Diverse infective and lytic machineries identified in genome analysis of tailed coliphages against broad spectrum multidrug-resistant Escherichia coli / Diversas maquinarias infecciosas y líticas identificadas en el análisis del genoma de colifagos con cola contra Escherichia coli multirresistente de amplio espectro

The emergence of multidrug-resistant (MDR) E. coli with deleterious consequences to the health of humans and animals has been attributed to the inappropriate use of antibiotics. Without effective antimicrobials, the success of modern medicine in treating infections would be at an increased risk. Bacteriophages could be used as an alternative to antibiotics for controlling the dissemination of MDR bacteria. However, before their use, the bacteriophages have to be assessed for the safety aspect. In this study, three broad host range highly virulent coliphage genomes were sequenced, characterized for infective and lytic potential, and checked for the presence of virulence and resistance genes. The genome sequencing indicated that coliphages ϕEC-S-21 and ϕEC-OE-11 belonged to Myoviridae, whereas coliphage ϕEC-S-24 belonged to the Autographiviridae family derived from the Podoviridae family. The genome size of the three coliphages ranged between 24 and 145 kb, with G + C content ranging between 37 and 51%. Coding sequences (CDS) ranged between 30 and 251 amino acids. The CDS were annotated and the proteins were categorized into different modules, viz., phage structural proteins, proteins associated with DNA replication, DNA modification, bacterial cell lysis, phage packaging, and uncharacterized proteins. The presence of tRNAs was detected only in coliphage ϕEC-OE-11. All three coliphages possessed diverse infective and lytic mechanisms, viz., lytic murein transglycosylase, peptidoglycan transglycosylase, n-acetylmuramoyl-l-alanine amidase, and putative lysozyme. Furthermore, the three coliphage genomes showed neither the presence of antibiotic resistance genes nor virulence genes, which makes them desirable candidates for use in phage therapy-based applications.(AU)

Protection of Enterococcus faecalis in mixed cultures with carbapenemase-producing Escherichia coli and Bacteroides fragilis: effect of the bacterial load

Introducción. Este estudio explora los efectos del tamaño del inóculo y el pH en la actividad de imipenem versus tigeciclina frente a E. coli, B. fragilis y E. faecalis, en cultivo individual y mixto. Métodos. Los valores de CMI/CMB (mg/L) de tigeciclina e imipenem fueron 0,12/>=16 y 4/4 para E. coli, 0,12/0,5 y >=16/>=16 para B. fragilis, y 0,12/>=16 y 2/>=16 para E. faecalis, respectivamente. Se realizaron curvas de letalidad en caldo Brucella suplementado a pH 7 o 5,8 con dos inóculos finales (≈105 o ≈107 ufc/ml) de cada aislado (cultivos individuales) y de un inóculo mixto en proporción 1:1:1. Los tubos se incubaron durante 48h a 37ºC en anaerobiosis. Las concentraciones antibióticas finales (concentraciones estimadas en colon) fueron 1,50 mg/L de tigeciclina y 26,40 mg/L de imipenem. Se usaron como control curvas de crecimiento bacteriano en medio sin antibiótico y los experimentos se realizaron por triplicado. Resultados. Imipenem mostró efecto inóculo frente a E.coli y B. fragilis, con reducciones del inóculo inicial en los experimentos realizados con inóculo estándar en contraposición a los crecimientos del inóculo inicial observados en los experimentos realizados con inóculo alto, tanto en cultivos individuales como mixtos. Frente a E. faecalis imipenem no presentó efecto inóculo en cultivos individuales, con marcadas reducciones del inóculo inicial con independencia del tamaño del mismo. Sin embargo en cultivo mixto la protección indirecta de E. faecalis por los dos aislados gramnegativos produjo un recrecimiento bacteriano. Esta protección fue dependiente del tamaño del inóculo ya que ocurrió en los experimentos con inóculo alto pero no en los realizados con inóculo estándar. Tigeciclina redujo el inóculo inicial de los tres aislados con independencia del tipo de cultivo (individual/mixto) o las condiciones experimentales (pH/tamaño del inóculo), con menores reducciones en el caso de E. faecalis tolerante a este antibiótico. Conclusión: La actividad carbapenemasa fue inóculo independiente para autoprotección y protección indirecta de E. faecalis (AU)

Introduction. This study explores effects of pH and inoculum size on imipenem versus tigecycline activity against E. coli, B. fragilis and E. faecalis, both in individual and mixed cultures. Methods. MIC/MBCs (mg/L) of tigecycline and imipenem were 0.12/>=16 and 4/4 for E. coli, 0.12/0.5 and >=16/>=16 for B. fragilis, and 0.12/>=16 and 2/>=16 for E. faecalis, respectively. Killing curves in supplemented Brucella broth were performed at pH 7 or 5.8, with two final inocula (≈105 or ≈107 cfu/ml) of each isolate (individual cultures) and with 1:1:1 mixed inocula. Tubes were 48h incubated at 37ºC in anaerobiosis. Final concentrations (estimated concentrations in colon) were 1.50 mg/L for tigecycline and 26.40 mg/L for imipenem, with antibiotic-free curves as controls. Experiments were performed in triplicate. Results. Imipenem showed inoculum effect against E.coli and B. fragilis, with reductions in initial inocula in experiments with standard inocula contrasting with increases in experiments with high inocula (both individual and mixed cultures). Against E. faecalis no inoculum effect for imipenem was observed in individual cultures, with marked reductions in initial inocula regardless inoculum size. However in mixed experiments the indirect protection of E. faecalis by the two gramnegatives resulted in bacterial regrowth. This protection was inoculum-dependant since it occurred with high but not with standard inocula. Tigecycline reduced initial inocula of the three isolates regardless culture type (individual/mixed) or experimental conditions (pH/inocula size), with lower reductions for the tolerant E. faecalis. Conclusion. Carbapenemase activity was inoculum-dependant for self-protection and indirect protection of E. faecalis (AU)