Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Resultados 1 - 20 de 24
Filtrar
1.
Appetite ; 192: 107121, 2024 01 01.
Artículo en Inglés | MEDLINE | ID: mdl-37972656

RESUMEN

Although concern is frequently expressed regarding the potential impact of baby food pouch use and Baby-Led Weaning (BLW) on infant health, research is scarce. Data on pouch use, BLW, energy intake, eating behaviour and body mass index (BMI) were obtained for 625 infants aged 7-10 months in the First Foods New Zealand study. Frequent pouch use was defined as ≥5 times/week during the past month. Traditional spoon-feeding (TSF), "partial" BLW and "full" BLW referred to the relative proportions of spoon-feeding versus infant self-feeding, assessed at 6 months (retrospectively) and current age. Daily energy intake was determined using two 24-h dietary recalls, and caregivers reported on a variety of eating behaviours. Researchers measured infant length and weight, and BMI z-scores were calculated (World Health Organization Child Growth Standards). In total, 28% of infants consumed food from pouches frequently. Frequent pouch use was not significantly related to BMI z-score (mean difference, 0.09; 95% CI -0.09, 0.27) or energy intake (92 kJ/day; -19, 202), but was associated with greater food responsiveness (standardised mean difference, 0.3; 95% CI 0.1, 0.4), food fussiness (0.3; 0.1, 0.4) and selective/restrictive eating (0.3; 0.2, 0.5). Compared to TSF, full BLW was associated with greater daily energy intake (BLW at 6 months: mean difference 150 kJ/day; 95% CI 4, 297; BLW at current age: 180 kJ/day; 62, 299) and with a range of eating behaviours, including greater satiety responsiveness, but not BMI z-score (6 months: 0.06 (-0.18, 0.30); current age: 0.06 (-0.13, 0.26)). In conclusion, neither feeding approach was associated with weight in infants, despite BLW being associated with greater energy intake compared with TSF. However, infants who consumed pouches frequently displayed higher food fussiness and more selective eating.


Asunto(s)
Ingestión de Energía , Fenómenos Fisiológicos Nutricionales del Lactante , Humanos , Lactante , Conducta Alimentaria , Conducta del Lactante , Alimentos Infantiles , Estudios Retrospectivos , Destete
2.
Matern Child Nutr ; : e13715, 2024 Sep 02.
Artículo en Inglés | MEDLINE | ID: mdl-39219400

RESUMEN

Optimal nutrition during infancy is critical given its influence on lifelong health and wellbeing. Two novel methods of infant complementary feeding, commercial baby food pouch use and baby-led weaning (BLW), are becoming increasingly popular worldwide. Household food insecurity may influence complementary feeding practices adopted by families, but no studies have investigated the use of BLW and baby food pouches in families experiencing food insecurity. The First Foods New Zealand study was a multicentre, observational study in infants 7.0-9.9 months of age. Households (n = 604) were classified into one of three categories of food insecurity (severely food insecure, moderately food insecure, and food secure). The use of complementary feeding practices was assessed via a self-administered questionnaire, both at the current age (mean 8.4 months) and retrospectively at 6 months. Mothers experiencing severe food insecurity had 5.70 times the odds of currently using commercial baby food pouches frequently (≥5 times/week) compared to food secure mothers (95% CI [1.54, 21.01]), reporting that pouches were 'easy to use' (89%) and made it 'easy to get fruits and vegetables in' (64%). In contrast, no evidence of a difference in the prevalence of current BLW was observed among mothers experiencing moderate food insecurity (adjusted OR; 1.28, 95% CI [0.73, 2.24]) or severe food insecurity (adjusted OR; 1.03, 95% CI [0.44, 2.43]) compared to food secure mothers. The high prevalence of frequent commercial baby food pouch use in food insecure households underscores the need for research to determine whether frequent pouch use impacts infant health.

