Activity of Telithromycin Against Multi-Drug ResistantStreptococcus pneumoniaeand Molecular Characterization of Macrolide and Tetracycline Resistance Determinants

A novel ketolide, RBx 14255, with activity against multidrug-resistant Streptococcus pneumoniae

We present here the novel ketolide RBx 14255, a semisynthetic macrolide derivative obtained by the derivatization of clarithromycin, for its in vitro and in vivo activities against sensitive and macrolide-resistant Streptococcus pneumoniae. RBx 14255 showed excellent in vitro activity against macrolide-resistant S. pneumoniae, including an in-house-generated telithromycin-resistant strain (S. pneumoniae 3390 NDDR). RBx 14255 also showed potent protein synthesis inhibition against telithromycin-resistant S. pneumoniae 3390 NDDR. The binding affinity of RBx 14255 toward ribosomes was found to be more than that for other tested drugs. The in vivo efficacy of RBx 14255 was determined in murine pulmonary infection induced by intranasal inoculation of S. pneumoniae ATCC 6303 and systemic infection with S. pneumoniae 3390 NDDR strains. The 50% effective dose (ED50) of RBx 14255 against S. pneumoniae ATCC 6303 in a murine pulmonary infection model was 3.12 mg/kg of body weight. In addition, RBx 14255 resulted in 100% survival of mice with systemic infection caused by macrolide-resistant S. pneumoniae 3390 NDDR at 100 mg/kg four times daily (QID) and at 50 mg/kg QID. RBx 14255 showed favorable pharmacokinetic properties that were comparable to those of telithromycin.

Antibiotic Usage Prior and During Hospitalization for Clinical Severe Pneumonia in Children under Five Years of Age in Rabat, Morocco

Scarce and limited epidemiological, clinical and microbiological data are available regarding pediatric respiratory tract infections in the Kingdom of Morocco, a middle-income country in Northwestern Africa. Data on antibiotic usage for such infections are also scarce. A good understanding of pre-admission and intra-hospital usage of antibiotics in children with respiratory infections linked with an adequate surveillance of the antibiotic susceptibility from circulating pathogens could help policy makers improve their recommendations on management of respiratory infections. We hereby present data on antibiotic usage prior and during admission and antibiotic susceptibility of major circulating respiratory pathogens in children under five years of age admitted to the Hôpital d’Enfants de Rabat, Morocco, with a diagnosis of clinical severe pneumonia (using World Health Organization (WHO) standardized case definitions) during a period of 14 months (November 2010–December 2011), as part of a larger hospital-based surveillance study designed to understand the etiology and epidemiology of severe pneumonia cases among children.

Cefditoren versus community-acquired respiratory pathogens: time-kill studies

The time-kill method was used to determine the bactericidal activity of cefditoren compared with oral cephalosporins, amoxicillin, amoxicillin/clavulanate and levofloxacin against a randomly selected group of strains isolated from community-acquired respiratory tract infections (CARTIs). Cefditoren was the only agent showing significant bactericidal activity (>or=3 log(10 )reduction of viable cells) within 4 h against all Streptococcus pneumoniae strains, both penicillin-susceptible (PEN S) or -resistant (PEN R), as well as against Streptococcus pyogenes, and Moraxella catarrhalis. Against beta-lactamase positive strains of Haemophilus influenzae, cefditoren was comparable to the quinolone and more active than other cephalosporins at 24 h. Cefditoren showed the best killing kinetic profiles and this observation may be important when choosing an oral third-generation cephalosporin as initial or sequential therapy.

