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S A Lerner

Publications and source records attributed to S A Lerner.

At least 19 recordsLinked to original sources
PubMed1995

Characterization of fluoroquinolone-resistant mutant strains of Mycobacterium tuberculosis selected in the laboratory and isolated from patients.

To examine the mechanism of resistance to fluoroquinolones in Mycobacterium tuberculosis, we selected spontaneous fluoroquinolone-resistant mutants from a susceptible strain, H37Rv, and studied the susceptibilities of these mutants and two fluoroquinolone-resistant clinical isolates (A-382, A-564) to various fluoroquinolones and to isoniazid and rifampin. Furthermore, since mutations within the quinolone resistance-determining region of the structural gene encoding the A subunit of DNA gyrase are the most common mechanism of acquired resistance, we amplified this region by PCR and compared the nucleotide sequences of the fluoroquinolone-resistant strains with that of the susceptible strain. Fluoroquinolone-resistant mutants of H37Rv appeared at frequencies of 2 x 10(-6) to 1 x 10(-8). For three mutants selected on ciprofloxacin, ofloxacin, and sparfloxacin, respectively, and the two clinical isolates, MICs of ciprofloxacin and ofloxacin were as high as 16 micrograms/ml, and those of sparfloxacin were 4 to 8 micrograms/ml. They displayed cross-resistance to all fluoroquinolones tested but not to isoniazid or rifampin. Sparfloxacin and FQ-A (PD 127391-0002) were the most potent fluoroquinolones. All of the fluoroquinolone-resistant strains (MICs, > or = 4 micrograms/ml) had mutations in the quinolone resistance-determining region which led to substitution of the Asp residue at position 87 (Asp-87) by Asn or Ala or the substitution of Ala-83 by Val in the A subunit of DNA gyrase. Similar mutations have been noted in other bacterial species and recently in mycobacteria. The broad resistance to fluoroquinolones that arose readily by point mutation in the laboratory and apparently during inadequate therapy, as was the case in the clinical isolates, may ultimately lead to to serious restriction of the use of these drugs in the treatment of tuberculosis.

Aged↗
PubMed1995

Effects of Asp-179 mutations in TEMpUC19 beta-lactamase on susceptibility to beta-lactams.

To examine the effect of disruption of the salt bridge (between Arg-164 and Asp-179 [numbering of Ambler et al. (Biochem J. 267:269-272, 1991)]) that anchors the conserved omega-loop in class A beta-lactamases, we obtained mutant enzymes with each of the 19 other amino acid residues replacing Asp-179 in the TEM beta-lactamase encoded by pUC19 and studied the level of resistance to various beta-lactams conferred by each enzyme. All mutations of Asp-179 compromised the level of resistance to ampicillin, but most of them enhanced resistance to ceftazidime. In contrast, mutations of Asp-179 generally impaired the low levels of resistance to cefepime and aztreonam. One might expect to find clinical isolates with mutant TEM beta-lactamases with replacements of Asp-179 that express an expanded spectrum of resistance to beta-lactams including ceftazidime.

Ampicillin Resistance↗
PubMed1994

Purification and characterization of aminoglycoside 3'-phosphotransferase type IIa and kinetic comparison with a new mutant enzyme.

Aminoglycoside 3'-phosphotransferase [APH(3')s] provide an important means for high-level resistance to neomycin- and kanamycin-type aminoglycoside antibiotics. A four-step purification which affords milligram quantities of homogeneous APH(3') type IIa [APH(3')-IIa] is described. The kinetic parameters for the turnover of five substrates by the enzyme were determined, and the pH dependence and metal activation for catalysis were investigated. All five cysteines in the amino acid sequence of the enzyme exist in their reduced forms; hence, there are no disulfide bonds in the protein. Modification of the cysteine thiols by S-cyanylation showed essentially no effect on the enzymatic activity. A mutant enzyme derived from APH-3'-IIa, which possesses a conservative Glu-182-Asp point mutation and which provides diminished resistance to G418 (R. L. Yenofsky, M. Fine, and J. W. Pellow, Proc. Natl. Acad. Sci. USA 87:3435-3439, 1990), was also purified to homogeneity. Kinetic analysis of this mutant protein indicated an increase of approximately ninefold in the Km for Mg2+ ATP. Insofar as Km may approximate Ks, this finding argues for the involvement of residue 182 in the binding of Mg2+ ATP. Thus, purified APH(3')-IIa and a point mutant derivative enzyme were characterized enzymologically, and the roles of metal cofactors and the five reduced cysteine residues were probed in the wild-type enzyme.

