Growth of bacteria in enteral feeding solutions.

Solutions of Clinifeed ISO, Triosorbon, Vivonex Standard (full- and half-strength) and Vivonex HN were experimentally contaminated with two strains each of Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella aerogenes, Escherichia coli and Enterobacter cloacae at concentrations of 10(2)-10(3) organisms/ml. Samples were incubated at 4, 25 or 37 degrees C and viable counts were made at 0, 4, 8 and 24 h. No increase in numbers of any of the organisms was observed in any of the feeds during 24 h at 4 degrees C. All organisms multiplied rapidly in Clinifeed ISO and in Triosorbon at 25 and 37 degrees C. There was less rapid growth in half-strength Vivonex Standard at 25 degrees C, although at 37 degrees C all strains multiplied rapidly except for the two S. aureus strains, the growth of which was inhibited in half-strength Vivonex Standard at both 25 and 37 degrees C. In full-strength Vivonex Standard at 25 degrees C, only P. aeruginosa showed any increase in numbers during 24 h, whereas P. aeruginosa, K. aerogenes and E. cloacae all multiplied at 37 degrees C. None of the test organisms multiplied in full strength Vivonex HN at any of the temperatures studied. The results of the study show that bacteria survive and may multiply even in feeds with low pH and high osmolarity, and emphasise the importance of strict hygiene during the preparation and handling of all enteral feeds.

Microbiological quality of products used in enteral feeds.

The microbiological quality of 19 commonly used nasogastric feeds and feed ingredients was determined. Thirteen of the products yielded no viable micro-organisms while six, all of which were powders containing milk or whey proteins, gave aerobic viable counts from 50-3000 organisms g-1. Possible microbial limits for enteral feeds are discussed with reference to those already suggested for special dietary products, infant formulas and non-sterile pharmaceuticals.

Assessment of the suitability of food colouring materials as indicators of bacterial contamination of enteral feeds.

The suitability of using food colouring materials in enteral feeds as indicators of bacterial contamination was examined. Experiments using Triosorbon, Clinifeed ISO or Vivonex Standard plus amaranth, carmoisine, ponceau 4R, sunset yellow FCF, tartrazine or erythrosine demonstrated that although the change in appearance of coloured feed could be linked with the presence of high numbers of bacteria in the feed, the converse was not always true.

The potential of Escherichia coli in enteral feeds to cause food poisoning: a study under simulated ward conditions.

The growth of Escherichia coli over a period of 8 h under simulated ward conditions was compared in feeding systems containing either Clinifeed ISO or Nutrient Broth. In both, counts increased from 10(2) to 10(7) ml-1. Other systems containing Clinifeed ISO were inoculated with E. coli and sampled over 24 h. At 8 and 16 h the contaminated reservoir was replaced, refilled or replaced together with the gastric drip line. When the reservoir was replaced or refilled it was always recontaminated by residual organisms. Even when the reservoir and drip line were replaced, although the contents of the reservoir were sterile, E. coli was still detected in feed collected from the end of the fine-bore tube. Experiments with varying numbers of E. coli in the inoculum demonstrated that even one organism in the reservoir could, within 16 h, multiply to a level that might be harmful, especially to compromised patients.

The effect of handling procedures on microbial contamination of enteral feeds.

Three of the most commonly used delivery systems in enteral feeding were evaluated for potential routes of contamination during assembly and delivery of feeds. Assembly of systems wearing sterile gloves gave no contamination in the feeds but all systems were contaminated when assembled either with bare unprotected hands or with hands experimentally contaminated with bacterial cells. Delivery of contamination-free feed was only possible with the use of sterile gloves.

Microbiological evaluation of four enteral feeding systems which have been deliberately subjected to faulty handling procedures.

