine, citrate, or pyruvate as aroma compound precursors allowed us to determine metabolic differences between the studied strains. GM70 (cit⁺ type I) showed an active citrate metabolism, with increased levels of diacetyl and acetoin generation relative to Com12 or to citrate defective IQ110 strains. In addition, in the experimental conditions tested, a defective citrate-fermenting phenotype for the Com12 strain was found, while its leucine degradation and pyruvate metabolism were conserved. In conclusion, rational selection of E. faecium strains could be performed based on genotypic and phenotypic analyses. This would result in a performing strain, such as GM70, that could positively contribute to flavor, with typical notes of diacetyl, acetoin, 3-methyl butanal, and 3-methyl butanol in an adjuvant culture.

L,D-Transpeptidase Specific Probe Reveals Spatial Activity of Peptidoglycan Cross-Linking

Peptidoglycan (PG) is a cross-linked, meshlike scaffold endowed with the strength to withstand the internal pressure of bacteria. Bacteria are known to heavily remodel their peptidoglycan stem peptides, yet little is known about the physiological impact of these chemical variations on peptidoglycan cross-linking. Furthermore, there are limited tools to study these structural variations, which can also have important implications on cell wall integrity and host immunity. Cross-linking of peptide chains within PG is an essential process, and its disruption thereof underpins the potency of several classes of antibiotics. Two primary cross-linking modes have been identified that are carried out by D,D-transpeptidases and L,D-transpeptidases (Ldts). The nascent PG from each enzymatic class is structurally unique, which results in different cross-linking configurations. Recent advances in PG cellular probes have been powerful in advancing the understanding of D,D-transpeptidation by Penicillin Binding Proteins (PBPs). In contrast, no cellular probes have been previously described to directly interrogate Ldt function in live cells. Herein, we describe a new class of Ldt-specific probes composed of structural analogs of nascent PG, which are metabolically incorporated into the PG scaffold by Ldts. With a panel of tetrapeptide PG stem mimics, we demonstrated that subtle modifications such as amidation of iso-Glu can control PG cross-linking. Ldt probes were applied to quantify and track the localization of Ldt activity in Enterococcus faecium, Mycobacterium smegmatis, and Mycobacterium tuberculosis. These results confirm that our Ldt probes are specific and suggest that the primary sequence of the stem peptide can control Ldt cross-linking levels. We anticipate that unraveling the interplay between Ldts and other cross-linking modalities may reveal the organization of the PG structure in relation to the spatial localization of cross-linking machineries.

Probiotic characteristics of bacteriocin-producing Enterococcus faecium strains isolated from human milk and colostrum

As potential probiotic traits of human milk-isolated bacteria have increasingly been recognized, this study aimed to evaluate the probiotic properties of bacteriocin-producing Enterococcus faecium strains isolated from human milk and colostrum. Among 118 human milk- and colostrum-isolated lactic cocci, only 29 were identified as Enterococcus. Of these, only four Enterococcus faecium isolates exhibited bacteriocigenic activity against several pathogenic Gram-positive bacteria, including Listeria monocytogenes. These isolates exhibited high acid (up to pH 3.0) and bile tolerance (0.5% oxgall) in simulated gastrointestinal conditions, demonstrating their ability to survive through the upper gastrointestinal tract. All of the E. faecium strains were shown to be sensitive to most of the antibiotics including vancomycin, tetracycline, rifampicin, and erythromycin, while they were resistant to kanamycin and chloramphenicol. None of the strains showed any virulence (gelE, agg2, clyA, clyB, clyM) and antibiotic resistance genes (vanA, vanB, ermB, tetM, and aac(6')-le-aph(2″)-la). In addition, all the strains were able to assimilate cholesterol, ranging between 25.2-64.1% and they exhibited variable adherence (19-36%) to Caco-2 cells. Based on the overall results of this in vitro study, four of the E. faecium strains isolated from human milk and colostrum can be considered as promising probiotic candidates; however, further in vivo evaluations are required.

Direct-fed microbials containing lactate-producing bacteria influence ruminal fermentation but not lactate utilization in steers fed a high-concentrate diet

