Resistance to the Bacteriocin Lcn972 Deciphered by Genome Sequencing.

In view of the current threat of antibiotic resistance, new antimicrobials with low risk of resistance development are demanded. Lcn972 is a lactococcal bacteriocin that inhibits septum formation by binding to the cell wall precursor lipid II in Lactococcus. It has a species-specific spectrum of activity, making Lcn972 an attractive template to develop or improve existing antibiotics. The aim of this work was to identify mutations present in the Lcn972-resistant clone Lactococcus cremoris D1-20, previously evolved from the sensitive strain L. cremoris MG1614. Whole-genome sequencing and comparison over the reference genome L. cremoris MG1363 identified several unexpected mutations in the parental strain MG1614, likely selected during in-house propagation. In the Lcn972R clone, two previously identified mutations were mapped and confirmed. Additionally, another transposition event deregulating cellobiose uptake was identified along with three point mutations of unknown consequences for Lcn972 resistance. Two new independent evolution experiments exposing L. cremoris MG1614 to Lcn972 revealed transposition of IS981 into the LLMG_RS12285 locus as the predominant mutation selected by Lcn972. This event occurs early during evolution and was found in 100% of the evolved clones, while other mutations were not selected. Therefore, activation of LLMG_RS12285 coding for a putative anti-ECF (extra-cytoplasmic function) sigma factor is regarded as the main Lcn972 resistance factor in L. cremoris MG1614.

Mutations Selected After Exposure to Bacteriocin Lcn972 Activate a Bce-Like Bacitracin Resistance Module in Lactococcus lactis.

Resistance against antimicrobial peptides (AMPs) is often mediated by detoxification modules that rely on sensing the AMP through a BceAB-like ATP-binding cassette (ABC) transporter that subsequently activates a cognate two-component system (TCS) to mount the cell response. Here, the Lactococcus lactis ABC transporter YsaDCB is shown to constitute, together with TCS-G, a detoxification module that protects L. lactis against bacitracin and the bacteriocin Lcn972, both AMPs that inhibit cell wall biosynthesis. Initially, increased expression of ysaDCB was detected by RT-qPCR in three L. lactis resistant to Lcn972, two of which were also resistant to bacitracin. These mutants shared, among others, single-point mutations in ysaB coding for the putative Bce-like permease. These results led us to investigate the function of YsaDCB ABC-transporter and study the impact of these mutations. Expression in trans of ysaDCB in L. lactis NZ9000, a strain that lacks a functional detoxification module, enhanced resistance to both AMPs, demonstrating its role as a resistance factor in L. lactis. When the three different ysaB alleles from the mutants were expressed, all of them outperformed the wild-type transporter in resistance against Lcn972 but not against bacitracin, suggesting a distinct mode of protection against each AMP. Moreover, P ysaD promoter fusions, designed to measure the activation of the detoxification module, revealed that the ysaB mutations unlock transcriptional control by TCS-G, resulting in constitutive expression of the ysaDCB operon. Finally, deletion of ysaD was also performed to get an insight into the function of this gene. ysaD encodes a secreted peptide and is part of the ysaDCB operon. YsaD appears to modulate signal relay between the ABC transporter and TCS-G, based on the different response of the P ysaD promoter fusions when it is not present. Altogether, the results underscore the unique features of this lactococcal detoxification module that warrant further research to advance in our overall understanding of these important resistance factors in bacteria.

Trastornos musculoesqueléticos en los técnicos de laboratorio / Musculoskeletal Problems in Laboratory Technicians

OBJETIVO: analizar la prevalencia de síntomas musculoesqueléticos de origen laboral en los técnicos de laboratorio y su relación con los factores personales y organizacionales, así como con la falta de formación específica en riesgos ergonómicos. METODOLOGÍA: se aplica a una muestra de 460 técnicos de laboratorio, el Cuestionario Nórdico Estandarizado de Kuorinka validado en población española y una encuesta de caracterización de la muestra que contempla tanto variables personales como aspectos organizativo. Para realizar el análisis estadístico se aplicó el programa R. RESULTADOS: el 84.5% de la muestra estudiada presenta dolencias musculares, con mayor porcentaje en mujeres, siendo el cuello la parte más afectada. La probabilidad de sufrir molestias se multiplica por ocho en personas mayores de 46 años y las variables que se asociaron significativamente fueron: el sexo, el nivel de educación, la formación específica en riesgos ergonómicos y la antigüedad en el puesto de trabajo. Las principales causas asociadas fueron: posturas forzadas y movimientos repetitivos debido a tareas realizadas en campana, al deficiente diseño de alturas de planos de trabajo, al uso de micropipeta, microscopio, microtomo y ordenador. CONCLUSIONES: existe un elevado riesgo de padecer problemas músculoesqueléticos relacionados con la actividad de técnico de laboratorio. Se requieren medidas de intervención en el entorno de trabajo bajo criterios ergonómicos y se hace imprescindible implementar planes de formación de riesgos específicos, acordes a las actividades desarrolladas por estos profesionales

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Adaptive Evolution of Industrial Lactococcus lactis Under Cell Envelope Stress Provides Phenotypic Diversity.

