Fosfomycin Ineffective in Vitro But Shows In Vivo Efficacy Against Listeriosis

Filed in archive Diagnostics, Methodologies and Instrumentation , Drugs, Vaccines and Therapeutics , Microbiology on May 12, 2006

For an antibiotic candidate to be considered for human clinical trials, it first has to show efficacy under laboratory conditions. If a compound does not inhibit the growth of microorganisms under in vitro conditions, the drug candidate does not advance into in vivo trials. A new study published in Nature Medicine, however, indicate that using this screening methodology, we might actually be missing out on compounds which do not show antimicrobial properties under lab conditions, but to which microbes are in fact, susceptible to under in vivo conditions, as a result of its pharmacokinetics and -dynamics in the body.

In this particular paper, the researchers showed that despite it being ineffective in laboratory tests, fosfomycin can actually treat listeriosis, a type of food poisoning caused by the bacterium Listeria monocytogenes. Listeriosis is particularly alarming, because although the number of annual cases is relatively small, out of the 2,500 Americans that get infected annually, about 500 of them die. This new finding not only adds to the repertoire of antibiotics proven effective against Listeriosis, but also challenges the accuracy of the extent of antibiotic resistance.

"Our results illustrate that antibiotic resistance in the laboratory does not always mean that the drug will not work in the infected patient. This work brings some optimism to the highly worrying problem of the increasing resistance to antibiotics.

Our findings warn about the need to revise laboratory methods currently in use to determine the susceptibility or resistance of bacteria to such drugs, so that the tests reflect better what actually happens in the body."

Read more from the University of Bristol: New Treatment for Food Poisoning.