Reservoirs of coagulase negative staphylococci in preterm infants

Intravenous antibiotics in preterm infants have a negative effect upon microbiome development throughout preterm life

BACKGROUND

Intestinal dysbiosis is implicated in the origins of necrotising enterocolitis and late-onset sepsis in preterm babies. However, the effect of modulators of bacterial growth (e.g. antibiotics) upon the developing microbiome is not well-characterised. In this prospectively-recruited, retrospectively-classified, case-control study, high-throughput 16S rRNA gene sequencing was combined with contemporaneous clinical data collection, to assess the within-subject relationship between antibiotic administration and microbiome development, in comparison to preterm infants with minimal antibiotic exposure.

RESULTS

During courses of antibiotics, diversity progression fell in comparison to that seen outside periods of antibiotic use (-0.71units/week vs. + 0.63units/week, p < 0.01); Enterobacteriaceae relative abundance progression conversely rose (+ 10.6%/week vs. -8.9%/week, p < 0.01). After antibiotic cessation, diversity progression remained suppressed (+ 0.2units/week, p = 0.02).

CONCLUSIONS

Antibiotic use has an acute and longer-lasting impact on the developing preterm intestinal microbiome. This has clinical implications with regard to the contribution of antibiotic use to evolving dysbiosis, and affects the interpretation of existing microbiome studies where this effect modulator is rarely accounted for.

Non-aureus staphylococci in fecal samples of dairy cows: First report and phenotypic and genotypic characterization

The aims of this study were to determine whether non-aureus staphylococci (NAS) are present in rectal feces of healthy dairy cows, and if so, to delineate species to which they belong and to study several phenotypic and genotypic traits as a first step toward determining the potential impact of fecal shedding of NAS on bovine udder health. Fecal samples were aseptically collected from the rectum of 25 randomly selected clinically healthy dairy cows in a commercial dairy herd using an automated milking system. Fecal NAS were isolated and then identified at the species level using transfer RNA-intergenic spacer PCR and sequencing of the 16S rRNA housekeeping gene. Strain typing was performed using random amplification of polymorphic DNA (RAPD)-PCR. The antimicrobial resistance profiles, biofilm formation, and growth and inhibitory characteristics of all NAS isolates were evaluated. Half of the cows were shedding NAS, resulting in 31 NAS isolates belonging to 11 different species. The most prevalent species were Staphylococcus rostri (23%, n = 7), Staphylococcus cohnii (16%, n = 5), and Staphylococcus haemolyticus (13%, n = 4) with all Staphylococcus agnetis, Staphylococcus chromogenes, and Staph. rostri isolates belonging to the same strain according to RAPD banding patterns. Acquired antimicrobial resistance was observed in 28 of the 31 NAS isolates, mainly due to β-lactamase production. Most of the isolates (84%, n = 27) had a weak biofilm-forming potential, but only 2 contained the bap gene. The ica and aap genes were not detected in any of the isolates. In vitro growth of Staphylococcus aureus and Streptococcus dysgalactiae was inhibited by Staph. agnetis isolates, and Staph. chromogenes isolates were able to inhibit the growth of Strep. dysgalactiae and Streptococcus uberis. All fecal isolates were able to grow when oxygen and iron were limitedly available, mimicking the growth conditions in the mammary gland.

Bacterial Colonization of the Hospitalized Newborn: Competition Between Staphylococcus aureus and Staphylococcus epidermidis

BACKGROUND

In adults, Staphylococcus epidermidis and Staphylococcus aureus compete for colonization of the nasal mucosa and S. epidermidis strains that produce the Esp serine protease eradicate S. aureus nasal colonization. Whether similar phenomena are seen in newborn infants is unknown.

METHODS

Nasal swabs were obtained on admission and discharge from newborn infants (n = 90 and 83, respectively) in the neonatal intensive care unit at UC Davis Children's Hospital. Swabs were cultured for S. aureus and S. epidermidis. S. epidermidis isolates were tested for Esp expression, overall secreted protease activity and biofilm inhibition.