3.
Am J Clin Nutr ; 120(1): 102-110, 2024 07.
Artículo en Inglés | MEDLINE | ID: mdl-38890036

RESUMEN

BACKGROUND: Obtaining valid estimates of nutrient intake in infants is currently limited by the difficulties of accurately measuring human milk intake. Current methods are either unsuitable for large-scale studies (i.e., the gold standard dose-to-mother stable isotope technique) or use set amounts, regardless of known variability in individual intake. OBJECTIVES: This cross-sectional study aimed to develop equations to predict human milk intake using simple measures and to carry out external validation of existing methods against the gold standard technique. METHODS: Data on human milk intake were obtained using the dose-to-mother stable isotope technique in 157 infants aged 7-10 mo and their mothers. Predictive equations were developed using questionnaire and anthropometric data (Model 1) and additional dietary data (Model 2) using lasso regression. Bland-Altman plots and intraclass correlation coefficients (ICC) also assessed the validity of existing methods (FITS and ALSPAC studies). RESULTS: The strongest univariate predictors of human milk intake in infants of 8.3 mo on average (46% female) were infant age, infant body mass index (BMI), number of breastfeeds a day, infant formula consumption, and energy from complementary food intake. Mean [95% confidence interval (CI)] differences in predicted versus measured human milk intake [mean (SD): 762 (257) mL/day] were 0.0 mL/day (-26, 26) for Model 1 (ICC 0.74) and 0.5 mL/day (-21, 22) for Model 2 (ICC 0.83). Corresponding differences were -197 mL/day (-233, -161; ICC 0.32) and -175 mL/day (-216, -134; ICC 0.41) for the methods used by FITS and ALSPAC, respectively. CONCLUSIONS: The Human Milk Intake Level Calculation provides substantial improvements on existing methods to estimate human milk intake in infants aged 7-10 mo, while utilizing data commonly collected in nutrition surveys. Although further validation in an external sample is recommended, these equations can be used to estimate human milk intake at this age with some confidence. This clinical trial was registered at http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=379436) as ACTRN12620000459921.


Asunto(s)
Fenómenos Fisiológicos Nutricionales del Lactante , Leche Humana , Humanos , Estudios Transversales , Lactante , Femenino , Masculino , Lactancia Materna , Fórmulas Infantiles , Dieta , Ingestión de Energía , Índice de Masa Corporal
4.
Nutrients ; 16(18)2024 Sep 19.
Artículo en Inglés | MEDLINE | ID: mdl-39339764

RESUMEN

OBJECTIVE: Most wet commercial infant foods are now sold in squeezable 'pouches'. While multiple expert groups have expressed concern about their use, it is not known how commonly they are consumed and whether they impact energy intake or body mass index (BMI). The objectives were to describe pouch use, and determine associations with energy intake and BMI, in infants and young children. METHODS: In this observational cross-sectional study of 933 young New Zealand children (6.0 months-3.9 years), pouch use was assessed by a questionnaire ('frequent' use was consuming food from a baby food pouch ≥5 times/week in the past month), usual energy intake using two 24-h recalls, and BMI z-score calculated using World Health Organization standards. RESULTS: The sample broadly represented the wider population (27.1% high socioeconomic deprivation, 22.5% Maori). Frequent pouch use declined with age (infants 27%, toddlers 16%, preschoolers 8%). Few children were both frequent pouch users and regularly used the nozzle (infants 5%, toddlers 13%, preschoolers 8%). Preschoolers who were frequent pouch users consumed significantly less energy than non-users (-580 kJ [-1094, -67]), but infants (115 [-35, 265]) and toddlers (-206 [-789, 378]) did not appear to have a different energy intake than non-users. There were no statistically significant differences in the BMI z-score by pouch use. CONCLUSIONS: These results do not support the strong concerns expressed about their use, particularly given the lack of evidence for higher energy intake or BMI.


