Antimicrobial activity of Enterococcus faecalis against Listeria monocytogenes

Six strains of Enterococcus faecalis were tested for antimicrobial activity against Listeria monocytogenes. Using the agar spot test, E. faecalis NRIC 1143 and 1144 showed strong activity against all of five strains of L. monocytogenes tested. Antimicrobial activities of these strains were inhibited by some proteolytic enzymes.     

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.     

Antimicrobial activity of bacteriocin S760 produced by Enterococcus faecium strain LWP760

Antimicrobial activity of bacteriocin S760 (enterocin) produced by Enterococcusfaecium strain LWP760 was studied. Bacteriocin S760 is a cationic, hydrophobic, and heat stable peptide with the molecular weight of 5.5 kDa and pl of 9.8. Enterocin S760 is shown to inhibit in vitro the growth both of sensitive and resistant to antibacterials gramnegative and grampositive bacteria of 25 species. MICs of the bacteriocin S760 vary between 0.05-1.6 mg/l for Escherichia coli 0157:H117, Salmonella typhimurium, Salmonella enteritidis, Campylobacter jejuni, Yersinia enterocolitica, Yersinia pseudotuberculosis, Listeria monocytogenes and Clostridium perfringens, that are main food-borne pathogens, and from 0.4-1.6 mg/l for Streptococcus pyogenes, Streptococcus pneumoniae and Corynebacterium diphteriae. It is also active against antibioticresistant strains of Staphylococcus aureus, Enterobacter cloacae, Acinetobacter baumannii (with MICs of 0.05-3 mg/l), Klebsiella pneumoniae (with MICs of 6 mg/l), Pseudomonas aeruginosa (with MICs of 0.4-25 mg/1), as well against fungi belonging to species of Candida albicans, Candida krusei and Aspergillus niger (with MICs of 0.1-0.2 mg/l). Enterocin S760 is a novel antimicrobial agents useful in medicine, veterinary and food industry.     

Antimicrobial resistance of Listeria spp. recovered from processed bison

AIMS: The current study examined the antimicrobial susceptibility of 86 Listeria spp. isolated from processed bison carcasses. MATERIALS AND METhods: Susceptibility to 25 antimicrobial agents was determined using E-test and National Antimicrobial Resistance Monitoring System (NARMS) panels. Most Listeria isolates (88-98%) exhibited resistance to bacitracin, oxacillin, cefotaxime, and fosfomycin. Resistance to tetracycline (18.6%) was also common. Of the 16 tetracycline-resistant Listeria isolates, 15 carried tetM and 2 contained integrase of Tn1545 transposons. Rifampicin and trimethoprim-sulfamethoxazole were the most active antimicrobial agents against Listeria spp., with a MIC(90) of 0.38 microg ml(-1). Ampicillin, erythromycin, penicillin, gentamicin, and tobramycin also exhibited good activity against Listeria spp., with MIC(90) not exceeding 1 microg ml(-1). Differences in resistance among Listeria spp. was displayed, as Listeria innocua strains were more resistant than other Listeria species. CONCLUSIONS: The study showed that Listeria monocytogenes strains from bison were susceptible to the antibiotics most commonly used to treat human listeriosis. However, the presence of antimicrobial resistance in L. innocua indicates the potential for transfer of resistance and a conjugative transposon to L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings of our study will provide useful information for the development of public health policy in the use of antimicrobials in food animal production.     

Antimicrobial activity of Pseudomonas spp. against food poisoning bacteria and moulds

M.H. LAINE, M.T. KARWOSKI, L.B. RAASKA AND T.-M. MATTILA-SANDHOLM. 1996. The present study demonstrates the siderophore production of two strains of Pseudomonas fluorescens and two of Ps. chlororaphis . The antimicrobial activities of these strains were studied against Salmonella typhimurium, Staphylococcus aureus, Fusarium culmorum, F. oxysporum and Aspergillus niger . Despite equal siderophore activities with various Pseudomonas spp. as measured by the chrome azurol S assay, the study shows how siderophore activity does not correlate with the antibacterial activity against food pathogens or with the antimould activity against pathogenic moulds. Furthermore, the results illustrate how siderophores are able to act both as growth inhibitors and stimulators.     

