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| Year : 2009 | Volume
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| Issue : 4 | Page : 613-617 |
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| The prevalence of virulence genes of E. coli strains isolated from children with urinary tract infection |
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Shohreh Farshad1, Fatemeh Emamghorashi2
1 Prof. Alborzi Clinical Microbiology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
2 Pediatric Department, Jahrom University of Medical Sciences, Jahrom, Iran
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| Date of Web Publication | 8-Jul-2009 |
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 Abstract | | |
To evaluate the prevalence of virulence genes in E. coli strains isolated from urine samples of children with urinary tract infection(UTI) and their correlation with clinical data, we isolated E. coli strains from urine samples of children with UTI during the period of August 2005 - August 2006 and studied them for the presence of the virulence genes by PCR. A total of 96 E. coli strains were isolated. The prevalence of genes, pyelonephritis associated pili (pap genes), S-family adhesions (sfa gene), hemolysin (hly gene), and cytotoxic nercotizing factor type 1 (cnf-1-1 gene) among the isolated strains was 27.1%, 14.6%, 13.5% and 22.9 %, respectively. Pyelonephritis was more prevalent in the cases with positive virulence genes. The results showed significant correlation between age of the patient and the presence of the genes (P< 0.05). Cnf-1 gene was significantly more common in samples of patients with abnormal finding on the ultrasound of kidneys (P= 0.049). Our study demonstrated higher prevalence of pyelonephritis in the presence of E. coli virulence genes. Detection of the genes in urine samples may help in the management of UTI.
How to cite this article:
Farshad S, Emamghorashi F. The prevalence of virulence genes of E. coli strains isolated from children with urinary tract infection. Saudi J Kidney Dis Transpl 2009;20:613-7 |
How to cite this URL:
Farshad S, Emamghorashi F. The prevalence of virulence genes of E. coli strains isolated from children with urinary tract infection. Saudi J Kidney Dis Transpl [serial online] 2009 [cited 2021 Jan 18];20:613-7. Available from: https://www.sjkdt.org/text.asp?2009/20/4/613/53250 |
| Introduction | |  |
E. coli accounts for as much as 90% of urinary tract infections (UTI) and displays variable virulence properties. [1] Several genes encode urovirulent factors such as hemolysin (hly gene), cytotoxic nercotizing factor type 1 (cnf-1-1 gene), pyelonephritis associated pili (pap genes) and S-family adhesions (sfa gene). [2] Some genes, such as the hly pap or p fimbriae and cnf-1 1 play an important role in the pathogenesis of E. coli strains. [3],[4],[5]
In the present study, we evaluated the prevalence of the virulence genes, and their correlation with clinical data in uropathogenic E. coli strains isolated from children with UTI.
| Subjects and Methods | | |
We studied children with UTI referred to Motahary hospital and clinic, Jahrom, Iran during the period of August 2005 - August 2006.
Diagnosis of UTI was established by clinical symptoms and laboratory investigations (colony count of more than 10 5 colony forming unit/mL in meadstream sampling, 10 4 cfu/mL in urine sampling by catheterization and any count in suprapubic sampling). None of the patients was immune compromised.
Acute pyelonephritis was clinically defined as fever (temperature > 38.5°C), lumbar tenderness, and sepsis in neonate. Cystitis was considered when dysuria and pyuria were present without fever. Data including age, sex, previous history of infection, recent antibiotic usage and history of hospitalization during the previous 28 days were collected on all the patients with community acquired UTI in questionnaire forms. The exclusion criterion was nosocomial infection, which was defined as infection noted 48 h after admission or within four weeks after a previous discharge.
Isolation of Bacteria
E. coli strains were isolated from urine samples and identified using standard methods. [6] Urine culture was considered positive if at least 10 5 colony forming unit of E. coli per mL of cleanvoided urine were grown in the culture media. The strains were then stored and sub cultured for further analysis as previously described in literature. [7] ,[8]
DNA extraction
E. coli isolates were grown in Luria Bertani broth at 37°C overnight. Bacteria were then pelleted from broth, resuspended in sterile distilled water and boiled at 95°C for ten min. After centrifugation, the supernatants were stored as DNA template at -20°C until they were used in the PCR.
PCR assay
Detection of pap, sfa, cnf-1, and hly genes was performed by amplifying the genes by PCR. The primers sequences were previously reported in the literature, [9] and obtained from TIB MOLBIOL Syntheselabor GmbH (Berlin, Germany). Descriptions and sequences of the PCR primers used in this study are shown in [Table 1]. Other enzymes and chemicals were provided by Cinnagen Chemical Company (Tehran, Iran). Amplification was performed in a thermal cycler (Eppendorf, Germany) according to the methods described by Yamamoto et al. [10] Expected sizes of the amplicons were ascertained by electrophoresis in 1.5 % agarose gel with an appropriate molecular size marker (100-bp DNA ladder, MBI, Fermentas, Lithuania).
| Statistical Analysis | | |
Statistical analysis was performed using SPSS software for Windows, version 11.5 (SPSS). Descriptive analyses were performed for parametric and non parametric variables. Student 't' test, Chi square, and logistic regression were done for evaluation of variables correlation. P value less than 0.05 was considered as significant.
| Results | | |
A Total of 96 E. coli strains were isolated from 96 (60 female (62.5%) and 36 male 37.5%) children with UTI referred during the study period. The patients' ages ranged from one month to 14 years with a mean of 21.8 ± 26.9 months. There were 49.2% of cases that were diagnosed as cystitis, and 50.8% as acute pyelonephritis. Pyelonephritis was more prevalent in girls than boys (63.2% vs. 36.4%, P= 0.04). Only 37 patients had ultrasound of the kidneys. Fourteen cases had abnormal findings that included reflux, UPJ stenosis, multicystic kidney, and single kidney [Table 2].
