Background and Objectives: Urinary Tract Infections (UTI) are the second most common infections after the respiratory tract infections and constitute a great proportion of prescription of antibiotics. The present study was designed to determine the etiology of uropathogens and their susceptibility pattern in outpatients and inpatients of our hospital so as to arrive at an empirical treatment for patients with UTI. Materials and Methods : A total of 924 urine samples were obtained from inpatients and outpatients with a clinical diagnosis of UTI. The samples were cultured and antibiotic susceptibility of isolates determined by disc diffusion method. Results: Of 924 urine samples processed (828 from inpatients and 96 from outpatients), 262 (28.35%) yielded bacterial isolates. About 216 (26.08%) samples from inpatients and 46 (47.9%) from outpatients showed significant bacteriuria. Escherichia coli predominated in both groups, followed by Klebsiella spp., Pseudomonas spp., Acinetobacter spp., and Enterobacter spp., which were isolated from only the inpatient samples. Sensitivity to nitrofurantoin varied from 73% to 94% and fluoroquinolone resistance was documented as 11%-80%. Resistance to amikacin, ceftazidime, and ceftriaxone was less than 25%. Imipenem resistance was found in <5% of the bacterial isolates. Conclusion: E. coli and Klebsiella spp. are the major uropathogens. Resistant strains are prevalent in the community, as evident by the fact that there is not much difference in resistance patterns of isolates from inpatients and outpatients. Taking into account the resistant pattern, nitrofurantoin represents the option of first choice for empirical therapy of uncomplicated UTI.
Keywords: Antibiotic, empirical, urinary tract infections
Urinary Tract Infections (UTI) are the second most common infections after respiratory tract infections and constitute a great proportion of prescription of antibiotics. With the advent of novel antibiotics, though a significant reduction in the prevalence of infectious diseases was seen worldwide in the initial years, eventually a new form of infectious diseases caused by drug-resistant bacteria has evolved. The use of an antibiotic has been correlated with the subsequent development of resistance to it. , The organisms causing UIT are often the intestinal flora.  Antibiotic resistance is common in intestinal bacteria due to therapy for infections other than UTI.  Antibiotic resistance among uropathogens has increased over the past 30 years. ,, Resistance to ampicillin increased from 12% to 43% in Britain between 1971 and 1992. The resistance rates were 56% to ampicillin, 24% to ampicillin/sulbactam, 15% to ciprofloxacin, 36% to trimethoprim-sulfamethoxazole and 75% to cefuroxime according to a study from Turkey.  According to a recent study from India, resistance rates among uropathogens were very high, with 76% strains resistant to third-generation cephalosporins.  The empirical therapy should be based on the local data about the prevalent uropathogens and their antimicrobial resistance. The present study was, therefore, designed to determine the etiology of uropathogens and their susceptibility pattern in outpatients and inpatients of our hospital so as to arrive at an empirical treatment for patients with UTI.
This prospective study was conducted in the department of microbiology from June 2010 to October 2010 over a period of five months. The urine samples were obtained from inpatients and outpatients of our teaching hospital with a clinical diagnosis of suspected UTI.
The samples included midstream urine specimen, catheterized urine samples, supra-pubic aspirates collected in sterile universal bottles (approximately 15 ml). A total of 924 samples were processed during the study period. The uncentrifuged samples were inoculated with a calibrated loop delivering 0.001 ml of urine sample onto Cystine Lactose Electrolyte Deficient medium (CLED) agar and blood agar plates. The inoculated culture plates were incubated at 37°C for 24 hr. A significant bacterial count was taken as any count equal to or more than 10 5 /ml of urine for Gram-negative bacteria and 10 3 -10 4 /ml of urine for Gram-positive bacteria. The isolates were identified by biochemical tests as per standard methods. 
Antimicrobial susceptibility testing was performed on Mueller-Hinton Agar (MHA) plates (HiMedia Laboratories, Mumbai) by disc diffusion method. Each strain was inoculated onto MHA plate and antibiotic discs were placed on the inoculated MHA plates, which were then incubated at 37°C for 24 hr. The following antimicrobial discs were tested for Gram-negative isolates: ampicillin (10 μg), nalidixic acid (30 μg), ciprofloxacin (5 μg), nitrofurantoin (300 μg), trimethoprim-sulfamethoxazole (1.25/23.75 μg), cefuroxime (30μg), ceftriaxone (30 μg), ceftazidime (30 μg), imipenem (10 μg), and amikacin (30 μg). The antimicrobials tested for Gram-positive isolates were the following: ampicillin (10 μg), ciprofloxacin (5 μg), trimethoprim-sulphamethoxozole (1.25/23.75 μg), nitrofurantoin (300 μg), cefuroxime (30 μg), ceftriaxone (30 μg), oxacillin (1 μg), and vancomycin (30 μg). The results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI) criteria.  Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 were used as the standard control strains.
