Time- and dose-dependent effect of fosfomycin on suppression of infection-induced endotoxin shock in mice

Bacteriophage-antibiotic combinations against ciprofloxacin/ceftriaxone-resistant Escherichia coli in vitro and in an experimental Galleria mellonella model

Escherichia coli is the most common cause of Gram-negative prosthetic joint infections (PJIs) and ciprofloxacin is the first-line antibiofilm antibiotic. Due to the emergence of fluoroquinolone resistance, management of E. coli PJIs has become challenging and is associated with high treatment failure rates. We evaluated the efficacy of a newly isolated bacteriophage ɸWL-3 as a therapeutic agent in combination with ciprofloxacin, fosfomycin, gentamicin, meropenem or ceftriaxone against biofilm of a ciprofloxacin/ceftriaxone-resistant E. coli strain and the ATCC 25922 reference strain. ɸWL-3 was first characterised in terms of virion morphology, absorption rate, burst size and killing kinetics against both E. coli strains. The tested antibiotics presented high inhibitory concentrations (ranging from 16 to >1024 μg/mL) when tested alone against biofilms. Co-administration of ɸWL-3 with antibiotics improved the antibiotic efficacy against biofilm, especially after staggered exposure, reducing the minimum biofilm bactericidal concentration (MBBC) up to 512 times. The in vivo antimicrobial activity of ɸWL-3/fosfomycin combination against both E. coli strains was assessed in a Galleria mellonella invertebrate infection model. Treatment of infected larvae after lethal doses of E. coli resulted in enhanced survival rates when combinatorial therapy with ɸWL-3/fosfomycin was applied on E. coli ATCC 25922-infected larvae compared with monotherapy, but not for EC1-infected larvae, which we speculated could be due to higher release of endotoxins in a shorter period in EC1-infected larvae exposed to ɸWL-3. Our study provides new insights into the use of bacteriophages and antibiotics in the treatment of biofilm-associated infections caused by antibiotic-resistant bacteria.

Assessing the emergence of resistance: the absence of biological cost in vivo may compromise fosfomycin treatments for P. aeruginosa infections

BACKGROUND

Fosfomycin is a cell wall inhibitor used efficiently to treat uncomplicated urinary tract and gastrointestinal infections. A very convenient feature of fosfomycin, among others, is that although the expected frequency of resistant mutants is high, the biological cost associated with mutation impedes an effective growth rate, and bacteria cannot offset the obstacles posed by host defenses or compete with sensitive bacteria. Due to the current scarcity of new antibiotics, fosfomycin has been proposed as an alternative treatment for other infections caused by a wide variety of bacteria, particularly Pseudomonas aeruginosa. However, whether fosfomycin resistance in P. aeruginosa provides a fitness cost still remains unknown.

PRINCIPAL FINDINGS

We herein present experimental evidence to show that fosfomycin resistance cannot only emerge easily during treatment, but that it is also cost-free for P. aeruginosa. We also tested if, as has been reported for other species such as Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis, fosfomycin resistant strains are somewhat compromised in their virulence. As concerns colonization, persistence, lung damage, and lethality, we found no differences between the fosfomycin resistant mutant and its sensitive parental strain. The probability of acquisition in vitro of resistance to the combination of fosfomycin with other antibiotics (tobramycin and imipenem) has also been studied. While the combination of fosfomycin with tobramycin makes improbable the emergence of resistance to both antibiotics when administered together, the combination of fosfomycin plus imipenem does not avoid the appearance of mutants resistant to both antibiotics.

CONCLUSIONS

We have reached the conclusion that the use of fosfomycin for P. aeruginosa infections, even in combined therapy, might not be as promising as expected. This study should encourage the scientific community to assess the in vivo cost of resistance for specific antibiotic-bacterial species combinations, and therefore avoid reaching universal conclusions from single model organisms.

