Efficacy of colistin alone and in various combinations for the treatment of experimental osteomyelitis due to carbapenemase-producing Klebsiella pneumoniae

Objectives: In a new experimental model of carbapenemase-producing Klebsiella pneumoniae osteomyelitis we evaluated the efficacy of colistin alone and in various combinations and examined the emergence of colistin-resistant strains and cross- resistance to host defence peptides (HDPs).Methods: KPC-99YC is a clinical strain with intermediate susceptibility to meropenem (MIC = 4 mg/L) and full susceptibility to gentamicin, colistin and tigecycline (MICs = 1 mg/L) and fosfomycin (MIC = 32 mg/L). Time–kill curves were performed at 4× MIC. Osteomyelitis was induced in rabbits by tibial injection of 2 × 108 cfu. Treatment started 14 days later for 7 days in seven groups: (i) control; (ii) colistin; (iii) colistin + gentamicin; (iv) colistin + tigecycline; (v) colistin + meropenem; (vi) colistin + meropenem + gentamicin; and (vii) colistin +  fosfomycin.Results: In vitro, colistin was rapidly bactericidal, but regrowth occurred after 9 h. Combinations of colistin with meropenem or fosfomycin were synergistic, whereas combination with tigecycline was antagonistic. In vivo, colistin alone was not effective. Combinations of colistin with meropenem or fosfomycin were bactericidal (P  < 0.001) and the addition of gentamicin enhanced the efficacy of colistin + meropenem (P = 0.025). Tigecycline reduced the efficacy of colistin (P = 0.007). Colistin-resistant strains emerged in all groups except colistin + fosfomycin and two strains showed cross-resistance to HDP LL-37.Conclusions: In this model, combinations of colistin plus meropenem, with or without gentamicin, or colistin plus fosfomycin were the only effective therapies. The combination of colistin and tigecycline should be administered with caution, as it may be antagonistic in vitro and in vivo

Are animals a source of Stenotrophomonas maltophilia in humaninfections? Contributions of a nationwide molecular study

AbstractStenotrophomonas maltophilia (Sm) is an archetypal environmental opportunistic bacterium responsible for health careassociatedinfections. The role of animals in human Sm infections is unknown. This study aims to reveal the genetic andphylogenetic relationships between pathogenic strains of Sm, both animal and human, and identify a putative role for animalsas a reservoir in human infection. We phenotypically and genotypically characterized 61 Sm strains responsible for animalinfections (mainly respiratory tract infections in horses) from a French nationwide veterinary laboratory network. We testedantimicrobial susceptibility and performed MLST and genogrouping using the concatenation of the seven housekeeping genesfrom the original MLST scheme. Excluding the eight untypeable strains owing to the lack of gene amplification, only 10 out ofthe 53 strains yielded a known ST (ST5, ST39, ST162, ST8, ST27, ST126, ST131). The genogroup distribution highlighted notonly genogroups (genogroups 5 and 9) comprised exclusively of animal strains but also genogroups shared by human and animalstrains. Interestingly, these shared genogroups were primarily groups 2 and 6, which have previously been identified as the twomost frequent genogroups among human-pathogenic Sm strains, especially among respiratory pathogens. The antimicrobialsusceptibility testing underlined the presence of acquired resistance: 18.8 and 7.5% of the tested isolates were resistant to thesulfonamide-trimethoprim combination and ciprofloxacin, respectively. Animal strains of Sm shared phylogenetic traits withsome of the most successful human strains. The exact relationships between the human and animal strains, and the geneticsupport of these common traits, need to be determined

Prologue - Summary and a Survey of Issues Faced by East Asia Today

Objectives The origin of KPC is unknown. The aim of this study was to detect progenitors of KPC in silico and to functionally verify their β-lactam hydrolysis activity.Methods The sequence of KPC-2 was used to mine the NCBI protein sequence database. The best non-KPC hits were analysed by amino acid (aa) alignment and phylogenetic tree construction. Genes encoding KPC-2 homologues were expressed in Escherichia coli. The carbapenemase activities of the recombinant strains were characterized by the CarbaNP test and UV spectrophotometry and MICs of selected β-lactams were determined.Results Genes encoding the closest KPC-2 homologues were identified on the chromosome of Chromobacterium piscinae strain ND17 (CRP-1, 76% aa identity), Chromobacterium sp. C-61 (CRS-1, 70% aa identity) and Chromobacterium haemolyticum DSM19808 (CRH-1, 69% aa identity). All three Chromobacterium β-lactamases were phylogenetically more related to KPC than to other Ambler class A β-lactamases. The 27 bp region preceding the start codon of blaCRP-1 displayed high nucleotide identity to the corresponding region upstream from blaKPC (74%). Heterologous expression of blaCRP-1 and to a lesser extent of blaCRH-1 in E. coli significantly increased the MICs of meropenem and most cephalosporins. The CarbaNP test was positive for both recombinant strains, but spectrophotometric analysis confirmed higher carbapenemase activity for CRP-1-producing clones.Conclusions The recovery of three class A β-lactamases with up to 76% aa identity to KPC from distinct Chromobacterium species is highly indicative of the role played by this genus in the evolution of KPC