Urinary tract infections (UTIs) are some of the most common infections
experienced by humans, exceeded in frequency among ambulatory patients
only by respiratory and gastrointestinal infections.It is also the most
common cause of nosocomial infections in adults. A total of 1,814 urine
samples were collected in sterile universal containers from patients attending
University of Nigeria Teaching Hospital between April 2004 and March 2005
and studied. The commonest isolates were Escherichia coli, Staphylococcus
aureus, Streptococcus faecalis and Proteus spp. (These represented 46.3%,
30.7%, 9.1% and 5.4% of isolates respectively). The Gram-positive organisms
were very sensitive to Augmentin and the Fluoroquinolones. E. coli showed
the highest sensitivity to Nitrofurantoin (76%) while it was also very
susceptible to the Fluoroquinolones (74%).
The study clearly shows that Nitrofurantoin is a very effective first
line drug for UTIs.
Key words : UTI, Urinary Tract Infection, Antibiotic
Sensitivity Patterns, Antibiogram.
Urinary tract infection (UTI) is a
broad term that encompasses both asymptomatic microbial colonization of
the urine and symptomatic infection with microbial invasion and inflammation
of urinary tract structures(1). Apart from the outer one-third of the
female urethra, the urinary tract is normally sterile(2).From a microbiologic
perspective, urinary tract infection exists when pathogenic microorganisms
are detected in the urine, urethra, bladder, kidney, or prostate. In most
instances, growth of more than 105 organisms per milliliter from a properly
collected midstream "clean-catch" urine sample indicates infection.
However, significant bacteriuria is lacking in some cases of true UTI.
Especially in symptomatic patients, a smaller number of bacteria (102
to 104/mL) may signify infection. In urine specimens obtained by suprapubic
aspiration or "in-and-out" catheterization and in samples from
a patient with an indwelling catheter, colony counts of 102 to 104/mL
generally indicate infection. Conversely, colony counts of >105/mL
of midstream urine are occasionally due to specimen contamination, which
is especially likely when multiple species are found(3).
Urinary tract infections (UTIs) are some of the most common infections
experienced by humans, exceeded in frequency among ambulatory patients
only by respiratory and gastrointestinal infections(4). Every female has
a 20% life time risk of coming down with a UTI(5). In children approximately
5% of girls and 1% of boys have a UTI by 11 years of age(6). It is also
the most common cause of nosocomial infections in adults.
The major organisms causing UTIs in the Eastern Nigeria environment are
the Coliforms, Staphylococcus aureus and Proteus spp(7). Antibiotics which
recommended to treat UTIs include Ampicillin, Trimethoprim-Sulfamethoxazole,
Flouroquinolones and Nitrofurantoin(8). However due to incessant abuse
and misuse of these antibiotics, extensive resistance of micro-organisms
to these antibiotics has developed.This study is aimed at establishing
the main organisms causing of UTIs in this environment and ascertaining
the extent of resistance of the causal organisms to commonly prescribed
In a study done in July 1995 at Seychelles' Victoria Hospital(9), E. coli
isolates from urine samples of UTI patients showed a 78.6% resistance
against Ampicillin and Amoxicillin and a 54.8% resistance against Cotrimoxazole.
The same E. coli isolates showed a 75% susceptibility to Gentamicin, Nalidixic
acid and Nitrofurantoin. Also, Proteus spp isolated in the study showed
a 100% resistance to Nitrofurantoin but were susceptible to Ampicillin,
Septrin, Gentamicin, Nalidixic acid. Klebsiella spp. were resistant to
Ampicillin, Cotrimoxazole but susceptible to Gentamicin, Nitrofurantoin,
Nalidixic acid. Pseudomonas spp were susceptible to only Gentamicin and
In a similar study conducted by Jha and Bapat(10) in Nepal in 2005, E.coli
was the most prevalent organism isolated (49%) and it showed a 100% susceptibility
to Nitrofurantoin and considerable resistance to amoxicillin and ciprofloxacin.
S. aureus was 88.8% susceptible to 2nd generation Cephalosporin, 77.7%
susceptible to Nitrofurantoin and 75% susceptible to NorfloxacinA study
carried out in 1990(11) on all women aged 15- 44 who had ever presented
to the GP's clinic with symptoms of UTI, it was noted that after 28 days,
patients with initial amoxicillin prescription were likely to come back
for a second prescription (i.e relapse with amoxicillin noted Another
study carried out in 2003 by Dr Joseph Ehimmadu(12) of the Faculty of
Pharmaceutical Sciences, ABU Zaria showed large isolates of Pseudomonas
aeruginosa (53.4%), Staph aureus (43.3%) and E. coli (40.7%) in the urine
samples. Ciprofloxacin was shown to be the most effective antibiotic and
Amoxicillin the least effectivein the study.Gupta et al(13) and Prais
et al(14) found out in their respective studies that a Trimethoprim and
sulphamethoxazole combination was not effective for the treatment of urinary
tract infections as all the uropathogens from inpatients and outpatients
showed high degrees of resistance to co-trimoxazole.In Canada, Allen UD
et al(15) discovered that selective antimicrobial pressure and multiple
admissions to hospital were among the risk factors associated with antimicrobial
resistance in children. While in Singapore, Chan RK et al (16) found out
from their study of nosocomial UTIs that the two main complicating factors
in nosocomial UTIs were urogenital instrumentation (70.4%) and diabetes
mellitus (24.2%) and the commonest organism isolated in their study was
Materials and Methods
A total of 1,814 urine samples were collected in sterile universal containers
from patients attending University of Nigeria Teaching Hospital between
April 2004 and March 2005 and studied. All samples showing significant
bacteriuria were studied and isolates identified using standard bacteriogical
methods. Antibiotic sensitivity testing was performed on sensitivity test
agar (Biotec, UK) using the disc diffusion method in accordance with the
National Committee for Clinical Laboratory Standards. Interpretation as
'Sensitive' or 'Resistant' was done on the basis of the diameters of zones
of inhibition of bacterial growth as recommended by the disc manufacturer.