Asunto(s)
Índice de Masa Corporal , Ingestión de Energía , Alimentos Infantiles , Humanos , Lactante , Masculino , Estudios Transversales , Preescolar , Femenino , Nueva Zelanda , Conducta Alimentaria , Encuestas y Cuestionarios
5.
Nutrients ; 16(10)2024 May 15.
Artículo en Inglés | MEDLINE | ID: mdl-38794732

RESUMEN

Iron deficiency in infants can impact development, and there are concerns that the use of baby food pouches and baby-led weaning may impair iron status. First Foods New Zealand (FFNZ) was an observational study of 625 New Zealand infants aged 6.9 to 10.1 months. Feeding methods were defined based on parental reports of infant feeding at "around 6 months of age": "frequent" baby food pouch use (five+ times per week) and "full baby-led weaning" (the infant primarily self-feeds). Iron status was assessed using a venepuncture blood sample. The estimated prevalence of suboptimal iron status was 23%, but neither feeding method significantly predicted body iron concentrations nor the odds of iron sufficiency after controlling for potential confounding factors including infant formula intake. Adjusted ORs for iron sufficiency were 1.50 (95% CI: 0.67-3.39) for frequent pouch users compared to non-pouch users and 0.91 (95% CI: 0.45-1.87) for baby-led weaning compared to traditional spoon-feeding. Contrary to concerns, there was no evidence that baby food pouch use or baby-led weaning, as currently practiced in New Zealand, were associated with poorer iron status in this age group. However, notable levels of suboptimal iron status, regardless of the feeding method, emphasise the ongoing need for paying attention to infant iron nutrition.


Asunto(s)
Hierro , Estado Nutricional , Destete , Humanos , Nueva Zelanda/epidemiología , Lactante , Femenino , Masculino , Hierro/sangre , Fenómenos Fisiológicos Nutricionales del Lactante , Alimentos Infantiles/análisis , Anemia Ferropénica/epidemiología , Anemia Ferropénica/sangre , Deficiencias de Hierro
6.
Food Microbiol ; 30(1): 274-80, 2012 May.
Artículo en Inglés | MEDLINE | ID: mdl-22265312

RESUMEN

The aim of this work was to investigate how production and freeze-drying conditions of Bifidobacterium animalis subsp. lactis INL1, a probiotic strain isolated from breast milk, affected its survival and resistance to simulated gastric digestion during storage in food matrices. The determination of the resistance of bifidobacteria to simulated gastric digestion was useful for unveiling differences in cell sensitivity to varying conditions during biomass production, freeze-drying and incorporation of the strain into food products. These findings show that bifidobacteria can become sensitive to technological variables (biomass production, freeze-drying and the food matrix) without this fact being evidenced by plate counts.


Asunto(s)
Bifidobacterium/metabolismo , Microbiología de Alimentos/métodos , Liofilización/métodos , Bifidobacterium/aislamiento & purificación , Reactores Biológicos , Concentración de Iones de Hidrógeno , Cinética , Microscopía Electrónica de Rastreo
7.
JMIR Res Protoc ; 10(4): e29048, 2021 Apr 21.
Artículo en Inglés | MEDLINE | ID: mdl-33881411

