FIG 2.
In vitro competition experiments among different blaPDC alleles. Competition experiments were performed in the absence or presence of ceftazidime (CAZ [A and C]) or aztreonam (AZT [B and D]). PAΔA strains expressing PDC-461, PDC-462, PDC-463, or PDC-464 (i.e., PAΔA-461, PAΔA-462, PAΔA-463, and PAΔA-464, respectively) were competed against PAΔA expressing PDC-3 (PAΔA-3). Fitness (S) relative to PAΔA-3 for (A) ceftazidime or (B) aztreonam is shown. Then, PAΔA-461, PAΔA-462, PAΔA-463, and PAΔA-464 were competed against each other in the absence of antibiotics or presence of (C) ceftazidime or (D) aztreonam. (See Text S1 in the supplemental material for the antibiotic concentration scheme.) Measurements were carried out in triplicate for at least two independent experiments, and the results are expressed as means ± standard errors of the means (SEM). Statistically significant differences at P < 0.0001, P < 0.01, and P < 0.05 are identified by ****, **, and *, respectively (two-way analysis of variance [ANOVA] followed by Tukey’s multiple-comparison test).