Direct-fed microbials (DFM) have been shown to improve gain and growth efficiency and also modulate ruminal fermentation. In Exp. 1,72 beef steers were used to compare a lactate-producing bacterial (LAB) DFM consisting primarily of Lactobacillus acidophilus and Enterococcus faecium,and a lactate-producing and lactate-utilizing (LAB/LU) DFM consisting primarily of L. acidophilus and Propionibacterium both fed at 10(9) cfu/d. Steers were fed a corn-based finishing diet for 153 d and then slaughtered for collection of carcass characteristics. In Exp. 2, 12 ruminally cannulated steers were fed acorn-based finishing diet and treated with 10(9) cfu/d of LAB DFM. Rumen fluid was sampled on d 14 and 28 over a 12-h period. Steers were ruminally dosed with a 2-L solution of neutralized DL-lactate (0.56 M)and Cr-EDTA (13.22 M) 3 h postfeeding on d 15 and 29. Ruminal samples were collected at 10- and 20-minintervals for the first and second hour postdosing. No differences (P ≥ 0.14) between control (CON) and LAB for DMI, ADG, growth efficiency, or carcass characteristics were observed. Dry matter intake was greater (P = 0.04) for LAB/LU than LAB from d 0 to 28 but did not differ (P ≥ 0.29) thereafter. Average daily gain was greater (P = 0.04) and efficiency tended(P = 0.06) to be greater for LAB than LAB/LU over the entire 153 d. In Exp. 2, total VFA concentration and molar proportions of butyrate were unaffected(P ≥ 0.24). Molar proportions of acetate exhibited a DFM by hour interaction (P = 0.04); however, on average, molar proportion of acetate was 4.4% greater for DFM. Conversely, DFM did not affect the molar proportion of propionate (P = 0.39). On average,molar proportions of propionate tended to increase(P = 0.07), and acetate tended to decrease (P = 0.07)across days. Mean daily ruminal pH was similar for CON on d 14 and 28, whereas mean pH increased from d 14 to 28 for DFM (DFM × day; P = 0.08).Minimum pH remained unchanged for CON over time but increased from d 14 to 2 for DFM (DFM × day;P = 0.10). Maximum pH decreased from d 14 to 28 in CON but increased over time with DFM (DFM × day;P = 0.05). DL- and L-lactate utilization were unaffected by DFM (P ≥ 0.33) or day (P ≥ 0.50). Although the LAB DFM did not impact growth performance, itd id modulate ruminal fermentation, as evidenced by shifts in ruminal VFA profile and pH; however, DFM did not appear to influence ruminal lactate utilization.

Prebiotics and age, but not probiotics affect the transformation of 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) by fecal microbiota - An in vitro study

Heterocyclic aromatic amines (HAAs) are carcinogens which are formed in meat cooked using high-temperature methods. The human gastrointestinal (GI) microbiota plays a crucial role in maintaining health in humans of different ages, and especially in the elderly. However, the GI microbiota, whose metabolism and composition changes with age, may also be responsible for the activation of mutagenic substances reaching the colon with diet. Probiotics and prebiotics are promising in terms of reducing the destructive effects of HAAs. The aim of the study was to determine if fecal microbiota derived from the feces of 27 volunteers: infants (up to 18 months), adults (aged 23-39 years), the sub-elderly (aged 64-65 years), and the elderly (aged 76-87 years), and the presence of probiotics or prebiotics, affected the transformation of IQ (2-amino-3-methylimidazo[4,5-f]quinoline) to 7-OH-IQ (2-amino-3,6-dihydro-3-methyl-7H-imidazo[4,5-f]quinoline-7-one). The compounds were identified using LC-MS(n), NMR, and FTIR. Their genotoxicity was compared in the comet assay. Individual strains capable of IQ transformation were also identified. 7-OH-IQ was detected in six persons (two children and four elderly individuals). The degree of IQ conversion ranged from 26% (4-month-old girl) to 94% (81-year-old woman) of the initial quantity. Four Enterococcus isolates: two Enterococcus faecium and two Enterococcus faecalis strains, as well as one Clostridium difficile strain (LOCK 1030, from the culture collection) converted IQ to 7-OH-IQ. The genotoxicity of samples containing 7-OH-IQ was even three times higher (P < 0.05) than those with IQ and was correlated with the degree of IQ conversion and 7-OH-IQ concentration.

Functional Analysis of Genes Involved in the Biosynthesis of Enterocin NKR-5-3B, a Novel Circular Bacteriocin

A putative biosynthetic gene cluster of the enterocin NKR-5-3B (Ent53B), a novel circular bacteriocin, was analyzed by sequencing the flanking regions around enkB, the Ent53B structural gene, using a fosmid library. A region approximately 9 kb in length was obtained, and the enkB1, enkB2, enkB3, and enkB4 genes, encoding putative biosynthetic proteins involved in the production, maturation, and secretion of Ent53B, were identified. We also determined the identity of proteins mediating self-immunity against the effects of Ent53B. Heterologous expression systems in various heterologous hosts, such as Enterococcus faecalis and Lactococcus lactis strains, were successfully established. The production and secretion of the mature Ent53B required the cooperative functions of five genes. Ent53B was produced only by those heterologous hosts that expressed protein products of the enkB, enkB1, enkB2, enkB3, and enkB4 genes. Moreover, self-immunity against the antimicrobial action of Ent53B was conferred by at least two independent mechanisms. Heterologous hosts harboring the intact enkB4 gene and/or a combination of intact enkB1 and enkB3 genes were immune to the inhibitory action of Ent53B.

IMPORTANCE

In addition to their potential application as food preservatives, circular bacteriocins are now considered possible alternatives to therapeutic antibiotics due to the exceptional stability conferred by their circular structure. The successful practical application of circular bacteriocins will become possible only if the molecular details of their biosynthesis are fully understood. The results of the present study offer a new perspective on the possible mechanism of circular bacteriocin biosynthesis. In addition, since some enterococcal strains are associated with pathogenicity, virulence, and drug resistance, the establishment of the first multigenus host heterologous production of Ent53B has very high practical significance, as it widens the scope of possible Ent53B applications.

