The Bacterial Insertion Sequence Element IS 256 Occurs Preferentially in Nosocomial Staphylococcus epidermidis Isolates: Association with Biofilm Formation and Resistance to Aminoglycosides

Abstract

Staphylococcus epidermidis is a normal constituent of the healthy human microflora, but it is also the most common cause of nosocomial infections associated with the use of indwelling medical devices. Isolates from device-associated infections are known for their pronounced phenotypic and genetic variability, and in this study we searched for factors that might contribute to this flexibility. We show that mutator phenotypes, which exhibit elevated spontaneous mutation rates, are rare among both pathogenic and commensal S. epidermidis strains. However, the study revealed that, in contrast to those of commensal strains, the genomes of clinical S. epidermidis strains carry multiple copies of the insertion sequence IS256, while other typical staphylococcal insertion sequences, such as IS257 and IS1272, are distributed equally among saprophytic and clinical isolates. Moreover, detection of IS256 was found to be associated with biofilm formation and the presence of the icaADBC operon as well as with gentamicin and oxacillin resistance in the clinical strains. The data suggest that IS256 is a characteristic element in the genome of multiresistant nosocomial S. epidermidis isolates that might be involved in the flexibility and adaptation of the genome in clinical isolates.Staphylococcus epidermidis is a normal constituent of the healthy human skin and mucosal microflora. In recent decades, however, the bacterium has emerged as a nosocomial multiresistant pathogen and is now the most common cause of deviceassociated infections. Little is known of the factors that have contributed to this development, but the increasing number of immunocompromised patients, the use of indwelling medical devices, and a high selective pressure by antibiotics offer bacteria a novel ecological niche. It is unclear why just staphylococci were able to occupy this niche and by which factors pathogenic S. epidermidis differ from their commensal counterparts. In recent years, it has been shown that the ability to form biofilms on medical devices is a characteristic feature of nosocomial S. epidermidis isolates. Moreover, clinical S. epidermidis isolates exhibit an extraordinarily high phenotypic and genotypic flexibility. Thus, variants of the same parent strain can differ in terms of colony morphology, growth rate, hemolysis, biofilm formation, and antibiotic susceptibility (4, 7). The molecular mechanisms involved in this phenomenon are poorly understood, but it is assumed that the generation of phenotypic and genotypic variants is an evolutionary advantage that helps staphylococci to adapt to changing environmental conditions. The purpose of this study was therefore to search for genetic factors and mechanisms in clinical S. epidermidis that might contribute to this process. Previous studies have shown that staphylococcal biofilm formation is a highly variable factor which is influenced by both regulatory processes and genetic mechanisms such as phase variations, mutations, and chromosomal rearrangements (5,10,26,(32)(33)(34). The observation t...

Genetic determinants and biofilm formation of clinicalStaphylococcus epidermidisisolates from blood cultures and indwelling devises

“…Same results were reported by Kozitskaya et al [14]. Moreover, 47% of the IS256-and ica-positive S. epidermidis isolates shared a multi-resistant profi le (PEN-OXA-CIP-GEN-ERY-CLI), and 66% were resistant toward PEN-OXA-GEN. Also, Kozitskaya et al [14] described the correlation between IS256 and the resistance toward oxacillin and gentamicin. The insertion element IS256 more frequently occurs in multi-resistant and ica-positive isolates.…”

“…Chaieb et al [31] determined higher proportion of icaA/D-positive isolates (72.7%), which phenotypically produced biofi lm. Probably, other factors besides the ica genes may have an infl uence in biofi lm formation [14]. Other factors, e.g., environment, nutrition subinhibitory concentrations of diverse antibiotics (tetracycline, gentamicin, clindamycin, teicoplanin), and stress (temperature, osmolarity), might have a signifi cant role in biofi lm formation and/or repression [17].…”

“…That means pathogenicity appears to be a complex phenomenon, which could be accounted for not only by large genetic differences but also by small variations in gene contents. This prompted us to perform a detailed comparative pheno-and genotypic analysis of S. epidermidis isolates from different sampling sites, complementing the previous approaches used to differentiate pathogenic strains from the non-pathogenic ones [14].…”

Comparative Epidemiology of Staphylococcus epidermidis Isolates from Patients with Catheter-Related Bacteremia and from Healthy Volunteers

“…Additionally, all isolates were tested for the presence of arc(A) and ica(A), to assess the presence of the ACME and the ica operon, respectively (4,21).…”

“…Compared to the planktonic state, biofilm confers to S. epidermidis increased mechanical, metabolic, immune, and antibiotic resistance and its production is essentially mediated by the production of a polysaccharide intercellular adhesin (PIA) encoded by the accessory intercellular adhesion (ica) operon (4). Another genetic locus, the arginine catabolic mobile element (ACME), is thought to play an important role in the pathogenicity of S. epidermidis.…”