The present study was designed to investigate the levels of contamination in four currently used 1000 mL, 'ready-to-hang', enteral feeding systems--Osmolite (Ross Ready-To-Hang), Steriflo, Dripac-flex and Easybag, when faulty handling procedures were used during assembly of the systems. The top of the nutrient container and the proximal (container) end of the pump set of each system were touched during assembly by a researcher whose hands had been deliberately contaminated with Klebsiella aerogenes. Once assembled systems were run continuously for 24 h delivering 1000 mL of feed. Feed samples for microbiological analysis were taken from the distal (patient) end of the feeding tube at 0 h and 24 h and from the feed remaining in the nutrient container at the end of administration (24 h). Five systems of each type were run. Five controls were also run for each type of system, where all procedures were carried out wearing sterile gloves. Eighty-seven percent of feed samples collected from the Osmolite systems and 80% of those from the Steriflo systems were found to contain K. aerogenes, with 13% of feed samples from both systems containing > or = 10(4) cfu/mL, a level of contamination, considered by many, as that above which feed is unacceptable for patient consumption. The percentage of feed systems containing the test organism was much lower in the Dripac-flex and Easybag systems, with K. aerogenes being detected in 27% and 13% of samples respectively. No feed samples from either of these systems contained > or = 10(4) cfu/mL. From the results it can be concluded that deviation from the manufacturers instructions when assembling enteral feeding systems can lead to bacterial contamination of these systems. The results also highlight the effect that system design, such as recessed pump set spikes and recessed nutrient container seals (both of which prevent care workers accidentally touching parts of the feeding system which may come into contact with the feed) have on reducing the number of bacteria gaining entry to the feed in the systems.

Re-use of enteral feeding tubes--a potential hazard to the patient? A study of the efficiency of a representative range of cleaning and disinfection procedures.

Some hospitals and manufacturers are now recommending that patients (particularly those on home enteral feeding) remove and re-insert their tubes on a daily basis. This study was carried out to evaluate the effectiveness of a representative range of currently used cleaning procedures in removing bacteria from the lumina of these tubes. One thousand-ml portions of feed experimentally contaminated with 10(2)-10(3) Klebsiella aerogenes ml(-1) were perfused through three types of commonly used polyurethane enteral feeding tubes for 15 h. The tubes were then cleaned by a range of methods including rinsing them with sterile water, sterile water and detergent and/or disinfection with hypochlorite solution. A further 1000-ml sterile feed was then perfused through the tubes for 15 h and it was found that residual organisms in the tubes multiplied to yield levels of 10(6)-10(9) colony-forming units (cfu) ml(-1) in the feed collected from the distal ends of the tubes after 15 h. It is concluded that none of the cleaning methods tested can be recommended as being totally effective in removing bacteria from the lumina of contaminated tubes.

The effect of handling procedures on microbial contamination of enteral feeds--a comparison of the use of sterile vs non-sterile gloves.

The use of non-sterile disposable gloves to reduce the level of microbial contamination introduced into enteral feeds during the assembly of the feeding systems was investigated. No contamination was detected in any of the feed samples collected from the systems assembled wearing non-sterile gloves. The number of microorganisms transferred to the surface of agar plates used for fingerprint cultures was reduced from an average of 43-54 colony forming units (cfu) per plate for volunteers with bare hands to less than 1 cfu when they wore non-sterile gloves. No contamination was detected on plates touched by volunteers wearing sterile gloves.

The bacteriological quality of hospital-prepared infant feeds.

Twenty-four pasteurized infant feeds, prepared in a Glasgow hospital, were examined microbiologically. All produced a satisfactory total aerobic mesophilic count of < or = 1.0 x 10(4) cfu/g (mean 6.3 x 10(1) cfu/g) within 1 h of preparation. Bacillus cereus was detected in two infant feeds immediately after preparation and one of these had a B. cereus count of 1.4 x 10(3) cfu/g exceeding the recommended safety limit of < or = 1.0 x 10(3) cfu/g. Subsequent storage over a 14 h period at 25 degrees C or greater resulted in the appearance of B. cereus in a further eight feeds, the majority of which exceeded the safety limit of 10(3) cfu/g. The microbiological quality of each infant feed depended on the type and number of organisms initially present, and on the temperature and duration of storage. Incubation of feeds at < or = 10 degrees C for 14 h did not alter the microbiological quality (P = 0.05). While Bacillus licheniformis and Bacillus subtilis were the predominant organisms isolated within 8 h of incubation (45.8 and 20.8% of feeds, respectively), additional storage resulted in the emergence of B.cereus I (25%) and II (20.8%) as dominant Bacillus spp. The addition of glucose polymers and other supplements to infant formulae did not affect the type and number of organisms present (P = 0.05). Diarrhoeal enterotoxin was detected in three of the five formulations which supported the growth of B. cereus II via the B. cereus enterotoxin reverse phase latex agglutination test BCET-RPLA system. Although the infant feeds were of similar microbiological quality (P = 0.05), the majority of Bacillus spp. isolated have been previously implicated in either foodborne illnesses and/or opportunist infections.