RESULTS

No infant had S. aureus on admission. S. epidermidis colonization was rare on admission in inborn infants (2.5%), but common in infants transferred from referring hospitals (50%). At discharge, most infants (96%) were colonized by staphylococci. S. aureus colonization was less common in infants with S. epidermidis colonization (9%) and more common in infants without S. epidermidis (77%) (relative risk of S. aureus colonization in infants colonized with S. epidermidis 0.18, 95% confidence interval: 0.089-0.34, P < 0.0001). Compared with S. epidermidis strains from infants without S. aureus, S. epidermidis from infants co-colonized with S. aureus had lower total proteolytic enzyme activity and decreased biofilm inhibition capacity, but did not have lower frequency of Esp positivity.

CONCLUSIONS

In hospitalized neonates, S. epidermidis colonization has a protective effect against S. aureus colonization. Secretion of proteases by S. epidermidis is a possible mechanism of inhibition of S. aureus colonization; however, in this cohort of neonates, the source of major protease activity is likely other than Esp.

Frequent nasopharyngeal suctioning as a risk factor associated with neonatal coagulase-negative staphylococcal colonisation and sepsis

INTRODUCTION

This case-control study aimed to determine whether catheter use was significantly associated with coagulase-negative staphylococci (CoNS) colonisation and/or sepsis in neonates.

METHODS

Weekly swabs of the nose, umbilicus, rectum, wounds, eye discharge and intravenous catheter tips (after removal) of infants admitted to the neonatal intensive care unit of Universiti Kebangsaan Malaysia Medical Centre, Malaysia, were cultured. CoNS sepsis was diagnosed if pure growth of CoNS was cultured from the peripheral blood specimen of symptomatic infants. For each infant with CoNS colonisation or sepsis, a control infant was retrospectively and randomly selected from unaffected infants in the ward. Multivariate analyses were performed to determine whether catheter use was a significant risk factor.

RESULTS

CoNS colonisation was detected in 113 (8.7%) infants. CoNS sepsis was found in 12 (10.6%) infants with CoNS colonisation and 7 (0.6%) infants without CoNS colonisation. Multivariate analysis showed that the following were significantly associated with CoNS colonisation: conjunctivitis (adjusted odds ratio [OR] 8.2, 95% confidence interval [CI] 1.9–34.8, p = 0.005); central venous catheters (adjusted OR 5.8, 95% CI 1.9–17.8, p = 0.002); and nasopharyngeal and/or oral suctioning more than twice in the 48 hours before positive culture (adjusted OR 7.3, 95% CI 3.3–16.2, p < 0.001). Exposure to frequent nasopharyngeal and/or oral suctioning (adjusted OR 20.8, 95% CI 3.5–125.3, p = 0.001) was the only significant factor associated with CoNS sepsis.

CONCLUSION

Infants requiring more than two nasopharyngeal and/or oral suctions in the previous 48 hours were found to have a higher risk of developing CoNS colonisation and sepsis.

Intestinal colonization patterns of staphylococci in preterm infants in relation to type of enteral feeding and bacteremia

OBJECTIVE

This study investigated the intestinal colonization with staphylococci in very low birth weight infants in relation to the type of enteral feeding and evaluated the intestine as potential source for staphylococcal bacteremia.

PATIENTS AND METHODS

Infants born in the Level III neonatal intensive care unit of a university hospital with a gestational age below 32 weeks and/or birth weight below 1,500 g were included in a prospective, observational study. The infants received either preterm formula or mother's own milk, with random allocation to raw or pasteurized milk. Precise viable staphylococcal counts of serial fecal specimens were examined in the first 8 weeks of life. In the case of bloodstream infection, fecal and blood isolates of staphylococci were compared by antibiotypes or pulsed-field gel electrophoresis.

RESULTS

One hundred fifty neonates, with a mean of 29 weeks of gestation and 1,260 g at birth, had 1,045 fecal samples analyzed and were found to be heavy carriers of staphylococci in the intestine with 10(6)-10(7) colony-forming units/g of feces from the first week of life. Colonization rate and patterns were not different in relation to the type of enteral feeding. In nearly 80% of 42 patients exhibiting a staphylococcal bloodstream infection, intestinal colonization retrieved a predominant strain that was different from the one recovered from the blood.

