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Clones and toxin genes' carriage of coagulase-negative staphylococci isolated from bacteraemic infants hospitalised in an intensive care unit

Abstract number: P1577

Giormezis N., Kolonitsiou F., Foka A., Hondrou V., Drosopoulou K., Mantagos S., Dimitriou G., Anastassiou E.D., Spiliopoulou I.

Objective: Coagulase-negative staphylococci (CNS), especially Staphylococcus epidermidis and S. haemolyticus, are the leading causative agents of neonatal nosocomial sepsis. High prevalence of resistance to methicillin and other antistaphylococcal agents is observed among CNS (MR-CNS), a key factor for persistence in neonatal intensive care units (NICUs). An extracellular polysaccharide intercellular adhesin (PIA) encoded by the ica operon has received much concern in biofilm formation. Of clinical importance is the production of TSST-1 and enterotoxins acting as superantigens by CNS. The aim of the present study was to investigate MR-CNS clonal dissemination in the NICU of our University Hospital during a two-year period in correlation to toxin genes' carriage and the presence of ica operon with biofilm formation.

Methods: A total of 180 CNS from 69 patients with bacteraemia were identified at species level by the API Staph System (bioMérieux) and by restriction fragment length polymorphism of the amplified tuf gene. The MICs of oxacillin, linezolid, vancomycin and teicoplanin were determined by the Etest (Ab Biodisk). Susceptibility against antistaphylococcal agents was tested by the disk diffusion method. Biofilm production was tested by the qualitative method. The presence of mecA gene, icaA and icaD (ica operon), tst (TSST-1) and the enterotoxins' genes sea, seb, sec and sed was tested by PCRs. Clones were defined by PFGE of chromosomal DNA SmaI digests.

Results: In total 177/180 CNS were mecA-positive (MR-CNS). Eighty-nine strains produced biofilm, 76 of them were ica-positive, while 63 additional CNS were ica-positive and biofilm-negative. The majority of isolates (>70%) were multi-resistant including 9 strains in vitro resistant to vancomycin (MIC > 32 mg/L). Table 1 summarises the results of species and clones identification in relation to toxin genes. Three clones were dominant during the two-year period: a and b among S. epidermidis and h in S. haemolyticus. Clone c emerged in 2007. tst gene carriage was clonal related among S. epidermidis and S. haemolyticus, but enterotoxin genes were more widely distributed.

Conclusions: Multi-resistant MR-CNS clones mainly S. epidermidis and S. haemolyticus were distributed in the NICU of our University Hospital during the two-year study period. Besides biofilm formation, a factor that might contribute to their clinical importance and virulence capacity is the toxin gene carriage of the superantigens family.

Table 1. Species identification of CNS, clones and toxin genes carriage

Species (no. of strains)Clones (no. of strains)Positive toxin genes (no. of strains)
  tstseasebsecsedtst/seatst/sec
S. epidermidis (106)a (63)1146112
 b (14)2
 c (10)1131
 Others (16 clones: 19 strains)21311
S. haemolyticus (59)h (44)10311
 Others (9 clones: 15 strains)13
S. hominis (9)Others (8 clones: 9 strains)11
S. saprophyticus (1)n
S. warneri (3)3 clones
S. lugdunensis (2)2 clones1
Total: 18043 clones2516013324

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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