Amino Acids↗
PubMed1994

Reversal of clavulanate resistance conferred by a Ser-244 mutant of TEM-1 beta-lactamase as a result of a second mutation (Arg to Ser at position 164) that enhances activity against ceftazidime.

The mutation of Arg-244 to Ser (Arg-244-->Ser mutation) in the TEM-1 beta-lactamase has been shown to produce resistance to inactivation by clavulanate in the mutant enzyme and resistance to ampicillin plus clavulanate in a strain of Escherichia coli producing this enzyme. The Arg-164-->Ser mutation in the TEM-1 beta-lactamase (TEM-12 enzyme) is known to enhance the activity of the enzyme against ceftazidime, resulting in resistance to the drug in a strain producing the mutant enzyme (D. A. Weber, C. C. Sanders, J. S. Bakken, and J. P. Quinn, J. Infect. Dis. 162:460-465, 1990). The doubly mutated derivative of the TEM-1 enzyme (Ser-164/Ser-244) retains the characteristics of the Ser-164 mutant enzyme, i.e., enhanced activity against ceftazidime and sensitivity to inactivation by clavulanate. It also confers the same phenotype as the Ser-164 mutant enzyme, i.e., resistance to ceftazidime and ampicillin, with reversal of this resistance in the presence of clavulanate. Thus, the Arg-164-->Ser mutation in the TEM-1 beta-lactamase suppresses the effect of the Arg-244-->Ser mutation which, by itself, reduces the sensitivity of the enzyme to inactivation by clavulanate.

Anti-Bacterial Agents↗
PubMed1992

Elucidation of the role of arginine-244 in the turnover processes of class A beta-lactamases.

The highly conserved arginine-244 of beta-lactamases has been postulated to play a role in their initial recognition of substrates, presumably through ion pairing interactions [Moews, P. C., Knox, J. R., Dideberg, O., Charlier, P., & Frère, J. M. (1990) Proteins: Struct., Funct., Genet. 7, 156-171]. However, in the Michaelis enzyme-substrate complex, no direct function has been attributed to this residue. Two mutants with substitutions of this residue in the TEM-1 beta-lactamase (lysine-244 and serine-244) have been prepared to explore whether the guanidinium group of arginine-244 plays a critical role in the turnover processes. The mutant enzymes are effective catalysts for the hydrolysis of both penicillins and cephalosporins, and the lysine mutant enzyme behaves virtually identically to the wild-type beta-lactamase. Comparative kinetic characterization of the serine mutant and wild-type enzymes attributed apparent binding energies of 1.3-2.3 kcal/mol for the penicillins and 0.3-1.0 kcal/mol for the cephalosporins to the transition-state species by arginine-244. Furthermore, it was shown that arginine-244 also contributes equally well to ground-state binding stabilization. These results were interpreted to indicate the involvement of a long hydrogen bond between arginine-244 and the substrate carboxylate, both in the ground and transition states. A reassessed picture for substrate anchoring involving interactions of the substrate carboxylate with the side chains of Ser-130, Ser-235, and Arg-244 is proposed to accommodate these observations.

Arginine↗
PubMed1992

Nephrotoxicity and ototoxicity of aztreonam versus aminoglycoside therapy in seriously ill nonneutropenic patients.

A randomized double-blind clinical trial was done of aztreonam versus aminoglycoside therapy for the empiric treatment of seriously ill nonneutropenic patients suspected of aerobic gram-negative bacterial infection. Each patient was treated for greater than or equal to 72 h with the study drug. Nephrotoxicity, defined by greater than or equal to 50% increase in baseline serum creatinine, occurred in 12 (15%) of 92 patients receiving aminoglycoside therapy and 1 (1%) of 92 patients receiving aztreonam (P less than .004). More severe nephrotoxicity, defined by greater than or equal to 100% increase in baseline serum creatinine, occurred in 6 (6.5%) of 92 patients receiving aminoglycoside therapy and in 1 of 92 receiving aztreonam (P less than .11). Patients with an elevated baseline total bilirubin level were most likely to develop nephrotoxicity. Auditory toxicity occurred in 2 (7%) of 28 evaluatable patients receiving aminoglycoside therapy and in 1 (3%) of 33 receiving aztreonam (P less than .58). One patient, who received aminoglycoside, developed vestibular toxicity. In nonneutropenic patients believed to be at increased risk for renal dysfunction, aztreonam is a less toxic alternative to aminoglycoside therapy for treatment of suspected aerobic gram-negative infection.

Aminoglycosides↗
PubMed1991

Single daily dose therapy with aminoglycosides.