CONCLUSIONS

In very low birth weight infants, predominance of staphylococci in the gut is not related to the type of enteral feeding. An endogenous origin of staphylococcal bloodstream infection seems to play a minor role.

Genetic relatedness of coagulase-negative Staphylococci from gastrointestinal tract and blood of preterm neonates with late-onset sepsis

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the first colonizers of gastrointestinal tract (GIT) and the commonest cause of late-onset sepsis (LOS) in preterm neonates. Intravascular catheters are considered a major source of CoNS bacteremia. However, several cases of LOS remain without an identified source. To elucidate whether GIT could be a potential source of invasive strains, we aimed to assess the molecular similarity between CoNS from blood and GIT in preterm neonates with LOS.

METHODS

Altogether 22 blood and 53 GIT isolates collected from 22 neonates with LOS caused by CoNS (Staphylococcus haemolyticus in 13, Staphylococcus epidermidis in 7 and Staphylococcus hominis in 2 patients) were included. Rectal swabs were collected twice weekly from birth, but only isolates obtained before LOS were analyzed. S. epidermidis isolates were typed by multilocus variable number of tandem repeats analysis and multilocus sequence typing, S. haemolyticus by pulsed-field gel electrophoresis.

RESULTS

Eighteen of 22 neonates had the same CoNS species in GIT and bloodstream; all these isolates from them (altogether 18 blood and 28 GIT isolates) underwent typing. The genotypic similarity between bloodstream and ≥1 antecedent GIT isolates was observed in 13 of 18 patients-3 of 7 with S. epidermidis and 10 of 11 with S. haemolyticus infection. The concordant GIT isolates were collected 0-7 days before the positive blood culture.

CONCLUSIONS

The similarity between CoNS from GIT and bloodstream indicates that preterm neonates harbour invasive strains in GIT before LOS. Whether there is a causal relationship between GIT colonization and LOS remains to be elucidated in further studies.

Neonatal immune responses to coagulase-negative staphylococci

PURPOSE OF REVIEW

Coagulase-negative staphylococci have emerged as the most common nosocomial pathogen in neonatal intensive care units worldwide. Our understanding of the interactions between coagulase-negative staphylococci and the immune system is incomplete, especially in the newborn. This review summarizes current knowledge on the human immune response to coagulase-negative staphylococci, with particular emphasis on the neonatal innate immune system.

RECENT FINDINGS

There are very limited data on innate immune responses to coagulase-negative staphylococci in neonates. Levels of serum proteins, including transplacental anti-coagulase-negative staphylococci immunoglobulin and complement, correlate with gestational age, and this relative deficiency in preterm infants contributes to their suboptimal opsonization and impaired bacterial killing of coagulase-negative staphylococci. In adults, coagulase-negative staphylococci elicit significant cytokine responses in vitro, which are probably partly mediated by Toll-like receptors, including Toll-like receptor type 2, but these pathways have not been characterized in the high-risk neonatal population.

SUMMARY

The susceptibility of human preterm neonates to coagulase-negative staphylococci relates partly to the immaturity of the neonatal immune response. Strategies to reduce the burden of coagulase-negative staphylococci infections require a thorough understanding of host-pathogen interactions, particularly the engagement of coagulase-negative staphylococci by the neonatal innate immune system.

Persistent Staphylococcus capitis septicemia in a preterm infant

A preterm infant had persistent Staphylococcus capitis septicemia with 11 consecutive positive blood cultures over a period of 33 days. The clinical evidence suggested that the source of infection probably originated from the gastrointestinal tract. The combination of rifampin and linezolid treatment, together with prolonged stoppage of enteral feeding, successfully terminated the infection. Rifampin and linezolid should be considered as alternative antimicrobial agents when glycopeptides fail to eradicate Gram-positive pathogens from the host.

Mucosa or skin as source of coagulase-negative staphylococcal bacteraemia?

