Xenorhabdus antibiotics: a comparative analysis and potential utility for controlling mastitis caused by bacteria.
OBJECTIVE
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.


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.


CONCLUSIONS
These results indicate that Xenorhabdus antibiotics are effective against mastitis isolates and should be further evaluated for their potential in mastitis control or prevention.
Furgani
G
G
Department of Genetics, Faculty of Natural Sciences, Eötvös University, Budapest, Hungary.
Böszörményi
E
E
Fodor
A
A
Máthé-Fodor
A
A
Forst
S
S
Hogan
J S
JS
Katona
Z
Z
Klein
M G
MG
Stackebrandt
E
E
Szentirmai
A
A
Sztaricskai
F
F
Wolf
S L
SL
D000818:Animals; D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000494:pharmacology / Q000627:therapeutic use; D002417:Cattle; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000187:drug effects; D005260:Female; D007211:Indoles / Q000138:chemical synthesis / Q000494:pharmacology; D007711:Klebsiella pneumoniae / Q000187:drug effects; D008414:Mastitis, Bovine / Q000188:drug therapy* / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D012988:Soil Microbiology; D013045:Species Specificity; D013211:Staphylococcus aureus / Q000187:drug effects; D020593:Xenorhabdus / Q000378:metabolism*
D000900:Anti-Bacterial Agents; D007211:Indoles; C109330:nematophin