Lactococcus lactis is widely used as a starter in the manufacture of cheese and fermented milk. Its main role is the production of lactic acid, but also contributes to the sensory attributes of cheese. Unfortunately, the diversity of suitable strains to be commercialized as dairy starters is limited. In this work, we have applied adaptive evolution under cell envelope stress (AE-CES) as means to provide evolved L. lactis strains with distinct physiological and metabolic traits. A total of seven strains, three of industrial origin and four wild nisin Z-producing L. lactis, were exposed to subinhibitory concentrations of Lcn972, a bacteriocin that triggers the cell envelope stress response in L. lactis. Stable Lcn972 resistant (Lcn972R) mutants were obtained from all of them and two mutants per strain were further characterized. Minimal inhibitory Lcn972 concentrations increased from 4- to 32-fold compared to their parental strains and the Lcn972R mutants retained similar growth parameters in broth. All the mutants acidified milk to a pH below 5.3 with the exception of one that lost the lactose plasmid during adaptation and was unable to grow in milk, and two others with slower acidification rates in milk. While in general phage susceptibility was unaltered, six mutants derived from three nisin Z producers became more sensitive to phage attack. Loss of a putative plasmid-encoded anti-phage mechanism appeared to be the reason for phage susceptibility. Otherwise, nisin production in milk was not compromised. Different inter- and intra-strain-dependent phenotypes were observed encompassing changes in cell surface hydrophobicity and in their autolytic profile with Lcn972R mutants being, generally, less autolytic. Resistance to other antimicrobials revealed cross-protection mainly to cell wall-active antimicrobials such as lysozyme, bacitracin, and vancomycin. Finally, distinct and shared non-synonymous mutations were detected in the draft genome of the Lcn972R mutants. Depending on the parental strain, mutations were found in genes involved in stress response, detoxification modules, cell envelope biogenesis and/or nucleotide metabolism. As a whole, the results emphasize the different strategies by which each strain becomes resistant to Lcn972 and supports the feasibility of AE-CES as a novel platform to introduce diversity within industrial L. lactis dairy starters.

Resistance to bacteriocin Lcn972 improves oxygen tolerance of Lactococcus lactis IPLA947 without compromising its performance as a dairy starter.

BACKGROUND: Lactococcus lactis is the main component of the mesophilic starters used in cheese manufacture. The success of milk fermentation relies on the viability and metabolic activity of the starter bacteria. Therefore, robust strains able to withstand the harsh conditions encountered during cheese manufacture and starter production are demanded. In this work, we have applied adaptive evolution under cell envelope stress imposed by the cell wall active bacteriocin Lcn972 to evolve strains with more robust phenotypes. RESULTS: Consecutive exposure of the starter strain L. lactis IPLA947 to Lcn972 yielded a stable mutant, L. lactis R5, with enhanced survival when challenged with hydrogen peroxide. L. lactis R5 exhibited faster growth rates in aerobic fermentations in broth and was able to acidify milk to a lower pH in aerated milk cultures. The improved behavior of L. lactis R5 in the presence of oxygen did not translate into a better performance in the presence of heme (i.e. respiration metabolism) or into higher survival during storage at cold temperatures or after freeze-drying compared to the wild type L. lactis IPLA947. L. lactis R5 retained the same milk acidification rate and no changes in the consumption of lactose and production of organic acids were noticed. However, the profile of volatile compounds revealed a significant increase in 3-hydroxy-2-butanone (acetoin) in curds manufactured with L. lactis R5. CONCLUSIONS: Based on our results, L. lactis R5 can be proposed as a suitable dairy starter with improved survival under oxidative stress and enhanced metabolic traits. The results support the notion that adaptive evolution under cell envelope stress might be useful to generate strain diversity within industrial L. lactis strains.

Haemodynamic effects of non-invasive ventilation in patients with obesity-hypoventilation syndrome.

BACKGROUND AND OBJECTIVE: Although it has been reported that pulmonary hypertension is more frequent in patients with obesity-hypoventilation syndrome than in patients with 'pure' obstructive sleep apnoea syndrome, little is known about the haemodynamic repercussions of this entity. The aim was to describe the haemodynamic status, as assessed by echocardiography and 6-min walk test (6MWT), of patients with a newly diagnosed, most severe form of obesity-hypoventilation syndrome, and to evaluate the impact of non-invasive ventilation in these patients. METHODS: A prospective, descriptive, and single-centre follow-up study was conducted. At baseline, patients underwent echocardiography, spirometry, static lung volume measurement, 6MWT, overnight pulse-oximetry and polygraphic recording. Changes in echocardiography and 6MWT were assessed after 6 months of non-invasive ventilation. Right ventricular overload was defined on the basis of right ventricular dilatation, hypokinesis, paradoxical septal motion and/or pulmonary hypertension. RESULTS: Thirty patients (20 women; mean age 69 ± 11) were tested. The percentage of patients with right ventricular overload did not change significantly after non-invasive ventilation (43.3-41.6%; P = 0.24). In patients with right ventricular overload at diagnosis, pulmonary artery systolic pressure decreased significantly at six months (58 ± 11 to 44 ± 12 mm Hg; P = 0.014), and mean distance on 6MWT increased from 350 ± 110 to 426 ± 78 m (P = 0.006), without significant changes in body mass index. CONCLUSIONS: Right ventricular overload is a frequent finding in patients with the most severe form of obesity-hypoventilation syndrome. Treatment with non-invasive ventilation is associated with a decrease in pulmonary artery systolic pressure at six months and an increase in the distance covered during the 6MWT.