Antimicrobial susceptibility of Escherichia coli and other coliforms isolated from urine of asymptomatic students in Bayelsa State, Nigeria

Abstract

This study investigated the isolation rate and antimicrobial susceptibility of Escherichia coli and other coliforms from asymptomatic male and female students of Niger Delta University in Bayelsa State, Nigeria. E. coli and other coliforms from midstream clean-catch urine samples of asymptomatic male and female students were isolated and tested for their susceptibility to commonly used antimicrobial agents using the disk diffusion protocol described by the Clinical Laboratory Standards Institute (CLSI). Of the few subjects that harbored E. coli, more were males. Zone sizes for both isolate groups from males were higher than those from females. E. coli were more susceptible to the antimicrobials than the non -E. coli (unclassified coliform) isolates for both subjects, although the overall susceptibility of both isolate groups was poor. Gentamicin was the most active (64.5% for E. coli and 33.3% for unclassified coliforms) while tetracycline was the least (22.7% for E. coli and 0% for unclassified coliforms). The most common resistance phenotypes were "ATCtGSNa" (for E. coli) and "ATCtGSNaNC" (for unclassified coliforms); "ATCtGSNaNC" was observed in both isolate groups. Multiple antibiotic resistances were observed significantly in both E. coli (83.9%) and the unclassified coliforms (100%). As against 9.7% of the E. coli isolates, 40% of the unclassified coliforms were resistant to all the antimicrobials. MAR indices were very high (all above 0.2) in both isolate groups. Although asymptomatic male students of Niger Delta University harbored more E. coli than the female students, isolates from the female students pose greater risk of antimicrobial resistance owing to their lower susceptibility to antimicrobials compared with those from their male counterparts. The prior exposure of all the isolates to antibiotics as suggested by their high MAR indices provides justification for continuous monitoring of bacterial susceptibility to antibiotics before prescription in order to ensure adequate treatment of infections arising from urinary pathogens and reduction in the spread of bacteria resistant strain.

Full text

African Journal of Microbiology Research Vol. 5 (3), pp. 184-191, February 2010
Available online http://www.academicjournals.org/ajmr
ISSN 1996-0808 © 2010 Academic Journals
Full Length Research Paper
Antimicrobial susceptibility of Escherichia coli and
other coliforms isolated from urine of asymptomatic
students in Bayelsa State, Nigeria
Yakubu B. Ngwai1*, Mark O. Akpotu2, Ruth E. Obidake2, Adebukola A. Sounyo2, Adebola
Onanuga2 and Samuel O. Origbo2
1Microbiology Unit, Department of Biological Sciences, Nasarawa State University, P. M. B. 1022, Keffi, Nasarawa State,
Nigeria.
2Department of Pharmaceutical Microbiology and Biotechnology, Faculty of Pharmacy, Niger Delta University,
Wilberforce Island, P. M. B. 071, Yenagoa, Nigeria.
Accepted 8 April, 2010
This study investigated the isolation rate and antimicrobial susceptibility of Escherichia coli and other
coliforms from asymptomatic male and female students of Niger Delta University in Bayelsa State,
Nigeria. E. coli and other coliforms from midstream clean-catch urine samples of asymptomatic male
and female students were isolated and tested for their susceptibility to commonly used antimicrobial
agents using the disk diffusion protocol described by the Clinical Laboratory Standards Institute (CLSI).
Of the few subjects that harbored E. coli, more were males. Zone sizes for both isolate groups from
males were higher than those from females. E. coli were more susceptible to the antimicrobials than the
non - E. coli (unclassified coliform) isolates for both subjects, although the overall susceptibility of both
isolate groups was poor. Gentamicin was the most active (64.5% for E. coli and 33.3% for unclassified
coliforms) while tetracycline was the least (22.7% for E. coli and 0% for unclassified coliforms). The
most common resistance phenotypes were “ATCtGSNa” (for E. coli) and “ATCtGSNaNC” (for
unclassified coliforms); “ATCtGSNaNC” was observed in both isolate groups. Multiple antibiotic
resistances were observed significantly in both E. coli (83.9%) and the unclassified coliforms (100%).
As against 9.7% of the E. coli isolates, 40% of the unclassified coliforms were resistant to all the
antimicrobials. MAR indices were very high (all above 0.2) in both isolate groups. Although
asymptomatic male students of Niger Delta University harbored more E. coli than the female students,
isolates from the female students pose greater risk of antimicrobial resistance owing to their lower
susceptibility to antimicrobials compared with those from their male counterparts. The prior exposure
of all the isolates to antibiotics as suggested by their high MAR indices provides justification for
continuous monitoring of bacterial susceptibility to antibiotics before prescription in order to ensure
adequate treatment of infections arising from urinary pathogens and reduction in the spread of bacteria
resistant strain.
Key words: Escherichia coli, urine, asymptomatic, antimicrobial susceptibility.
INTRODUCTION
Urine contains a variety of fluids, salts and waste
products; it usually does not have bacteria (Adult Health
Advisor, 2005). When bacteria get into the bladder or
*Corresponding author. E-mail: ngwaiyb@yahoo.co. Tel: +234-
80-52991889.
kidney and multiply in the urine, they cause a urinary tract
infection (UTI), the most common type being a bladder
infection often called cystitis characterized by a syndrome
involving dysuria, frequency, urgency and occasionally
suprapubic tenderness (Akram et al., 2007). The
presence of symptoms of lower tract without upper tract
symptoms does not exclude upper tract infection, which
is also often present (Sobel and Kaye, 2000). However,

