|Year : 2016 | Volume
| Issue : 4 | Page : 288-290
Importance of identification of lactose nonfermenting Escherichia coli and their prevalence in urinary isolates
Trupti Bajpai1, Maneesha Pandey2, Meena Varma3, Ganesh Bhatambare4
1 Department of Microbiology, Sri Aurobindo Institute of Medical Sciences, Medical College and Post Graduate Institute, Indore, Madhya Pradesh; Department of Biochemistry, SOS, IGNOU, New Delhi, India
2 Department of Biochemistry, SOS, IGNOU, New Delhi, India
3 Department of Biochemistry, Sri Aurobindo Institute of Medical Sciences, Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
4 Department of Microbiology, Sri Aurobindo Institute of Medical Sciences, Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
|Date of Web Publication||14-Sep-2016|
Dr. Trupti Bajpai
Assistant Professor, Department of Microbiology, Sri Aurobindo Institute of Medical Sciences Medical College and PG Institute, Indore-Ujjain Road, MR-10 Crossing, Indore, Madhya Pradesh
Source of Support: None, Conflict of Interest: None
Introduction: Escherichia coli is one of the most common bacteria causing urinary tract infection. Accurate identification of urinary isolates is highly desirable and frequently challenging. Our study aims at identifying the “atypical” phenotype of E. coli by conventional, automated, and molecular methods and studying its prevalence among all the urinary isolates of E. coli. Materials and Methods: The present prospective study was conducted in the Department of Microbiology of a teaching tertiary care hospital of Central India for 6 months during the year 2014–2015. A total of 592 urine samples were processed. Identification of different urinary isolates was done by conventional and automated methods and by molecular method in special cases. Results: Two hundred and sixty-one uropathogens were isolated during the study. Among these, 110 (42.1%) isolates were E. coli, of which 4 (3.6%) isolates were confirmed as “atypical” E. coli by automated and molecular method. Conclusions: Our study highlights the challenges in the identification of atypical urinary isolates of E. coli. Accurate identification is essential for implicating proper antibiotic treatment.
Keywords: 16S ribosomal RNA sequencing, atypical Escherichia coli, VITEK-2 Compact
|How to cite this article:|
Bajpai T, Pandey M, Varma M, Bhatambare G. Importance of identification of lactose nonfermenting Escherichia coli and their prevalence in urinary isolates. CHRISMED J Health Res 2016;3:288-90
|How to cite this URL:|
Bajpai T, Pandey M, Varma M, Bhatambare G. Importance of identification of lactose nonfermenting Escherichia coli and their prevalence in urinary isolates. CHRISMED J Health Res [serial online] 2016 [cited 2023 Mar 28];3:288-90. Available from: https://www.cjhr.org/text.asp?2016/3/4/288/190581
| Introduction|| |
Urinary tract infection (UTI) is one of the most important causes of morbidity and mortality and Escherichia More Details coli is the most frequently isolated urinary pathogen. It exists as a commensal in the gastrointestinal tract and provides the pool for the initiation of UTI. These isolates express chromosomally encoded virulence markers, which are responsible for their varying levels of pathogenicity.,
Some of the strains of these isolates are often multi-drug resistant. Proper susceptibility data from the specified area are required, if empirical antibiotics are to be administered in this group of patients. Moreover, this demands accurate identification which is frequently challenging in the need of proper sample collection and transport due to variation in phenotypic characteristics such as motility, gas production, and lactose-fermenting capabilities, and also due to the lack of full battery of biochemical tests in several laboratories.
Our study aims at identifying the “atypical” phenotype of E. coli by conventional, automated, and molecular methods and studying its prevalence among all the urinary isolates of E. coli.
