SUMMARY
Objectives
The aim of this study was to determine the antibiotic resistance of infectious and non-infectious E. coli species in order to increase the success of empirical antibiotic treatment in urinary system infections.
Methods
The antibiotic susceptibility of 464 E. coli strains that were isolated from urine samples of patients who visited Derince Training and Research Hospital Emergency Department between January 1 and December 31, 2012 were retrospectively evaluated from records. The antibiogram results were classified as susceptible, moderately susceptible or resistant. Moderately susceptible strains were assumed to be resistant.
Results
Bacterial proliferation was seen in 563 (28.1%) of the 1998 urine cultures tested. One hundred and twelve cultures could not be evaluated due to contamination, and there was no proliferation in 1323 cultures. E. coli strains were isolated in 464 (82.4%) of the cultures in which proliferation was seen. Three hundred and sixty seven (79%) of the patients were female, 97 (21%) were male, and the mean age of all of the patients was 41.1±24.1 years (min: 1, max: 90). The antibiograms of the E. coli strains revealed that meropenem had the lowest resistance (0%), while ampicillin-sulbactam had the highest resistance (36.8%).
Conclusions
In this study, we investigated the antibiotic resistance of E. coli strains isolated from urine cultures in our region. Future studies, perhaps similar to this one, can be performed in the future to increase the success of treatments.
Key words: Culture, E. coli, emergency, urine
ÖZET
Amaç
Bu çalışmada üriner sistem enfeksiyonlarında ampirik antibiyotik tedavi başarısını artırmak için enfeksiyon etkeni olan veya olmayan E.coli suşlarının çeşitli antibiyotik türlerine direnci araştırıldı.
Gereç ve Yöntem
1 Ocak-31 Aralık 2012 tarihleri arasında Derince Eğitim ve Araştırma Hastanesi acil servisine başvuran hastaların mikrobiyoloji laboratuvarına gönderilmiş idrar örneklerinden izole edilen 464 E.coli suşunun antibiyotik duyarlılıkları bilgisayar kayıtları üzerinden retrospektif olarak değerlendirildi. Antibiyogram sonuçları duyarlı, orta duyarlı ve dirençli olarak sınıflandırıldı. Orta duyarlı suşlar dirençli kabul edildi.
Bulgular
1998 idrar kültüründen 563'ünde (%28.1) üreme oldu. Kültürlerin 112'si kontaminasyon nedeniyle değerlendirilemedi, 1323 kültürde ise üreme olmadı. Üreme olan kültürlerden 464'ünde (%82.4) E.coli suşları izole edildi. Hastaların 367'si (%79) kadın 97'si (%21) erkek, tüm hastaların yaş ortalaması 41.1±24.1 (min: 1, maks: 90) idi. E.coli suşlarına karşı antibiyogramlar incelendiğinde, direncin en düşük görüldüğü antibiyotik meropenem (%0), en yüksek görüldüğü antibiyotik ise ampisilinsulbaktam olarak saptandı (%36.8).
Sonuç
Bölgemizde idrar kültürlerinden izole edilen E.coli suşlarına karşı antibiyotik dirençlerini incelediğimiz çalışmamızın benzerlerinin ilerleyen dönemde yapılmasının tedavi başarısına yardımcı olacağını düşünmekteyiz.
Anahtar sözcükler: Kültür, E.coli, acil, idrar
Introduction
Urinary system infection is defined by the existence of bacteria in the kidneys, collecting duct system, and/or urinary bladder, as well as pyuria and clinical symptoms. Its severity ranges from asymptomatical bacteriuria to pyelonephritis. [1] Urinary system infection is the most common type of infection in adults.[2] 25–35% of women between the ages of 20–40 years have urinary system infection,[3] and there are 5 million attacks of cystitis in our country every year.[4] E. coli is present in 50–90% of these infections. Antibiotics are commonly used to treat urinary system infections, although they should be used with caution. The most important issues to monitor during antibiotic treatment are duration of treatment, toxicity of the medication, and cost. Antibiotics used should not spoil the intestinal, perineal and vaginal flora, but should be effective against E. coli colonization.[5] Local antibiotic resistance should be followed up regularly in order to successfully treat urinary system infections.[6] Several studies have shown that antibiotic resistance is increased in E. coli strains that cause urinary system infections. Antibiotic resistance is particularly common with cotrimoxazole and betalactams, which are relatively old molecules.[7] However, more recent research has indicated that resistance is increasing in fluoroquinolones as well.[8] In this study, the antibiotic resistance of infectious and non-infectious E. coli species was investigated to increase the success of empirical antibiotic treatment in urinary system infections.
Materials and Methods
Patients with symptoms of urinary tract infection who presented at Derince Training and Research Hospital Emergency Department, Turkey, between January and December 2012 were included in this study. Clinical evidence for urinary tract infection included dysuria, fever, urgency, frequency, suprapubic or flank pain, or other clinical presentations consistent with a urinary tract infection. For patients with more than one sample, we included only the first positive sample. The antibiotic susceptibility of 464 E. coli strains was retrospectively evaluated from hospital records. The ethics committee approved this study. The urine samples were isolated in a sterile way, inoculated in 5% sheep blood agar (RTA) and EMB (RTA) via a quantitative method, and were placed in an incubator (37°C) for 24–48 hours. Bacteria were detected by gram staining, evaluating colony morphology, and by traditional biochemical tests (TSI agar, Simmon's citrate agar, movement medium, Christensen urea agar, reactions in indol medium, catalase, oxidase, coagulase, esculin hydrolysis). Bacteria were identified by an automated Phoenix system (BBL Becton Dickinson). Antibiotic susceptibility in proliferating bacteria was evaluated by the Kirby-Bauer disc diffusion method in accordance with the CLSI (Clinical Laboratory Standards Institute) criteria using Müler-Hinton agar (RTA) for automated systems. Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 29213), Staphylococcus aureus (ATCC 25923) and Pseudomonas aeruginosa (ATCC 27853) were used as quality controls. The antibiogram results were classified as susceptible, moderately susceptible or resistant. Moderately susceptible strains were assumed to be resistant.