A novel enterocin T1 with anti-Pseudomonas activity produced by Enterococcus faecium T1 from Chinese Tibet cheese

An enterocin-producing Enterococcus faecium T1 was isolated from Chinese Tibet cheese. The enterocin was purified by SP-Sepharose and reversed phase HPLC. It was identified as unique from other reported bacteriocins based on molecular weight (4629 Da) and amino acid compositions; therefore it was subsequently named enterocin T1. Enterocin T1 was stable at 80-100 °C and over a wide pH range, pH 3.0-10.0. Protease sensitivity was observed to trypsin, pepsin, papain, proteinase K, and pronase E. Importantly, enterocin T1 was observed to inhibit the growth of numerous Gram-negative and Gram-positive bacteria including Pseudomonas putida, Pseudomonas aeruginosa, Pseudomonas fluorescens, Escherichia coli, Salmonella typhimurium, Shigella flexneri, Shigella sonnei, Staphylococcus aureus, Listeria monocytogenes. Take together, these results suggest that enterocin T1 is a novel bacteriocin with the potential to be used as a bio-preservative to control Pseudomonas spp. in food.

Solution Structure of Enterocin HF, an Antilisterial Bacteriocin Produced by Enterococcus faecium M3K31

The solution structure of enterocin HF (EntHF), a class IIa bacteriocin of 43 amino acids produced by Enterococcus faecium M3K31, was evaluated by CD and NMR spectroscopy. Purified EntHF was unstructured in water, but CD analysis supports that EntHF adopts an α-helical conformation when exposed to increasing concentrations of trifluoroethanol. Furthermore, NMR spectroscopy indicates that this bacteriocin adopts an antiparallel β-sheet structure in the N-terminal region (residues 1-17), followed by a well-defined central α-helix (residues 19-30) and a more disordered C-terminal end (residues 31-43). EntHF could be structurally organized into three flexible regions that might act in a coordinated manner. This is in agreement with the absence of long-range nuclear Overhauser effect signals between the β-sheet domain and the C-terminal end of the bacteriocin. The 3D structure recorded for EntHF fits emerging facts regarding target recognition and mode of action of class IIa bacteriocins.

Aerobic stability of maize silage stored under plastic films with different oxygen permeability

BACKGROUND

The most important factor that can influence silage quality is the degree of anaerobiosis maintained during conservation. The quality of the plastic film is a key factor, since the permeability of polyethylene to oxygen is too high for silage conservation. The aim of this work was to assess the effects of the interaction between three plastic films with different degrees of oxygen permeability and two different maize silage conservation times on fermentation, microbial quality and aerobic stability.

RESULTS

The conservation time affected the pH, lactic and acetic acids, 1,2-propanediol and lactic/acetic acid ratio, with higher pH, lower lactic acid concentration and lactic/acetic acid ratio but higher acetic acid and 1,2-propanediol concentrations being found in silages conserved for 110 days versus silages conserved for 55 days. The plastic film affected the pH, lactic and acetic acids and lactic/acetic acid ratio. The yeast count was lower and aerobic stability higher for silage conserved under the oxygen barrier film for both conservation periods.

CONCLUSION

The positive interaction between length of storage and the increased anaerobiosis of silage during conservation provided by the oxygen barrier compared with polyethylene film helped reduce the yeast count and increase the aerobic stability of maize silage, even when less acetic acid was produced during ensiling.

[Changes in the phase variant spectra in the populations of lactic acid bacteria under antibiotic treatment]

Effect of the antibiotics kanamycin and ampicillin on growth and phase variation of the populations of four strains of lactic acid bacteria (Lactobacillus sp. M67AT, L. casei MB, Enterococcus faecium M, and E. faecium M3185) was studied. The presence of antibiotics in the medium resulted in a dose-dependent decrease in viable cell numbers and in partial or complete substitution of the dominant S variant with the minor Sm and Sb variants. The variants differed in colony morphology, as well as in some physiological, biochemical, biotechnological, and probiotic characteristics. The Sm type variants of all strains exhibited the highest resistance to antibiotics. High production of exopolysaccharides was found in Sb variants of lactobacilli and in S variants of enterococci. The highest antibacterial activity was found in Sm variants of lactobacilli, especially in Lactobacillus sp. M76AT The latter is biotechnologically the most promising strain, since all variants fermented milk yielding the products with uniformly pronounced functional and organoleptic properties. These patterns are of importance for the understanding of the mechanisms of antibiotic resistance and for selection of the variants with desired properties, as well as for quality control of the lactic acid bacteria starter cultures.

