Heterogeneity of class I beta-lactamase expression in clinical isolates of Pseudomonas aeruginosa

Abstract

Expression of chromosomal ,B-lactamase was examined in 85 clinical isolates of Pseudomonas aeruginosa.P-Lactamase assays with and without cefoxitin induction revealed four phenotypes of enzyme expressioll: low basal, inducible; moderate basal, inducible; moderate basal, constitutive; and high basal, constitutive. The isoelectric points of the major ,-lactamase bands were 9.4, 9.2, and 8.4. These results indicate that there is a limited heterogeneity in expression of chromosomal P-lactamase of P. aeruginosa.Virtually every strain of Pseudomonas aeruginosa produces a chromosomal P-lactamase that belongs to Richmond-Sykes class I (10). Under normal conditions, this enzyme is expressed at a very low basal level; however, it can be induced to much higher levels with such compounds as benzylpenicillin, cefoxitin, or imipenem (1, 6, 9-11, 13). Mutants of P. aeruginosa altered in their expression of class I 3-lactamase have also been described. These include mutants partially or fully derepressed for enzyme expression, those with little or no enzyme, and mutants expressing moderate levels of ,-lactamase constitutively (2-6, 11, 14). These altered states of enzyme expression are often associated with changes in susceptibility to various 3-lactam antibiotics. To date, most studies concerning the production single patient during a course of antimicrobial therapy. A second isolate fromn the same patient was included only if it was altered in its expression of ,-lactamase in comparison to the first isolate or was a different strain. Strain identity was based upon serotype (serotyping was kindly performed by Charles Zierdt, National Institutes of Health, Bethesda, Md.).,-Lactamase expression in each of the 85 isolates was examined in sonic extracts prepared with or without 2 h of induction with 100 ,ug of cefoxitin per ml (3). The isoelectric point (pI) of each enzyme. was determined before and after induction as described previously (12). In each isoelectric focusing run, controls were included to mnonitor run-to-iruri variations. These controls consisted of sonic extracts pre-

High-level beta-lactamase activity in sputum samples from cystic fibrosis patients during antipseudomonal treatment

“…In all but two of the patients, no detectable P-lactamase activity was found in sputum at day 15 (13). The results of this study confirm this information.…”

Synergic interaction between ascorbic acid and antibiotics against Pseudomonas aeruginosa

“…It should be noted that this data was obtained for only one strain of P. aeruginosa and using a ten-fold higher concentration of ascorbic acid than our study. Since all ampicillin-resistant P. aeruginosa isolates tested in the present study were able to produce this enzyme (Magalhães et al, 1997), the heterogeneity of β-lactamases or the different amounts produced could explain this alternate response to ascorbic acid exposure, or indicate the presence of different mechanisms of ampicillin resistance (Sanders et al, 1988;Bryan, 1988). As expected, ascorbic acid alone at 1 mg mL -1 concentration did not affect bacterial growth (Table 2).…”

Characterization of a novel extended-spectrum beta-lactamase from Pseudomonas aeruginosa

“…Protein molecular mass reference markers are shown on the left (sizes are in kilodaltons). DISCUSSION P. aeruginosa RNL-i, isolated from the urinary tract of an infected patient, encodes two 13-lactamases: a likely cephalosporinase with a pI of 8.7 (ranking within the pI range of cephalosporinases of P. aeruginosa (38]) and a novel 13-lactamase, PER-i, with a pI of 5.4. The PER-i enzyme is an extended-spectrum cephalosporin-hydrolyzing 13-lactamase sensitive to inhibition by clavulanic acid, imipenem, and cephamycins, and its gene appears to be chromosomally encoded.…”