The small RNA chaperone Hfq is required for the virulence of Yersinia pseudotuberculosis

Bacterial small, noncoding RNAs (sRNAs) participate in the posttranscriptional regulation of gene expression, often by affecting protein translation, transcript stability, and/or protein activity. For proper function, many sRNAs rely on the chaperone Hfq, which mediates the interaction of the sRNA with its target mRNA. Recent studies have demonstrated that Hfq contributes to the pathogenesis of a number of bacterial species, suggesting that sRNAs play an essential role in the regulation of virulence. The enteric pathogen Yersinia pseudotuberculosis causes the disease yersiniosis. Here we show that Hfq is required by Y. pseudotuberculosis to cause mortality in an intragastric mouse model of infection, and a strain lacking Hfq is attenuated 1,000-fold compared to the wild type. Hfq is also required for virulence through the intraperitoneal route of infection and for persistence of the bacterium in the Peyer's patches, mesenteric lymph nodes, and spleen, suggesting a role for Hfq in systemic infection. Furthermore, the Deltahfq mutant of Y. pseudotuberculosis is hypermotile and displays increased production of a biosurfactant-like substance, reduced intracellular survival in macrophages, and decreased production of type III secretion effector proteins. Together, these data demonstrate that Hfq plays a critical role in the virulence of Y. pseudotuberculosis by participating in the regulation of multiple steps in the pathogenic process and further highlight the unique role of Hfq in the virulence of individual pathogens.

Immunomodulatory effects of fosfomycin in experimental human endotoxemia

To evaluate the effect of fosfomycin on proinflammatory cytokines, a bolus of 2 ng of bacterial lipopolysaccharide/kg of body weight was injected intravenously into healthy volunteers. After 2 h, subjects received 8 g of fosfomycin or placebo in a randomized crossover study design. The resulting concentrations of tumor necrosis factor alpha, interleukin-1beta (IL-1beta), and IL-6 expressed as protein and mRNA levels were almost identical with and without fosfomycin.

A Citrus Flavonoid Hesperidin Suppresses Infection-Induced Endotoxin Shock in Mice

Administration of a citrus flavonoid hesperidin (HES) to mice before LPS challenge significantly reduced tumor necrosis factor (TNF)-alpha production in a dose-dependent manner. Treatment of HES 3 h before intraperitoneal (i.p.) infection with 10(8) CFU Salmonella typhimurium aroA resulted in rescue from lethal shock as similar to LPS-nonresponder mice. Not only bacterial numbers in livers and spleens but also plasma LPS levels significantly decreased by pretreatment with HES. In addition, HES markedly suppressed plasma levels of TNF-alpha and high mobility group box chromosomal protein 1 (HMGB-1), decreased the number of apoptotic cells in livers and normalized the activated states of blood coagulation factors such as prothrombin time and platelet numbers caused by infection. Pretreatment of LPS with HES suppressed the chromogenic Limulus reaction.

Limitation of Polymyxin B on Suppression of Endotoxin Shock Induced by Salmonella Infection in Mice

The protective effects of an antibiotic polymyxin B (PLB), having lipopolysaccharide (LPS)-binding activity, on infection-induced endotoxin shock in mice were investigated. Infection with 10(8) colony forming units of an attenuated Salmonella typhimurium aroA strain caused lethal endotoxin shock to ddY mice. Treatment with PLB 1 h post infection (p.i.) resulted in significant reduction of mortality and bacterial numbers in livers. In addition, treatment with PLB 1 h p.i. resulted in a transient increase at the early stage and gradual decline in plasma LPS levels. Although plasma levels of sCD14 and high mobility group box chromosomal protein-1 (HMGB-1) increased according with progression of infection, increases in plasma levels of sCD14 and HMGB-1 were downregulated by treatment with PLB 1 h p.i. However, the lethal shock was not blocked by treatment with anti-CD14 monoclonal antibody at 3 h and 6 h p.i. Interestingly, administration of PLB 6 h p.i. did not show any protective activities, indicating that a time window for effective PLB action is present.