Direct isolation of coagulase-negative staphylococci from neonatal blood samples

How can the microbiologist help in diagnosing neonatal sepsis?

Neonatal sepsis can be classified into two subtypes depending upon whether the onset of symptoms is before 72 hours of life (early-onset neonatal sepsis—EONS) or later (late-onset neonatal sepsis—LONS). These definitions have contributed greatly to diagnosis and treatment by identifying which microorganisms are likely to be responsible for sepsis during these periods and the expected outcomes of infection. This paper focuses on the tools that microbiologist can offer to diagnose and eventually prevent neonatal sepsis. Here, we discuss the advantages and limitation of the blood culture, the actual gold standard for sepsis diagnosis. In addition, we examine the utility of molecular techniques in the diagnosis and management of neonatal sepsis.

Blood cultures in newborns and children: optimising an everyday test

Effective use of blood cultures is a key component of the management of septic newborns and children. The technical and practical aspects of paediatric practice and the heightened susceptibility of children to infection because of immunological immaturity make automatic extrapolation of adult data difficult and potentially unfounded.

Low-dose vancomycin prophylaxis reduces coagulase-negative staphylococcal bacteraemia in very low birthweight infants

Very low birthweight (VLBW) infants undergoing neonatal intensive care are at risk of infection with coagulase-negative staphylococci (CONS). This study investigates the efficacy of twice daily, 1 h infusions of vancomycin (5 mg kg) in reducing CONS infection in VLBW infants receiving parenteral nutrition. Of 72 infants in the study, 37 were randomized to vancomycin and 35 to the control group. Clinical variables and mortality were similar in both groups. In the vancomycin group, 11 infants had one or more episodes of CONS bacteraemia compared with 17 in the control group. Two babies in the treatment group had more than one episode of CONS bacteraemia, compared with nine in the control group (P = 0.02). There were 13 episodes of CONS bacteraemia in the vancomycin group compared with 29 in the control group. When only positive blood-cultures associated with a rise in C-reactive protein were considered, there were six episodes of CONS bacteraemia in the vancomycin group compared with 18 in the control group. Similarly there were five infants with one or more CONS infections compared with 11 in controls and one with more than one episode compared with six in the control group (P = 0.05). Prophylaxis with intermittent low-dose vancomycin infusions may help reduce recurrent CONS bacteraemia in VLBW infants receiving parenteral nutrition.

Rapid diagnosis of catheter-related sepsis using the acridine orange leukocyte cytospin test and an endoluminal brush

BACKGROUND

In neonates, the acridine orange leukocyte cytospin (AOLC) test has been found to be a highly sensitive test for the detection of infected i.v. catheters in situ, which provides a result in less than 1 hour. Preliminary data suggested that the AOLC test was of limited value in adults. We report here a modification of the test for adult patients with indwelling central venous catheters.

METHODS

A prospective study was performed on two groups of 50 adult patients with suspected sepsis and a central venous catheter. The AOLC test was carried out after the clinical decision to remove the catheter had been made. In group 1 patients, a blood sample was withdrawn from the catheter for the AOLC test. In the patients in group 2, an endoluminal brush was used to "sweep" the catheter before the collection of the blood sample. Results of the AOLC test were compared with culture of the removed catheter tip.

RESULTS

From the catheters in group 1 (no brush), 17 catheter tips were found to be infected, but the AOLC was positive in only two patients (12%). In group 2 (brush), 18 tips were infected, and the AOLC test was positive in 15 patients (83%). The use of the endoluminal brush significantly improved the yield of the AOLC test (p < .01) to levels reported in neonates. The AOLC test produced no false positives in either group

CONCLUSION

When used independently, the AOLC test was not sensitive enough to detect catheter-related sepsis. However, in combination with an endoluminal brush, the AOLC test was much more sensitive and has the potential to provide a simple, rapid, and accurate diagnostic test for catheter-related sepsis, which does not require removal of the catheter.

Reservoirs of coagulase negative staphylococci in preterm infants

This investigation was undertaken to determine the magnitude of, and interrelations between, reservoirs of coagulase negative staphylococci on infants' skin at various sites (including sites used for insertion of intravascular catheters) and in faeces during the first six months of life. Sites with large numbers of coagulase negative staphylococci were identified by sampling 16 skin sites and stools from 20 preterm neonates at 8-30 days of life. A more detailed survey of numbers and types of coagulase negative staphylococci in stool and at six skin sites of 10 preterm infants was then performed over the first six months of life. Isolates of coagulase negative staphylococci were collected and characterised by speciation, antibiotic susceptibility profiling, and plasmid restriction fragment length polymorphism analysis. Large, relatively stable reservoirs were identified in the faeces, around the ear, and in the axilla and nares. Skin on the forearm and leg, sites at which peripheral catheters are frequently sited, carried small unstable numbers of coagulase negative staphylococci, which were usually indistinguishable from coagulase negative staphylococci isolated from other body sites on the same baby. Contamination of catheter insertion sites with coagulase negative staphylococci from reservoir sites on the same baby could explain these observations. These data suggest that interventions reducing cross-contamination between sites on the same baby might be as important in preventing coagulase negative staphylococcal bacteraemias as measures taken to prevent cross infection between babies. Procedures which are likely to result in heavy coagulase negative staphylococcal contamination of the hands of healthcare staff, such as changing soiled nappies, should receive particular attention.

Development of cutaneous microflora in premature neonates

Coagulase-negative staphylococci (C-NS) are a frequent cause of bacteraemia in premature neonates. It is likely that the strains of C-NS causing bacterial sepsis in premature neonates have their origin on the patient's skin surface. We have studied the quantitative development of the skin microflora at eight sites on premature neonates. A swab wash method was used to sample and enumerate the cutaneous microflora of premature neonates admitted to an intensive care unit with respiratory distress syndrome. The numbers of bacteria present on the skin increased rapidly by 100-fold in the first week of life. The species of C-NS found on neonatal skin were similar to those found on adult skin. However, the bacterial population was 10(3) lower by comparison. There was considerable variation in numbers of bacteria and in the proportion resistant to antibiotics from day to day. There appeared to be no association between antibiotic usage and the proportion of isolates resistant to antibiotics, although the resident bacteria were in many cases resistant to a variety of antibiotics. C-NS were isolated from 92% of samples from which bacteria were isolated. Staphylococcus epidermidis was found at all sites and accounted for 82% of each colonial type of staphylococcus isolated. Other organisms isolated included Propionibacterium sp, alpha-haemolytic streptococci, aerobic spore-bearing bacilli, aerobic coryneforms, Candida albicans, Klebsiella oxytoca, Pityrosporum sp, Klebsiella pneumoniae, and Escherichia coli. The results of this study suggest that the skin of premature neonates is colonised with antibiotic resistant C-NS during the first week of life and that the chance of contamination of an intravascular catheter at insertion increases during this period.

Swab-wash method for quantitation of cutaneous microflora

We describe a comparison of the scrub-wash method of Williamson and Kligman and a swab-wash method for the enumeration of cutaneous microflora. The swab-wash method provides a less traumatic alternative to the scrub-wash method and can be used to sample the cutaneous microflora of premature neonates.