血流感染粪肠球菌和屎肠球菌的临床分布及耐药研究

回顾性分析上海市某三甲医院血培养阳性标本中粪肠球菌和屎肠球菌的临床分布及对抗菌药物的耐药特征,为临床治疗其所致感染奠定基础。收集上海市某三甲医院2012年2月—2016年9月血流感染患者血液标本中的粪肠球菌和屎肠球菌,采用法国生物梅里埃公司的VITEK 2Compact全自动细菌鉴定和药敏分析系统进行细菌鉴定及药敏测定,研究细菌临床分布特点及对常用抗菌药物的耐药特征。共分离获得30株粪肠球菌和17株屎肠球菌。粪肠球菌样本主要来自泌尿科、消化科和血液科,所占比例分别为13.33%、16.67%和10.00%。粪肠球菌对青霉素、氨苄西林、环丙沙星、左氧氟沙星、四环素和红霉素的耐药率分别为13.33%、10.00%、36.67%、33.33%、66.67%和60.00%。屎肠球菌样本主要来自消化科(29.41%),其对以上抗菌药物的耐药率分别为88.24%、82.35%、88.24%、76.47%、23.53%和70.59%。屎肠球菌对青霉素、氨苄西林、环丙沙星和左氧氟沙星的耐药率显著高于粪肠球菌,而对四环素的耐药率显著低于粪肠球菌。两者均对替加环素、利奈唑胺和万古霉素敏感,但万古霉素对屎肠球菌的最低抑菌浓度显著低于粪肠球菌。结果提示,屎肠球菌对青霉素、氨苄西林、环丙沙星、左氧氟沙星的耐药率高于屎肠球菌,对万古霉素敏感,且其万古霉素最低抑菌浓度低于粪肠球菌。本研究为治疗这两种细菌所致感染的经验性用药提供了数据支持。     

Identification of a broadly active phage lytic enzyme with lethal activity against antibiotic-resistant Enterococcus faecalis and Enterococcus faecium

Enterococcus faecalis and Enterococcus faecium infections are increasingly difficult to treat due to high levels of resistance to antibiotics. PlyV12, a bacteriophage lytic enzyme, was isolated and shown to effectively kill both E. faecalis and E. faecium (including vancomycin-resistant strains), as well as other human pathogens. We propose its development and use as an alternative therapeutic tool.     

Antimicrobial activity of Staphylococcus xylosus from Italian sausages against Listeria monocytogenes

One hundred and twenty-five isolates of Micrococcaceae from Italian salami were tested for antagonistic activities against Listeria monocytogenes. Four isolates, identified as Staphylococcus xylosus , inhibited the growth of all five strains of L. monocytogenes tested. The antagonistic substances produced by strains 39A and 41A were inactivated by some proteases, whereas those from strains 1E and 27E were inactivated only by esterase and lipase. They are neither bacteriophages, nor lytic enzymes like lysostaphin.     

Time-kill study and synergistic activity of cell-wall inhibitor antibiotics in combination with gentamicin against Enterococcus faecalis and Enterococcus faecium

The synergy between gentamicin and vancomycin, teicoplanin, ampicillin and linezolid was studied by time-kill method. Two clinical vancomycin resistant enterococci (VRE) and two vancomycin susceptible enterococci (VSE) isolates were used. Different concentrations of antibiotics were combined. Two VSE strains and the control strain exhibited synergism with the combination of gentamicin, vancomycin, teicoplanin, ampicillin and linezolid. Two VRE strains exhibited synergism with the combination of gentamicin and ampicillin. Synergy between gentamicin and vancomycin, teicoplanin and linezolid was not observed against these isolates. The VRE isolates were positive for vanA, aac (6')-Ie aph (2") and aph (3')-IIIa genes and their vancomycin, teicoplanin and gentamicin MICs were 512 μg/ml, 512 μg/ml and >4000 μg/ml, respectively. In order to treat serious enterococcal infections, further clinical evaluation is needed to examine the in vitro combined effects of gentamicin and vancomycin, teicoplanin and linezolid.     

