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Ultrastructural analysis of slime positive & slime negative Staphylococcus epidermidis isolates in infectious
1Department of Ocular Microbiology, Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India. niruni2000@yahoo.com
Background & Objective:
Slime is a major determinant of Staphylococcus epidermidis adherence. The established methods of laboratory detection of slime production by this organism i.e., Christensen's tube method and congo red agar plate method, can both yield inconclusive and/or intermediate results. We, therefore tried to find out electronmicroscopically the localization of slime in relation to the bacterial cell wall and look for the effect, if any of the slime location on the staphylococcal adherence as well as on the quantum of slime production.
Methods:
A total of 132 coagulase negative staphylococci from cases of infectious keratitis were identified as S. epidermidis following the recommended protocol. Slime was detected both by Christensen's tube method and congo red agar plate method. Antibiotic sensitivity testing was performed by standardized disc diffusion method. Adherence of the organisms to artificial surfaces was determined by a quantitative method and transmission electron microscopy was carried out by the conventional techniques.
Results:
Of the total 132 isolates, 57 (43.2%) were slime positive and 75 (56.8%) were slime negative. Twenty seven (47.4%) of the 57 slime producing organisms were multi drug resistant as compared to only 12 (16%) of 75 nonslime-producing organisms (P<0.001). A majority i.e., 45 (78.9%) of 57 adherent organisms were slime producers as against 12 (16%) of 75 nonadherent organisms. Electron microscopic study revealed a thick viscid layer of slime anchoring to the bacterial cell wall, especially in adherent organisms and those yielding positive slime test. Some of the organisms showed loose nonadherent slime and those were mostly nonadherent to artificial surfaces.
Interpretation & Conclusion:
Slime and multi drug resistance were the important virulence factors of S. epidermidis in bacterial keratitis. It was the adherent slime (i.e., slime in intimate association with the bacterial cell wall as shown by electron microscopy) only, which was responsible for resistance to multiple antibiotics and for the adhesion phenomenon observed in the quantitative slime test.
Insights
Adherent slime produced by Staphylococcus epidermidis is linked to increased antibiotic resistance and organism adhesion in infectious keratitis. Electron microscopy confirmed this slime layer
Area of Science:
- Microbiology
- Ocular infections
- Bacterial pathogenesis
Background:
- Slime production is a key factor in Staphylococcus epidermidis adherence.
- Conventional methods for detecting slime (Christensen's tube, Congo red agar) can produce ambiguous results.
- Understanding slime's role in bacterial keratitis is crucial for effective treatment.
Purpose of the Study:
- To investigate the ultrastructural localization of slime in Staphylococcus epidermidis.
- To determine the effect of slime location on bacterial adherence to artificial surfaces.
- To correlate slime production and location with antibiotic resistance in infectious keratitis.
Main Methods:
- Identification and characterization of 132 Staphylococcus epidermidis isolates from infectious keratitis cases.
- Slime detection using Christensen's tube and Congo red agar methods.
- Quantitative assessment of bacterial adherence and antibiotic sensitivity testing.
- Transmission electron microscopy (TEM) to visualize slime-cell wall association.
Main Results:
- 57% of isolates were slime-positive; 43.2% were slime-negative.
- Slime-producing organisms showed significantly higher rates of multi-drug resistance (47.4% vs. 16%).
- A strong correlation was observed between slime production, adherence to artificial surfaces (78.9%), and positive slime tests.
- Electron microscopy revealed adherent slime layers associated with the bacterial cell wall in positive isolates.
Conclusions:
- Adherent slime, intimately associated with the bacterial cell wall, is a critical virulence factor in Staphylococcus epidermidis keratitis.
- This adherent slime is directly responsible for enhanced bacterial adhesion and multi-drug resistance.
- Electron microscopy provides a definitive method for assessing slime's role in virulence.
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