International Journal of Infectious Diseases (2009) 13, 140—144
http://intl.elsevierhealth.com/journals/ijid
Causative agents and antimicrobial susceptibilities
of urinary tract infections in the northwest of Iran
Safar Farajnia a,b, Mohammad Yousef Alikhani c,*, Reza Ghotaslou d,
Behrooz Naghili e, Ailar Nakhlband a
a
Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical Sciences, Tabriz, Iran
c
Department of Microbiology, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
d
Department of Microbiology, Tabriz University of Medical Sciences, Tabriz, Iran
e
Research Center for Infectious and Tropical Disease, Tabriz University of Medical Sciences, Tabriz, Iran
b
Received 12 December 2007; received in revised form 15 March 2008; accepted 23 April 2008
Corresponding Editor: Andy I.M. Hoepelman, Utrecht, The Netherlands
KEYWORDS
Urinary tract infection;
UTI;
Causative agents;
Antimicrobial resistance
Summary
Background: The empirical therapy of urinary tract infections (UTI) relies on the predictability of
the agents causing UTI and knowledge of their antimicrobial susceptibility patterns.
Methods: In a prospective study undertaken over a 14-month period, 5136 samples from patients
suspected of having a UTI were analyzed, of which 676 were culture-positive. Isolated bacteria
were identified by standard tests, and antibiotic susceptibility was determined by disk diffusion
method.
Results: According to our results, Escherichia coli was the most common etiological agent of UTI
(74.6%), followed by Klebsiella spp (11.7%), Staphylococcus saprophyticus (6.4%), and Pseudomonas
aeruginosa (2.2%). Analysis of the frequency of isolated bacteria according to the age of the patients
revealed that Klebsiella infections are more prevalent in the older age groups (>10 years) and
Pseudomonas infections are more prevalent in children and the elderly (<9 years and >60 years).
Results of antimicrobial susceptibility analysis for E. coli, as the most prevalent cause of UTI, to
commonly used antibiotics are as follows: amikacin (97.8%), gentamicin (97%), ciprofloxacin (94%),
nitrofurantoin (87.1%), nalidixic acid (93.7%), trimethoprim—sulfamethoxazole (48.2%), cephalexin
(76%), and ampicillin (6.9%).
Conclusions: The results show that the antimicrobial resistance patterns of the causes of UTI are
highly variable and continuous surveillance of trends in resistance patterns of uropathogens is
important.
# 2008 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +98 811 8276295; fax: +98 811 8276299.
E-mail address: alikhani43@yahoo.com (M.Y. Alikhani).
1201-9712/$36.00 # 2008 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijid.2008.04.014
141
Urinary tract infections in the northwest of Iran
Figure 1
Frequency of isolated bacteria from positive urine samples according to patient gender.
Introduction
Urinary tract infections (UTIs) are one of the most common
infectious diseases, and nearly 10% of people will experience
a UTI during their lifetime.1,2 UTIs are the most common
infections after upper respiratory tract infections.3 The
infections may be symptomatic or asymptomatic, and either
type of infection can result in serious sequelae if left
untreated.4 Although several different microorganisms can
cause UTIs, including fungi and viruses, bacteria are the
major causative organisms and are responsible for more than
95% of UTI cases.5 Escherichia coli is the most prevalent
causative organism of UTI and is solely responsible for more
than 80% of these infections. An accurate and prompt diagnosis of UTI is important in shortening the disease course and
for preventing the ascent of the infection to the upper
urinary tract and renal failure.6
Treatment of UTI cases is often started empirically. Therapy is based on information determined from the antimicrobial resistance pattern of the urinary pathogens. However,
because of the evolving and continuing antibiotic resistance
Table 1
phenomenon, regular monitoring of resistance patterns is
necessary to improve guidelines for empirical antibiotic
therapy.6—8 The aim of this study was to determine the
causative agents of UTIs and their susceptibility patterns
to commonly used antibiotics in patients from the East
Azerbaijan province of Iran.
Methods
Study design
This study was conducted in the microbiology section of the
Central Laboratory of Tabriz University of Medical Sciences.
