Relation of Enterococcus faecalis and Enterococcus faecium isolates from foods and clinical specimens

In vitro activities of thiazolidione derivatives combined with daptomycin against clinical Enterococcus faecium strains

Background

Previous reports have demonstrated two thiazolidione derivatives (H2-60 and H2-81) can robustly inhibit the planktonic growth and biofilm formation of S. epidermidis and S. aureus by targeting the histidine kinase YycG. Whereas the antibacterial and anti-biofilm activity of these two thiazolidione derivatives (H2-60 and H2-81) against Enterococcus faecium remains elusive. Here, the pET28a-YycG recombinant plasmid were in vitro expressed in E. coli competent cell BL21 (DE3) and induced to express YycG’ protein (conding HisKA and HATPase_c domain) by 0.5 mM IPTG and was purified by Ni – NTA agarose and then for the autophosphorylation test. Antimicrobial testing and time-killing assay were also be determined. Anti-biofilm activity of two derivatives with sub-MIC concentration towards positive biofilm producers of clinical E. faecium were detected using polystyrene microtiter plate and CLSM.

Results

The MICs of H2-60 and H2-81 in the clinical isolates of E. faecium were in the range from 3.125 mg/L to 25 mg/L. Moreover, either H2-60 or H2-81 showed the excellent bactericidal activity against E. faecium with monotherapy or its combination with daptomycin by time-killing assay. E. faecium planktonic cells can be decreased by H2-60 or H2-81 for more than 3 × log10 CFU/mL after 24 h treatment when combined with daptomycin. Furthermore, over 90% of E. faecium biofilm formation could markedly be inhibited by H2-60 and H2-81 at 1/4 × MIC value. In addition, the frequency of the eradicated viable cells embedded in mature biofilm were evaluated by the confocal laser microscopy, suggesting that of H2-60 combined with ampicillin or daptomycin was significantly high when compared with single treatment (78.17 and 74.48% vs. 41.59%, respectively, P < 0.01).

Conclusion

These two thiazolidione derivatives (H2-60 and H2-81) could directly impact the kinase phosphoration activity of YycG of E. faecium. H2-60 combined with daptomycin exhibit the excellent antibacterial and anti-biofilm activity against E. faecium by targeting YycG.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02423-8.

Antimicrobial resistance and genetic diversity of Enterococcus faecalis from yolk sac infections in broiler chicks

Despite restrictions on the use of antibiotics in poultry, the percentage of multidrug resistant bacteria, isolated from both adult birds and chicks, remains high. These bacteria can spread between countries via hatching eggs or chicks. Antibiotic resistant bacteria can also pose a threat to hatchery and farm workers or to consumers of poultry. The aim of the study was to perform a phenotypic and genotypic analysis of the drug resistance of E. faecalis isolates from yolk sac infections in broiler chicks from Poland and the Netherlands and to determine their genetic diversity. The tests revealed resistance to antibiotics from category D, that is, tetracycline (69.7%); category C – lincomycin (98.7%), erythromycin (51.3%), aminoglycosides (high-level streptomycin and kanamycin resistance – 10.5% and 3.95%, respectively), and chloramphenicol (7.9%); and category B – ciprofloxacin (25% with resistance or intermediate resistance). No resistance to penicillin, ampicillin, high-level gentamicin, tigecycline, or linezolid was noted. Various combinations of the erm(B), tet(M), tet(L), tet(O), ant(6)-Ia, aph(3′)-IIIa, ant(4′)-Ia, cat, and msr(A/B) genes were detected in all isolates (irrespective of the drug-resistance phenotype). Among isolates that carried the tet(M) and/or the tet(L) gene, 28% also had the Int-Tn gene, in contrast with isolates possessing tet(O). There were 28 sequence types and 43 PFGE restriction patterns. About 60% of isolates were of sequences types ST59, ST16, ST116, ST282, ST36, and ST82. Nine new sequence types were shown (ST836-ST844). In conclusion, broiler chicks can be a source of drug-resistant sequence types of E. faecalis that are potentially hazardous for people and animals. Restrictive programs for antibiotic use in broiler breeding flocks should be developed to decrease drug resistance in day-old chicks and reduce economic losses during rearing.