Nosocomial bacteraemia is associated with significant morbidity, mortality, and cost worldwide, and is most commonly caused by coagulase-negative staphylococci (CONS). Establishing the source of CONS bacteraemia is therefore important in the prevention and management of this infection. CONS infections are presumed to originate at the cutaneous sites of central venous catheters (CVCs), a belief that has led to prevention strategies that focus almost exclusively on the skin. However, mucosal colonisation by CONS is well established, suggesting that mucosal sites might be an important source of CONS bacteraemia. We review the published material that evaluates the source(s) of CONS. We included only studies that used a strict definition of CONS bacteraemia, evaluated skin and other potential sources of CONS, and studied the molecular association between CONS blood isolates and their potential sources. Three published reports fulfilled our criteria. In cancer patients with CONS or CONS bacteraemia, most of the colonising strains that had a molecular match with the strain recovered from the blood of the same patient were mucosal isolates; by contrast, no association was seen between CONS blood and skin isolates. Furthermore, in several patient populations evidence was reported of mucosal colonisation by CONS and in several reports experimental and clinical mucosal translocation of CONS with subsequent bacteraemia was documented. Together these data indicate that mucosal sites are an important source of CONS bacteraemia. Clinical strategies for the treatment of patients with a positive blood culture for CONS, the widespread use of antimicrobial-coated CVCs, and maximum barrier protection for CVC insertion should be reassessed, and strategies to decrease mucosal colonisation by CONS should be developed.

Do antimicrobial-impregnated central venous catheters prevent catheter-related bloodstream infection?

Controversy surrounds the role of central venous catheters (CVCs) impregnated with antimicrobial agents in the prevention of catheter-related bloodstream infection (CRBSI). We reviewed the current literature to evaluate the efficacy of antimicrobial-impregnated CVCs for preventing CRBSI. Eleven randomized studies published in article form were identified that included a control group that received nonimpregnated CVCs. We evaluated study methodologies, inclusion of key patient characteristics, use of clinically relevant end points, and molecular-relatedness studies. Review of these 11 trials revealed several methodological flaws, including inconsistent definitions of CRBSI, failure to account for confounding variables, suboptimal statistical and epidemiological methods, and rare use of clinically relevant end points. This review also failed to demonstrate any significant clinical benefit associated with the use of antimicrobial-impregnated CVCs for the purpose of reducing CRBSI or improving patient outcomes. More rigorous studies are required to support or refute the hypothesis that antimicrobial-impregnated CVCs reduce the rate of or prevent CRBSI.

Infection rates in surgical neonates and infants receiving parenteral nutrition: a five-year prospective study

We performed a prospective, observational, cohort study on 208 surgical neonates and infants between 1992 and 1997. Surveillance cultures of the oropharynx and rectum were obtained at the start of parenteral nutrition and thereafter twice weekly. Blood cultures were taken on clinical indication only. Microbial translocation was diagnosed when the micro-organisms in the blood were not distinguishable from those carried in the oropharynx and/or rectum. Liver function was monitored weekly and when septicaemia was suspected. The incidence of septicaemia was 15%. The predominant micro-organisms (86%) were the low-level pathogens, coagulase-negative staphylococci and enterococci. Potential pathogens, including aerobic Gram-negative bacilli, were responsible for the remainder. Microbial translocation was responsible for 84% of septicaemic episodes in 76% of patients. The potential pathogens caused septicaemia significantly later than coagulase-negative staphylococci, at a time when liver function was significantly more impaired. In neonates and infants receiving parenteral nutrition, septicaemia is mainly a gut-derived phenomenon and requires novel strategies for prevention.

