The ica operon and biofilm production in coagulase-negative Staphylococci associated with carriage and disease in a neonatal intensive care unit

Abstract

Coagulase-negative staphylococci (CoNS) are a major cause of sepsis in the neonatal intensive care unit (NICU). We evaluated the hypothesis that the ica operon and biofilm production are associated with CoNS disease in this setting. CoNS associated with bacteremia or blood culture contamination and from the skin of infants with CoNS bacteremia or healthy controls were obtained during a prospective case-control study on a busy NICU. A total of 180 strains were identified, of which 122 (68%) were Staphylococcus epidermidis and the remainder were S. capitis (n = 29), S. haemolyticus (n = 11), S. hominis (n = 9), S. warneri (n = 8), and S. auricularis (n = 1). The presence of the genes icaA, icaB, icaC, and icaD was determined by PCR, and biofilm production was examined using qualitative (Congo red agar [CRA]) and quantitative (microtiter plate) techniques. There were no significant differences in the presence of the ica operon or CRA positivity among the four groups of strains. However, quantitative biofilm production was significantly greater in strains isolated from either the blood or the skin of neonates with S. epidermidis bacteremia. We conclude that the quantity of biofilm produced may be associated with the ability to cause CoNS infection. This conclusion suggests that the regulation of biofilm expression may play a central role in the disease process.

FIG. 1.

Density plots showing results of assessment of biofilm production. (A) Distribution of biofilm production in CRA-positive CoNS strains and CRA-negative strains. (B) Distributions of biofilm production in S. epidermidis strains with and without the ica operon. Absorbance in the microtiter plate assay is plotted against the Epanechnikov kernel density (see the text for details).

FIG. 2.

Biofilm production by strains in the four clinical groups. As some of the microtiter plate assay absorbance values were negative after subtraction of background, 0.2 was added to all values prior to log transformation. The horizontal line represents the median value of each distribution. For statistical comparisons between groups, see the text. OD, optical density.