Characterization of Enterococcus Isolates Colonizing the Intestinal Tract of Intensive Care Unit Patients Receiving Selective Digestive Decontamination

Enterococci have emerged as important opportunistic pathogens in intensive care units (ICUs). In this study, enterococcal population size and Enterococcus isolates colonizing the intestinal tract of ICU patients receiving Selective Digestive Decontamination (SDD) were investigated. All nine patients included in the study showed substantial shifts in the enterococcal 16S rRNA gene copy number in the gut microbiota during the hospitalization period. Furthermore, 41 Enterococcus spp. strains were isolated and characterized from these patients at different time points during and after ICU hospitalization, including E. faecalis (n = 13), E. faecium (n = 23), and five isolates that could not unequivocally assigned to a specific species (E. sp. n = 5) Multi locus sequence typing revealed a high prevalence of ST 6 in E. faecalis isolates (46%) and ST 117 in E. faecium (52%). Furthermore, antibiotic resistance phenotypes, including macrolide and vancomycin resistance, as well as virulence factor-encoding genes [asa1, esp-fm, esp-fs, hyl, and cyl (B)] were investigated in all isolates. Resistance to ampicillin and tetracycline was observed in 25 (61%) and 19 (46%) isolates, respectively. Furthermore, 30 out of 41 isolates harbored the erm (B) gene, mainly present in E. faecium isolates (78%). The most prevalent virulence genes were asa1 in E. faecalis (54%) and esp (esp-fm, 74%; esp-fs, 39%). Six out of nine patients developed nosocomial enterococcal infections, however, corresponding clinical isolates were unfortunately not available for further analysis. Our results show that multiple Enterococcus species, carrying several antibiotic resistance and virulence genes, occurred simultaneously in patients receiving SDD therapy, with varying prevalence dynamics over time. Furthermore, simultaneous presence and/or replacement of E. faecium STs was observed-, reinforcing the importance of screening multiple isolates to comprehensively characterize enterococcal diversity in ICU patients.

Synergistic Antibacterial Effect of the Combination of ε-Polylysine and Nisin against Enterococcus faecalis

This study evaluated the antibacterial effect of the combination of ε-polylysine (ε-PL) and nisin against Enterococcus faecalis strains. The combination of ε-PL and nisin showed synergistic antibacterial activity against three Enterococcus strains. Scanning electron microscopy and a membrane permeability assay revealed that the combined treatment with ε-PL and nisin synergistically damaged the cell morphology of E. faecalis strain R612Z1 cells. Both ε-PL and nisin can dissipate the transmembrane electric potential of E. faecalis R612Z1 cells, but these peptides did not affect the transmembrane pH gradient. The combination of ε-PL and nisin can produce a high reactive oxygen species level in E. faecalis R612Z1 cells. The results indicated that the uptake of ε-PL into cells was promoted through nisin and that the combination of ε-PL and nisin could produce a high reactive oxygen species level in E. faecalis R612Z1 cells, leading to cell growth inhibition.

The origin of endodontic Enterococcus faecalis explored by comparison of virulence factor patterns and antibiotic resistance to that of isolates from stool samples, blood cultures and food

AIM

To elucidate the origin of Enterococcus faecalis isolated from secondary root canal infections and the possibility for a foodborne transmission by comparing them to strains recovered from food, blood and stool regarding putative virulence factors and antibiotic susceptibility profiles, where strains from common origin were hypothesized to harbour similar characteristics.

METHODOLOGY

A total of 108 E. faecalis strains recovered in the county of Stockholm, Sweden, were screened using PCR for putative virulence factors esp, cylA, gelE/gelatinase-negative phenotype (ef1841/fsrC), efaA, ace and asa1. The minimum inhibitory concentration (MIC) for ampicillin, piperacillin-tazobactam, imipenem, gentamicin, vancomycin, ciprofloxacin and linezolid was determined using the agar dilution method.