The effect of system design on bacterial contamination of enteral tube feeds.

The effect of recent changes in system design on the levels and incidence of bacterial contamination in enteral tube feeds was examined by comparing two different systems. Adult patients who had been identified as requiring enteral tube feeding were allocated to receive sterile, whole protein enteral feed from either 2 x 1000 mL triple foil laminated pouches (Nutrison Standard, Nutrison Pack, Nutricia Ltd, UK) attached to a Flocare 800 pack giving set or from 2 x 1000 mL rigid plastic bottles (Osmolite, Ross Ready-to-Hang, Abbott Laboratories, UK) connected to a Patrol Pump set. Samples of feed from the nutrient containers were sent for microbiological analysis each time the container was changed (12 and 24 h) and samples from the distal ends of giving sets after 24 h.Bacterial contamination was found in a significantly lower number of Nutrison Packs (14/120; 12%) as compared with Ross Ready-to-Hang containers (25/120; 21%) (Fisher's exact test, 1 tailed test, P > or = 0.05). However, both the level and frequency of contamination of the feed samples collected from the distal ends of the giving sets of both types of system were similar to each other but higher than those from the nutrient containers (57/120 contaminated giving sets as compared with 39/240 nutrient containers; P > or = 0.00001). On 32/120 patient days only the giving set samples were contaminated. The results highlight the important role that improvements in system design, such as the use of recessed spikes on giving sets have in reducing the risk of bacterial contamination of enteral tube feeds introduced due to faulty handling procedures, and further implicate retrograde spread of the patients' own flora as a source of contamination in the giving set.

A comparative study of the numbers of bacteria present in enteral feeds prepared and administered in hospital and the home.

Levels and types of bacterial contamination were compared in enteral feeds prepared and administered in hospital or in the home. Samples of feed administered to children suffering from cystic fibrosis were collected for microbiological analysis immediately after preparation, immediately prior to use (unless administered after preparation) and at the end of feeding. No bacteria were detected in 51 (70%) of the 73 feeds sampled on the hospital ward, and in most of the remaining feeds viable counts were less than 10(1) colony-forming units (cfu) ml-1. However, only four (18%) of the feeds sampled in the home were free from bacterial growth and the remaining 18 feeds contained from 10(1) to more than 10(6) cfu ml-1. Bacteria isolated from feeds sampled both in hospital and the home, included Staphylococcus spp., Bacillus spp., viridans and faecal streptococci, Klebsiella spp. and Enterobacter spp. Enterobacter cloacae was isolated from 11 of the 73 hospital feeds and four of the 22 home feeds. Staphylococcus aureus was isolated from five of the home feeds but from none of the hospital feeds. The higher incidence and numbers of bacteria found in home enteral feeds indicate that further, more detailed studies need to be carried out to find the sources and routes of this contamination and devise methods to minimize the problem.

Scanning electron microscopy of the internal wall topography of enteral feeding tubes.

A range of commercially available naso-gastric and naso-enteric tubes was examined by scanning electron microscopy (S.E.M.). Surface irregularities in which micro-organisms could become trapped were observed on the internal walls of all the samples. Fine bore tubes which had been perfused for 8 h with a milk based feed experimentally contaminated with Staphylococcus aureus showed patches of residual feed and S. aureus cells on their interior surfaces. The potential hazards of entrapment and/or attachment of micro-organisms to the interior walls of these tubes are discussed.

Decanting--a source of contamination of enteral feeds?

The techniques of opening and decanting ready-to-use enteral feeds packaged in bottles (crown-cap and screw-cap), cans and tetrapaks were evaluated as potential routes for the contamination of these feeds. It was found that the outsides of the feed containers, bottle openers, scissors and the experimenters' hands all acted as sources of contamination during the transfer of feeds to the nutrient container. The main source of contamination appeared to be the experimenters' hands with counts up to 10(2) cfu ml(-1) being recorded for feeds that had been decanted from screw-cap bottles, cans and tetrapaks by experimenters with either unprotected bare hands or hands experimentally contaminated with K. aerogenes. Levels of contamination and the number of samples contaminated after opening and decanting were consistently higher for cans and tetrapaks than for crown-cap or screw-cap bottles. Disinfection of feed containers followed by the use of sterile gloves and/or disinfected openers yielded bacteria-free feed from all the types of feed container studied.