An antilisterial bacteriocin BacFL31 produced by Enterococcus faecium FL31 with a novel structure containing hydroxyproline residues

A new bacterium called FL31, which was selected for its antimicrobial activity against the pathogenic bacterium Listeria monocytogenes, was identified as Enterococcus faecium and noted to produce an antibacterial proteinaceous substance (BacFL31). The active peptide from the cell-free supernatant of E. faecium FL31 was purified in four steps and the results revealed a single band with an estimated molecular mass of approximately 3.5 kDa. The N-terminal amino acid sequence of the purified BacFL31 "GLEESXGHXGQXGPXGPXGAXGP" (X = hydroxyproline) showed the presence of six hydroxyproline residues. It displayed a bactericidal mode of action against L. monocytogenes. Its application at 400 AU/g was also noted to constitute an effective approach for preventing the contamination and growth of the pathogenic bacterium L. monocytogenes during the storage of minced beef meat at 4 °C.

Dietary Enterococcus faecium NCIMB 10415 and zinc oxide stimulate immune reactions to trivalent influenza vaccination in pigs but do not affect virological response upon challenge infection

Swine influenza viruses (SIV) regularly cause significant disease in pigs worldwide. Since there is no causative treatment of SIV, we tested if probiotic Enterococcus (E.) faecium NCIMB 10415 or zinc (Zn) oxide as feed supplements provide beneficial effects upon SIV infection in piglets. Seventy-two weaned piglets were fed three different diets containing either E. faecium or different levels of Zn (2500 ppm, Zn^high; 50 ppm, Zn^low). Half of the piglets were vaccinated intramuscularly (VAC) twice with an inactivated trivalent SIV vaccine, while all piglets were then infected intranasally with H3N2 SIV. Significantly higher weekly weight gains were observed in the E. faecium group before virus infection, and piglets in Zn^high and E. faecium groups gained weight after infection while those in the control group (Zn^low) lost weight. Using ELISA, we found significantly higher H3N2-specific antibody levels in the E. faecium+VAC group 2 days before and at the day of challenge infection as well as at 4 and 6 days after challenge infection. Higher hemagglutination inhibition (HI) titers were also observed in the Zn^high+VAC and E. faecium+VAC groups at 0, 1 and 4 days after infection. However, there were no significant differences in virus shedding and lung lesions between the dietary groups. Using flow cytometry analysis significantly higher activated T helper cells and cytotoxic T lymphocyte percentages in the PBMCs were detected in the Zn^high and E. faecium groups at single time points after infection compared to the Zn^low control group, but no prolonged effect was found. In the BAL cells no influence of dietary supplementation on immune cell percentages could be detected. Our results suggest that feeding high doses of zinc oxide and particularly E. faecium could beneficially influence humoral immune responses after vaccination and recovery from SIV infection, but not affect virus shedding and lung pathology.

[Antibiotic resistance and siderophore production in enterococci]

INTRODUCTION

Enterococci belong to the normal bacterial flora of the gastrointensinal tract of humans. Enterococci are regarded as harmless commensal, and are even believed to have probiotic characteristics. However, they can cause variety of infections, including endocarditis, bloodstream infections and urinary tract infections. During the past several decades, enterococci, and particularly Enterococcus faecalis and E. faecium, have been identified as an important cause of nosocomial infections. Enterococci are intrinsically resistant to a broad range of antimicrobials. Infection caused by resistant strains are difficult to treat. Iron is an essential element for bacteria, but is not easily available in host organisms. Enterococci are iron dependent bacteria. Competition for iron between the host and bacteria is an important factor determining the course of bacterial infections. A common strategy among bacteria living in iron-limited environments is the secretion of siderophores, which can bind poorly soluble iron and make it available to cells via active transport mechanisms. The aim of the presented study was to evaluate the correlation between antibiotic resistance and siderophore production of bacteria of the genus Enterococcus.

METHODS

The study included 55 bacterial strains from genus Enterococcus belonging to two species--Enterococcus faecalis and E. faecium. Antimicrobial susceptibility tests were carried out using disc diffusion methods with guidelines of European Committee on Antimicrobial Susceptibility Testing (EUCAST). Total siderophore activity in the culture supernatants was measured using chrome azurol S. Hydroxamate siderophores were assayed using a chemical-specific assay.

RESULTS

Antibacterial susceptibility pattern reveals that E. faecium is more resistant than E. faecalis. A significant correlation was found between resistance to fluoroquinolnes and siderophores production. Ciprofloxacin- and norfloxacin-resistant enterococal strains produced siderophores in large quantity.

CONCLUSIONS

One of the most common infections caused by enterococci are urinary tract infections. Fluoroquinolones are an important group of antimicrobial agents used in this type of infection. Fluoroquinolones resistance of enterococci associated with increased synthesis of siderophores result in the increased virulence that may decide on the severity of the infection and the effectiveness of the treatment.