bacteria found in the urinary tract of older adults, without
symptoms or associated consequences often referred to
as asymptomatic bacteria, is also a well recognized
phenomenon which may not require antibiotics.
Asymptomatic bacteriuria occur reliably more frequently
in females as compared with males and it is a major
criterion of urinary tract infection (Nurullaev, 2004).
Bacterial infections of the urinary tract in humans are
the most frequent bacterial disease, affecting outpatients,
hospitalized patients and apparently healthy populations;
and more common in females than males by virtue of the
shortened urethra (Piatti et al., 2008; Todar, 2008;
Sheffield and Cunningham, 2005; Olaitan, 2006).
Worldwide, about 150 million people are diagnosed with
UTI each year, costing the global economy in excess of 6
billion US dollars (Gonzalez and Schaeffer, 1999). Risk
factors for UTIs include diabetes, sickle cell disease,
anatomical malformation of the urinary tract, poor toilet
habits, pregnancy in women and prostrate enlargement in
men (Wikipedia, 2009: http://en.wikipedia.org/wiki/).
UTIs are often treated with different broad-spectrum
antibiotics even when one with a narrow spectrum of
activity may be appropriate because of concerns about
infection with resistant organisms. Fluoroquinolone are
preferred as initial agents for empiric therapy of UTI in
areas where resistance is likely to be of concern (Biswas
et al., 2006; Schaeffer, 2002). This is because they have
high bacteriological and clinical cure rates, as well as low
rates of resistance among most common uropathogens
(Tankhiwale et al., 2004; Gupta et al., 2002; Goldstein,
2000).
Escherichia coli is recognized as one of the most
frequently isolated bacteria in asymptomatic bacteriuria
and UTIs (Stamm, 1994; Todar, 2008). E. coli is the
predominant facultative anaerobe of the human colonic
microflora; most E. coli strains are harmless to humans,
but pathogenic strains can cause gastroenteritis, urinary
tract infections and neonatal meningitis; and in rare
cases, hemolytic-uremic syndrome (HUS), peritonitis,
mastitis, septicemia and gram-negative pneumonia
(Todar, 2008). Uropathogenic E. coli (UPEC) cause 90%
of the urinary tract infections (UTIs) in anatomically-
normal, unobstructed urinary tracts; the bacteria colonize
from the feces or perineal region and ascend the urinary
tract to the bladder (Todar, 2008). A typical patient with
uncomplicated cystitis is a sexually-active female who
was first colonized in the intestine with an uropathogenic
E. coli strain that was later propelled into the bladder from
the periurethral region during sexual intercourse.
No report is available on the isolation frequency and
antimicrobial susceptibility of E. coli from the student
population: a sexually active age group, of the Niger
Delta University in Bayelsa State, Nigeria. It was
therefore thought necessary to investigate the isolation
frequency of E. coli and other coliforms in asymptomatic
male and female undergraduate students of the
University; and also to study the effects on the bacteria
isolated of commonly used antimicrobial agents in the
Ngwai et al. 185
area.
MATERIALS AND METHODS
Sample collection
A total of 240 midstream clean-catch urine samples (120 each from
male and female) were collected between June and October 2008
into sterile containers from asymptomatic students of Niger Delta
University in Bayelsa State, Nigeria at the two campuses (College
of Health Sciences and the Main Campus). Only students of age 18
- 35 years (males) and 15 - 30 years (females) and who were not
on antimicrobial therapy as at sample collection or had not taken
antimicrobial two weeks prior to sampling time were included in this
study.
Isolation and identification of E. coli and other coliforms from
urine
Urine samples were immediately (or within 6 h of collection)
inoculated on MacConkey agar (Fluka Biochemical, Germany)
prepared according to the manufacturer’s instruction and incubated
aerobically at 37°C for 24 h. Pink colonies from the MacConkey
agar were further sub-cultured on eosin methylene blue (EMB) agar
(International Diagnostics Group, UK) prepared according to the
manufacturers instruction and incubated at 37°C for 24 h. Colonies
that had metallic sheen on EMB were presumptively taken as E. coli
and further characterized microscopically (as gram-negative rod)
and biochemically (as Indole (+), Citrate (-) and Urea (-)). The pink
colonies from MacConkey agar that did not produce metallic sheen
on EMB were designated as unclassified coliforms. Well isolated
organisms were maintained on nutrient agar (Fluka Biochemical,
Germany) prior to antimicrobial susceptibility testing.
Antimicrobial susceptibility test
Antimicrobial susceptibilities of the isolates to eight common
antimicrobial agents were determined by the disc diffusion method
for rapidly growing aerobic organisms in accordance with the
guidelines of the Clinical Laboratory Standards Institute (CLSI),
formerly National Committee on Clinical Laboratory Standards
(NCCLS) (CLSI, 2006). Briefly, four well isolated colonies from 24-h
nutrient agar culture were transferred to tubes containing Mueller
Hinton broth (Fluka Biochemical, Germany) and incubated at 37°C
for 24 h. The bacterial suspension was adjusted using sterile saline
(0.85% w/v NaCl: Scharlau, Brazil) to the turbidity of 0.5 McFarland
standard (prepared by adding 0.5 ml of a 1.175% (w/v) of barium
chloride dehydrate (BaCl2.2H2O: BDH Chemical Ltd, Poole,
England) to 99.5 ml of 1% (v/v) sulphuric acid (H2SO4: Fluka
Biochemical, Germany). The surfaces of Mueller Hinton agar (Fluka
Biochemical, Germany) were streaked with the adjusted
suspensions within five minutes of adjusting turbidity; and the
inoculums were allowed to dry for five minutes. Multo disks (Abidec
Company, England) containing ampicillin (25 µg), tetracycline (25
µg), Cotrimoxazole (25 µg), gentamicin (10 µg), streptomycin (25
µg), nalidixic acid (30 µg), nitrofurantoin (200 µg) and colistin (25
µg) were placed on the inoculated agar surfaces (in triplicates),
allowed to stand for 15 min and then incubated in inverted position
at 37°C for 24 h. The zones of inhibition were finally measured,
including the diameter of the disk using a ruler to the nearest
millimeter and recorded. A control organism such as E. coli ATCC
9637 (instead of ATCC 25922 due to its unavailability in the
laboratory) was used to validate the accuracy of the antimicrobial
susceptibility tests. Isolates were classified as “Resistant”,
“Intermediate susceptible” or “Susceptible” based on the standard

