beta-Lactamase stability and in vitro activity of oral cephalosporins against strains possessing well-characterized mechanisms of resistance

Metabolic reprogramming of the glutathione biosynthesis modulates the resistance of Salmonella Derby to ceftriaxone

Salmonella, a foodborne pathogen, has become a major public health concern because of its widespread drug resistance, including resistance to multiple drugs such as third-generation cephalosporin, ceftriaxone (CRO). However, the metabolic profile changes and associated mechanisms engendered by cephalosporin-resistant mutations remain uncharted. In this study, we have employed the LC-MS/MS metabolomics platform to determine the metabolic profiles of 138 strains of Salmonella. Our results show that metabolic profiles correspond to specific serotypes, sources, processing stages, and antibiotic resistance patterns. Notably, we observed that Salmonella Derby (S. Derby) with drug resistance to CRO has a different metabolic status with changes in glutathione biosynthesis. Specifically, glutathione oxidized (GSSG) and citrulline abundances are greatly suppressed in CRO-resistant S. Derby. Furthermore, exogenous GSSG or citrulline, but not glutathione reduced (GSH), restored the susceptibility of multidrug-resistant S. Derby to CRO. This study establishes a strategy based on functional metabolomics to manage the survival of antibiotic-resistant bacteria.

Conjugation to Enterobactin and Salmochelin S4 Enhances the Antimicrobial Activity and Selectivity of β-Lactam Antibiotics against Nontyphoidal Salmonella

The pathogen Salmonella enterica is a leading cause of infection worldwide. Nontyphoidal Salmonella (NTS) serovars typically cause inflammatory diarrhea in healthy individuals, and can cause bacteremia in immunocompromised patients, children, and the elderly. Management of NTS infection poses a challenge because antibiotic treatment prolongs fecal shedding of the pathogen and is thus not recommended for most patients. In recent years, the emergence of antibiotic resistance in NTS has also become a major issue. Thus, new therapeutic strategies to target NTS are needed. Here, we evaluated whether six siderophore-β-lactam conjugates based on enterobactin (Ent) and salmochelin S4 (digulcosylated Ent, DGE) provide antimicrobial activity against the two highly prevalent NTS serovars Typhimurium and Enteritidis by targeting the siderophore receptors FepA and/or IroN. The conjugates showed 10- to 1000-fold lower minimum inhibitory concentrations against both serovars Typhimurium and Enteritidis compared to the parent antibiotics under iron limitation and were recognized and transported by FepA and/or IroN. NTS treated with the Ent/DGE-β-lactam conjugates exhibited aberrant cellular morphologies suggesting inhibition of penicillin-binding proteins, and the conjugates selectively killed NTS in coculture with Staphylococcus aureus. Lastly, the DGE-based conjugates proved to be effective at inhibiting growth of NTS in the presence of the Ent-sequestering protein lipocalin-2. This work describes the successful use of siderophore-antibiotic conjugates against NTS and highlights the opportunity for narrowing the activity spectrum of antibiotics by using Ent and DGE to target enteric bacterial pathogens.

Enterobactin- and salmochelin-β-lactam conjugates induce cell morphologies consistent with inhibition of penicillin-binding proteins in uropathogenic Escherichia coli CFT073