Genetic basis for in vitro and in vivo resistance to lincosamides, streptogramins A, and pleuromutilins (LSAP phenotype) in Enterococcus faecium

As opposed to Enterococcus faecalis, which is intrinsically resistant to lincosamides, streptogramins A, and pleuromutilins (LSAP phenotype) by production of the ABC protein Lsa(A), Enterococcus faecium is naturally susceptible. Since this phenotype may be selected for in vivo by quinupristin-dalfopristin (Q-D), the aim of this study was to investigate the molecular mechanism of acquired LSAP resistance in E. faecium. Six LSAP-resistant in vitro mutants of E. faecium HM1070 as well as three different pairs of clinical isolates (pre- and postexposure to Q-D) were studied. The full genome sequence of an in vitro mutant (E. faecium UCN90B) was determined by using 454 sequencing technology and was compared with that of the parental strain. Single-nucleotide replacement was carried out to confirm the role of this mutation. By comparative genomic analysis, a point mutation was found within a 1,503-bp gene coding for an ABC homologue showing 66% amino acid identity with Lsa(A). This mutation (C1349T) led to an amino acid substitution (Thr450Ile). An identical mutation was identified in all in vitro and in vivo resistant strains but was not present in susceptible strains. The wild-type allele was named eat(A) (for Enterococcus ABC transporter), and its mutated allelic variant was named eat(A)v. The introduction of eat(A)v from UCN90B into HM1070 conferred the LSAP phenotype, whereas that of eat(A) from HM1070 into UCN90B restored susceptibility entirely. This is the first description of the molecular mechanism of acquired LSAP resistance in E. faecium. Characterization of the biochemical mechanism of resistance and the physiological role of this ABC protein need further investigations.

A LacI-family regulator activates maltodextrin metabolism of Enterococcus faecium

Enterococcus faecium is a gut commensal of humans and animals. In the intestinal tract, E. faecium will have access to a wide variety of carbohydrates, including maltodextrins and maltose, which are the sugars that result from the enzymatic digestion of starch by host-derived and microbial amylases. In this study, we identified the genetic determinants for maltodextrin utilization of E. faecium E1162. We generated a deletion mutant of the mdxABCD-pulA gene cluster that is homologous to maltodextrin uptake genes in other Gram-positive bacteria, and a deletion mutant of the mdxR gene, which is predicted to encode a LacI family regulator of mdxABCD-pulA. Both mutations impaired growth on maltodextrins but had no effect on the growth on maltose and glucose. Comparative transcriptome analysis showed that eight genes (including mdxABCD-pulA) were expressed at significantly lower levels in the isogenic ΔmdxR mutant strain compared to the parental strain when grown on maltose. Quantitative real-time RT-PCR confirmed the results of transcriptome analysis and showed that the transcription of a putative maltose utilization gene cluster is induced in a semi-defined medium supplemented with maltose but is not regulated by MdxR. Understanding the maltodextrin metabolism of E. faecium could yield novel insights into the underlying mechanisms that contribute to the gut commensal lifestyle of E. faecium.

The Enterococcus faecium enterococcal biofilm regulator, EbrB, regulates the esp operon and is implicated in biofilm formation and intestinal colonization

Nowadays, Enterococcus faecium is one of the leading nosocomial pathogens worldwide. Strains causing clinical infections or hospital outbreaks are enriched in the enterococcal surface protein (Esp) encoding ICEEfm1 mobile genetic element. Previous studies showed that Esp is involved in biofilm formation, endocarditis and urinary tract infections. In this study, we characterized the role of the putative AraC type of regulator (locus tag EfmE1162_2351), which we renamed ebrB and which is, based on the currently available whole genome sequences, always located upstream of the esp gene, and studied its role in Esp surface exposure during growth. A markerless deletion mutant of ebrB resulted in reduced esp expression and complete abolishment of Esp surface exposure, while Esp cell-surface exposure was restored when this mutant was complemented with an intact copy of ebrB. This demonstrates a role for EbrB in esp expression. However, during growth, ebrB expression levels did not change over time, while an increase in esp expression at both RNA and protein level was observed during mid-log and late-log phase. These results indicate the existence of a secondary regulation system for esp, which might be an unknown quorum sensing system as the enhanced esp expression seems to be cell density dependent. Furthermore, we determined that esp is part of an operon of at least 3 genes putatively involved in biofilm formation. A semi-static biofilm model revealed reduced biofilm formation for the EbrB deficient mutant, while dynamics of biofilm formation using a flow cell system revealed delayed biofilm formation in the ebrB mutant. In a mouse intestinal colonization model the ebrB mutant was less able to colonize the gut compared to wild-type strain, especially in the small intestine. These data indicate that EbrB positively regulates the esp operon and is implicated in biofilm formation and intestinal colonization.