Although aminoglycosides are generally infused every 8 or 12 h, recent data suggest that administration of the total daily dose every 24 h may reduce the risk of oto- and nephrotoxicity and improve efficacy. Aminoglycosides kill bacteria in a dose-dependent manner (i.e. the higher the drug level, the more rapid and complete the bactericidal effect), and exert a post-antibiotic effect (delay in regrowth after the drug concentration falls below its minimum inhibitory concentration for the strain). Moreover, survivors after initial aminoglycoside exposure are temporarily relatively insensitive to the drug, so longer interdose intervals allow recovery of greater sensitivity. Thus, dosing to achieve higher peak drug levels less often would seem desirable. In several animal models of infection, greater efficacy and less oto- and nephrotoxicity have been associated with once daily dosing of aminoglycosides. Several clinical studies have indicated the importance of high peak serum aminoglycoside levels for efficacy. Limited studies of once daily dosing of these drugs in man have suggested that it is at least as favourable as conventional dosing. Nonetheless, despite the obvious advantages of cost and convenience and the theoretical and experimental indication that once daily dosing is advantageous, we need to test this concept in the clinical situation. Large prospective, randomized, double-blind, comparative studies of once daily and conventional dosing regimens in the treatment of various infections in different patient populations are required.

Aminoglycosides↗
PubMed1991

Isolation and characterization of a species-specific DNA probe for Candida albicans.

As a model for the isolation of species-specific sequences of DNA, we isolated and characterized a species-specific DNA fragment from the Candida albicans genome. We used a series of differential colony hybridization experiments, in which a C. albicans genomic library was hybridized with genomic DNA probes from related organisms to minimize the number of potentially specific C. albicans DNA fragments to be tested. Six clones were tested by dot blot analysis, and one of them, a 1348 bp EcoRI DNA fragment, was confirmed as specific for C. albicans. This species-specific fragment could be utilized as a DNA probe for rapid, sensitive, and specific diagnosis of C. albicans DNA in clinical specimens.

Base Sequence↗
PubMed1991

Teicoplanin pharmacokinetics in intravenous drug abusers being treated for bacterial endocarditis.

The pharmacokinetics of teicoplanin were determined after multiple 30-min intravenous infusions of 10 to 15 mg/kg every 12 to 24 h in 11 intravenous drug abuse (IVDA) patients being treated for bacterial endocarditis. Multiple serum samples were obtained over 7 to 14 days. Twenty-four-hour urine collections were obtained on days 1 and 5. Serum concentration-time data were analyzed by using multiple-dose pharmacokinetic analysis (NONLIN84). Results were compared with pharmacokinetic parameters derived from previous studies in normal healthy volunteers following multiple intravenous infusions of teicoplanin (3 to 6 mg/kg/day). Total and renal clearances of teicoplanin in IVDA patients were found to be significantly greater and more highly variable than those observed previously in normal healthy volunteers. As a result, predicted steady-state trough concentrations in serum may vary up to fivefold. The mechanism responsible for this variation appears to be related to the glomerular filtration rate. In IVDA patients, individualized teicoplanin dosage may be required in the treatment of bacterial endocarditis.

Adult↗
PubMed1991

Bone-fill in guided tissue regeneration of periodontal defects.

The feasibility of regeneration and attachment of periodontal ligament and alveolar bone after surgical treatment of periodontal defects is documented in the literature. This article presents four cases of clinical and radiographic evidence showing apparent new attachment after root isolation with expanded polytetrafluoroethylene (PTFE) periodontal material, following the principle of guided tissue regeneration. Combination one-, two-, and three-wall angular bony defects of molars and incisors were exposed and root planed. A skirt of PTFE periodontal material was sutured into place and removed after 6 weeks in situ. Reductions in probed pocket depths and gain in bone-fill, as revealed by radiography, were achieved in every case. Maximum regeneration of alveolar bone was 6 mm in the two-wall angular defect of a first molar; minimum gain in bone height was 3 mm.

Aged↗
PubMed1990

Emergence of teicoplanin resistance during therapy of Staphylococcus aureus endocarditis.

Serial isolates of Staphylococcus aureus showing two- to eightfold increases in teicoplanin minimum inhibitory concentrations (MICs) and twofold or less increases in MICs of other glycopeptides were recovered from the blood of a patient with endocarditis in whom drug therapy was unsuccessful. Comparable resistance emerged during teicoplanin treatment of rabbits with endocarditis caused by the original susceptible parent strain. For the parent strain, spontaneous resistance to teicoplanin at concentrations of 2-10 times the MIC was detected in vitro at frequencies of 10(-7) to 10(-9). Similar results were found for isolates of S. aureus from other geographic locations. Resistance was constitutive and not plasmid mediated, and its acquisition was not associated with changes in cytoplasmic membrane proteins. Teicoplanin was less effective than vancomycin at inhibiting peptidoglycan synthesis in resistant strains, suggesting that there is differential interference with the access of teicoplanin to or interaction with its target(s). Alternatively, teicoplanin and vancomycin may differ in some detail(s) of their mechanism of action against S. aureus.

