aeruginosa, isogenic ampG and ampP insertional inactivation mutants were constructed in the prototypic P. aeruginosa strain PAO1, referred to as PAOampG see more and PAOampP, respectively. The β-lactamase activity in the two isogenic mutants, PAOampG and PAOampP, was
compared to PAO1. In the absence of β-lactam antibiotics, all strains showed a basal level of β-lactamase activity (Table 1). Upon challenge with 500 μg/ml of benzyl-penicillin, this level was elevated 10-fold (p < 0.05) in PAO1 (Table 1). However, the β-lactamase activities of PAOampP and PAOampG remained low in the presence of β-lactam antibiotic, indicating a loss of β-lactamase induction (Table 1). The loss of inducibility in PAOampG could be partially restored by expressing ampG in trans, whereas the β-lactamase inducibility of PAOampP was completely recovered when ampP was supplied in trans (Table 1). Both PAOampP and PAOampG mutants had the other copy Protein Tyrosine Kinase inhibitor of the permease gene intact. These observations suggest that ampG and ampP are individually important members of the β-lactamase induction system.
To confirm that ampG and ampP play independent roles, cross-complementation of PAOampP with pAmpG, and PAOampG with pAmpP was performed. Similar to the mutants, the cross-complemented strains did not show inducible β-lactamase activity (Table 1). Table 1 β-lactamase activity of P. aeruginosa PAO1, PAOampG and PAOampP in the absence Selleck Osimertinib and presence of β-lactam Strain and plasmid Relevant genotypes (PI3K Inhibitor Library order supplement in trans) β-lactamase activitya Uninduced Induced b PAO1 ampG + ampP + 22.2 ± 9.7 221.4c ± 9.2 PAOampG ampG – ampP + 20.4 ± 6.2 28.8d ± 3.3 PAOampP ampG + ampP – 4.2 ± 6.2 32.2d ± 3.3 PAOampG/pKKF69 ampG – ampP + (ampG + ) 8.4 ± 1.4 87.6 ± 14.4 PAOampP/pKKF73 ampG + ampP – (ampP + ) 8.8 ± 1.8 217.9 ± 35.5 PAOampG/pKKF73 ampG – ampP + (ampP + ) 2.1 ± 2.0 14.4 ± 1.9
PAOampP/pKKF69 ampG + ampP – (ampG + ) 5.3 ± 1.9 10.6 ± 2.7 a Cultures at OD600 of 0.6-0.8 were divided in two. One set was induced with 500 μg/ml benzyl-penicillin for three hours before harvesting. Assays were performed on sonicated lysate using nitrocefin as a chromogenic substrate. One milliunit of β-lactamase is defined as 1 nanomole of nitrocefin hydrolyzed per minute per microgram of protein. Assays were performed in triplicate. b Induction was carried out using 500 μg/ml benzyl-penicillin c p < 0.05 compared to uninduced PAO1 d p < 0.05 compared to induced PAO1 To further understand the role of ampG and ampP in β-lactamase induction, β-lactamase activity was assayed at different concentrations of benzyl-penicillin in PAO1, PAOampG and PAOampP (Figure 5). Upon encounter with the inducer (25 μg/ml), there was approximately 38% induction (Figure 5). For strain PAO1, this increase in β-lactamase activity continued in a dose-dependent manner until the maximum level of β-lactamase activity was reached when 100 μg/ml of benzyl-penicillin was added (Figure 5).