RESULTS

Next to strains from blood, the food isolates presented the highest average number of virulence determinants and were frequently enriched with asa1 coding for aggregation substance. None of the endodontic strains carried cylA, and the gelatinase-negative phenotype caused by a deletion dominated the group. Altogether, the most prevalent genes were gelE, efaA and ace, and a combination of them was equally present in approximately 80% of the strains from food, stool and root canals in comparison with 43.3% of the blood isolates. High-level resistance to ciprofloxacin and gentamicin was observed in 30% of the blood isolates, whereas the isolates from other origins, with single exceptions, were susceptible to all tested antibiotics.

CONCLUSIONS

Evidence for a foodborne transmission, explaining the high reported prevalence of E. faecalis in root filled teeth, could not be determined based on the similarities in virulence factor patterns and antibiotic susceptibility. The only linkage between isolates from food and root canals consisted of a shared common combination of the genes gelE, efaA and ace. The high occurrence of putative virulence traits in food isolates questions the safety of E. faecalis in food products.

Antimicrobial action of oleanolic acid on Listeria monocytogenes, Enterococcus faecium, and Enterococcus faecalis

This study investigated the antimicrobial action of oleanolic acid against Listeria monocytogenes, Enterococcus faecium, and Enterococcus faecalis. To determine the cytotoxicity of oleanolic acid, HEp-2 cells were incubated with oleanolic acid at 37^oC. MICs (minimal inhibition concentrations) for L. monocytogenes, E. faecium, and E. faecalis were determined using two-fold microdilutions of oleanolic acid, and bacterial cell viability was then assessed by exposing the bacteria to oleanolic acid at 2 × MIC. To investigate the mode of antimicrobial action of oleanolic acid, we measured leakage of compounds absorbing at 280 nm, along with propidium iodide uptake. Scanning electron microscope (SEM) images were also analysed. The viability of HEp-2 cells decreased (P < 0.05) at oleanolic acid concentrations greater than 128 μg mL^-1. The MICs were 16-32 μg mL^-1 for L. monocytogenes and 32-64 μg mL^-1 for E. faecium and E. faecalis, and bacterial cell viability decreased (P < 0.05) about 3-4 log CFU mL^-1 after exposure to 2 × MIC of oleanolic acid. Leakage of 280 nm absorbing materials and propidium iodide uptake was higher in oleanolic acid –treated cells than in the control. The cell membrane was damaged in oleanolic acid-treated cells, but the control group had intact cell membrane in SEM images. The results indicate that oleanolic acid can kill L. monocytogenes, E. faecium, and E. faecalis by destroying the bacterial cell membrane.

Dramatic increase in vancomycin-resistant enterococci in Germany

OBJECTIVES

Among European countries, Germany has one of the highest proportions of vancomycin-resistant Enterococcus faecium bloodstream infections. The aim of this study was to investigate the development of vancomycin-resistant enterococci (VRE) in German hospitals and to consider the regional distribution of VRE in Germany.

METHODS

Data from three components of the German national nosocomial surveillance system (KISS) from the period 2007-12 were used for analysis: ICU-KISS data on nosocomial primary bloodstream infections and urinary tract infections from intensive care units (ICUs); OP-KISS data on surgical site infections from surgical departments; and Pathogen-KISS data concentrating on VRE cases (infections and colonizations) in ICUs. Trends over time were calculated and a map according to German federal states was prepared.

RESULTS

Data from up to 645 ICUs and 681 surgical departments for 2 year periods from 2007 to 2012 were analysed. The proportion of VRE increased significantly for surgical site infections (526%; P < 0.01) and bloodstream infections (265%; P < 0.01) and non-significantly for urinary tract infections (278%; P = 0.07). A large subgroup of ICUs also reported VRE cases in the same period, with a significant increase of 282%. The mapping of federal states showed large variation in VRE proportions and incidence rates in a belt of states with significantly higher VRE proportions from west (North Rhine-Westphalia) to east (Saxony).