RESUMEN

BACKGROUND: The complementary feeding period is a time of unparalleled dietary change for every human, during which the diet changes from one that is 100% milk to one that resembles the usual diet of the wider family in less than a year. Despite this major dietary shift, we know relatively little about food and nutrient intake in infants worldwide and virtually nothing about the impact of baby food "pouches" and "baby-led weaning" (BLW), which are infant feeding approaches that are becoming increasingly popular. Pouches are squeezable containers with a plastic spout that have great appeal for parents, as evidenced by their extraordinary market share worldwide. BLW is an alternative approach to introducing solids that promotes infant self-feeding of whole foods rather than being fed purées, and is popular and widely advocated on social media. The nutritional and health impacts of these novel methods of infant feeding have not yet been determined. OBJECTIVE: The aim of the First Foods New Zealand study is to determine the iron status, growth, food and nutrient intakes, breast milk intake, eating and feeding behaviors, dental health, oral motor skills, and choking risk of New Zealand infants in general and those who are using pouches or BLW compared with those who are not. METHODS: Dietary intake (two 24-hour recalls supplemented with food photographs), iron status (hemoglobin, plasma ferritin, and soluble transferrin receptor), weight status (BMI), food pouch use and extent of BLW (questionnaire), breast milk intake (deuterium oxide "dose-to-mother" technique), eating and feeding behaviors (questionnaires and video recording of an evening meal), dental health (photographs of upper and lower teeth for counting of caries and developmental defects of enamel), oral motor skills (questionnaires), and choking risk (questionnaire) will be assessed in 625 infants aged 7.0 to 9.9 months. Propensity score matching will be used to address bias caused by differences in demographics between groups so that the results more closely represent a potential causal effect. RESULTS: This observational study has full ethical approval from the Health and Disability Ethics Committees New Zealand (19/STH/151) and was funded in May 2019 by the Health Research Council (HRC) of New Zealand (grant 19/172). Data collection commenced in July 2020, and the first results are expected to be submitted for publication in 2022. CONCLUSIONS: This large study will provide much needed data on the implications for nutritional intake and health with the use of baby food pouches and BLW in infancy. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12620000459921; http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=379436. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/29048.

8.
Benef Microbes ; 7(2): 289-97, 2016.
Artículo en Inglés | MEDLINE | ID: mdl-26689226

RESUMEN

The human intestinal microbiota plays an important role in human health. While adhesion to gastrointestinal mucosa is a prerequisite for colonisation, inhibition of adhesion is a property which may prevent or reduce infections by food borne pathogens. Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus represent the two lactic bacteria constituting the yoghurt culture. These starter cultures have been claimed to be probiotic. In our study we compared two S. thermophilus strains (i.e. lysogenic strain J34 and corresponding non-lysogenic [prophage-cured] strain J34-6), with respect to (1) their in vitro adhesion properties to HT29 cells and (2) their cell surface hydrophobicities. Effects of the two strains on inhibition of adhesion of the pathogens Listeria monocytogenes Scott A, Staphylococcus aureus 6732 and Salmonella enteritidis S489 were studied in vitro with HT29 cell cultures. Lysogenic strain J34 was shown to be considerably more effective than the non-lysogenic derivative strain J34-6.


Asunto(s)
Células Epiteliales/microbiología , Intestinos/microbiología , Listeria monocytogenes/fisiología , Profagos/fisiología , Staphylococcus aureus/fisiología , Streptococcus thermophilus/fisiología , Streptococcus thermophilus/virología , Adhesión Bacteriana , Células HT29 , Humanos , Intestinos/citología , Lisogenia , Yogur/microbiología
9.
Biochimie ; 70(3): 437-42, 1988 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-3139063

RESUMEN

Ropy Streptococcus (Lactococcus) cremoris strains isolated from a ropy Swedish sour milk ("longfil") and a ropy Finnish milk product ("Viili") were screened for their plasmid-encoded functions. Curing experiments strongly indicated that the ropy phenotype was linked to a 17-Md plasmid in the Swedish strains and to a 30 Md plasmid in the Finnish strains. Comparative restriction endonuclease analysis and DNA/DNA-hybridization studies revelated that plasmids from both strain families shared homologous DNA regions. Though be Swedish ropy strains harbored a conjugative 45-Md lactose plasmid, no cotransfer of the 17 Md plasmid occurred.


Asunto(s)
Productos Lácteos , Lactosa/metabolismo , Plásmidos , Streptococcus/genética , Animales , Bovinos , ADN Bacteriano/análisis , Fermentación , Microbiología de Alimentos , Hibridación de Ácido Nucleico , Fenotipo , Países Escandinavos y Nórdicos , Streptococcus/metabolismo
10.
FEMS Microbiol Lett ; 62(1): 69-73, 1991 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-1903350

RESUMEN

Bacteriophage P008 revealed irreversible and uniform adsorption to cell walls of L. lactis subsp. 'diacetylactis' F7/2, whereas phage P127 adsorbed reversibly to a limited number of receptor sites on cell walls of L. lactis subsp. cremoris Wg2-1. Neither extraction of lipids, cell wall- and membrane-teichoic acids nor enzymatic degradation of proteins altered the binding efficiencies of both cell wall fractions. However, phage binding was inhibited, when cell walls were subjected to lysozyme, metaperiodate, or acid treatments. This reflects that a carbohydrate component embedded in the peptidoglycan matrix is part of the phage receptors of strains F7/2 and Wg2-1.