Phenotypic and genotypic characterisation of blood isolates of coagulase-negative staphylococci in the newborn

Coagulase-negative staphylococci (CNS) are the leading cause of late-onset sepsis in newborns (>72 h of age). Our aim was to determine whether phenotypic and/or genotypic differences existed between blood isolates of CNS regarded as inducers of sepsis or as contaminants. Ninety-seven bloodisolates of CNS recovered from newborns at the neonatal intensive care unit, Orebro, Sweden in 1983-1997 were analysed. Twenty-nine of them (30%) were classified as sepsis isolates and 68 (70%) as contaminants. The most prevalent species was Staphylococcus epidermidis (n=59). Staphylococcus haemolyticus (n=16) was most often isolated from newborns with the lowest gestational age and birth weight. Biochemical typing using the Phene Plate system (PhP) and genotyping using pulsed-field gel electrophoresis (PFGE) showed that the S. epidermidis isolates regarded as inducers of sepsis (n=16) were more homogeneous than isolates considered contaminants (n=37). One main genotypic group, representing seven (44%) isolates, was identified among the sepsis isolates. Phenotypically the S. epidermidis sepsis isolates comprised three major clusters. In contrast, among the S. epidermidis contaminants, eight genotypic groups and two phenotypic clusters were identified. The dominating genotypic group among the sepsis isolates of S. epidermidis may represent strains with higher invasive capacity.

Rapid PCR detection of the methicillin resistance gene, mecA, on the hands of medical and non-medical personnel and healthy children and on surfaces in a neonatal intensive care unit

The hands of medical personnel are the chief vectors for transmission of antibiotic-resistant bacteria and probably serve as an important reservoir for antibiotic resistance genes in hospitals. In this survey we examined different reservoirs of the methicillin resistance gene, mecA, using a simplified PCR method. Samples (n = 151) were taken from the hands of medical and non-medical personnel and healthy children and from surfaces in a neonatal intensive care unit (NICU). We also performed sampling from 4 different body sites in 5 of the medical personnel. Fifteen out of 16 nurses (94%) from the ICU carried the mecA gene on their hands, whereas only 35% of the paediatric nurses were mecA-positive. Of all medical personnel, 44% carried the mecA gene on their hands. There was a significant difference (p < 0.015) between medical and non-medical personnel in terms of the carriage rate of mecA. Four samples from surfaces in a NICU--2 ventilators, 1 bench and 1 telephone--were positive for mecA. Our results are comparable with those from previous studies on reservoirs of methicillin-resistant coagulase-negative staphylococci using conventional culture techniques.

Bacterial colonization of toys in neonatal intensive care cots

OBJECTIVES

To investigate the bacteria and fungi contaminating toys in neonatal intensive care unit (NICU) cots, the colonization rates, and factors that influence them.

METHODS

A cross-sectional, longitudinal bacteriologic survey of all toys in the cots of infants in an NICU. All the toys in an infant's cot were cultured weekly for 4 weeks. Data were collected on the infant's postnatal age, the type of cot, whether humidity was added, characteristics of the toy, and any infant infections.

RESULTS

Over the 4-week period, there were 86 cultures from 34 toys of 19 infants. Bacteria were grown from 84/86 (98%): 84 of the cultures grew coagulase-negative Staphylococcus, 50 Micrococcus sp, 21 Bacillus sp, 13 methicillin-resistant Staphylococcus aureus, 12 diphtheroids, 4 group B streptococcus, 3 S aureus, 3 nonhemolytic streptococci, 3 group D streptococci, 4 alpha-hemolytic streptococci, and 2 coliforms. None grew fungi. The colonization rate did not differ with cot type, presence of humidity, size of the toy, toy fiber length, or the fluffiness score. Eight (42%) of the infants had positive blood culture results and 5/8 of the isolates (63%) were of the same type as that colonizing their corresponding toy.

IMPLICATIONS

With time, all the toys in NICU cots became colonized with bacteria. Many were potentially pathogenic. Toys may be reservoirs for potential infantile nosocomial sepsis. infant, newborn, toys, infection, neonatal intensive care.

Bactericidal activity against coagulase-negative staphylococci is impaired in infants receiving long-term parenteral nutrition

OBJECTIVE

To examine the role of total parenteral nutrition (TPN) in predisposing infants to infection caused by coagulase-negative staphylococci.

SUMMARY BACKGROUND DATA

Total parenteral nutrition is an important means of providing essential nutrients to newborn infants. However, its use has been associated with complications, particularly infection caused by coagulase-negative staphylococci. Recent data suggest that TPN may modulate immune function; however, reports directly indicating impaired immunity against coagulase-negative staphylococci during TPN are limited.