In polymerase chain reaction analysis [Figure 1], the prevalence of virulence genes ranged from 13.5% for hly to 27.1 % for pap. Of the two studied adhesin coding genes, pap was more prevalent (n=26, 27.1 %) than sfa (n=14, 14.6%), while of the two studied toxin coding genes, cnf-1 was more prevalent (n=22, 22.9 %) than hly (n=13, 13.5 %). Of all isolates, 32 (33.3 %) revealed at least one gene and 14 (6.3%) revealed all four genes.
The results showed a significant correlation between the age of the patients and presence of genes. By using Medcalc software, we could define a cut point of 36 months, so the prevalence of genes pap and sfa was more common in patients older than 36 months (P< 0.05), however, hly was more common in patients younger than 48 months (66.7% vs. 33.3%, (P< 0.05), [Table 2].
Pyelonephritis was diagnosed in 66.7%, 62.5%, 63.6%, and 85.7% of the cases positive for pap, sfa, cnf-1 and hly, respectively. Furthermore, there was a significant correlation between the presence of cnf-1 and abnormal findings on kidney ultrasound; 83.3% of patients with cnf-1 gene in their urine samples had abnormal findings (P= 0.019).
| Discussion | | |
In the present study, we found that 27.1%, 22%, 14.6%, and 13.5% of E. coli isolated from urine samples of children with UTI were positive for pap, cnf-1, sfa, and hly genes, respectively. Various studies investigated the prevalence of virulence genes of E. coli isolates from cases of UTI. A study from Spain showed that almost 70% of the urinary strains carried at least one of the target virulence genes. [11] Silveira and co workers found prevalence of 38.5%, 15.4%, and 7.7% for the phenotypes of pap +sfa + - afa + , sfa-related sequences genes positive and pap + - sfa + , respectively, in uropathogenic E. coli strains, while only two cases were positive for cnf-1 gene. [12] Arisoy studied 161 E. coli strains isolated from children with UTI and found that 58.4% was positive for at least one virulence gene; prevalence of genes were found as 22.98%, 9.94%, 6.21%, and 1.24% for pap, cnf-1, sfa, and hly, respectively. [9]
Our results highlight higher frequency of pap compared with the rest of the genes, and this may indicate a crucial role of the virulence genes in E. coli associated UTI. In uropathogenic E. coli, the presence of P fimbriae has been clearly established as a factor that promotes urinary tract colonization and invasion. Bacterial adhesion to the bladder mucosa is a critical step for the establishment of E. coli bacteriuria. [13] ,[14] Indeed, two genes in the pap class were found to play more important role in the development of E. coli bacteremia in patients with UTI than in those with acute cholangitis. [15]
Moreover, an important role of pap adhesion genes in the pathophysiology of pyelonephritis caused by E. coli has been reported in several studies. [16],[17],[18],[19] In our study, pyelonephritis was more prevalent in the cases with virulence genepositive E. coli isolates; 66.6%, 62.5%, 63.3% and 85.7% of cases that were positive for pap, sfa, cnf-1 and hly, respectively, developed pyelonephritis. In another study, 25 of 42 cases with pyelonephritis were positive for pap gene, but only 6 of 58 strains isolated from cases with cystitis were positive for this gene. Furthermore, in our study, the prevalence of hly and cnf-1 in pyelonephritis was 34% and 21.9%, respectively. [20] Chatal showed that pap operons were found in 79.4% of the pyelonephritis strains, either alone (51.5% of the isolates) or in association with either the afa or sfa/foc operon (27.9%). Those observations, which confirmed the high prevalence of pap operons among E. coli strains associated with pyelonephritis, also indicated that the afa and sf a lf oc operons represented uropathogenic determinants per se. [8]
The ability to adhere to epithelial surfaces has been shown to be a prerequisite for E. coli strains to colonize the urinary tract, i.e., to cause UTI in the absence of urological abnormalities. Surveys of patients with acute pyelonephritis have suggested that urinary tract abnormalities or medical intervention may allow nonpathogenic organisms' access to the kidneys. [2] Accordingly, some investigators have proposed that the absence of adhesive properties in a pyelonephritis isolate could be used as an indicator of a possible underlying anatomic abnormality or medical illness, warranting further investigation of patients. [21] In our study, the prevalence of pap and sfa was lower in patients with abnormal findings on kidney ultrasound, but the prevalence of cnf-1 was significantly higher in these patients (P= 0.019).
In conclusion, our study found higher prevalence of pyelonephritis in the presence of virulence genes (pap, sfa, hly and cnf-1) of uropathogenic E. coli strains. Detection of the genes in urine samples may help predict incidence of pyelonephritis.
| Acknowledgement | | |
This work was supported by research grant #83-14 from Professor Alborzi Clinical Microbiology Research Center, Shiraz University of Medical Sciences. The authors would like to thank Mr. Mehdi Kalani and Mrs. Marzieh Hosseini for their assistance in bacterial isolation, identification, purification and molecular diagnosis.
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Correspondence Address:
Fatemeh Emamghorashi
Pediatric Department, Jahrom University of Medical Sciences, Jahrom
Iran
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PMID: 19587502 
[Figure 1]
[Table 1], [Table 2] |
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