Table 1

Flea blockage and mortality during a 4-week period after infection with Ymt+ or Ymt Yersinia pestis. The results of three experiments with each bacterial strain are shown. The ymtH188N allele (6) was introduced into Y. pestis KIM6+ by allelic exchange (27) and confirmed by DNA sequence analysis. Y. pestis KIM5Δymt has a 1320–base pair in-frame deletion of ymt (14). Y. pestis KIM6+ymtH188N was complemented by transformation with pCH16, which contains a wild-type copy of ymt(14). Y. pestis KIM5Δymt was complemented by reinserting a full-length copy of ymtdownstream of the deleted allele. Y. pestis KIM5 has a deletion of the chromosomal pigmentation locus that contains thehms genes previously shown to be required by Y. pestis to block fleas (19). Therefore, KIM5 strains were transformed with pHMS1, which contains hmsHFRS (28). All of the Y. pestis strains used lack the 70-kb virulence plasmid, which is not required to infect or block fleas (19).

Fleas infected withFleas blocked (%) Excess mortality* (%)Fleas (n)
Y. pestisKIM6+2439100
3846100
3430103
Y. pestis KIM6+00109
ymtH188N03103
00107
Y. pestis KIM6+3244109
ymtH188N(pCH16)2342107
2938109
Y. pestis KIM5 (pHMS1)2750106
3260109
3644108
Y. pestis KIM5Δymt30109
(pHMS1)0789
00112
Y. pestisKIM5Δymt::ymt2255106
(pHMS1)2937109
3046108
  • * Percent mortality of infected fleas minus percent mortality of uninfected control fleas.