Antibiotics against which sensitivity was tested in the present study
included Co-trimoxazole, Ampicillin, Ofloxacin, Ciprofloxacin, Gentamicin,
Nitrofurantoin, Augmentin and Tetracycline.Statistics collected were analysed
by the Statistical Program for the Social Sciences SPSS version 13.
A total of 791 urine specimens (43.61% of all urine specimen received
by the laboratory within the period) showed significant bacteruria and
the organisms isolated were tested for antibiotic sensitivity.The commonest
isolates were Escherichia coli, Staphylococcus aureus, Streptococcus faecalis
and Proteus spp. (These represented 46.3%, 30.7%, 9.1% and 5.4% of isolates
respectively). There were only 13 isolates of Pseudomonas spp in the series
studied. (Table 1).The Gram-positive organisms were very sensitive to
Augmentin and the Fluoroquinolones. S. aureus was 85% and 87% sensitive
to Augmentin and Ciprofloxacin respectively while it was only 60% sensitive
to Gentamicin which had a low sensitivity to gram positives. Surprisingly,
Nitrofurantoin was 86% sensitive to S. aureus but only 67% sensitive to
S. faecalis. The gram positives were highly resistant to Nalidixic acid,
Cotrimoxazole and Tetracycline. (See Table 2).
E. coli showed the highest sensitivity to Nitrofurantoin (76%) while it
was also very susceptible to the Fluoroquinolones (74%), and moderately
susceptible to the Aminoglycosides (52%) however it was resistant to other
antibiotics studied in the series especially Amoxicillin (12%) and Cotrimoxazole
(13%). On the other hand Proteus showed a marked resistance to Nitrofurantoin
(29%) but it was very sensitive to the Fluoroquinolones, Augmentin and
Gentamicin. Pseudomonas spp. were only sensitive to the Fluoroquinolones
(62%) and were relatively resistant to other antibiotics in the series
studied. (Table 2)Irrespective of the organism isolated, the Fluoroquinolones
were active against 80.3% of all organisms isolated while Nitrofurantoin
was active against 75.2% of all organisms. Cotrimoxazole was active against
only 13.6% of organisms isolated.
Discussion and Conclusion
Escherichia coli is still the major causative organism in Urinary Tract
Infections as affirmed in this study accounting for almost half off all
cases(7). The role of Staph aureus as a cause of UTI is gradually increasing
and this may be due to an increasing virulence.The Fluoroquinolones have
always been a reliable therapeutic intervention in UTI because of their
broad spectrum activity as well as strong action on gram-negatives. However
it is advocated that they should be used as a last line (not a first line
antibiotic) due to their serious side effects profile especially younger
patients and their cost. Some low cost alternatives which were used in
the past include Cotrimoxazole, Amoxicillin, Augmentin, and Nitrofurantoin.
From this study, it can be seen that Cotrimoxazole is virtually useless
against pathogens that cause UTI as it was only active against about 14%
of all isolated organisms. Amoxicillin and Augmentin are only slightly
better.A clear alternative as a first-line drug against UTI before culture
and sensitivity is Nitrofurantoin. It showed strong activity against about
75% of all isolated organisms and was very active against Escherichia
coli and Staph aureus particularly. It is also very cheap and readily
available in developing countries. However it has a very weak activity
against Proteus spp and Pseudomonas spp. It has also been shown to be
very safe in pregnancy(17) and also a recent study in India showed that
Nitrofurantoin had the best in-vitro susceptibility profile against E.coli(18).
The consistent and high-level susceptibility of E. coli to nitrofurantoin
may be influenced by nitrofurantoin's narrow spectrum of activity, limited
indication (treatment of acute cystitis), narrow tissue distribution (low
or undetectable serum concentrations), and limited contact with bacteria
outside the urinary tract(19). There is a reluctance among doctors to
Nitrofurantoin and this may be due its sideEffect profile but it is clearly
a very important drug in Urinary Tract Infections.This study also shows
clearly that there is clearly little benefit in Gentamicin in UTIs except
indicated specifically by an antibiogram as the drug is expensive and
has a large side effect profile and its activity against all organisms
causing UTIs is about 50:50. In conclusion one can truly affirm that the
choice of drugs in the treatment of UTI is quite narrow today due to the
widescale resistance that the common UTI pathogens show to drugs which
have been used previously. Drugs like Cotrimoxazole which used to be the
mainstay for outpatient treatment of UTI cannot be considered as effective
first line therapy due to this massive resistance. But it is clear that
Nitrofurantoin still has a role to play in the treatment of UTI as its
antibiotic sensitivity profile is very effective.
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