Identification and Antibiotic Sensitivity of UTI Pathogens Using Raman Spectroscopy

Abstract

Conventional methods of Urinary Tract Infection (UTI) diagnosis require determining the concentration and identity of the involved bacteria, as well as their susceptibility to various antibiotics, the so-called antibiogram. Such assays require repeated culturing of a sample and need at least 48 hours in order for bacterial colonies to be grown, counted, and exposed to antibiotics. However, the patient cannot remain untreated during this rather prolonged period before definitive diagnosis of the suspected infection becomes available. As a result, physicians prescribe broad spectrum antibiotics prior to antibiogram availability. This practice has many undesirable consequences, both short term and long term: (i) unsuccessful treatments leading to chronic infections, (ii) increased health care costs, and, most importantly, (iii) increased antibiotic resistance by a growing number of bacterial strains (Gruneberg, 1994; Casadevall, 1996; Cosgrove, S. & Carmeli, 2003; Alanis, 2005). Given these concerns, it is obvious that rapid and accurate identification of UTI pathogens as well as determination of their susceptibility to antibiotics would offer significant clinical benefits. Such methodologies are currently being developed and include the promising application of Raman spectroscopy for the diagnosis of UTIs. Recently, rapid diagnosis methods based on polymerase chain reaction (PCR) have been developed in order to bypass the need for culturing (Mothershed & Whitney, 2006) as well as to identify genes that confer antibiotic resistance (Rolain et al., 2004). Although such PCR assays are fast and very sensitive, they typically require species and strain specific probes that may or may not be available for a particular organism. In addition, amplification methods, like PCR, suffer from contamination problems, complex interpretation of results, as well as high costs. Mass Spectrometry is another method that has been proposed as an alternative approach for bacterial diagnostics without culturing (Chen et al., 2008). However, like the PCR approach, Mass Spectrometry also depends on prior knowledge of the pathogen under study and suffers from increased complexity and cost. Vibrational spectroscopies, like Raman spectroscopy, have been used, for the last few years, to detect bacteria with minimal sample manipulation (Maquelin et al., 2000; Schuster, 2000a, 2000b). Classification of bacterial species, as well as of subspecies, has been achieved with great accuracy and speed, especially with Surface Enhanced Raman Spectroscopy (SERS) (Kneipp et al., 2006) which allows enhancement of the inherently weak Raman signal. More