Aims:  Broad‐spectrum antibiotics produced by symbiotic bacteria [entomopathogenic bacterium (EPB)] of entomopathogenic nematodes keep monoxenic conditions in insect cadavers in soil. This study evaluated antibiotics produced by EPB for their potential to control plant pathogenic bacteria and oomycetes. Methods and Results:  Entomopathogenic bacterium produce antibiotics effective against the fire blight bacterium Erwinia amylovora, including streptomycin resistant strains, and were as effective in phytotron experiments as kasugamycin or streptomycin. Xenorhabdus budapestensis and X. szentirmaii antibiotics inhibited colony formation and mycelial growth of Phytophthora nicotianae. From X. budapestensis, an arginine‐rich fraction (bicornutin) was adsorbed by Amberlite® XAD 1180, and eluted with methanol : 1 n HCI (99 : 1). Bicornutin inactivated zoospores, and inhibited germination and colony formation of cystospores at <<25 ppm. An UV‐active molecule (bicornutin‐A, MW = 826), separated by HPLC and thin‐layer chromatography, was identified as a novel hexa‐peptide : RLRRRX. Conclusions:  Xenorhabdus budapestensis produces metabolites with strong antibacterial and cytotoxic activity. Individual compounds can be isolated, identified and patented, but their full antimicrobial potential may be multiplied by synergic interactions. Significance and Impact of the Study:  Active compounds of two new Xenorhabdus species might control plant diseases caused by pathogens of great importance to agriculture such as Erw. amylovora and P. nicotianae.

Aims:  The role of antibiotics produced by bacterial symbionts of entomopathogenic nematodes is to suppress growth of microbes in the soil environment. These antibiotics are active against Gram‐positive and Gram‐negative bacteria, and were tested against mastitis isolates from dairy cows. Methods and Results:  Two bioassays were adapted for Xenorhabdus antibiotics; an overlay method on agar plates, and serially diluted, cell‐free, Xenorhabdus cultures. The antimicrobial activities of the liquid cultures of 13 strains from five Xenorhabdus species were further evaluated. Antimicrobial activities of the type strains of X. nematophila, X. budapestensis and X. szentirmaii were tested on mastitis isolates of Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae with both bioassays. A previously reported antibiotic from X. nematophila, nematophin, was synthesized in three steps from tryptamine and 4‐methyl‐2‐oxovaleric acid sodium salt. Conclusions:  The antibiotics of all three Xenorhabdus strains were powerful in either bioassay, but the sensitivity of the isolates differed from each other. While Kl. pneumoniae was the least susceptible, Staph. aureus had the highest sensitivity to each Xenorhabdus strain. Xenorhabdus szentirmaii and X. budapestensis were more potent antibiotic producers than X. nematophila, and raceme nematophin was ineffective against all mastitis isolates. Significance and Impact of the Study:  These results indicate that Xenorhabdus antibiotics are effective against mastitis isolates and should be further evaluated for their potential in mastitis control or prevention.

Erwinia amylovora is one of the most frequently occurred plant pathogenic bacterium. It causes necrosis and blight symptoms on host plantsand it lead to considerable yield losses throughout the world on apple trees. There is no effective chemical treatment is currently available against fire blight. The purpose of the present study was to search a new, alternative control method. The evaluation of the plant protection potential of an enriched fraction of Xenorhabdus budapestensis cell-free conditioned media was investigated. Purified samples were tested in vitro and in plantaagainst the phytopathogenic bacterium. A reproducible method for isolation of a peptide-rich fraction from Xenorhabdus cell-free conditionedmedia was established. The process resulted in 400 mg of dry sample prepared from three litres of Xenorhabdus cell culture. Significant correlation was found between the concentration of the purified preparation and the induced inactivation zones against Erwinia amylovora Ea1 in agardiffusion test method. The minimum inhibitory concentration and minimum bactericidal concentration of the purified fraction against Ea1strain were 8 ;g/mL and 16 ;g/mL, respectively. In planta experiments were tested on an apple cultivar (‘Watson Jonathan’) susceptible to fireblight. The effective range of concentration was 62-200 μg/mL, while treatment with 300 μg/mL and larger amounts caused necrotic symptomson the petals of flowers. Current study pointed to the effectiveness of the compounds produced by X. budapestensis against fire blight. Thedevelopment of a commercially applicable formulation of these compounds would allow growers to effectively control fire blight in apple and pearorchards.