The design and synthesis of narrow-spectrum antibiotics that target a specific bacterial strain, species, or group of species is a promising strategy for treating bacterial infections when the causative agent is known. In this work, we report the synthesis and evaluation of four new siderophore-β-lactam conjugates where the broad-spectrum β-lactam antibiotics cephalexin (Lex) and meropenem (Mem) are covalently attached to either enterobactin (Ent) or diglucosylated Ent (DGE) via a stable polyethylene glycol (PEG3) linker. These siderophore-β-lactam conjugates showed enhanced minimum inhibitory concentrations against Escherichia coli compared to the parent antibiotics. Uptake studies with uropathogenic E. coli CFT073 demonstrated that the DGE-β-lactams target the pathogen-associated catecholate siderophore receptor IroN. A comparative analysis of siderophore-β-lactams harboring ampicillin (Amp), Lex and Mem indicated that the DGE-Mem conjugate is advantageous because it targets IroN and exhibits low minimum inhibitory concentrations, fast time-kill kinetics, and enhanced stability to serine β-lactamases. Phase-contrast and fluorescence imaging of E. coli treated with the siderophore-β-lactam conjugates revealed cellular morphologies consistent with the inhibition of penicillin-binding proteins PBP3 (Ent/DGE-Amp/Lex) and PBP2 (Ent/DGE-Mem). Overall, this work illuminates the uptake and cell-killing activity of Ent- and DGE-β-lactam conjugates against E. coli and supports that native siderophore scaffolds provide the opportunity for narrowing the activity spectrum of antibiotics in clinical use and targeting pathogenicity.

Spectrofluorimetric determination of cefixime using terbium-danofloxacin probe

OBJECTIVES

Cefixime (Cfx), is a semi-synthetic third-generation oral cephalosporin antibiotic that is prescribed for the treatment of susceptible infections. There are some procedures for the determination of Cfx in pharmaceutical formulations and biological samples. Herein a spectrofluorimetric method was proposed for Cfx determination based on the fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx.

MATERIALS AND METHODS

Cfx was detected based on fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx with maximum excitation and emission wavelengths at 347 nm and 545 nm, respectively. The quenched fluorescence intensity of Tb(3+)- Dano system is proportional to the concentration of Cfx. The optimum conditions for the determination of Cfx were studied.

RESULTS

The maximum response was achieved under optimum conditions of [Tris buffer]= 0.008 mol/l (pH 6.5), [Tb(3+)]=1×10(-4) mol/l and [Dano]=1×10(-4) mol/l. The developed method was evaluated in terms of accuracy, precision and limit of detection. The linear concentration ranges for quantification of Cfx were 8.8×10(-8)-8.8×10(-7) mol/l and 1.1×10(-7)-8.8×10(-7) mol/l in standard and human serum samples with the detection limits (S/N=3) of 2.8×10(-8) mol/l and 3.9×10(-8) mol/l, respectively. The Cfx was determined in pharmaceutical tablets and spiked serum samples and the results were satisfactory.

CONCLUSION

This method is simple, practical and relatively interference-free for determination of Cfx in pharmaceutical tablets and serum samples.

Oral cephalosporins: current perspectives

Oral cephalosporins had been, for years, a small group of compounds belonging to the first or second-generation cephalosporins, with a limited antimicrobial spectrum. New oral first-generation cephalosporins include cefprozil and loracarbef, similar to cefadroxil and cefaclor, respectively, with activity similar to cefaclor but with pharmacokinetic improvements. Second-generation oral cephalosporins are esters of already available cephalosporins, and third-generation oral cephalosporins include a number of drugs whose activity is similar to available parenteral drugs, showing pharmacokinetic advantages and, some of them, better resistance to hydrolysis mediated by extended wide-spectrum beta-lactamases. They may be a good alternative against mild to moderate ENT infections, UTIs, STDs, lower respiratory tract and skin and soft tissue infections, mainly in the outpatient setting.

3-Aminoquinazolinediones as a New Class of Antibacterial Agents Demonstrating Excellent Antibacterial Activity Against Wild-Type and Multidrug Resistant Organisms

The 3-aminoquinzolinediones represent a new series of antibacterial agents structurally related to the fluoroquinolones. They are inhibitors of bacterial gyrase and topoisomerase IV and demonstrate clinically useful antibacterial activity against fastidious Gram-negative and Gram-positive organisms, including multidrug- and fluoroquinolone-resistant organisms. These agents also demonstrate in vivo efficacy in murine systemic infection models.

