Effects of Sublethal Concentrations of Benzylpenicillin on Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa produces a low basal level of β-lactamase (0.002 to 0.004 IU/mg of protein when benzylpenicillin is used as substrate). The β-lactamase specific activity can be increased several hundredfold by growing the bacteria in the presence of β-lactam antibiotics. This induction was studied in Pseudomonas aeruginosa 1822s. The single-cell resistance to benzylpenicillin was 750 μg/ml. In liquid culture all concentrations of benzylpenicillin tested (25 to 2,000 μg/ml) affected the bacteria similarly: β-lactamase formation was induced, the cells became cholate sensitive, growth rate decreased, filaments were formed, and β-lactamase was excreted. The effect appeared earlier the higher the concentration of the antibiotic. Most of the effects obtained are concerned with the functioning of the outer membrane. The excretion of β-lactamase seems to be due to an opening of the periplasmic volume rather than to lysis of the cells. Carbenicillin gave the same effects as benzylpenicillin at the same concentrations; the 10-fold lower resistance to carbenicillin than to benzylpenicillin can be explained by the inability of the inducible β-lactamase to hydrolyze carbenicillin. The induced β-lactamase was first cell bound and to a great extent located in the periplasmic volume, but later it was excreted into the medium. This extracellular activity was responsible for the detoxification of the medium. This is analogous to the behavior of gram-positive bacteria rather than to that of Enterobacteriaceae .

Beta-lactamase Induction in Nosocomial Staphylococcus aureus Strains Cultured from the Nasal Cavity and Wound of Patients

“…The result supports the findings of (Nordstrom & Sykes, 1973;Okonogi, Kuno,& Higashide, 1986;Raimondi, Sisto & Nikaido, 2007) who reported that the specific activity of β-lactamase increased linearly with increasing concentrations of inducer. In addition, Khan, Sallum, Zheng, Nau & Hassan (2014) in their study on rapid determination of β-lactamase and antibiotic activity detected β-lactamase in the absence of inducer however, at a lower level when compared with induction.…”

Induction Kinetics of β-Lactamase Biosynthesis in Pseudomonas aeruginosa

“…This conclusion is strenghtened by the fact that the lag before enzyme production starts is shorter the more inducer is added (26); at 4,000 ;&g of benzylpenicillin per ml the lag was only a few minutes (Fig. 5).…”

“…This makes the induction of fl-lactamase a rather unphysiological response, since growth is greatly impaired by these high concentrations of antibiotic inducer (32). At nonlethal concentrations of inducer, the lag period before induction is more than a generation and is dependent on the concentration of inducer (26). Nonlethal concentrations of penicillin cause drastic changes in the functioning of the outer cell envelope (26).…”

“…At nonlethal concentrations of inducer, the lag period before induction is more than a generation and is dependent on the concentration of inducer (26). Nonlethal concentrations of penicillin cause drastic changes in the functioning of the outer cell envelope (26). In this context it may be appropriate to recall that Saz and Lowery (36,37) have reported that some synthetic cyclic peptides can act as inducers and substrates of,-lactamases in staphylococci (36) and Bacillus cereus (37).…”

“…All strains of Pseudomonas aeruginosa contain a basal level of 6-lactamase (26). The formation of this enzyme is induced by the addition of P-lactam antibiotics.…”