|LETTER TO THE EDITOR
|Year : 2012 | Volume
| Issue : 2 | Page : 104-105
Serratia marcescens in light of biofilm
Rajdeep Saha1, Kalidas Rit2, Rupali Dey2
1 Department of Microbiology, Calcutta National Medical College, Kolkata, West Bengal, India
2 Institute of Postgraduate Medical Education and Research, A.J.C Bose Road, Kolkata, West Bengal, India
|Date of Web Publication||7-Mar-2013|
DA-18, Sector-1, Salt Lake City, Kolkata- 700064, West Bengal
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Saha R, Rit K, Dey R. Serratia marcescens in light of biofilm
. Ann Nigerian Med 2012;6:104-5
Biofilms are complex communities of single or multiple species of microorganisms that develop on abiotic (rocks) and biotic (host mucosal tissues) surfaces. A biofilm is composed of extracellular polysaccharide (EPS) produced by bacterial cells. Biofilm strains are frequently embedded in the EPS matrix.  Biofilm formation on a urinary catheter is favored due to many reasons like prolonged catheterization, lack of proper aseptic measures during catheter insertion and removal, incompletely treated (urinary tract infection) UTI, and underlying medical diseases like diabetes mellitus.
Serratia marcescens, a Gram-negative rod belonging to the family Enterobacteriaceae, is involved in nosocomial infections, particularly catheter-associated bacteremia, UTI, and wound infections.  S. marcescens may also be found in environments such as dirt, supposedly "sterile" places, and the subgingival biofilm of teeth. 
This study was carried out to study biofilm formation over a urinary catheter persisting for more than 1 month and to compare the minimum inhibitory concentration (MIC) value of antibiotic acting against the planktonic variety of isolated bacteria and minimum biofilm eliminating concentration (MBEC) value of sessile form of the same bacteria.
A total of 203 patients, who were catheterized for more than 1 month, were selected randomly. After collection of urine by aspirating with sterile syringe and needle, the urinary catheter was removed aseptically. About 6 inch catheter tips were collected. They were thoroughly washed with sterile normal saline to remove debris. Catheter tips were scraped with an inoculation loop and scraped material was inoculated on blood agar and MacConkey's agar. After 24 hours of incubation at 37 °C in incubator, isolates were identified by gram stain and biochemical reactions.  Antibiotic sensitivity was done by the Kirby-Bauer method with following antibiotic disks-amikacin, ciprofloxacin, cefoxitin, nitrofurantoin, aztreonam, piperacillin-tazobactum, imipenem.  The MIC value of isolated bacteria was determined by broth dilution with amikacin. Biofilm formation was detected by Mile's method. 
The MBEC value of amikacin was detected with the biofilm colonizers. The MBEC value of amikacin for the biofilm producing strain on the catheter was compared with MIC value of isolated bacterial strain from urine.
Out of 203 urinary catheter samples, biofilm was detected over 122 catheter samples out of which 8 (6.5%) samples were Serratia marcescens isolates [Figure 1]. They were chosen for MIC and MBEC determination with Amikacin. MIC and MBEC values were obtained using various amikacin concentrations - 200 μg/ml, 100 μg/ml, 50 μg/ml, 25 μg/ml, 12·5 μg/ml, 6·25 μg/ml, 3 μg/ml, 1.5 μg/ml. In all eight isolates, the MBEC value of sessile form of bacteria within biofilm was much higher than the MIC value of its planktonic form.
The biofilms on urinary catheters pose special problems in their management due to their high treatment refractoriness and persistent source of infections. In this study, it has been shown that, sessile forms of serratia have higher resistance to antimicrobial drugs (MBEC) than their respective planktonic forms (MIC), so any treatment based on the in vitro drug sensitivity test for planktonic form of isolates may not be effective for eliminating same organisms residing within biofilm.
| References|| |
|1.||Flemming HC, Neu TR, Wozniak DJ. The EPS Matrix: The "House of Biofilm Cells". J Bacteriol 2007;189:7945-7. |
|2.||Haddy RI, Mann BL, Nadkarni DD, Cruz RF, Elshoff DJ, Buendia FC, et al. Nosocomial infection in the community hospital: Severe infection due to Serratia species. J Fam Pract 1996;42:273-7. |
|3.||Barbosa FC, Irino K, Carbonell GV, Mayer MP. Characterization of Serratia marcescens isolates from subgingival biofilm, extraoral infections and environment by prodigiosin production, serotyping, and genotyping. Oral Microbiol Immunol 2006;21:53-60. |
|4.||Winn W Jr, Allen S, Janda W, Koneman E, Procop G, Schreckenberger P, et al. Antimicrobial Susceptibility Testing. Koneman's Color Atlas and Textbook of Diagnostic Microbiology. 6 th ed. Philadelphia, Pennsylvania: Lippincott Williams and Wilkins; 2006. p. 1443-75. |
|5.||Miles AA, Misra SS, Irwin JO. The estimation of the0 bactericidal power of the blood. J Hyg (Lond) 1938;38:732-49. |