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Indian Journal of Medical Microbiology, Vol. 27, No. 4, October-December, 2009, pp. 377-378 Correspondence Potential of biofilm formation by staphylococci on polymer surface and its correlation with methicillin susceptibility *A Chaudhury, M Nagaraja, AG Kumar Department of Microbiology, SV Institute of Medical Sciences, Tirupati, Andhra Pradesh -517 507, India Correspondence Address: *Department of Microbiology, SV Institute of Medical Sciences, Tirupati, Andhra Pradesh -517 507, India, ach1964@rediffmail.com Date of Submission: 13-Dec-2008 Code Number: mb09108 PMID: 19736417 DOI: 10.4103/0255-0857.55450 Dear Editor, Staphylococcus epidermidis and Staphylococcus aureus are major causes of colonization and bio film formation in intravenous catheters. This frequently leads to catheter associated blood stream infection. Polysaccharide inter cellular adhesin (PIA) plays an important role in pathogenesis as it mediates the contact of bacterial cells with each other, resulting in the accumulation of a multilayered bio film. PIA production is under the control of the ica operon and this operon has been well documented not only in S. epidermidis [1] but also in S.aurues. [2] It has been documented that the regulation of ica operon expression and the resultant bio film formation may be altered by various environmental factors like anaerobicity, CO 2 levels, glucose and osmotic changes. In recent years, the influence of methicillin susceptibility on bio film formation and ica expression among S. aureus isolates have been studied, revealing some important findings; [3] though similar studies have not been done for S. epidermidis . Our study has examined the methicillin sensitivity / resistance on bio film formation among S. aureus and S. epidermidis isolates from venous catheter tips. Isolates of Staphylococci from venous catheters have been used. A total of 60 representative strains consisting 15 each of methicillin sensitive S. aureus (MSSA), methicillin resistant S. aureus (MRSA), methicillin sensitive S. epidermidis (MSSE) and methicillin resistant S. epidermidis (MRSE) were included. Methicillin sensitivity testing was done using oxacillin, 1 µg disks (Hi-media, India) and reconfirmed with cefoxitin, 30 ìg disks (Hi Media, India). The antibogram of the S. aureus and the S. epidermidis strains were studied and only those strains which differed in their susceptibility patterns included in the study. This was done to ensure that the strains were clonally distinct. For quantitative bio film measurement, the method suggested by Rachid et al, [4] with slight modifications, was used. An 1:100 dilution of overnight broth culture of the organism was done in Brain heart infusion broth (Hi-Media) with or without 4% Sodium chloride or 1% Glucose. This was transferred to 96 well polystyrene flat bottomed ELISA plates (Tarsons, India) and incubated overnight at 37 0 C, followed by washing, air drying and staining with crystal violet solution. The plates were read at 490 nm and optical density of greater than 0.120 was considered bio film positive. Among the MRSA stains, six could produce biofilms without any external influence while four additional strains were able to produce the same under the influence of glucose [Table - 1]. One strain was bio film positive in the presence of Sodium Chloride as well as glucose. In contrast, none of the MSSA could produce bio film with or without Glucose, but two could produce it in the presence of Sodium Chloride. The S. epidermidis strain exhibited much less bio film forming potential with only one strain each of MSSE and MRSE showing this effect independently. Two additional strains of MSSE were bio film positive in presence of glucose. The single strain of bio film positive MRSE strain was able to produce it in glucose, but not in the presence of sodium chloride. Bio film formation among S. epidermidis and to some extent S. aureus is a well documented phenomenon, particularly with reference to the production of PIA. However, only limited studies have been done in the recent years to find out the effect of methicillin susceptibility/ resistance on PIA production. In our study, a greater number of MRSA could produce bio film compared to the other three groups (MSSA, MSSE and MRSE). The latter three groups showed very limited potential to form bio film on smooth surfaces, even in the presence of glucose or sodium chloride. Bio film formation among MRSA strain was significantly increased under the influence of glucose, although the same could not be seen in presence of sodium chloride. However, among the S. epidermidis strains, none of the MRSE strains could produce bio film in the presence of sodium chloride. Glucose was able to induce bio film formation in two and one additional strain among MSSE and MRSE respectively, while sodium chloride was unable to induce bio film production in any of the MRSE strains. Sodium chloride is a known activator of ica operon transcription and from our study; it is more likely to induce bio film formation among methicillin sensitive isolates. Among MRSA isolates, bio film formation seems to be predominantly glucose induced. There seems to be a complex relationship in terms of bio film formation and its regulation under the influence of sodium chloride or glucose which may be resolved if a larger series is studied. The other important finding of our study was the variability of adherence of the strains to the polymer surfaces. Although the isolates were all from plastic catheters, they showed varying ability in their adherence potential to polystyrene surface in vitro. It seems likely that there may be strain to strain variation in the expression of genes responsible for PIA production and/ or protein adhesins which play an important role in bio film formation. Another probable explanation is the more complex milieu existing in the inserted catheter under in vivo conditions where various host proteins may form a coating on the catheter surface. The organisms can anchor themselves directly to those proteins and other substances using multiple receptors and surface proteins. Further studies are needed to elucidate the factors influencing ica expression and the different mechanisms involved in bio film formation among methicillin susceptible/resistant strains. This will give a more comprehensive picture of Staphylococcus induced catheter related infection and effective therapeutic interventions. References
Copyright 2009 - Indian Journal of Medical Microbiology The following images related to this document are available:Photo images[mb09108t1.jpg] |
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