Metabolites of Lactobacillus plantarum 2142 prevent oxidative stress-induced overexpression of proinflammatory cytokines in IPEC-J2 cell line

Probiotics have already proven beneficial effects in the treatment of several intestinal infections, but the underlying mechanisms how the probiotics can affect responses of porcine IPEC-J2 enterocytes to oxidative stress remained to be elucidated. The immunomodulatory effect of five bacterial strains (Lactobacillus plantarum 2142, Lactobacillus casei Shirota, Bifidobacterium animalis subsp. lactis BB-12, Bacillus amyloliquefaciens CECT 5940 and Enterococcus faecium CECT 4515) on 1 mM peroxide-triggered upregulation of interleukin (IL)-8 and tumor necrosis factor alpha (TNF-α) level was screened by q RT-PCR. Our data revealed that spent culture supernatant (SCS) of L. plantarum 2142 had significant lowering effect on IL-8 and TNF-α level with concomitant promoting activity on protective Hsp70 gene expression. According to our results, lactic acid (racemic, D: - and L: -lactic acid) and acetic acid produced by lactobacilli had no protective effect in quenching upregulation of proinflammatory cytokines. Furthermore, L. plantarum 2142-specific supernatant peptides were detected by gel electrophoresis and capillary zone electrophoresis.

Multifunctional properties of soy milk fermented by Enterococcus faecium strains isolated from raw soy milk

Lactic acid bacteria (LAB) isolated from soy milk were used to produce a multifunctional fermented food. Seven isolates were screened for their ability to produce peptides and free isoflavones in soy milk. The antihypertensive, antioxidant, and anti-inflammatory properties of the resulting fermented soy milks were evaluated in vitro using biochemical assays. Isolates 1-5 were found to be producers of fermented soy milk with angiotensin I converting enzyme inhibitory activity (ACEI). Isolate 3 was found to be a producer of free isoflavones that increased the antioxidant and anti-inflammatory potential of fermented soy milk. LAB isolates 2-5 were submitted to genetic profiling and a characterization scheme. These isolates were identified as Enterococcus faecium , and none of them contained virulence determinants or resistance to antibiotics. In conclusion, this study shows that the application of E. faecium isolate 3 for multifunctional food production from soy milk could be a promising strategy in the prevention therapy against cardiovascular disease.

AsrR is an oxidative stress sensing regulator modulating Enterococcus faecium opportunistic traits, antimicrobial resistance, and pathogenicity

Oxidative stress serves as an important host/environmental signal that triggers a wide range of responses in microorganisms. Here, we identified an oxidative stress sensor and response regulator in the important multidrug-resistant nosocomial pathogen Enterococcus faecium belonging to the MarR family and called AsrR (antibiotic and stress response regulator). The AsrR regulator used cysteine oxidation to sense the hydrogen peroxide which results in its dissociation to promoter DNA. Transcriptome analysis showed that the AsrR regulon was composed of 181 genes, including representing functionally diverse groups involved in pathogenesis, antibiotic and antimicrobial peptide resistance, oxidative stress, and adaptive responses. Consistent with the upregulated expression of the pbp5 gene, encoding a low-affinity penicillin-binding protein, the asrR null mutant was found to be more resistant to β-lactam antibiotics. Deletion of asrR markedly decreased the bactericidal activity of ampicillin and vancomycin, which are both commonly used to treat infections due to enterococci, and also led to over-expression of two major adhesins, acm and ecbA, which resulted in enhanced in vitro adhesion to human intestinal cells. Additional pathogenic traits were also reinforced in the asrR null mutant including greater capacity than the parental strain to form biofilm in vitro and greater persistance in Galleria mellonella colonization and mouse systemic infection models. Despite overexpression of oxidative stress-response genes, deletion of asrR was associated with a decreased oxidative stress resistance in vitro, which correlated with a reduced resistance to phagocytic killing by murine macrophages. Interestingly, both strains showed similar amounts of intracellular reactive oxygen species. Finally, we observed a mutator phenotype and enhanced DNA transfer frequencies in the asrR deleted strain. These data indicate that AsrR plays a major role in antimicrobial resistance and adaptation for survival within the host, thereby contributes importantly to the opportunistic traits of E. faecium.

Multiple antibiotic-resistant isolates of the opportunistic pathogen Enterococcus faecium have emerged and spread worldwide. However, studies aimed at identifying mechanisms that underlie the transformation of E. faecium from its commensal nature into a nosocomial pathogen are scarce. We report pleiotropic roles for a novel oxidative-sensing regulator, called AsrR (antibiotic and stress response regulator), in E. faecium. Based on transcriptomic analysis, phenotypic studies, and animal models, we demonstrate that asrR deletion is responsible for i) diminished susceptibility to penicillins, vancomycin, and cationic antimicrobial peptides, ii) increased adhesion to human cells and biofilm formation, iii) a mutator phenotype and enhanced DNA transfer frequencies, iv) decreased resistance to oxidative stress both in vitro and in murine macrophages, and v) increased host-persistence in both insect and mouse models. AsrR is a stress-sensor and is promptly inactivated in the presence of hydrogen peroxide. Therefore, oxidative stress, which is a main challenge during infection, may be a significant signal used by E. faecium to promote opportunistic traits. This provides a significant resource combining, for the first time in E. faecium, a global transcriptomic approach and a thorough phenotypic study, which places AsrR as a key regulator modulating pathogenicity, antimicrobial resistance, and environmental adaptation.

