PASSAGE OF PSEUDOMONAS-AERUGINOSA IN COMPROMISED MICE

There was no appreciable increase in virulence of P. aeruginosa PAO-1 after 6 passes through infections in mice. When strain PAO-1 was passed through mice compromised with Fe and methotrexate, virulence of the passed bacteria increased for normal and compromised mice. Bacteria harvested from i.p. passage in compromised mice were more virulent than bacteria harvested from intrathoracic passage. These bacteria expressed LD50 values distinctive of the respective bacterial isolate when injected i.p., intrathoracically or i.v. Differences between bacteria from i.p. and intrathoracic passage were apparently due to differences in selective pressures in the 2 infection sites, because intrathoracically passed bacteria assumed virulence characteristics of the i.p. passed bacteria after i.p. passage in compromised mice.