186 Afr. J. Microbiol. Res.
Table 1. Isolation rate of E. coli and unclassified coliforms.
Number of urine
specimens screened
Number (%) positive for
E. coli
Number (%) positive for
Coliforms Total isolation rate (%)
Male
(n = 120)
Female
(n = 120)
Male
(n = 120)
Female
(n = 120)
Escherichia coli
(n = 240)
Coliforms
(n = 240)
240 21 (17.5) 10 (8.3) 2 (1.7) 13 (10.8) 12.9 6.3
interpretation chart updated according to the current CLSI (formerly
NCCLS) standard.
RESULTS
Bacteria isolated from urine
A total number of 31 (12.9%) E. coli and 15 (6.3%)
unclassified coliforms was obtained from the 240 urine
specimens screened (Table 1). As against generally held
opinion, the isolation rate of E. coli obtained from our
study was rather low; and more from male specimens.
However, unclassified coliforms were more in the female
urine samples. The precise identity of the unclassified
coliforms was not further determined due to unavailability
of confirmatory tests at the laboratory where the bench
work was carried out. These isolates were gram-negative
rods and lactose fermenting on MacConkey agar, yielding
pink-colored colonies; some were large and mucoid.
However, these isolates did not produce metallic sheen
on EMB agar (and were therefore not E. coli species).
Antimicrobial susceptibility of the isolates
The measured inhibition zone diameters (in millimeters)
and interpretation are as given in Table 2 (for E. coli) and
Table 3 (for unclassified coliforms). Zone sizes obtained
for the isolates from male subjects were generally higher
than those from female isolates for both isolate groups.
The percentage susceptibilities (shown in Table 4)
indicate that the E. coli were generally more susceptible
to the antimicrobials tested than the non - E. coli
(unclassified coliform) isolates, although the overall
susceptibility of both isolate groups was poor. For the E.
coli, susceptibility was in the order: gentamicin >
streptomycin > nitrofurantoin > colistin > nalidixic acid >
cotrimoxazole > ampicillin > tetracycline; and for the
unclassified coliforms, the order of susceptibility was:
gentamicin > nitrofurantoin and colistin > streptomycin
and nalidixic acid > cotrimoxazole > ampicillin >
tetracycline.
Distribution of resistance phenotypes in the isolates
The most common resistance phenotypes were
“ATCtGSNa” (for E. coli) and “ATCtGSNaNC” (for
unclassified coliforms) (Table 5). Resistance phenotypes
observed only in E. coli were: “Na”, “AT”, “AC”, “CtN”,
“ATN”, “TGNa”, “TNaC”, “NaNC”, “ATCtS, “ANaNC”,
“ATCtSC”, “ATCtNaN”, “ATNaNC”, “TCtGNC”,
“ATCtGSNa”, “ATCtSNC”, “ATCtSNaC”, “ATCtNaNC”
and “TCtGSNaN”; those observed only in the unclassified
coliforms were: “ATCtC”, “TNaNC”, “ATCtSNa”,
“ATCtGSNaC”, “ATCtGSNaN” and “ATCtSNaNC”; and
those shared by both isolate groups were: “ATC”,
“ATCtGSN” and “ATCtGSNaNC”.
Multiple antibiotic resistance (MAR) in the isolates
and MAR indices
Multiple antibiotic resistances (Table 6), defined here as
resistance to at least three antibiotics, were observed
significantly in both E. coli (83.9%) and the unclassified
coliforms (100%). As against 9.7% of the E. coli isolates,
40% of the unclassified coliforms were jointly resistant to
all the antimicrobials tested. MAR indices (Table 7) were
very high, all above 0.2 in both isolate groups.
DISCUSSION
The very low isolation rate of E. coli obtained from our
study is not in agreement with some previous reports that
suggest E. coli as the most frequently isolated bacteria
from urine in UTIs (Stamm, 1994; Todar, 2008).
Many urinary tract bacteria are capable of expressing
resistance in one form or another. While colistin sulphate
may be ineffective because of cross-resistance (Mordi
and Erah, 2006), the higher resistances observed in the
present study to the orally available and cheap drugs
namely ampicillin, tetracycline, cotrimoxazole, nalidixic
acid and nitrofurantoin, could be due to their free access,
misuse and abuse. Some studies (Ehinmidu, 2003; Inabo
and Obanibi, 2005; Mordi and Erah, 2006) have reported
similar observation. The -lactam group of antibiotics is
the most commonly used worldwide in human and
veterinary medicine (Sanders and Sanders, 1992;
Livermore, 1996), and this explains the many reported
cases of ampicillin resistance in E. coli worldwide
(Gruneberg, 1984; Lamikanra and Ndep, 1989; Manges
et al., 2001; Ehinmidu, 2003; Xiao et al., 2005). The
widespread and inappropriate use of antibiotics is re-
cognized as a significant contributing factor to the spread