Reducing bacterial contamination in enteral tube feeds.

It is well known that enteral tube feeds may become contaminated with bacteria and other microorganisms during preparation and administration and that this may lead to the development of infectious complications in patients. This article describes potential sources and routes of microbial contamination of these feeds and suggests procedures that can be implemented to reduce the risk of contamination.

Microbiological aspects of the preparation and administration of naso-gastric and naso-enteric tube feeds in hospitals--a review.

The reported instances of microbial contamination of naso-gastric and naso-enteric feeds are reviewed and the significance of contamination discussed. Possible sources of contamination are suggested and factors affecting the rate of growth of organisms in feeds and feeding systems are considered. Comparisons are made with the in-use contamination of intravenous feeds.

Cleaning and disinfection of blenders used in hospital kitchens.

The efficiency of a range of methods used to clean and disinfect blenders was compared. Blenders with metal, plastic and glass goblets were experimentally contaminated with Klebsiella aerogenes after which they were cleaned and disinfected by (a) cold water rinse, (b) detergent wash, (c) detergent wash and disinfectant soak, (d) detergent wash and boiling water rinse and (e) autoclaving. Autoclaving was the only procedure that sterilized the blenders but this could only be used for blenders with metal goblets. A detergent wash with or without chemical disinfection followed by a boiling water rinse was found to be the most effective method of cleaning and disinfecting all three types of blender.

Decanting versus sterile pre-filled nutrient containers--the microbiological risks in enteral feeding.

A simulated ward study was carried out to compare the microbiological risk of assembling and running four different enteral feeding systems for 24 h. Assembly was carried out, (i) according to manufacturers' instructions with hands either covered by disposable gloves or deliberately contaminated with a test organism, or (ii) touching both the nutrient container top and pump set connector with hands deliberately contaminated with K. aerogenes. Two of the systems were ready-to-hang types (pack and bottle), the other two required feed to be decanted from either bottles or cans. When manufacturers' instructions were followed and disposable gloves worn, organisms were only detected in feeds decanted from cans and at levels < or = 20 cfu ml(-1). However, when systems were assembled following manufacturers' instructions, but with contaminated hands, no organisms were found in either of the ready-to-hang systems but average bacterial counts in samples from systems where the feed was decanted from bottles were 1.8 x 10(3) cfu ml(-1) at 24 h and 9.3 x 10(5) cfu ml(-1) for those where feed was decanted from cans. When systems were deliberately touched with contaminated hands, no organisms were detected in any feed samples from the pack system at 24 h, while bacterial counts for the other three systems ranged from 10(1) to 10(5) cfu ml(-1). The results highlight the important role played by system design in reducing both the level and incidence of bacterial contamination of enteral tube feeds and indicate that ready-to-hang feeding systems should be the preferred choice. However, if decanting of feeds cannot be avoided then strict adherence to manufacturers' instructions and the use of disposable gloves is to be advised.

Studies on the Bacillus flora of milk and milk products.

Bacillus licheniformis and B. cereus were the most commonly isolated species of Bacillus found in milk at all stages of processing. Bacillus licheniformis was ubiquitous in the farm environment and counts in raw milks heat-treated in the laboratory were higher during the winter months, whilst B. cereus was associated with cattle feed throughout the year, and tended to be more common in raw milks during the summer months. Although B. licheniformis was usually isolated in larger numbers than B. cereus, this pattern changed after raw and pasteurized milks and reconstituted milk powders were pre-incubated at ambient temperatures, and B. cereus came to dominate the Bacillus population, reaching levels associated with enterotoxin production. Investigation of the growth kinetics of strains of both species showed that B. cereus grew faster than B. licheniformis at ambient temperatures. It is suggested that post-pasteurization contamination, which is commonly blamed for spoilage of milk and milk products by B. cereus, is not necessarily the most important source of this organism.