Adult↗
PubMed1989

Randomized, double-blind comparative study of intravenous ciprofloxacin versus ceftazidime in the treatment of serious infections.

We compared intravenously administered ciprofloxacin with ceftazidime in a randomized, double-blind study. Patients received ciprofloxacin 200 mg intravenously every 12 hours or ceftazidime 2 g intravenously every eight hours, with placebo infusions to maintain blinding. Therapy with metronidazole was added for suspected or documented intra-abdominal infection. Thirty-two of the 57 ciprofloxacin-treated patients were evaluable for determination of efficacy and had 41 bacterial isolates from 34 sites. Thirty-six of the 56 ceftazidime patients were evaluable for determination of efficacy and had 41 bacterial isolates from 38 sites. Seven of 35 bacteremic patients had no identifiable primary focus. The most commonly isolated pathogens were Escherichia coli, Streptococcus pneumoniae, Staphylococcus aureus, and Klebsiella pneumoniae. Cure rates and bacteriologic eradication rates were comparable. Nine patients did not improve. Patients with treatment failures in the ciprofloxacin group included a quadriplegic patient with relapse of urinary tract infection with bacteremia (K. pneumoniae). Another patient with bacteremia (Pseudomonas aeruginosa), pneumonia (Proteus vulgaris), and urinary tract infection (P. vulgaris, Providencia sp.) died on the first treatment day. The third patient (S. aureus and Streptococcus pneumoniae pneumonia) had a new aspiration pneumonia develop on the third day; the pneumococcus also persisted. Undrained S. pneumoniae empyema caused the fourth ciprofloxacin treatment failure, and the fifth patient had a relapse of S. aureus pneumonia with bacteremia. One ceftazidime-treated patient died of pneumococcal pneumonia on the first day. Another had persistent Staphylococcus epidermidis and Listeria bacteremia despite 48 hours of treatment. Two other patients had pneumonia (S. aureus and P. aeruginosa, respectively) and completed full courses of ceftazidime therapy without improvement. Five patients had pneumococcal bacteremia; four patients were cured: one of two patients in the ciprofloxacin group and three of three patients in the ceftazidime group. Significant increases in the number of platelets (four patients with ciprofloxacin treatment, one patient with ceftazidime treatment) and declines in the number of platelets (one patient with ciprofloxacin treatment, one patient with ceftazidime treatment) were observed. Intravenously administered ciprofloxacin is comparable with ceftazidime and is a safe and effective antibiotic for the treatment of patients with serious infections, including bacteremia.

Bacterial Infections↗
PubMed1988

Serious infections due to penicillin-resistant strains of viridans streptococci with altered penicillin-binding proteins.

We investigated the mechanism of resistance to penicillin in two penicillin-resistant clinical isolates of viridans streptococci that caused life-threatening infections in two patients not receiving chronic penicillin therapy. The first was a strain of Streptococcus intermedius that was isolated from the cerebrospinal fluid of a patient with post-neurosurgical meningitis. The second was a strain of Streptococcus mitis recovered from the bloodstream of a leukemic patient with neutropenia. Both patients failed to respond to penicillin. The mechanism of resistance in these strains was associated with diminished affinity for penicillin of their penicillin-binding proteins, as compared with those of penicillin-susceptible control strains. We conclude that penicillin-resistant viridans streptococci may cause serious infections even in patients not receiving chronic penicillin therapy, that this resistance is clinically significant and may result in failure of penicillin therapy, and that the mechanism of resistance in these strains is associated with diminished affinity of the penicillin-binding proteins for penicillin.

Adult↗
PubMed1988

Monitoring beta-lactamase activity in vivo by 13C nuclear magnetic resonance spectroscopy.