Comparative analysis of the first complete Enterococcus faecium genome

Vancomycin-resistant enterococci (VRE) are one of the leading causes of nosocomial infections in health care facilities around the globe. In particular, infections caused by vancomycin-resistant Enterococcus faecium are becoming increasingly common. Comparative and functional genomic studies of E. faecium isolates have so far been limited owing to the lack of a fully assembled E. faecium genome sequence. Here we address this issue and report the complete 3.0-Mb genome sequence of the multilocus sequence type 17 vancomycin-resistant Enterococcus faecium strain Aus0004, isolated from the bloodstream of a patient in Melbourne, Australia, in 1998. The genome comprises a 2.9-Mb circular chromosome and three circular plasmids. The chromosome harbors putative E. faecium virulence factors such as enterococcal surface protein, hemolysin, and collagen-binding adhesin. Aus0004 has a very large accessory genome (38%) that includes three prophage and two genomic islands absent among 22 other E. faecium genomes. One of the prophage was present as inverted 50-kb repeats that appear to have facilitated a 683-kb chromosomal inversion across the replication terminus, resulting in a striking replichore imbalance. Other distinctive features include 76 insertion sequence elements and a single chromosomal copy of Tn1549 containing the vanB vancomycin resistance element. A complete E. faecium genome will be a useful resource to assist our understanding of this emerging nosocomial pathogen.

[Methodical approaches to isolation of teichoic acids from native cells of lactic acid bacteria probiotic strains]

Teichoic acids of lactic acid bacteria probiotic strains have been obtained by extraction from native cells, followed by purification of extracts using ion exchange chromatography. Selected fractions contained high concentrations of phosphorus and did not contain nucleic acids. The content of teichoic acid depended on the species and strain specificity. Heterogeneity of the studied biomolecules was revealed.

Interactive effects of pH and temperature on the bacteriocin stability by response surface analysis

The combined influence of pH and temperature on bacteriocins produced by three lactic acid bacteria, Pediococcus pentosaceus MMZ26, Enterococcus faecium MMZ17 and Lactococcus lactis MMZ25, isolated from Tunisian traditional dry fermented meat was studied using a second order orthogonal factorial design and response-surface methodology (RSM). This method allows estimating the interactive effects of pH and temperature on the stability of each bacteriocin. The high heat stability of the three bacteriocins was demonstrated, with optimum values at light acidic pH around 5.0, temperature below 90 degrees C and short incubation times. This study contributes to a better understanding of relation between bacteriocins production and stability in order to enhance their, in situ, application as a food and feed biopreservative in fermented and/or heated food products.

Influence of enterococcal surface protein (esp) on the transport of Enterococcus faecium within saturated quartz sands

Enterococcus was selected by US EPA as a Gram-positive indicator microorganism for groundwater fecal contamination. It was recently reported that enterococcal surface protein (esp) was more prevalent in Enterococcus from human sources than in Enterococcus from nonhuman sources and esp could potentially be used as a source tracking tool for fecal contamination (Scott et al., 2005). In this research, we performed laboratory column transport experiments to investigate the transport of Enterococcus faecium within saturated quartz sands. Particularly, we used a wild type strain (E1162) and a mutant (E1162Δesp) to examine the influence of esp on the transport behavior of E. faecium. Our results showed that esp could significantly enhance the attachment of E. faecium cells onto the surface of silica sands and thus lower the mobility of E. faecium within sand packs. Cell surface properties (e.g., zeta potential) were determined and the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to explain the effects of esp on the retention of E. faecium. Overall, our results suggested that E. faecium strains with esp could display lower mobility within saturated sand packs than E. faecium strains without esp. The disparity in the transport behavior of E. faecium with and without esp could limit the effectiveness of esp as a source tracking tool within the groundwater system.

Antibiotic resistance genes and virulence factors in Enterococcus faecium and Enterococcus faecalis from diseased farm animals: pigs, cattle and poultry

Eighty enterococcal isolates (E. faecium, n = 38, E. faecalis, n = 42) from diseased farm animals (swine, cattle, poultry) in Lithuania have been studied for the prevalence of antibiotic resistance and for resistance and virulence genetic determinants. 86% of E. faecium and 71% of E. faecalis isolates were multidrug resistant (resistant to three or more unrelated antibiotics). Resistance to aminoglycosides, tetracycline and erythromycin was found most frequently in both species (61%, 69%) and was linked to aph(3')-IIIa, aac(6')-Ie-aph(2")-Ia, ant(6)-Ia (aminoglycoside resistance), tetM, tetL (tetracycline resistance), ermA, ermB (erythromycin resistance) gene combinations, which were supplemented with chloramphenicol resistance genes catA7, catA8 (E. faecalis) and catA9 (E. faecium). All E. faecalis isolates harboured genes coding for virulence factors agg, esp, fsr gelE alone or in combinations with the high prevalence of esp gene in isolates from cattle (63%) and pigs (79%). The origin-dependent incidence of agg gene variants prgB and asp1 was observed. The results indicate the existence of a large pool of potentially virulent and multidrug resistant E. faecalis in diseased farm animals posing risk to humans.