Antibacterial activity of cefditoren against major community-acquired respiratory pathogens recently isolated in Italy

In this study we evaluated the in vitro activities of cefditoren--a broad-spectrum oral cephalosporin--and other comparator agents against 2,396 fresh isolates from community-acquired respiratory tract infections, collected from 6 clinical Italian microbiology laboratories. On penicillin-susceptible pneumococci and Streptococcus pyogenes, cefditoren demonstrated to be the most active antibiotic (MIC(90)values of 0.03 and 0.06 mg/L respectively), showing only a slight decrease in potency on penicillin-intermediate and resistant pneumococci (MIC(90)value 0.5 mg/L, 1.0 mg/L respectively). All the other comparators displayed MIC(90 )values of 4 - 8 mg/L for penicillins and of 4 to >64 mg/L for the oral cephalosporins. Cefditoren and levofloxacin were the most active against MSSA (MIC(90)0.5 mg/mL). Cefditoren displayed a uniformly potent inhibitory activity (MIC(90)of 0.03 mg/L) against all strains of Haemophilus influenzae, regardless of their ampicillin resistance (mediated or not by beta-lactamase production), while against Moraxella catarrhalis MIC(90)values were higher against beta-lactamase-positive (0.25 mg/L). Cefditoren was active also against Klebsiella pneumoniae and Escherichia coli : in this case its activity was comparable with that of levofloxacin. In conclusion, cefditoren, due to its potent activity, is a new effective therapeutic option for the treatment of respiratory tract infections.

Evaluation of the in vitro activity of tigecycline against multiresistant Gram-positive cocci containing tetracycline resistance determinants

This study was undertaken to test the in vitro activity of tigecycline against 117 clinically relevant Gram-positive pathogens and to correlate this activity with their resistance gene content. Overall, tigecycline showed a minimal inhibitory concentration (MIC) range of 0.015-0.5mg/L, able to inhibit potently all multiresistant streptococci, enterococci and MR staphylococci. Tigecycline was active against methicillin-resistant Staphylococcus aureus (MRSA) and enterococci, with MICs for 90% of the organisms (MIC(90)) of 0.25 mg/L and 0.12 mg/L, respectively, being more active than linezolid (MIC(90)=2 mg/L) and quinupristin/dalfopristin (MIC(90)=0.5 and 2-4 mg/L, respectively). Molecular characterisation of resistance determinants demonstrated the concomitant presence of different classes of genes: in particular, tet(M), erm(B) and erm(C) in Streptococcus agalactiae; tet(O), variably associated with different erm genes, in Streptococcus pyogenes; vanA, tet(M) and erm(B) in Enterococcus faecalis, and vanA and erm(B) in Enterococcus faecium. All the MRSA strains harboured SCCmec and erm genes and 50% possessed tet(K) with tet(M) genes. Staphylococcus epidermidis strains were only resistant to erythromycin. These results clearly demonstrate that tigecycline has a MIC(90) range of 0.015-0.5 mg/L both against tetracycline-susceptible and -resistant isolates carrying other resistance determinants, suggesting that this drug could play an important role in the treatment of infections caused by these multiresistant Gram-positive pathogens.

The mef(E)-carrying genetic element (mega) of Streptococcus pneumoniae: insertion sites and association with other genetic elements

The structure of the macrolide efflux genetic assembly (mega) element, its genomic locations, and its association with other resistance determinants and genetic elements were investigated in 16 Streptococcus pneumoniae isolates carrying mef(E), of which 1 isolate also carried tet(M) and 4 isolates also carried tet(M) and erm(B). All isolates carried a mega element of similar size and structure that included the operon mef(E)-msr(D) encoding the efflux transport system. Among tetracycline-susceptible isolates, six different integration sites were identified, five of which were recognized inside open reading frames present in the R6 genome. In the five isolates also carrying tet(M), mega was inserted in different genetic contexts. In one isolate, it was part of previously described Tn916-like element Tn2009. In another isolate, mega was inserted in a transposon similar to Tn2009 that also included an erm(B) element. This new composite transposon was designated Tn2010. Neither Tn2009 nor Tn2010 could be transferred by conjugation to pneumococcal or enterococcal recipients. In the three isolates in which mega was not physically linked with tet(M), this gene was associated with erm(B) in transposon Tn3872, a Tn916-like element. Homologies between the chromosomal insertions of these composite transposons and sequences of multidrug-resistant pneumococcal genomes in the databases indicate the presence of preferential sites for the integration of composite Tn916-like elements carrying multiple resistance determinants in S. pneumoniae.