Erwinia amylovora is one of the most frequently occurred plant pathogenic bacterium. It causes necrosis and blight symptoms on host plants and it lead to considerable yield losses throughout the world on apple trees. There is no effective chemical treatment is currently available against fire blight. The purpose of the present study was to search a new, alternative control method. The evaluation of the plant protection potential of an enriched fraction of Xenorhabdus budapestensis cell-free conditioned media was investigated. Purified samples were tested in vitro and in planta against the phytopathogenic bacterium. A reproducible method for isolation of a peptide-rich fraction from Xenorhabdus cell-free conditioned media was established. The process resulted in 400 mg of dry sample prepared from three litres of Xenorhabdus cell culture. Significant correlation was found between the concentration of the purified preparation and the induced inactivation zones against Erwinia amylovora Ea1 in agar diffusion test method. The minimum inhibitory concentration and minimum bactericidal concentration of the purified fraction against Ea1 strain were 8 μg/mL and 16 μg/mL, respectively. In planta experiments were tested on an apple cultivar ('Watson Jonathan') susceptible to fire blight. The effective range of concentration was 62-200 µg/mL, while treatment with 300 µg/mL and larger amounts caused necrotic symptoms on the petals of flowers. Current study pointed to the effectiveness of the compounds produced by X. budapestensis against fire blight. The development of a commercially applicable formulation of these compounds would allow growers to effectively control fire blight in apple and pear orchards.

Bevezetés: A folyamatosan megjelenő multirezisztens kórokozók és a bevetett új antibiotikumok között állandó "harc" folyik. A klinikumban és az állatgyógyászatban használt antibiotikumok jelentős része már nem hatékony. Eltérő hatásmechanizmusú antibakteriális peptidek alkalmazása alternatív megoldást jelenthet. A rovarpatogén Xenorhabdus budapestensis baktérium szintetizálni képes különböző antimikrobiális hatású fehérjekomponenseket (bicornutin-A, fabclavin). Célkitűzés: Xenorhabdus budapestensis antibakteriális hatásának mérése zoonózist okozó baktériumokon in vitro. Módszer: Gram-pozitív (Rhodococcus equi, Erysipelothrix rhusiopathia, Staphylococcus aureus, Streptococcus equi, Corynebacterium pseudotuberculosis, Listeria monocytagenes) és Gram-negatív (Salmonella gallinarum, Salmonella derbi, Bordatella bronchoseptica, Escherichia coli, Pasteurella multocida, Aeromonas hydrophila) tesztbaktériumo-kon sejtmentes fermentlé és a tisztítottfehérje-biopreparátum antibakteriális hatásának mérése agardiffúzióval véres agaron. Eredmények: A Xenorhabdus budapestensis fehérjéket termel, amelyek hígításaitól függően erős antibakteriális aktivitást fejtettek ki a tesztelt baktériumokon. A tisztított frakció hatása erősebb volt, mint a sejtmentes fermentlé. A Gram-pozitív baktériumok érzékenyebbek voltak. Következtetések: A Xenorhabdus budapestensis antimikrobiális hatású fehérjéi hatékonyságot mutattak a zoonózist okozó baktériumokon, és potenciális esélyük lehet e szervezetek elleni bevetésre, illetve azok megelőzésében a jövőben. Orv. Hetil., 2015, 156(44), 1782-1786. Kulcsszavak: Xenorhabdus budapestensis, fabclavin, bicornutin-A, zoonózis, antimikrobiális hatásXenorhabdus budapestensis entomopathogenic bacteria cell free conditioned medium and purifi ed peptide fraction effect on some zoonotic bacteria Introduction: Many multi-resistant patogens appear continuously resulting in a permanent need for the development of novel antibiotics. A large number of antibiotics introduced in clinical and veterinary practices are not effective. Antibacterial peptides with unusual mode of action may represent a promising option against multi-resistant pathogens. The entomopathogenic Xenorhabdus budapestensis bacteria produce several different antimicrobial peptides compounds such as bicornutin-A and fabclavin. Aim: The aim of the authors was to evaluate the in vitro antibacterial effect of Xenorhabdus budapestensis using zoonotic patogen bacteria. Method: Cell-free conditioned media and purifi ed peptide fractions of Xenorhabdus budapestensis were tested on Gram-positive (Rhodococcus equi, Erysipelothrix rhusiopathia, Staphylococcus aureus, Streptococcus equi, Corynebacterium pseudotuberculosis, Listeria monocytage-