Comparison of the efficacy, safety and acceptability of cefixime and amoxicillin/clavulanate in acute otitis media

BACKGROUND

Use of a beta-lactamase stable antibiotic is called for in cases of acute otitis media (AOM) likely to be caused by beta-lactamase-producing Haemophilus influenzae or Moraxella catarrhalis. Two beta-lactamase-stable agents commonly used for empirical treatment of AOM are amoxicillin/clavulanate and cefixime.

METHODS

A multicenter, randomized clinical trial compared cefixime (CFX; 8 mg/kg once daily) with amoxicillin/clavulanate (A/C; 40 mg/kg/day in three divided doses) for the treatment of children with AOM. Three hundred thirteen children were randomly assigned to a 10-day course of either CFX (n = 158) or A/C (n = 155). Based on history, physical examinations and otoscopic and tympanometric assessments, clinical responses were evaluated as cure, improvement, failure, relapse or nonevaluable. Compliance and patient/parent acceptability were also analyzed.

RESULTS

Overall favorable clinical responses (cure plus improvement) were comparable post-therapy for the two treatments (CFX = 76%; A/C = 77%). Significant differences in response rates for both treatments were noted among different geographic regions, with the highest response rates observed in the Northeast and South. Acceptability of CFX was significantly better than that of A/C (P = 0.0001), and the adverse experience rate was lower (P = 0.001). The most frequently reported adverse experiences were diarrhea (CFX 15.2%, A/C 29.7%) and vomiting (CFX 3.2%, A/C 10.32%). Relapse rates were 26% for CFX and 29% for A/C.

CONCLUSION

This study demonstrated that CFX has comparable clinical efficacy and a better adverse events profile than A/C when used to treat AOM of childhood.

Cefixime in the treatment of patients with lower respiratory tract infections: results of US clinical trials

Community-acquired acute lower respiratory tract infections are a common cause of illness, accounting for millions of physician visits and prescriptions each year. Cefixime is an extended-spectrum oral cephalosporin with activity against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, the most commonly isolated bacterial pathogens. This review presents the results of eight US studies comparing the efficacy and safety of cefixime with those of amoxicillin, amoxicillin/clavulanate, cefaclor, cephalexin, and cefuroxime axetil in the treatment of patients with acute lower respiratory tract infections. Data for 211 cefixime-treated patients and a range of 19 to 49 patients in the comparator treatment groups were included in the efficacy analysis. Clinical success (cure or improvement) was observed in 94% of cefixime-treated patients; clinical success rates in the comparator treatment groups ranged from 97% for cefuroxime axetil and cefaclor to 79% for amoxicillin/clavulanate. At the end of treatment, the overall eradication rate in the cefixime treatment group was 92% and ranged from 76% (cefaclor) to 98% (cefuroxime axetil) in the comparator treatment groups. The percentage of persistent organisms was highest in the cefaclor (24%) and cephalexin (21%) treatment groups. With the exception of the cephalexin group (4%), the incidence of patients who reported adverse experiences was similar across treatment groups (34% to 50%). Those involving the gastrointestinal tract were by far the most common, and most adverse experiences were rated as mild or moderate in severity.

5-day cefixime therapy for bacterial pharyngitis and/or tonsillitis: comparison with 10-day penicillin V therapy. Cefixime Study Group

In an open, controlled, randomized multicenter study, 160 children suffering from pharyngitis and/or tonsillitis were treated with either 8 mg cefixime/kg body weight once daily for 5 days or 20,000 I.U. penicillin V/kg body weight t.i.d. for 10 days. One hundred fifty-one children were evaluable for clinical efficacy. In the cefixime group, 65 (86.7%) children were cured, seven (9.3%) were significantly improved, one (1.3%) relapsed and in two (2.7%) therapy failed. Of the patients treated with penicillin V, 69 (90.8%) were cured, five (6.6%) improved, one (1.3%) relapsed and in one (1.3%) therapy failed. Elimination of initial pathogens occurred in 57 (82.6%) patients treated with cefixime and in 60 (88.2%) treated with penicillin V. At 3 to 4 weeks after the end of treatment, six relapses were seen in the cefixime group and eight in the penicillin V group. Mild-to-moderate adverse events that were possible related to the medication were seen in four children treated with cefixime and in five treated with penicillin V.