METHODS

Study 1 involved 31 infants younger than 4 months who had undergone surgery and were not receiving antibiotics; 20 were receiving TPN and 11 were receiving a normal enteral diet. An in vitro whole blood model was used to measure the host bactericidal activity against coagulase-negative staphylococci. Bacterial killing and phagocytosis were measured after a 45-minute challenge with viable coagulase-negative staphylococci. In study 2, whole blood killing and intracellular killing of coagulase-negative staphylococci were measured in five newborn infants (younger than 2 months) who were receiving long-term TPN (>10 days), five control infants receiving a normal enteral diet, and five healthy adults.

RESULTS

In study 1, infants receiving a normal enteral diet showed a high capacity to ingest and kill coagulase-negative staphylococci. In contrast, the blood of infants receiving long-term TPN showed a reduction in coagulase-negative staphylococci phagocytosis and killing. There were significant negative linear correlations between the duration of TPN and killing of coagulase-negative staphylococci and phagocytosis of coagulase-negative staphylococci. In study 2, infants receiving long-term TPN had lower whole blood killing and intracellular killing than infants receiving a normal enteral diet and healthy adult volunteers. These data seem to indicate a neutrophil dysfunction mediated by TPN in infancy.

CONCLUSIONS

Host defense mechanisms, including phagocytosis and killing of coagulase-negative staphylococci, are impaired during long-term TPN. The impaired bactericidal activity seems to be related to defective intracellular killing in neutrophils. These findings may explain the high rate of septicemia caused by coagulase-negative staphylococci in infants receiving TPN.

Evidence for nasal carriage of methicillin-resistant staphylococci colonizing intravascular devices

Nasal surveillance cultures were performed for 54 patients exhibiting >/=10(3) CFU of methicillin-resistant coagulase-negative staphylococci per ml in central venous catheter (CVC) rinse cultures over a 6-month period. Forty-two of the nasal cultures yielded growth of methicillin-resistant coagulase-negative staphylococci, and 33 of the 42 cultures contained organisms that belonged to the same species as the CVC isolates. Of the 33 same-species isolates, 20 appeared to be identical strains by pulsed-field gel electrophoresis analysis. These data suggest that measures should be taken to reduce cross-contamination between the respiratory tract and intravascular devices. However, the potential interest in detecting methicillin-resistant coagulase-negative staphylococcus carriage in high-risk patients is hampered by the lack of sensitivity of nasal surveillance cultures.

Intravenous lipid emulsions are the major determinant of coagulase-negative staphylococcal bacteremia in very low birth weight newborns

BACKGROUND

Intravenous lipid emulsions and the i.v. catheters through which they were administered were the major risk factors for nosocomial coagulase-negative staphylococcal (CONS) bacteremia among newborns in our neonatal intensive care units a decade ago. However, medical practice is changing, and these and other interventions may have different effects in the current setting.

OBJECTIVES

We determined the independent risk factors for CONS bacteremia in current very low birth weight newborns after adjusting for severity of underlying illness.

METHODS

We surveyed 590 consecutively admitted newborns with birth weights < 1500 g hospitalized in 2 neonatal intensive care units and conducted a case-control study in a sample of 74 cases of CONS bacteremia and 74 pairs of matched controls. Adjusted relative odds of bacteremia were estimated for a number of attributes and therapeutic interventions in 2 time intervals before CONS bacteremia: any time before bacteremia and the week before bacteremia.

RESULTS

Using conditional logistic regression to adjust for indicators of severity of illness, two procedures were independently associated with subsequent risk of CONS bacteremia at any time during hospitalization: i.v. lipids, odds ratio (OR) = 9.4 [95% confidence interval (CI) 1.2 to 74.2]; and any surgical or percutaneously placed central venous catheter, OR = 2.0 (95% CI 1.1 to 3.9). Considering only the week immediately preceding bacteremia, the independent risk factors were: mechanical ventilation, OR = 3.2 (95% CI 1.3 to 7.6); and short peripheral venous catheters, OR = 2.6 (95% CI 1.0 to 6.5).