| Materials and Methods|| |
The present prospective study was conducted from October 2014 to March 2015 in the Department of Microbiology of a teaching tertiary care hospital located in the Central India. Clean catch, midstream urine samples from 592 patients clinically suspected of UTI were subjected to microscopy and culture on blood agar, MacConkey agar, and UTI chromogenic media (HiMedia, Mumbai, India). The uropathogens isolated from the culture-positive samples were identified up to species level by conventional method (biochemical tests)., The isolates were further confirmed by automated method (VITEK 2-Compact System, BioMérieux Inc., France). If required, then, further confirmation was done by molecular method (16S ribosomal RNA [16S rRNA] sequencing) (Yaazh Xenomics, Mumbai, India). In 16S rRNA sequencing, genomic DNA was extracted, followed by its amplification (polymerase chain reaction). The amplified fragments were purified prior to sequencing. Bidirectional sequencing was performed for each amplified product by an automated sequencer., Analysis of sequencing data was performed by MicroSeq 500 software (Thermo Fisher Scientific, 168 Third Avenue, Waltham, MA USA). The consensus sequences were compared (online) with the published sequences available in GenBank at the website (http://www.ncbi.nlm.nih.gov/) using the nucleotide Basic Local Alignment Search Tool of the National Center for Biotechnology Information. The phylogenetic tree of the identified E. coli was analyzed. Data for the phylogenetic analysis were obtained from sequences contained in the GenBank nucleotide sequences database.,
| Results|| |
Out of 592 patient samples processed, a total of 243 (41%) urine samples were found to be culture-positive. Two hundred and sixty-one uropathogens were isolated from the 243 culture-positive samples (18 samples had mixed flora, i.e. two pathogens). Among these, 161 (61.6%) isolates were Gram-negative Bacilli, 56 (21.4%) were Gram-positive cocci, and 44 (16.8%) were Candida species. Among the 161 Gram-negative isolates, 149 (92.8%) were members of Enterobacteriaceae, 8 (4.9%) were Pseudomonas aeruginosa, and 4 (2.4%) were Acinetobacter species. Of the 149 members of Enterobacteriaceae, 110 (73.8%) were detected as E. coli. Among these 110 E. coli isolates, 4 (3.6%) isolates were confirmed as E. coli only by automated and molecular methods.
| Discussion|| |
It has traditionally been described that certain serotypes of E. coli were consistently associated with uropathogenicity. They were recognized for the first time in 1970s and are currently known as uropathogenic E. coli (UPEC). These are typical E. coli strains that differ from “atypical” or inactive strains of E. coli, which were identified as the causative agents of diarrheal diseases in 1971 known to present shigellosis-like symptoms. At present, they are known as enteroinvasive E. coli. The prevalence of “atypical” E. coli has been frequently reported from diarrheal cases. Here, we have reported their prevalence as uropathogens.
E. coli are Gram-negative bacilli, commonly found in the lower intestine of warm-blooded animals including humans. The harmless strains are a part of normal gut flora and benefit the host by producing Vitamin K2 and preventing the establishment of pathogenic bacteria in the intestine. UPECs are responsible for approximately 90% of UTIs in individuals with ordinary anatomy. These strains are motile, aerogenic lactose fermenters that can be very easily identified by conventional methods of identification in all clinical microbiology laboratories.
However, there are variants of E. coli that are termed as “inactive.” They are nonmotile, anaerogenic, nonlactose fermenters. Biochemically, they are very similar to Shigella species and such isolates pose a significant diagnostic challenge., Although biochemical and serological methods are typically used to distinguish these species, these approaches have suboptimal performance. Phenotypically, they share many common characteristics, but genotypically they could be considered as same species.
Even during our study, these isolates could not be confirmed as E. coli by conventional methods. Automated method could identify it as E. coli, but again 16S rRNA sequencing identified it as either Shigella sonnei or E. coli. It was finally confirmed as E. coli on the basis of the clinical sample from which it was isolated. Being a urinary isolate, it was finally confirmed as enteroinvasive strain of E. coli resembling Shigella species [Figure 1].
|Figure 1: Phylogenetic tree of Escherichia coli based on the nucleotide sequences of 16S ribosomal RNA genes|
Click here to view
A total of 3.6% of nonlactose fermenting E. coli urinary isolates were detected during our study. Our results were consistent with those of Thompson et al. (approximately 4%) and Versalovic et al. (approximately 5%), while it varied from 6.3% to 9% and 12.4%, respectively, in the studies conducted by Radha and Jeya  and Bhat and Bhat. It was found to be as high as 19.7% in the study authored by Chang et al.
| Conclusion|| |
Our study highlights some important points. First, unless colony characteristics are observed minutely and full battery of biochemical tests are put up and analyzed properly, E. coli isolates can often be misidentified as other members of Enterobacteriaceae and such misidentification can frequently lead to improper antibiotic treatment. Second, if the isolates are misidentified by conventional methods, then they should be identified by automated methods and further confirmed by molecular methods. Molecular methods cannot be introduced on the regular basis, but can be helpful during epidemiological studies. Based on our observation, the results of 16S rRNA should be interpreted carefully to avoid any kind of discrepancies.
The authors wish to thank the management, technical, and clinical staff of SAIMS Medical College and PG Institute, for their kind support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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