Asunto(s)
Bacteriófagos , Lactococcus lactis/análisis , Receptores Virales/análisis , Adsorción , Pruebas de Aglutinación , Bacteriófagos/ultraestructura , Pared Celular , Cromatografía en Capa Delgada , Lactococcus lactis/ultraestructura , Lectinas , Solubilidad
11.
FEMS Microbiol Lett ; 74(2-3): 175-80, 1992 Aug 15.
Artículo en Inglés | MEDLINE | ID: mdl-1526450

RESUMEN

Eighty-six strains of S. thermophilus were examined for their plasmid content. Thirteen strains were found to contain one or two plasmids ranging in size from 2.1 to 7.4 kb. DNA-DNA hybridization analysis revealed the presence of five distinct groups of DNA homology. The complete nucleotide sequence of plasmid pST1 (Accession number X65856), which belongs to the major homology group, was determined. It has a molecular size of 2093 bp, a GC content of 35% and contains one major open reading frame of 945 bp (ORF A). The predicted protein, designated Rep A, showed sequence homology with replication proteins from a group of plasmids which are known to replicate via single-stranded DNA intermediates (ssDNA plasmids).


Asunto(s)
ADN Helicasas , Proteínas de Unión al ADN , Plásmidos/genética , Proteínas , Streptococcus/genética , Transactivadores , Secuencia de Aminoácidos , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Secuencia de Bases , Datos de Secuencia Molecular , Homología de Secuencia de Ácido Nucleico , Streptococcus/química
12.
Heart ; 79(4): 350-5, 1998 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-9616341

RESUMEN

OBJECTIVE: To compare the ability of four risk models to predict operative mortality after coronary artery bypass graft surgery (CABG) in the United Kingdom. DESIGN: Prospective study. SETTING: Two cardiothoracic centres in the United Kingdom. SUBJECTS: 1774 patients having CABG. MAIN OUTCOME MEASURES: Risk factors were recorded for all patients, along with in-hospital mortality. Predicted mortality was derived from the American Society of Thoracic Surgeons (STS) risk program, Ontario Province risk score (PACCN), Parsonnet score, and the UK Society of Cardiothoracic Surgeons risk algorithm. RESULTS: There were significant differences (p < 0.05) between the British and American populations from which the STS risk algorithm was derived with respect to most variables. The observed mortality in the British population was 3.7% (65 of 1774). The mean predicted mortality by STS score, PACCN, Parsonnet score, and UK algorithms were 1.1%, 1.6%, 4.6%, and 4.7% respectively. The overall predictive ability of the models as measured by the area under the receiver operating characteristic curve were 0.64, 0.60, 0.73, and 0.75, respectively. CONCLUSIONS: There are differences between the British and American populations for CABG and the North American algorithms are not useful for predicting mortality in the United Kingdom. The UK Society of Cardiothoracic Surgeons algorithm is the best of the models tested but still only has limited predictive ability. Great care must be exercised when using methods of this type for comparisons of units and surgeons.