Urine samples were collected from 5136 outpatients suspected of having a UTI, who had not received antimicrobials
within the previous two months, and referred to the Central
Laboratory for urine culture. There were 3842 (74.8%) samples from female patients and 1294 (25.2%) from male
patients. Patient age ranged from 1.5 to 65 years (mean
age 28.2 years). All patients were from East Azerbaijan
province in the northwest of Iran. Adult patients were
Frequency of isolated bacteria from positive urine samples according to patient age
Organism
Age (years)
0—9
n (%)
10—19
n (%)
20—29
n (%)
Escherichia coli
Klebsiella spp
Enterobacter spp
Proteus spp
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus saprophyticus
Enterococci
60
2
2
2
5
1
3
-
61
9
1
1
5
1
153
19
4
2
1
4
10
2
Total (%)
75 (11.1)
(80)
(2.7)
(2.7)
(2.7)
(6.7)
(1.3)
(4)
(78.2)
(11.5)
(1.3)
(1.3)
(6.4)
(1.3)
78 (11.5)
(78.5)
(9.7)
(2.1)
(1.0)
(0.5)
(2.1)
(5.1)
(1.0)
195 (28.8)
30—39
n (%)
77
12
2
11
4
(72.6)
(11.3)
(1.9)
(10.4)
(3.8)
106 (15.7)
40—49
n (%)
50—59
n (%)
>60
n (%)
59
15
1
1
2
5
1
48
7
1
1
2
5
-
46
15
7
2
4
-
(70.2)
(17.9)
(1.2)
(1.2)
(2.4)
(6.0)
(1.2)
84 (12.4)
(75)
(10.9)
(1.6)
(1.6)
(3.1)
(7.8)
64 (9.5)
(62.2)
(20.3)
(9.5)
(2.7)
(5.4)
74 (10.9)
Total
n (%)
504
79
8
8
15
11
43
8
(74.6)
(11.7)
(1.2)
(1.2)
(2.2)
(1.6)
(6.4)
(1.2)
676 (100)
58
129
33
48
23
676
Total
1 (12.5%)
0 (0%)
3 (37.5%)
8
3 (37.5%)
2 (4.7%)
0 (0%)
6 (14.0%)
43
9 (20.9%)
2 (18.2%)
0 (0%)
0 (0%)
0 (0%)
11
N, number of isolates; AMK, amikacin; GEN, gentamicin; CIP, ciprofloxacin; NIT, nitrofurantoin; NAL, nalidixic acid; SXT, trimethoprim—sulfamethoxazole; CEP, cephalexin; AMP, ampicillin; CAR,
carbenicillin; VAN, vancomycin; OXA, oxacillin.
31
0
10
613
179
350
7 (87.5%)
0 (0%)
4 (50%)
8 (100%)
4 (50%)
7 (87.5%)
0 (0%)
6 (14.0%)
25 (58.1%)
5 (11.6%)
27 (62.8%)
0 (0%)
0 (0%)
8 (72.7%)
2 (18.2%)
2 (18.2%)
469
72
8
8
15
(51.8%)
(40.5%)
(37.5%)
(37.5%)
(100%)
261
32
3
3
15
(6.3%)
(13.9%)
(0%)
(0%)
(100%)
504
79
8
8
15
Escherichia coli
Klebsiella spp
Enterobacter spp
Proteus spp
Pseudomonas
aeruginosa
Staphylococcus
aureus
Staphylococcus
saprophyticus
Enterococci
11
1
0
0
2
(2.2%)
(1.3)
(0%)
(0%)
(13.3%)
15
15
2
0
4
(3.0%)
(19.0%)
(25%)
(0%)
(26.7%)
30
1
0
0
2
(6.0%)
(1.3%)
(0%)
(0%)
(13.3%)
65
36
3
5
15
(12.9%)
(45.6%)
(37.5%)
(62.5%)
(100%)
32
11
0
0
15
SXT
NAL
NIT
CIP
GEN
Over a 14-month period, 5136 urine samples from outpatients
were analyzed, of which 676 (13.2%) had significant bacteriuria. The rate of positive culture was 15.2% (583/3842) for
female subjects and 7.2% (93/1294) for male subjects. Gramnegative bacilli were responsible for 85.6% of cases followed
by Gram-positive cocci, responsible for 9.3% of cases.
Analysis of the results according to patient gender indicated that although E. coli is the predominant isolated
pathogen from both sexes, it occurred significantly more
frequently in women (76.5% in women compared to 62.4%
in men; p < 0.05), whereas the prevalences of UTI due to
Klebsiella pneumoniae and Pseudomonas aeruginosa were
higher in men than in women (22.6% and 7.5% in men compared to 9.9% and 1.4% in women, respectively; p < 0.01)
(Figure 1). The prevalence of UTI caused by Staphylococcus
saprophyticus in women (7%) was higher than in men (2.2%).
