Association Between Minimum Inhibitory Concentration, Beta-lactamase Genes and Mortality for Patients Treated With Piperacillin/Tazobactam or Meropenem From the MERINO Study.

INTRODUCTION: This study aims to assess the association of piperacillin/tazobactam and meropenem minimum inhibitory concentration (MIC) and beta-lactam resistance genes with mortality in the MERINO trial. METHODS: Blood culture isolates from enrolled patients were tested by broth microdilution and whole genome sequencing at a central laboratory. Multivariate logistic regression was performed to account for confounders. Absolute risk increase for 30-day mortality between treatment groups was calculated for the primary analysis (PA) and the microbiologic assessable (MA) populations. RESULTS: In total, 320 isolates from 379 enrolled patients were available with susceptibility to piperacillin/tazobactam 94% and meropenem 100%. The piperacillin/tazobactam nonsusceptible breakpoint (MIC >16 mg/L) best predicted 30-day mortality after accounting for confounders (odds ratio 14.9, 95% confidence interval [CI] 2.8-87.2). The absolute risk increase for 30-day mortality for patients treated with piperacillin/tazobactam compared with meropenem was 9% (95% CI 3%-15%) and 8% (95% CI 2%-15%) for the original PA population and the post hoc MA populations, which reduced to 5% (95% CI -1% to 10%) after excluding strains with piperacillin/tazobactam MIC values >16 mg/L. Isolates coharboring extended spectrum ß-lactamase (ESBL) and OXA-1 genes were associated with elevated piperacillin/tazobactam MICs and the highest risk increase in 30-day mortality of 14% (95% CI 2%-28%). CONCLUSIONS: After excluding nonsusceptible strains, the 30-day mortality difference from the MERINO trial was less pronounced for piperacillin/tazobactam. Poor reliability in susceptibility testing performance for piperacillin/tazobactam and the high prevalence of OXA coharboring ESBLs suggests that meropenem remains the preferred choice for definitive treatment of ceftriaxone nonsusceptible Escherichia coli and Klebsiella.

A minimal tiling path cosmid library for functional analysis of the Pseudomonas aeruginosa PAO1 genome.

Pseudomonas aeruginosa is an important pathogenic and environmental bacterium, with the most widely studied strain being PAO1. Using the PAO1 reference cosmid library and the recently completed PAO1 genome sequence, we have mapped a minimal tiling path across the genome using a two-step strategy. First, we sequenced both ends of a set of over 500 random and previously mapped clones to create a backbone. Second, we end-sequenced a second set of cosmid clones that were identified to lie within the larger gaps using hybridization of the reference library filters with probes designed against sequences at the center of each gap. The minimal tiling path was calculated using the program Domino (http://www.bit.uq.edu.au/download/), with the overlap between adjacent clones set to 5 kb (where possible) to minimize the chance of truncating genes. This yielded a minimal tiling cosmid library (334 clones) covering 93.7% of the genome in 57 contigs. This library has reduced to a workable set the number of clones required to represent the majority of the P. aeruginosa genome and gives the precise location of each cosmid, enabling most genes of interest to be located on clones without further screening. This library should prove a useful resource to accelerate functional analysis of the P. aeruginosa genome.

Zoocin A immunity factor: a femA-like gene found in a group C streptococcus.

A 6.8-kb fragment of Streptococcus equi subsp. zooepidemicus 4881 DNA containing the zoocin A gene (zooA) was cloned in Escherichia coli and sequenced. We have identified a gene we call zoocin A immunity factor (zif), which protects the producer cell from the otherwise lethal action of its own product. Transformation of Streptococcus gordonii DL1 with zooA and zif changed its phenotypic character from a non-zoocin A producing-zoocin A sensitive cell to a zoocin A producing-zoocin A resistant cell. zif has sequence homology to femA (factor essential for methicillin resistance) and lif (lysostaphin immunity factor). No differences were observed in amino acid or amino sugar compositions of peptidoglycan purified from zoocin A sensitive vs. zoocin A immune cells.