A total of 924 urine samples were processed (828 from inpatients and 96 from outpatients). Of these samples, 262 (28.35%) specimens yielded bacterial isolates. About 216 (26.08%) samples from inpatients and 46 (47.9%) from outpatients showed significant bacteriuria.
E. coli predominated in both groups followed by Klebsiella spp. and Citrobacter spp. [Table 1]. Proteus spp. and Staph. aureus were isolated from both groups, whereas Pseudomonas spp., Acinetobacter spp., and Enterobacter spp. were isolated from only the inpatient samples.
The antibiotic sensitivity pattern of Gram-negative isolates is shown in [Table 2]. A majority of isolates were resistant to trimethoprim-sulfamethoxazole, nalidixic acid, cefuroxime, and ampicillin. Sensitivity to nitrofurantoin varied from 73% to 94% with E. coli being the most sensitive and Proteus spp. as least sensitive. Fluoroquinolone resistance was documented as 11%-80%. Resistance to amikacin, ceftazidime, and ceftriaxone was less than 25%. Imipenem resistance was found in <5% of the bacterial isolates.
Among nine strains of Staph. aureus obtained, three were oxacillin resistant. All Staph. aureus strains were sensitive to vancomycin.
E. coli was the most common pathogen causing UTI in both inpatients and outpatients. Pseudomonas spp. and Acinetobacter spp. were isolated from hospitalized patients only. Similar results have been reported by other investigators. , Pseudomonas spp. is noted to survive and thrive well in soaps and disinfectants used for urethral catheterization. Gram-negative organisms were more prevalent than Gram-positive organisms in our set-up, which is similar to reports from other hospitals.  Staph. aureus was the only Gram-positive bacteria obtained in both groups.
The degree of resistance to routinely used antibiotics in both groups was almost similar. This is in contrast to some previous studies, which showed that resistance is more in isolates from hospitalized patients than the outpatients. , Recent studies have shown results similar to the present study.  This indicates that the drug-resistant strains have spread in the community.
A high degree of resistance to ampicillin, co-trimoxazole, nalidixic acid, and cefuroxime was found. These antibiotics have been used for many years to treat UTI. The fluoroquinolones with their broad-spectrum activity are still being used as one of the best treatment options for UTI.  In our study, the resistance to ciprofloxacin was variable among different species of isolates, with 89% of Enterobacter spp. strains and 20% of Proteus spp. being resistant. The overall susceptibility to this drug was 45%, which indicates that it may no more be advocated for empirical therapy of UTI.
Nitrofurantoin is a urinary antibiotic, hence not used for infections outside the urinary tract. This may be the reason that resistance to this agent has not occurred much. We found the average susceptibility to this drug to be 85%. As Pseudomonas spp. and Acinetobacter spp. have intrinsic resistance to this drug, we did not test our strains for this antibiotic. As nitrofurantoin has shown good effect on uropathogens (E. coli, Klebsiella spp., Proteus spp., Staph. aureus) that are responsible for community-acquired UTI, we recommend this drug for empirical therapy of UTI.
Third-generation cephalosporins, ceftriaxone, and ceftazidime showed good activity against the bacterial strains. Resistance to ceftriaxone and ceftazidime was <25% and <24%, respectively. This shows that the majority of bacterial strains in our community and hospital are not Extended-Spectrum Beta-Lactamase (ESBL) producers. This result is interesting and different from other studies, which have reported >76% of uropathogens as ESBL producers.  Hence, third-generation cephalosporin may be considered as the first line of therapy for UTI.
Resistance to Imipenem was very low (<5%). It was also noticed that resistance to this drug was seen only with Enterobacter spp., Citrobacter spp. and E. coli, whereas all strains of Klebsiella spp., Pseudomonas spp., Acinetobacter spp., and Proteus spp. were sensitive. Carbapenem is the final therapeutic option for any infection, and hence cannot be given for empirical therapy.
The aminoglycoside, amikacin was effective on >80% of bacterial isolates as also reported from other studies. , The activity of amikacin on Pseudomonas spp. (92%) and Acinetobacter spp. (100%) was good. Keeping in mind the toxicity of an aminoglycoside, it is suggested to keep this drug for second line therapy for UTI.
Our data report that E. coli and Klebsiella spp. are the major uropathogens. These reveal that the resistance to antimicrobials is increasing and such strains are prevalent in the community, as evident by the fact that there is not much difference in resistance patterns of isolates from inpatients and outpatients. Keeping the emerging antimicrobial resistance in mind, it is suggested to start antimicrobial therapy only after the sensitivity report from the microbiology laboratory. Taking into account the resistance pattern, nitrofurantoin represents the option of first choice for empirical therapy of uncomplicated UTI.
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]