A 13C-labeled cephalothin, 7 beta-(2-thienylacetamido)-3-[acetoxy-13C1]methyl-3-cephem-4- carboxylate (compound 1), has been prepared and used to monitor beta-lactamase activities by 13C nuclear magnetic resonance spectroscopy. Time-elapsed spectral analysis of the reaction of the labeled cephalothin with the TEM-2 beta-lactamase purified from Escherichia coli revealed the progressive loss of the cephalothin acetyl resonance at 176.8 ppm and accumulation of an acetate signal at 184.3 ppm. Spectral results identical to those observed in the in vitro experiment were obtained when compound 1 was incubated with cell suspensions of E. coli JSR-O (pBR322), which contains the plasmid-encoded TEM-2 beta-lactamase, and Enterobacter cloacae strains that contain a class I chromosomal beta-lactamase. Pseudo-first-order rate constants for the lactamase-catalyzed formation of acetate from cephalothin in vivo were obtained by integration of the 13C-acetyl resonances of compound 1 during timed incubations with cell preparations. These results constitute the first demonstration of the ability to monitor beta-lactamase activity in viable cells by nuclear magnetic resonance spectroscopy.

Cephalothin↗
PubMed1988

Isolation, characterization, and cloning of a plasmid-borne gene encoding a phosphotransferase that confers high-level amikacin resistance in enteric bacilli.

Clinical isolates of Klebsiella pneumoniae and Serratia marcescens at a hospital that had used amikacin as its principal aminoglycoside for the preceding 42 months demonstrated high-level resistance to amikacin (greater than or equal to 256 micrograms/ml), kanamycin (greater than or equal to 256 micrograms/ml), gentamicin (greater than or equal to 64 micrograms/ml), netilmicin (64 micrograms/ml), and tobramycin (greater than or equal to 16 micrograms/ml). The resistant strains contained an identical 6.8-kilobase plasmid, pRPG101. Transformation of pRPG101 into Escherichia coli produced high-level resistance to amikacin (greater than or equal to 256 micrograms/ml) and kanamycin (greater than or equal to 256 micrograms/ml) but unchanged susceptibilities to gentamicin, netilmicin, and tobramycin. The clinical isolates and transformants produced a novel 3'-phosphotransferase, APH(3'), that modified amikacin and kanamycin in vitro. The location and orientation of the amk gene encoding this APH(3') were determined by analysis of insertions in pRPG101 of the defective gene fusion phage Mu dII1681 (mini-Mulac). Cells containing plasmids with insertions into amk that had the lac operon fused to the amk promoter were selected as Lac+ and amikacin susceptible. A collection of these mini-Mulac insertions was mapped by restriction enzyme analysis. This characterization of amk facilitated its cloning as a 1.8-kilobase EcoRI-Bg/I fragment of pRPG101 into the pUC19 vector. E. coli strains containing this recombinant plasmid had APH(3') activity and demonstrated high-level resistance to amikacin and kanamycin (greater than or equal to 256 micrograms/ml) but were as susceptible to gentamicin, tobramycin, and netilmicin (less than or equal to 1.0 microgram/ml) as the strains harboring the original pRPG101 plasmid.

Amikacin↗
PubMed1987

Optimal duration of treatment of urinary tract infections.

An examination of the pathogenesis of urinary tract infections leads to an understanding of the appropriateness of a broad range of treatment duration for infections with different stages of invasiveness. The ultimate short course, single-dose, is reviewed, and duration of therapy is discussed for infections in various clinical contexts and with various presentations.

Anti-Bacterial Agents↗
PubMed1986

Comparative study of ototoxicity and nephrotoxicity in patients randomly assigned to treatment with amikacin or gentamicin.

Fifty-four patients treated with gentamicin and 52 patients treated with amikacin were evaluated for nephrotoxicity and ototoxicity in a prospective, randomized, blinded comparative trail. According to our definition of nephrotoxicity (an increase in serum creatinine levels to at least 50 percent and 0.5 mg/dl above the baseline value), nephrotoxicity occurred in eight (15 percent) of the patients who were treated with gentamicin and none of the patients who were treated with amikacin (p = 0.006). Using several other definitions of nephrotoxicity, the differences in incidence between the treatment arms were not significant. Nephrotoxicity appeared to be associated with impaired baseline renal function, greater age, and the presence of bacteremia. Ototoxicity occurred in six (11 percent) of the 54 gentamicin-treated patients; auditory toxicity occurred in three patients, and toxic changes were observed in three of the 33 patients who could also be evaluated for vestibular toxicity. Similarly, ototoxicity was observed in seven (13 percent) of the 52 amikacin-treated patients; auditory toxicity occurred in four patients, and of the 34 patients who could also be evaluated for vestibular toxicity, three exhibited vestibular toxicity without auditory toxicity are one experienced vestibular effects in addition to those affecting the cochlea. We observed a modest association of ototoxicity with nephrotoxicity and with an elevated mean trough aminoglycoside serum level. The results of this study indicate that amikacin may be less nephrotoxic than gentamicin in humans; however, the broad applicability of this finding to other patient populations is uncertain.

Adolescent↗