Susceptibility of respiratory tract pathogens in Finland to cefixime and nine other antimicrobial agents

The in vitro activity of cefixime and 9 other orally used antimicrobial agents against 545 selected clinical respiratory tract pathogens was tested using the plate-dilution method. Of the strains tested, 144 were Haemophilus influenzae strains, 151 group A streptococci, 105 pneumococci and 145 Moraxella catarrhalis isolates. Ciprofloxacin was the most active drug, with a minimal inhibitory concentration (MIC) of < 0.06 mg/l for more than 87% of the isolates. With cefixime, a MIC of 0.06 mg/l inhibited 55% of the strains tested and a MIC of 1.0 mg/l inhibited all except one of the 545 strains. One pneumococcal strain was resistant to cefixime. Beta-lactamase producing H. influenzae and M. catarrhalis strains were clearly more susceptible to cefixime than to other oral cephalosporins (cephalexin, cefaclor, cefuroxime). However, penicillin, ampicillin and cefuroxime were more effective against beta-hemolytic streptococci and pneumococci than was cefixime. The new third generation cephalosporin, cefixime, showed markedly better in vitro activity against certain major respiratory tract pathogens than the other peroral antimicrobials commonly used against respiratory tract infections.

In vitro activity of cefpodoxime and ten other cephalosporins against gram-positive cocci, Enterobacteriaceae and Pseudomonas aeruginosa, including beta-lactamase producers

Cefpodoxime, the deesterified part of the orally available cefpodoxime proxetil, is active against most Enterobacteriaceae with MIC50 of 0.06 to 2 mg/l. Only Enterobacter cloacae and Citrobacter freundii strains show MIC50 of 4 mg/l. Coagulase negative staphylococci have a MIC50 of 2, while Staphylococcus aureus strains have a MIC of 4 mg/l. In comparison to other orally available cephalosporins cefpodoxime is slightly less active than cefixime and cefotiam against gram-negative bacteria but more active than cefuroxime, cefaclor, and cephalexin. Against staphylococci the activity of cefpodoxime is comparable to that of cefotiam and cefuroxime and superior to cefaclor and cephalexin, while cefixime does not have sufficient activity against these species. Like all cephalosporins cefpodoxime has no activity against enterococci.

[Clinical experiences with cefixime in the treatment of bacterial infections of the lower respiratory tract]

In a prospective, open clinical trial 21 patients suffering from lower respiratory tract infections were treated with the new oral cephalosporin cefixime. The antibiotic was given at a dosage of 200 mg b. i. d. for seven to eleven days. Seventeen of 18 evaluable patients were cured or distinctly improved at the end of therapy as well as two days after the end of treatment. Clinical results correlated well with the results of the lung function tests, especially with the significant decrease of resistance. At the end of therapy all initially isolated pathogens were eradicated. The tolerability of cefixime was good, only in two patients treated mild and transient side effects were noticed (1 x diarrhea, 1 x epigastric pain).

[Treatment results using cefixime for bacterial respiratory tract infections]

In a prospective open clinical trial 20 patients with the diagnosis bacterial respiratory tract infection and underlying chronic obstructive lung disease were treated for 13 to 17 days with 200 mg cefixime b. i. d. 14 of 16 evaluable patients were treated successfully. In one patient the clinical symptoms remained unchanged and in another patient cefixime treatment failed. Ten of the 16 evaluable patients showed a positive baseline culture. In nine of these patients the initially isolated pathogens could be eliminated. In one patient, in whom cefixime therapy failed, change of pathogens was noticed after the end of treatment. Four of the 20 patients treated with cefixime reported side effects (gastritis, three; fungal dermatitis, one). In the patient with fungal dermatitis cefixime therapy was stopped.