METHODS AND RESULTS: The Rhizomucor pusillus proteinase (RPP) gene was sub-cloned into a pALF expression vector. The recombinant pALF-RPP vector was then electro-transferred into Lactococcus lactis. Finally, the milk coagulation ability of recombinant L. lactis carrying a RPP gene was evaluated. Nucleotide sequencing of DNA insertion from the clone revealed that the RPP activity corresponded to an open reading frame consisting of 1218 bp coding for a 43·45 kDa RPP protein. The RPP protein assay results indicated that the highest RPP enzyme expression with 870 Soxhlet units (SU) per ml and 7914 SU/OD were obtained for cultures which were incubated at pH 5·5 and 30°C. Interestingly, milk coagulation was observed after 205 min of inoculating milk with recombinant L. lactis carrying the RPP gene.
CONCLUSION: The recombinant L. lactis carrying RPP gene has the ability to function as a starter culture for acidifying and subsequently coagulating milk by producing RPP as a milk coagulant agent.
SIGNIFICANCE AND IMPACT OF THE STUDY: Creating a recombinant starter culture bacterium that is able to coagulate milk. It is significant because the recombinant L. lactis has the ability to work as a starter culture and milk coagulation agent.
OBJECTIVES: To determine the safety of shorter feeding intervals (two hours or shorter) versus longer feeding intervals (three hours or more) and to compare the effects in terms of days taken to regain birth weight and to achieve full feeding.
SEARCH METHODS: We used the standard search strategy of Cochrane Neonatal to run comprehensive searches in CENTRAL (2020, Issue 6) and Ovid MEDLINE and Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Daily and Versions, and CINAHL on 25 June 2020. We searched clinical trials databases and the reference lists of retrieved articles for randomised controlled trials (RCTs) and quasi-RCTs.
SELECTION CRITERIA: We included RCTs and quasi-RCTs comparing short (e.g. one or two hours) versus long (e.g. three or four hours) feeding intervals in preterm infants of any birth weight, all or most of whom were less than 32 weeks' gestation. Infants could be of any postnatal age at trial entry, but eligible infants should not have received feeds before study entry, with the exception of minimal enteral feeding. We included studies of nasogastric or orogastric bolus feeding, breast milk or formula, in which the feeding interval is the intervention.
DATA COLLECTION AND ANALYSIS: We used standard methodological procedures expected by Cochrane. We used the GRADE approach to assess the certainty of evidence. Our primary outcomes were days taken to achieve full enteral feeding and days to regain birth weight. Our other outcomes were duration of hospital stay, episodes of necrotising enterocolitis (NEC) and growth during hospital stay (weight, length and head circumference).
MAIN RESULTS: We included four RCTs, involving 417 infants in the review. One study involving 350 infants is awaiting classification. All studies compared two-hourly versus three-hourly feeding interval. The risk of bias of the included studies was generally low, but all studies had high risk of performance bias due to lack of blinding of the intervention. Three studies were included in meta-analysis for the number of days taken to achieve full enteral feeding (351 participants). The mean days to achieve full feeds was between eight and 11 days. There was little or no difference in days taken to achieve full enteral feeding between two-hourly and three-hourly feeding, but this finding was of low certainty (mean difference (MD) ‒0.62, 95% confidence interval (CI) ‒1.60 to 0.36). There was low-certainty evidence that the days taken to regain birth weight may be slightly longer in infants receiving two-hourly feeding than in those receiving three-hourly feeding (MD 1.15, 95% CI 0.11 to 2.20; 3 studies, 350 participants). We are uncertain whether shorter feeding intervals have any effect on any of our secondary outcomes including the duration of hospital stay (MD ‒3.36, 95% CI ‒9.18 to 2.46; 2 studies, 207 participants; very low-certainty evidence) and the risk of NEC (typical risk ratio 1.07, 95% CI 0.54 to 2.11; 4 studies, 417 participants; low-certainty evidence). No study reported growth during hospital stay.
AUTHORS' CONCLUSIONS: The low-certainty evidence we found in this review suggests that there may be no clinically important differences between two- and three-hourly feeding intervals. There is insufficient information about potential feeding complications and in particular NEC. No studies have looked at the effect of other feeding intervals and there is no long-term data on neurodevelopment or growth.