Spread of multiresistant gram-negative bacilli among severely immuno-compromised mice during prophylactic treatment with different oral antimicrobial drugs.

Gram-negative infections are generally regarded as a major cause of severe infections in granulocytopenic patients. To prevent such infections, selective decontamination (SD) of the digestive tract has been introduced. It is assumed that if SD is applied on all patients in an oncologic station it may not only provide protection to patients thus treated, but it may have also epidemiologic consequences. SD may considerably reduce the number of circulating (antibiotic-resistant) strains in the ward and therewith significantly further reduce the chance of severe infection during periods of granulocytopenia. Because the effect which different kinds of antibiotics may have on the accumulation and spread of resistant bacteria cannot be studied in patients, it was investigated experimentally. Groups of 15 conventional mice were lethally irradiated and each group was treated with one antibiotic. On the day of irradiation one mouse per cage was orally contaminated with a multi-resistant strain either of E. coli or Ps. aeruginosa. The spread of these strains among cage mates as well as their effect on mortality was investigated. It appeared that ampicillin promoted spread and enhanced mortality in comparison with a control group, whereas antibiotics currently used for SD did prevent spread of the multi-resistant strain and reduced mortality.