Chloride-Inducible Expression Vector for Delivery of Antimicrobial Peptides Targeting Antibiotic-Resistant Enterococcus faecium

Antibiotic-resistant enterococcal infections are a major concern in hospitals where patients with compromised immunity are readily infected. Enterococcus faecium bacteria are of particular interest as these pathogens account for over 80% of vancomycin-resistant enterococcal infections. Antimicrobial peptides (AMPs) produced at the site of infection by engineered bacteria may offer a potential alternative to traditional antibiotics for the treatment of resistant bacteria such as E. faecium. For this mode of delivery to be effective, it is essential to identify a suitable protein expression system that can be used in the desired delivery bacterium. In this study, we describe a promising chloride-inducible promoter and its application in the bacterial delivery of AMPs from Lactococcus lactis to reduce counts of E. faecium bacteria in vitro. Reporter gene studies show that at chloride concentrations found within the human intestines, the chloride-inducible promoter exhibits high levels of protein expression compared to those of the commonly used nisin-inducible promoter. These results indicate that this system is powerful and would not require the exogenous administration of an inducer molecule. In its application for AMP production against E. faecium in vitro, L. lactis producing AMPs under the chloride promoter rapidly decreased E. faecium counts by nearly 10,000-fold. As an extension of this application, we also demonstrate the potential in using this type of delivery system in combination with traditional antibiotics to slow the development of resistance. Collectively, this study shows the promise of using a chloride-inducible promoter for the bacterial delivery of AMPs in the body for the treatment of vancomycin-resistant enterococci (VRE) and other antibiotic-resistant bacteria.     

Changes in Antimicrobial Susceptibility of Native Enterococcus faecium in Chickens Fed Virginiamycin

The extent of transfer of antimicrobial resistance from agricultural environments to humans is controversial. To assess the potential hazard posed by streptogramin use in food animals, this study evaluated the effect of virginiamycin exposure on antimicrobial resistance in Enterococcus faecium recovered from treated broilers. Four consecutive broiler feeding trials were conducted using animals raised on common litter. In the first three trials, one group of birds was fed virginiamycin continuously in feed at 20 g/ton, and a second group served as the nontreated control. In the fourth trial, antimicrobial-free feed was given to both groups. Fecal samples were cultured 1 day after chickens hatched and then at 1, 3, 5, and 7 weeks of age. Isolates from each time point were tested for susceptibility to a panel of different antimicrobials. Quinupristin/dalfopristin-resistant E. faecium appeared after 5 weeks of treatment in trial 1 and within 7 days of trials 2 to 4. Following removal of virginiamycin in trial 4, no resistant isolates were detected after 5 weeks. PCR failed to detect vat, vgb, or erm(B) in any of the streptogramin-resistant E. faecium isolates, whereas the msr(C) gene was detected in 97% of resistant isolates. In an experimental setting using broiler chickens, continuous virginiamycin exposure was required to maintain a stable streptogramin-resistant population of E. faecium in the animals. The bases of resistance could not be explained by known genetic determinants.     

Antimicrobial activity of Leuconostoc gelidum against closely related species and Listeria monocytogenes

A newly isolated strain of Leuconostoc gelidum was evaluated for its ability to inhibit a wide spectrum of lactic acid bacteria, meat spoilage bacteria and food-related human pathogens, including Listeria monocytogenes. It was inhibitory to most of the lactobacilli, all the leuconostocs, and three strains of L. monocytogenes when tested both by direct and well diffusion methods. Cell-free extract retained activity after 60 min at 100 degrees C but was sensitive to protease. Dialysis suggested a molecular weight in excess of 10(4) daltons. The inhibitory effect was bactericidal and rapid.     