Asunto(s)
Algoritmos , Puente de Arteria Coronaria/mortalidad , Enfermedad Coronaria/mortalidad , Enfermedad Coronaria/cirugía , Medición de Riesgo , Anciano , Anciano de 80 o más Años , Área Bajo la Curva , Distribución de Chi-Cuadrado , Femenino , Humanos , Masculino , Estudios Prospectivos , Factores de Riesgo , Reino Unido
13.
Physiol Behav ; 28(2): 213-7, 1982 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-7079332

RESUMEN

Electrocorticographic activity (ECoG) was recorded from the frontal cortex of unanaesthetized, lactating rabbits, and analysed in relation to the suckling behaviour of the animals. Suckling lasted 2--5 minutes each day and was always associated with a desynchronized ECoG. Milk ejection was never seen during slow wave sleep. Mild sedation of the doe caused a dose-dependent block of milk yield but did not affect her willingness to suckle and the ECoG was desynchronized during nursing. In contrast to the rat, but similar to the pig, sleep is not a prerequisite for reflex milk ejection in the rabbit. Evidence presented implies that ECoG arousal may be important for this reflex in the rabbit.


Asunto(s)
Nivel de Alerta/fisiología , Lactancia , Conducta en la Lactancia/fisiología , Animales , Corteza Cerebral/fisiología , Sincronización Cortical , Electroencefalografía , Potenciales Evocados , Femenino , Eyección Láctea , Embarazo , Conejos , Fases del Sueño/fisiología
14.
Syst Appl Microbiol ; 21(1): 28-32, 1998 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-9741108

RESUMEN

Transformation with plasmid DNA of naturally competent cells of Bacillus subtilis 168 in milk products was studied. Plasmid pMG36enpr, a broad host-range lactococcal vector carrying an erythromycin resistance and the B. subtilis npr gene encoding neutral protease, was taken up by B. subtilis cells grown in UHT chocolate milk. Under these conditions competence was optimal during transition from exponential to stationary growth phase, resulting in 9 x 10(1) transformants per 0.01 microgram DNA. No manipulation of the cells was necessary for competence to develop. When cells were pregrown in synthetic medium, higher transformation rates were obtained in assays, where the subsequent transformation experiments were either done in chocolate milk diluted 1:1 (v/v) with synthetic growth medium (up to 8 x 10(2) transformants) or in undiluted chocolate milk (1 x 10(2) transformants). The number of transformants was reduced to 4 x 10 (1), when diluted milk or flavored milks were used. No transformants were obtained in diluted yoghurt. Controls, in which both the preculturing and the transformation assays were done in synthetic medium, gave the maximum number of transformants (4 x 10(3) transformants per 0.01 microgram DNA).


Asunto(s)
Bacillus subtilis/genética , Productos Lácteos/microbiología , Plásmidos/genética , Transformación Bacteriana , Bacillus subtilis/crecimiento & desarrollo , Medios de Cultivo
18.
J Bacteriol ; 157(3): 833-8, 1984 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-6321437

RESUMEN

Thirteen bacteriocin-producing strains of group N (lactic acid) streptococci were screened for their potential to transfer this property by conjugation to Streptococcus lactis subsp. diacetylactis Bu2-60. Bacteriocin production in three strains was plasmid encoded as shown by conjugal transfer and by analysis of cured, bacteriocin-negative derivatives of the donor strains and the transconjugants. With Streptococcus cremoris strains 9B4 and 4G6 and S. lactis subsp. diacetylactis 6F7 as donors, bacteriocin-producing transconjugants were isolated with frequencies ranging from ca. 2 X 10(-2) to 2 X 10(-1) per recipient cell. Bacteriocin-producing transconjugants had acquired a 39.6-megadalton plasmid from the donor strains 9B4 and 4G6, and a 75-megadalton plasmid from the donor strain 6F7. As shown by restriction endonuclease analysis, the plasmids from strains 9B4 and 4G6 were almost identical. The plasmid from strain 6F7 yielded some additional fragments not present in the two other plasmids. In hybridization experiments any of the three plasmids strongly hybridized with each other and with some other bacteriocin but nontransmissible plasmids from other S. cremoris strains. Homology was also detected to a variety of cryptic plasmids in lactic acid streptococci.