Comparison of nitroethane, 2-nitro-1-propanol, lauric acid, Lauricidin® and the Hawaiian marine algae, Chaetoceros, for potential broad-spectrum control of anaerobically grown lactic acid bacteria

The gastrointestinal tract of bovines often contains bacteria that contribute to disorders of the rumen, and may also contain foodborne or opportunistic human pathogens as well as bacteria capable of causing mastitis in cows. Thus there is a need to develop broad-spectrum therapies that are effective while not leading to unacceptably long antibiotic withdrawal times. The effects of the CH(4)-inhibitors nitroethane (2 mg/mL), 2-nitro-1-propanol (2 mg/mL), lauric acid (5 mg/mL), the commercial product Lauricidin® (5 mg/mL), and a finely ground product of the Hawaiian marine algae, Chaetoceros (10 mg/mL), were compared in pure cultures of Streptococcus agalactia, Enterococcus faecium, Streptococcus bovis, and in a mixed lactic acid rumen bacterial culture. Lauricidin® and lauric acid exhibited the most bactericidal acidity against all bacteria. These results suggest potential animal health benefits from supplementing cattle diets with lauric acid or Lauricidin® to improve the health of the rumen and help prevent shedding of human pathogens.

Biological neutralization of chlor-alkali industry wastewater

The present work reports biological neutralization of chlor-alkali industrial effluent by an alkaliphilic bacterium, isolated from the Gujarat coast, which was identified as Enterococcus faecium strain R-5 on the basis of morphological, biochemical and partial 16S rRNA gene sequencing. The isolate was capable of bringing down the pH of waste water from 12.0 to 7.0 within 3 h in the presence of carbon and nitrogen sources, with simultaneous reduction in total dissolved solutes (TDS) up to 19-22%. This bacterium produced carboxylic acid, as revealed by FT-IR analysis, which facilitated neutralization of alkaline effluent. The presence of unconventional raw materials viz. Madhuca indica flowers or sugar cane bagasse as carbon and nitrogen sources could effectively neutralize alkaline effluent and thus making the bioremediation process economically viable. The time required for neutralization varied with size of inoculum. To the best of our knowledge, this is the first report on biological neutralization of a chlor-alkali industrial effluent.

New noncovalent inhibitors of penicillin-binding proteins from penicillin-resistant bacteria

Background

Penicillin-binding proteins (PBPs) are well known and validated targets for antibacterial therapy. The most important clinically used inhibitors of PBPs β-lactams inhibit transpeptidase activity of PBPs by forming a covalent penicilloyl-enzyme complex that blocks the normal transpeptidation reaction; this finally results in bacterial death. In some resistant bacteria the resistance is acquired by active-site distortion of PBPs, which lowers their acylation efficiency for β-lactams. To address this problem we focused our attention to discovery of novel noncovalent inhibitors of PBPs.

Methodology/Principal Findings

Our in-house bank of compounds was screened for inhibition of three PBPs from resistant bacteria: PBP2a from Methicillin-resistant Staphylococcus aureus (MRSA), PBP2x from Streptococcus pneumoniae strain 5204, and PBP5fm from Enterococcus faecium strain D63r. Initial hit inhibitor obtained by screening was then used as a starting point for computational similarity searching for structurally related compounds and several new noncovalent inhibitors were discovered. Two compounds had promising inhibitory activities of both PBP2a and PBP2x 5204, and good in-vitro antibacterial activities against a panel of Gram-positive bacterial strains.

Conclusions

We found new noncovalent inhibitors of PBPs which represent important starting points for development of more potent inhibitors of PBPs that can target penicillin-resistant bacteria.

Biochemical characterization of a bacteriocin-like inhibitory substance produced by Enterococcus faecium MXVK29, isolated from Mexican traditional sausage

BACKGROUND

Enterococci are lactic acid bacteria that can produce bacteriocins, which may offer an additional hurdle to control the growth of food-borne pathogens; moreover, these bacteriocins may have great potential as natural biopreservatives. The aim of this work was to characterize a bacteriocin-like inhibitory substance (BLIS) with antilisterial activity produced by an enterococcal strain.

RESULTS

The bacteriogenic strain was isolated from Mexican fermented sausages and identified as Enterococcus faecium with 99% sequence similarity. Maximal activity was detected at 16 h, where bacterial growth was in middle of the stationary phase. The producer strain was not inhibited by its own antimicrobial peptide. BLIS showed a strong anti-Listeria activity and was inactivated by proteinase K. Heating (121 °C for 15 min) induced some inactivation, but thermotolerance was higher at acid pH values. The yield obtained with a pH-mediated purification process was 32.7%, showing a band with an estimated molecular weight of 3.5 kDa. Automated N-terminal Edman degradation showed the following sequence: YYGNGVTCGSHHCSVD.

CONCLUSION

Biochemical characteristics of BLIS produced by E. faecium MXVK29 suggested that it belongs to Class IIa of the Klaenhammer classification and could be considered as a natural food preservative, although further studies need to be performed.