Antimicrobial activity of Leuconostoc gelidum against closely related species and Listeria monocytogenes

H arding , C.D. & S haw , E.G. 1990. Antimicrobial activity of Leuconostoc gelidum against closely related species and Listeria monocytogenes. Journal of Applied Bacteriology 69 , 648–654.
A newly isolated strain of Leuconostoc gelidum was evaluated for its ability to inhibit a wide spectrum of lactic acid bacteria, meat spoilage bacteria and food-related human pathogens, including Listeria monocytogenes . It was inhibitory to most of the lactobacilli, all the leuconostocs, and three strains of L. monocytogenes when tested both by direct and well diffusion methods. Cell-free extract retained activity after 60 min at 100C but was sensitive to protease. Dialysis suggested a molecular weight in excess of 10⁴ daltons. The inhibitory effect was bactericidal and rapid.     

Efficacy of a variety of disinfectants against Listeria spp.

The efficacy of 14 disinfectants against Listeria innocua and two strains of Listeria monocytogenes in the presence of organic matter was studied. Quantitative efficacy tests were used. Many of the disinfectants tested were not as effective on Listeria spp. when the test organisms were dried onto the surface of steel disks (carrier tests) as they were when the organisms were placed in suspension (suspension test). The presence of whole serum and milk (2% fat) further reduced the disinfectant capacities of most of the formulations studied. Only three disinfectants (povidone-iodine, chlorhexidine gluconate, and glutaraldehyde) were effective in the carrier test in the presence of serum; however, all three were ineffective when challenged with milk (2% fat). Only one solution, sodium dichloroisocyanurate, was effective in the presence of milk. All but four formulations (chloramine-T, phosphoric acid, an iodophor, and formaldehyde) were effective in the suspension tests, regardless of the organic load. L. monocytogenes was observed to be slightly more resistant to disinfection than L. innocua was. There was no difference in disinfectant susceptibility between the two strains of L. monocytogenes. These findings emphasize the need for caution in selecting an appropriate disinfectant for use on contaminated surfaces, particularly in the presence of organic material.     

The mechanism of action of a citrus oil blend against Enterococcus faecium and Enterococcus faecalis

Aims:  The aim was to explore the mechanisms by which a blend of orange ( Citrus sinensis ) :  bergamot ( Citrus bergamia ) (1 : 1 v/v) EO (essential oil) (2% v/v) and its vapour (15 mg l⁻¹ air) brings about its antimicrobial effect against Enterococcus faecium and Enterococcus faecalis .
Methods and Results:  Cells were exposed to the blend in oil or vapour form in a sealed unit. Membrane permeability was measured using an NPN assay and intra and extracellular ATP concentrations were assessed using luminescence. Assays using 3,3-dipropylthiacarbocyanine and carboxyfluorescein diacetate succinimidyl ester measured membrane potential and intracellular pH changes. TEM images of treated cells indicate morphological differences and show the possible uptake of the EO into the cell. After cells were exposed to EO or vapour, cell permeability increased by ×2 and ×40 respectively. A decrease of 1·5 in intracellular pH, 20 a.u. in membrane potential and 18 pmol mg⁻¹ protein of intracellular ATP occurred.
Conclusions:  The EO blend affects the cell membrane and cell homeostasis resulting in inhibition of growth or cell death.
Significance and Impact of the Study:  Understanding the mechanisms by which EOs bring about their antibacterial effect could lead to an alternative to chemical-based bactericides for use against Enterococcus sp.     

Screening of nonpathogenic strains of Enterococcus faecium with antagonistic activity

Forty two strains of enterococci were isolated from feces of healthy adolescents. Strains were selected according to their antagonistic effects associated with bacteriocinogenic and microcinogenic activity. Resistance of enterococci to antibiotics, various concentrations of hydrochloric acid and bile, their level of production of organic acids and adhesiveness were determined. Characteristics related to pathogenicity were investigared in 5 microcinogenic strains of E. faecium with broad spectrum of antagonistic activity. Non-pathogenic microcin-producing strains of E. faecium resistant to physiological concentrations of hydrochloric acid and bile with broad spectrum of antagonistic activity against obligatory pathogenic and opportunistic microorganisms can be considered as possessing probiotic activity.     