Asunto(s)
Bacteriocinas/genética , Conjugación Genética , Lactococcus lactis/genética , Plásmidos , Streptococcus/genética , Bacteriocinas/biosíntesis , Secuencia de Bases , Enzimas de Restricción del ADN , ADN Bacteriano , Lactococcus lactis/metabolismo , Hibridación de Ácido Nucleico , Streptococcus/metabolismo , Temperatura
19.
Appl Environ Microbiol ; 59(10): 3378-84, 1993 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-16349070

RESUMEN

Direct electron microscopy of bacteriophages adsorbed to a carbon film without prior enrichment by specific host strains or concentration by physical or chemical methods was used to study the morphological diversity of natural bacteriophage assemblages in a North German lake. All samples contained a mixture of morphologically different tailed viruses, which were regarded as bacteriophages. Most of them had isometric heads and long noncontractile tails, belonging to morphotype B1 (Siphoviridae). In addition, members of morphotypes A1 (Myoviridae), B2 (Siphoviridae with elongated heads), and C1 (Podoviridae) were present in lower numbers. Only one cubic virus was detected, while no filamentous or pleomorphic phages were found. Up to 11 different phages per sample, and a total of 39 phages when all samples were considered together, could be distinguished by morphological criteria. The total number of phages was estimated to be on the order of 10/ml.

20.
Appl Environ Microbiol ; 66(7): 2951-8, 2000 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-10877791

RESUMEN

Bacteriophage lysins (Ply), or endolysins, are phage-encoded cell wall lytic enzymes which are synthesized late during virus multiplication and mediate the release of progeny virions. Bacteriophages of the pathogen Listeria monocytogenes encode endolysin enzymes which specifically hydrolyze the cross-linking peptide bridges in Listeria peptidoglycan. Ply118 is a 30.8-kDa L-alanoyl-D-glutamate peptidase and Ply511 (36.5 kDa) acts as N-acetylmuramoyl-L-alanine amidase. In order to establish dairy starter cultures with biopreservation properties against L. monocytogenes contaminations, we have introduced ply118 and ply511 into Lactococcus lactis MG1363 by using a pTRKH2 backbone. The genes were expressed under control of the lactococcal promoter P32, which proved superior to other promoters (P21 and P59) tested in this study. High levels of active enzymes were produced and accumulated in the cytoplasmic cell fractions but were not released from the cells at significant levels. Therefore, ply511 was genetically fused with the (SP)slpA nucleotide sequence encoding the Lactobacillus brevis S-layer protein signal peptide. Expression of (SP)slpA-ply511 from pSL-PL511 resulted in secretion of functional Ply511 enzyme from L. lactis cells. One clone expressed an unusually strong lytic activity, which was found to be due to a 115-bp deletion that occurred within the 3'-end coding sequence of (SP)slpA-ply511, which caused a frameshift mutation and generated a stop codon. Surprisingly, the resulting carboxy-terminal deletion of 80 amino acids in the truncated Ply511 Delta(S262-K341) mutant polypeptide strongly increased its lytic activity. Proteolytic processing of the secretion competent (SP)SlpA-Ply511 propeptide following membrane translocation had no influence on enzyme activity. Immunoblotting experiments using both cytoplasmic and supernatant fractions indicated that the enzyme was quantitatively exported from the cells and secreted into the surrounding medium, where it caused rapid lysis of L. monocytogenes cells. Moreover, transformation of pSL-PL511 delta C into L. lactis Bu2-129, a lactose-utilizing strain that can be employed for fermentation of milk, also resulted in secretion of functional enzyme and showed that the vector is compatible with the native lactococcal plasmids.


Asunto(s)
Bacteriófagos/enzimología , Clonación Molecular , Endopeptidasas/metabolismo , Lactococcus lactis/genética , Listeria monocytogenes/virología , Bacteriólisis , Bacteriófagos/genética , Membrana Celular/enzimología , Endopeptidasas/genética , Genes Reporteros , Immunoblotting , Lactococcus lactis/enzimología , Lactosa/metabolismo , Listeria monocytogenes/fisiología , Nucleasa Microcócica/genética , Regiones Promotoras Genéticas , Señales de Clasificación de Proteína
SELECCIÓN DE REFERENCIAS
Detalles de la búsqueda