Analysis of the frequency of isolated bacteria according to
patient age (Table 1) revealed that Pseudomonas infections
are more prevalent in children and the elderly (<9 years and
>60 years) and Klebsiella infections are more prevalent in
the older age groups (>10 years).
AMK
Isolation and identification of bacteria
Antibiotic
Results
N
Discrete variables were expressed as percentages and proportions were compared using the Chi-square test.10
Organism
Statistical analysis
Table 2
Antimicrobial susceptibility of isolates was tested by the disk
diffusion method according to the National Committee on
Clinical Laboratory Standards (NCCLS) recommendations,
using Mueller—Hinton medium.6 Antimicrobial agents tested
were amikacin, gentamicin, ciprofloxacin, nitrofurantoin,
nalidixic acid, trimethoprim—sulfamethoxazole, ampicillin,
cephalexin, oxacillin, and vancomycin (BD BBLTM Sensi-DiscTM).
Resistance rates of isolated bacteria from positive urine samples to commonly used antibiotics
Susceptibility testing
121
27
3
2
15
CEP
(24.0%)
(34.2%)
(37.5%)
(25%)
(100%)
AMP
(93.1%)
(91.1%)
(100%)
(100%)
(100%)
CAR
VAN
Samples for urine culture were tested within an hour of
sampling. All samples were inoculated on blood agar as well
as MacConkey agar and incubated at 37 8C for 24 hours, and
for 48 hours in negative cases. A specimen was considered
positive for UTI if a single organism was cultured at a concentration of 105 cfu/ml, or when a single organism was
cultured at a concentration of 104 cfu/ml and 5 leukocytes
per high-power field were observed on microscopic examination of the urine. Bacterial identification was based on
standard culture and biochemical characteristics of isolates.
Gram-negative bacteria were identified by standard biochemical tests.5,6 Gram-positive microorganisms were identified with the corresponding laboratory tests: catalase,
coagulase, CAMP test (for Streptococcus agalactiae), and
esculin agar (for enterococci).9
-
Isolation and identification of organisms
-
OXA
sampled by clean catch midstream urine and children aged
under 3 years were sampled using sterile urine bags.
20 (46.5%)
S. Farajnia et al.
4 (36.4%)
142
Urinary tract infections in the northwest of Iran
Antimicrobial susceptibility
The rates of resistance of isolates to a panel of antibiotics,
including penicillins, cephalosporins, quinolones, aminoglycosides, and trimethoprim—sulfamethoxazole, which are routinely used to treat UTI infections, are shown in Table 2. E. coli as
the predominant cause of UTI, showed the highest percentage
of resistance to ampicillin (93.1%) and the lowest resistance to
amikacin (2.2%). Klebsiella spp as the second most prevalent
pathogen of UTI displayed a similar resistance pattern and
were resistant to ampicillin in 91.1% of cases and susceptible to
amikacin in 98.7% of cases. P. aeruginosa showed the highest
antibiotic resistance rate and was significantly resistant to
most of the antibiotics (Table 1). In this study, staphylococci
were responsible for about 8% of UTI cases; among these, S.
saprophyticus was the most common species isolated. S.
saprophyticus and Staphylococcus aureus were resistant to
ampicillin in 58.1% and 72.7% of cases, respectively, whereas,
46.5% of S. saprophyticus and 36.4% of S. aureus were resistant
to oxacillin.
Discussion
Microbial infection of the urinary tract is one of the most
common infectious diseases worldwide. In this study, of 5136
patients from who urine samples were taken, only 13.2% had
a urinary tract infection. This is possibly because UTI symptoms are not a reliable indicator of infection and in children
younger than 2 years of age are non-specific. In our investigation, most of the urine samples were collected from
patients who did not have a combination of UTI symptoms,
and most of the subjects had been referred by general
practitioners not specialist physicians. These results indicate
that urine culture is necessary for a definitive diagnosis of
UTI, and that empirical therapy should only be done by
specialist physicians in cases where it is necessary. Our results
show a lower urinary tract infection rate of 7.2% in males.
The reason for this may be due to the higher number of
women than men in this study, and because males are less
prone to UTIs, possibly because of their longer urethra and
the presence of antimicrobial substances in prostatic fluid.