Statistical Analysis
Data from this study were recorded and evaluated using SPSS version 13.0 for Windows. The Chi-square test was used to evaluate categorical variables. Continuous variables were expressed as mean±standard deviation, minimum and maximum values were expressed as parenthetical values, and qualitative variables were expressed as number and percentage (%). P≤0.05 was regarded as statistically significant.
Results
Bacterial proliferation was detected in 563 (28.1%) of the 1998 urine cultures. One hundred and twelve cultures could not be evaluated due to contamination and there was no proliferation in 1323 cultures. E. coli strains were isolated in 464 (82.4%) of the cultures in which there was proliferation. Three hundred and sixty seven (79%) of the patients were female, 97 (21%) were male, and the mean age of all of the patients was 41.1±24.1 years (min:1, max:90). Antibiograms of the E. coli strains revealed that the lowest resistance was found in cultures treated with meropenem (0%), nitrofurantoin (3.9%), ceftazidime (8.2%), gentamicin (8.3%), and cefepime (9.5%). Those with the highest resistance included amoxicillin-clavulanic acid (23.4%), ampicillin-sulbactam (36.8%), norfloxacin (14.9%), cefazoline (15.1%), ceftriaxone (11.1%), cefuroxime (12.9%), ciprofloxacin (17.7%) and cotrimoxazole (28%) (Table 1).
Table 1.
Resistance rates of antibiotics
| Antibiotic | Resistance (%) |
|---|---|
| Meropenem | 0 |
| Nitrofurantoin | 3.9 |
| Ceftazidime | 8.2 |
| Gentamicin | 8.3 |
| Cefepime | 9.5 |
| Amoxicillin-Clavulanic Acid | 23.4 |
| Ampicillin-Sulbactam | 36.8 |
| Norfloxacin | 14.9 |
| Cefazoline | 15.1 |
| Ceftriaxone | 11.1 |
| Cefuroxime | 12.9 |
| Ciprofloxacin | 17.7 |
| Cotrimoxazole | 28 |
Discussion
The culture positivity ratio in our study was 28.1%, while those in previously published studies were 51.2% (in Ertuğrul et al.'s study),[4] 35% (in Gupta et al.'s study),[9] and 57.8% (in Pekdemir's study).[11] We hypothesize that the difference between the results of our study and others is that we included patients younger than 18 years, while the other studies did not. Urine culture is frequently used in female children younger than 10 years presenting to emergency service.
E. coli is the pathogen frequently responsible for urinary tract infection. Worldwide, the proliferation ratio of E. coli in urine cultures is 75–90%.[9] In our country, various studies have reported this ratio to be 65–80%.[10] E. coli was the most common pathogen (82.3%) in the current study, which is similar to previously reported results.
Ciprofloxacin and cotrimoxazole are antibiotics that are often used for the treatment of simple urinary tract infection. In our study, resistance to ciprofloxacin was 17.7%, which is similar to other studies, in which it was reported to be between 5–46%.4, 12, 13 When compared with other antibiotics included in our study, ciprofloxacin is the 4th most resistant molecule.
Resistance to cotrimoxazole was 28% in our study, which was lower than that found in Güneysel's study (34%)[14] and Pekdemir's study (40.4%).[11] Cotrimoxazole was the 2nd most resistant antibiotic used in our study. The results of our study and others suggest that cotrimoxazole is very resistant in empirical treatment.
In our study, the resistance ratios of ampicillin-sulbactam (36.8%), amoxicillin-clavulonic acid (23.4%) and ciprofloxacin (17.7%) were significantly higher than that of nitrofurantoin (3.9%) (p≤0.05). On average, nitrofurantoin is used at 400 mg/day in 4 equal doses to treat urinary tract infections in adults. At this concentration, it is only effective in the urine and kidneys, and is not effective in other tissues.[15] Cotrimoxazole and ciprofloxacin are most often used in the empirical treatment of simple urinary tract infections, and because they are used only twice a day, patient compliance is higher. These antibiotics are effective in tissues other than the urine and kidneys. In our study and others, nitrofurantion was more successful in treating urinary tract infections, but the guidelines of the Infectious Diseases Society of America (IDSA) indicate that there is no difference between nitrofurantoin and cotrimoxazole in seven day-treatment, and that more comparative studies are necessary.[16] Since susceptibility to nitrofurantoin is significantly high, we believe that future studies should compare its treatment with that of other oral antibiotics.
Limitations
One limitation of this study is its retrospective methodology, as the urine culture indications could not be determined clearly from the records. In addition, because not all of the medical records were clear, there is a possibility that we misclassified some of the patients. The external validity of this study is also limited because it was performed in a single center. Centers with different demographic characteristics and those in different geographic regions might have different resistance patterns.
Conclusion
It is important to evaluate local antibiotic resistance to ensure the successful treatment of urinary system infections. In this study, we investigated the antibiotic resistance among E. coli strains isolated from urine cultures in our region. Future studies similar to this can be performed in order to help increase the success of treatment.
Conflict of Interest
The authors declare that there is no potential conflicts of interest.
Footnotes
Published online: August 30, 2014
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