Lactic acid bacteria from chicken carcasses with inhibitory activity against Salmonella spp. and Listeria monocytogenes

This study was conducted to isolate psychrotrophic lactic acid bacteria (LAB) from chicken carcasses with inhibitory activity against strains of Salmonella spp. and Listeria monocytogenes. A total of 100 broiler samples were examined for the presence of LAB. Ninety-two LAB isolates that showed antimicrobial effects against Salmonella spp. and L. monocytogenes were further analysed to examine their LAB (Gram-positive, catalase negative, oxidase negative) and psychrotrophic characteristics (ability to grow at 7 °C). Fifty isolates were further selected and identified initially using standard biochemical tests in miniature (Micro-kits API CH 50) and then by sequencing of the 16s-23s rRNA gene boundary region (Intergenic Spacer Region). By molecular identification, these isolates were classified into 5 different LAB species: Lactobacillus salivarius, Lactobacillus reuteri, Lactobacillus johnsonii, Pediococcus acidilactici, and Lactobacillus paralimentarius. None of the isolates produced tyramine or histamine.     

New bisanthraquinone antibiotics and semi-synthetic derivatives with potent activity against clinical Staphylococcus aureus and Enterococcus faecium isolates

The escalation of antibiotic resistance among Gram-positive pathogens presents increasing treatment challenges and requires the development of innovative therapeutic agents. Here, we present the antimicrobial properties of structurally unusual bisanthraquinone metabolites produced by a marine streptomycete and four semi-synthetic derivatives. Biological activities were measured against clinically derived isolates of vancomycin-resistant Enterococcus faecium (VRE), and methicillin-susceptible, methicillin-resistant, and tetracycline-resistant Staphylococcus aureus (MSSA, MRSA, and TRSA, respectively). The most potent antibiotic displayed MIC₅₀ values of 0.11, 0.23, and 0.90 μM against a panel (n = 25 each) of clinical MSSA, MRSA, and VRE, respectively, and was determined to be bactericidal by time-kill analysis.     

Comparison of Enterococcus faecium and Enterococcus faecalis Strains Isolated from Water and Clinical Samples: Antimicrobial Susceptibility and Genetic Relationships

Enterococci are part of the normal intestinal flora in a large number of mammals, and these microbes are currently used as indicators of fecal contamination in water and food for human consumption. These organisms are considered one of the primary causes of nosocomial and environmental infections due to their ability to survive in the environment and to their intrinsic resistance to antimicrobials. The aims of this study were to determine the biochemical patterns and antimicrobial susceptibilities of Enterococcus faecalis and E. faecium isolates from clinical samples and from water (groundwater, water from the Xochimilco wetland, and treated water from the Mexico City Metropolitan Area) and to determine the genetic relationships among these isolates. A total of 121 enterococcus strains were studied; 31 and 90 strains were isolated from clinical samples and water (groundwater, water from the Xochimilco wetland, and water for agricultural irrigation), respectively. Identification to the species level was performed using a multiplex PCR assay, and antimicrobial profiles were obtained using a commercial kit. Twenty-eight strains were analyzed by pulsed-field gel electrophoresis (PFGE). E. faecium strains isolated from water showed an atypical biochemical pattern. The clinical isolates showed higher resistance to antibiotics than those from water. Both the enterococci isolated from humans, and those isolated from water showed high genetic diversity according to the PFGE analysis, although some strains seemed to be closely related. In conclusion, enterococci isolated from humans and water are genetically different. However, water represents a potential route of transmission to the community and a source of antimicrobial resistance genes that may be readily transmitted to other, different bacterial species.