Although the prevalence of pathogens in different parts of
the world is somewhat similar, antimicrobial resistance patterns reported from different regions are significantly different and antimicrobial resistance is increasing. The results
of our study show that among the heterogeneous causative
organisms of UTI, Enterobacteriaceae are the predominant
pathogens, followed by Gram-positive cocci. These findings
are consistent with reports published from other countries.11—13
The highest percentages of resistance were found for
ampicillin (90.7%), trimethoprim—sulfamethoxazole (51.8%),
and cephalexin (26.5%), whereas the highest percentages of
susceptibility were seen for amikacin (96.6%), ciprofloxacin
(95.1%), and gentamicin (92.9%); these results are basically in
agreement with other studies carried out around the world.
In other studies conducted on 311 urinary and fecal isolates of E. coli from the southeast and 76 clinical isolates of E.
coli from the capital city of Iran, similar susceptibility patterns were observed.14,15
Our study, as with previous studies, shows that E. coli is
the predominant etiology of UTI,16,17 and also reveals a very
143
high microbial resistance rate to antibiotics. This was especially the case for P. aeruginosa, which was totally resistant
to ampicillin, cephalexin, nitrofurantoin, nalidixic acid, and
trimethoprim—sulfamethoxazole; this resistance is higher
than that found in other reports.17,18 Most cases of urinary
infection with P. aeruginosa were in patients over 60 years of
age and under 9 years of age. This indicates that this bacterium is an opportunistic pathogen, causing infection in those
in a weak immunological condition.
Other surveys in Iran have shown a high resistance to
antibiotics. Khotaii et al. reported resistance rates of
87.5% to ampicillin, 39.5% to gentamicin, 67.5% to trimethoprim—sulfamethoxazole, and 57.7% to cephalothin.19 This
significantly higher bacterial resistance to antibiotics in
our region in comparison with other countries seems to be
due to a higher rate of antibiotic usage by families, even in
the absence of a prescription, and to the high percentage of
younger population, since UTIs are more common in the early
years of life.
Resistance to b-lactamase sensitive penicillins is highly
prevalent among these bacteria.20 In this study the resistance
rate to ampicillin was 58.1% for S. saprophyticus and 72.7%
for S. aureus. Resistance to oxacillin as a representative of blactamase resistant penicillins has developed in UTIs with
Gram-positive cocci isolated, where resistance rates to oxacillin were 46.5% for S. saprophyticus and 36.4% for S. aureus.
There were no significant differences observed in antimicrobial resistance by age or gender of patients.
S. saprophyticus is a prevalent pathogen during the period
of sexual activity in women. Although sexual transmission has
not been defined as the main transmission route of this
pathogen, frequent or recent sexual activity is a major risk
factor. The division time for this pathogen is longer than that
for other UTI pathogens, therefore a lower colony count
(100—1000) is of clinical worth.21 In this study S. saprophyticus was responsible for 7% of UTIs in women. The rate of
UTIs gradually increases with age to 30 years in women
(average 20—40 years). S. aureus is an important uropathogen and was responsible for 1.6% of UTI cases in our study. It
has been emphasized that any amount of this bacterium
should be subjected to antibiogram test.20
Over the last decade there has been a substantial
increase in resistance of uropathogens to antibiotics. Resistance rates among S. aureus strains are increasing, and a
major part of this species has become resistant to b-lactamase resistant penicillins.22,23 For such resistant species,
vancomycin is the effective choice of drug. Resistance to
vancomycin is reported among enterococci,24,25 but this
resistance has also begun to develop among staphylococci.26
In this study we concentrated on resistance to vancomycin
and fortunately resistant strains to vancomycin were not
observed, but 72.7% of cases were resistant to ampicillin and
36.4% to oxacillin.
The regional variations of resistance to antibiotics may be
explained in part by different local antibiotic practices.27,28
The influence of excessive and/or inappropriate antibiotic
use on the development of antibiotic-resistant strains, particularly broad-spectrum agents prescribed empirically, has
been demonstrated. Reducing the number of prescriptions of
a particular antibiotic can lead to a decrease in resistance
rates.29,30 Transmission of resistant isolates between people
and/or by consumption of foods originated from animals that
144
have received antibiotics and greater mobility of individuals
worldwide has also contributed to the expansion of antibiotic
resistance.31,32
In conclusion, because the pattern of sensitivity of bacteria to antibiotics varies over time and in different geographical regions, antibiotic treatment of infections should be
based on local experience of sensitivity and resistance patterns. In this study, nitrofurantoin and nalidixic acid were
found to be the most appropriate oral antibiotics, and amikacin and third-generation cephalosporins were the most
appropriate parenteral antibiotics, for the empirical therapy
of UTIs.
Conflict of interest: No conflict of interest to declare.
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