TABLE 3.

Effects of several stresses on the expression of β-galactosidase by wild-type K. pneumoniae LM21 and a chromosomal Φ (eef-lacZ) fusion

StressActivity for straina:
K. pneumoniae LM21::Φ (eef-lacZ)K. pneumoniae LM21
Control0.7 ± 0.65.46 ± 2.8
HCl (pH 3)48.3* ± 4.73.35 ± 1.2
Inorganic acid (pH 5.5)48.4* ± 2.66.68 ± 3.4
Bile salts (1%)0.2 ± 0.31.57 ± 0.7
NaCl (0.125 M)44.3* ± 0.68.74 ± 3.9
NaCl (0.5 M)39.5* ± 4.90.00 ± 0.0
  • a β-Galactosidase activities are expressed in Miller units as the means of a minimum of three experiments ± standard deviations. Strains initially were grown in LB broth and then diluted in LB broth alone (control) or supplemented with inorganic acid (HCl; pH 3), organic acids (pH 5.5), bile salts (1%), and NaCl (0.125 and 0.5 M). An asterisk indicates that the difference is statistically significant (P < 0.05 by the Student's test).