Enhancement of Biofilm Formation by Subinhibitory Concentrations of Macrolides in icaADBC- Positive and -Negative Clinical Isolates of Staphylococcus epidermidis

Abstract

Biofilm formation in Staphylococcus epidermidis is mediated by icaADBC-dependent and -independent pathways. Subinhibitory concentrations of erythromycin, azithromycin, and clarithromycin enhanced, in a dosedependent manner, the level of biofilm formation by 20% (21/105 isolates) by macrolide-resistant ica-positive and -negative isolates tested in vitro. The presence of ica, however, apparently produced an enhanced effect on biofilm formation. The levels of expression of the biofilm-related genes icaA, atlE, fruA, pyrR, sarA, and sigB were increased in response to erythromycin. The results likely underscore the potential clinical relevance of macrolide-induced biofilm growth.Staphylococcus epidermidis, a key nosocomial pathogen, is frequently associated with the use of indwelling medical devices and forms biofilms (9). The latter is mediated by icaADBC-dependent and -independent pathways (8, 17). The ica operon encodes enzymes that are involved in the production of polysaccharide intercellular adhesion (PIA), which mediates the intercellular adherence of bacteria and the accumulation of multilayer biofilms (8). Nevertheless, ica is not ubiquitously distributed in S. epidermidis (5,8,21), and icanegative isolates also produce biofilm (19). Furthermore, the impact of exogenous substances, such as antibiotics, on bacterial biofilm formation has also drawn much attention (3,6,7,11,12,23), although the numbers of studies performed with S. epidermidis are still limited. Macrolides, which include erythromycin (ERY), clarithromycin (CLR), and azithromycin (AZM), are among the most frequently used antibiotics in clinical settings. A subinhibitory concentration of ERY induced ica expression (20), suggesting a possible role of macrolides in biofilm formation, but the eradication of the slimelike glycocalyx matrix and, thus, the eradication of antibiofilm activity by a subinhibitory concentration of CLR in a CLRresistant isolate of S. epidermidis (whose ica status was unknown) were also reported (24). The study described here was thus carried out to investigate the role of macrolides in biofilm formation and its relation to the ica status of S. epidermidis. We show that a large number of clinical isolates of S. epidermidis had significantly enhanced levels of biofilm formation after treatment with macrolides and that biofilm formation was independent of the ica status.Of 121 S. epidermidis strains isolated from our hospital during the period from August 2007 to December 2008, 105 isolates (87%) were resistant to ERY (MIC Ͼ 8 g/ml), with most of the isolates being highly resistant to ERY, CLR, and AZM (MICs Ն 128 g/ml), although they were susceptible to vancomycin (VAN; MICs ϭ 1 to 2 g/ml). By using a microtiter plate assay for biofilm formation (1) with cells grown in tryptic soy broth medium, ERY at 1/4ϫ MIC (i.e., over the range of 4 to 32 g/ml) was found to significantly enhance the level of biofilm formation in 20% (21/105) of the ERY-resistant isolates (Tables 1 and 2). Two other macrolides, AZM and CLR, also caused a s...

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“…53 Interestingly, when antibiotics were added at low concentration in a BF-conditions, biofilm formation induction was achieved. Similar result were previously observed in Staphylococcus epidermidis isolates using macrolides 54 and in Salmonella enteric serovar Typhimurium in which biofilm and EPS production was improved after treatment with sub-inhibitory concentrations of cefotaxime. 55 It is worth to note that, when antibiotic was added at 24 h, the above mentioned induction of biofilm formation was not observed in the BF-conditions (not shown).…”

Activity of Gallidermin on Staphylococcus aureus and Staphylococcus epidermidis Biofilms

“…It has been reported that subinhibitory concentrations of various antibiotics even enhance staphylococcal biofilm formation, such as erythromycin (53), furanone (28), nafcillin (11), quinupristin-dalfopristin and tetracycline (46), and vancomycin (23). Gallidermin does not fall into this class of antibiotics, as biofilm formation is inhibited by concentrations that are subinhibitory for growth.…”

Extracellular DNA Impedes the Transport of Vancomycin in Staphylococcus epidermidis Biofilms Preexposed to Subinhibitory Concentrations of Vancomycin

“…Recent evidence has shown that subinhibitory concentrations of various antibiotics induced biofilm formation of S. epidermidis (2)(3)(4), which in part may explain some of the resistance to antibiotic therapy. In addition, although various antibiotics were able to reduce the biomass of S. epidermidis biofilms at sub-MICs, these biofilms exhibited an increased level of resistance to dicloxacillin, tetracycline, and rifampin (5).…”