CONCLUSIONS

During the last decade exposure to i.v. lipids any time during hospitalization has become an even more important risk factor for CONS bacteremia (OR = 9.4). Of these bacteremias 85% are now attributable to lipid therapy. In contrast the relative importance of intravenous catheters as independent risk factors has declined. Mechanical ventilation in the week before bacteremia has emerged as a risk factor for bacteremia.

Small volumes of enteral feedings normalise immune function in infants receiving parenteral nutrition

BACKGROUND/PURPOSE

Parenteral nutrition (PN) is associated with a risk of septicaemia. This may be caused by impairment of immune function related to PN. The authors investigated the effects of the addition of enteral feedings to PN on the immune status of human newborn infants.

METHODS

Ten surgical infants (age less than 6 months) requiring PN were studied in two consecutive phases: (A) after 31.1+/-6.0 days (mean +/- SEM) of PN with no enteral feeding (total PN); and (B) after 4.7+/-1.1 days from the addition of small volumes of enteral feeding to PN. Full blood count and liver function tests were not significantly different between phases A and B. A control group (n = 9) of infants receiving a normal enteral diet was also studied. Host bactericidal activity against coagulase-negative staphylococci (CNS) was measured by an in vitro whole blood model. Bacterial killing was measured after a 45-minute bacterial challenge using the Miles-Misra technique. Tumour necrosis factor-alpha (TNF-alpha) was measured by enzyme-linked immunosorbent assay (ELISA) after 2 hours of bacterial challenge.

RESULTS

The lowest level of CNS killing (37.7+/-5.2%), was observed in patients receiving total PN. This increased significantly after the addition of small enteral feeds (52.0+/-4.6%, P < .005) approaching the levels measured in controls (65.1+/-3.4%). TNF-alpha production was low during total PN (1467+/-297 pg/mL) and rose significantly after the addition of minimal enteral feeds (4,661+/-1,311 pg/mL, P < .05). The increase in CNS killing after the addition of small enteral feeds in patients on PN was significantly correlated with the duration of enteral feeding (r = 0.8, P = .006).

CONCLUSIONS

These results indicate that the introduction of small volumes of enteral feed improve the impaired killing of CNS and the abnormal cytokine response observed during total PN. This implies that stimulation of the gastrointestinal tract may modulate immune function in neonates and prevent bacterial infection.

Application of 16S rRNA gene PCR to study bowel flora of preterm infants with and without necrotizing enterocolitis

The purpose of the present study was to determine the extent to which bacteria not detected by culture contribute to the microbial flora of the bowel of preterm infants with and without neonatal necrotizing enterocolitis (NEC). Fecal samples from 32 preterm infants in special care baby units including samples from 10 infants with NEC were examined by culture and PCR amplification of the 16S rRNA gene (rDNA). The 16S rDNA V3 region was amplified with eubacterial primers, and the amplification products derived from the fecal sample DNA were compared with the products from individual cultured isolates by PCR and denaturing gradient gel electrophoresis (PCR-DGGE), allowing the DNA from uncultured bacteria to be identified. For the 22 infants without NEC weekly samples were examined for a mean of 5.3 postnatal weeks. The total number of types detected by culture combined with PCR-DGGE was 10.1 per infant, of which PCR-DGGE contributed 10.4% of the types identified. Additional types detected by PCR-DGGE were found in 14 (63.6%) of the 22 infants. The majority of the sequences associated with uncultured bacteria showed > 90% 16S rDNA sequence identity with sequences from culturable human enteric flora, and all were found in single infants with the exception of sequences indistinguishable by DGGE from seven infants. These sequences showed > 90% sequence identity with the 16S rDNA of Streptococcus salivarius and may have been derived from upper gastrointestinal or respiratory tract flora. In the present study uncultured bacteria detected by PCR-DGGE were no more frequent in fecal samples from infants with NEC than in samples from infants without NEC, although these findings do not exclude the possibility of unrecognized bacteria associated with the mucosa of the small intestine of infants with NEC.