CONCLUSIONS

The high overall VRE proportion in Germany is mainly due to the situation in four states. There is an urgent need to analyse the epidemiology of VRE in detail to develop appropriate infection control strategies.

Could chloramphenicol be used against ESKAPE pathogens? A review of in vitro data in the literature from the 21st century

The widespread use of antibiotics has been associated with the emergence of antimicrobial resistance among bacteria. 'ESKAPE' (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acintobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) pathogens play a major role in the rapidly changing scenario of antimicrobial resistance in the 21st century. Chloramphenicol is a broad spectrum antibiotic that was abandoned in developed countries due to its association with fatal aplastic anemia. However, it is still widely used in the developing world. In light of the emerging problem of multi-drug resistant pathogens, its role should be reassessed. Our paper reviews in vitro data on the activity of chloramphenicol against ESKAPE pathogens. Susceptibility patterns for Gram-positives were good, although less favorable for Gram-negatives. However, in combination with colistin, chloramphenicol was found to have synergistic activity. The risk-benefit related to chloramphenicol toxicity has not been analyzed. Therefore, extra precautions should be taken when prescribing this agent.

Enterococcus faecalis of human and poultry origin share virulence genes supporting the zoonotic potential of E. faecalis

Enterococcus faecalis is a major cause of nosocomial infections in humans and has been linked to severe extra-intestinal infections in poultry. A zoonotic potential has been suggested and the aim of the present study was to investigate similarities in virulence gene profiles of E. faecalis originating from infections in humans and poultry respectively. A total of 106 isolates of E. faecalis [26 human clinical isolates, 60 poultry clinical isolates (including two small-colony variants (SCVs) and 20 poultry cloacal isolates] were investigated for presence of seven virulence-associated genes: ace, asa1, cylA, efaA, EF0591, esp and gelE. For each gene, the PCR-amplification product was sequenced from one isolate in each group to explore intragenic variations between genes of human and poultry origin. Haemolytic and protease activities were assessed and isolates were assigned a sequence type (ST). Three of the seven genes investigated (ace, efaA and gelE) were present in all isolates. The asa1 was detected in 63/80 and 13/26 isolates of poultry and human origin respectively. For cylA, the numbers were 46/80 and 14/26 respectively. Among poultry isolates, esp and EF0591 were the least frequently observed genes (1/80 and 20/80 respectively); the prevalences among human isolates were 1/26 and 18/26 respectively. A high degree of similarity between genes in human and poultry isolates were confirmed by sequencing of amplification products. None of the cylA-positive isolates demonstrated haemolytic activity, while the phenotypic expression of gelatinase varied. The ST16 was the only ST shared by human and poultry isolates. The SCV isolates did not show a unique virulence profile or phylogeny. In conclusion, regardless of the distinct phylogenetic background of most E. faecalis isolates of human and poultry origin, we found major similarities in virulence gene profile and gene sequences in isolates from the two sources, supporting the zoonotic risk associated with this organism.

Multilocus sequence typing of Enterococcus faecalis isolates demonstrating different lesion types in broiler breeders

A total of 69 isolates of Enterococcus faecalis from broiler breeders demonstrating different lesion types and representing eight different flocks were characterized by multilocus sequence typing. Twenty isolates obtained from healthy birds representing two additional flocks were included for comparison. A total of 12 different sequence types (STs) was obtained. Correlation between ST and lesion type was not demonstrated. However, three STs (ST82, ST174, ST177) made up 81% of the isolates associated with lesions, indicating that these STs might be particularly associated with birds. In addition, ST174, the most frequently demonstrated ST, was only obtained from affected birds. Surprisingly, ST82, previously reported to be associated with amyloid arthropathy in layers worldwide, demonstrated a high degree of diversity as to lesion types, just as healthy carriers were demonstrated among broiler breeders. STs associated with healthy birds and lesions, respectively, did not demonstrate a phylogenetic relationship.