Ngwai et al. 187
Table 2. Susceptibilities of E. coli to common antibiotics.
Isolates
Source
Antibiotic inhibition zone diameter (mm) and interpretation*
Amp Tet Cot Gen Str Nal Nit Col
R I S R I S R I S R
I S
R I S R I S
R I S R
I S
EC1 Male 18 22
0 26
24 0 17
15
EC2 Male 2 2 2 16
0 18
16
6
EC3 Male 18 14 9 12
20 14
12
8
EC4 Male 12 16
20
14 18 14
16
8
EC5 Male 16 12 17
11
15 13 20
10
EC6 Male 1 1 2 2
6 1 16
10
EC7 Male 18 17
16
18
19 11 14
8
EC8 Male 1 2 2 19
16 7 0 10
EC9 Male 3 2 1 3
4 1 14
8
EC10 Male 16 1 1 2
2 1 1 12
EC11 Male 1 2 1 18
8 14
16
8
EC12 Male 1 12 14 16
14
10 3 8
EC13 Male 7 18
18
18
20 8 11
8
EC14 Male 0 2 2 0
4 2 18
12
EC15 Male 1 2 1 16
8 14
16
10
EC17 Male 8 12 0 15
18 13 14
0
EC18 Male 2 2 1 2
4 2 16
11
EC19 Male 22 17
18
16
21 12 17
18
EC20 Male 2 2 2 0
4 2 18
12
EC21 Male 16 16
2 22
16 18
2 14
EC24 Male 10 12 10 18
16 12 14
8
EC22b Female
13 8 13 14 15 16
10
10
EC23 Female
11 11 17
15
13
15
17
11
EC25 Female
9 11 19
13 17 15
15
8
EC26 Female
19 11 17
17
13
11 15
7
EC27 Female
5 2 0 14 5 15
0 7
EC28 Female
0 0 0 5
0 0 0 0
EC29 Female
0 0 0 0
1 0 0 7
EC30 Female
9 12 0 12
9 15
13
11
EC31 Female
0 0 0 14 0 10 21
4
EC32 Female
15 15
16
15
16 11 13
7
*Interpretation was based on the standard interpretation chart updated according to the M2-A9 (9th editon) CLSI (formerly NCCLS) Standard; EC- E. coli;
R- Resistance to the drug; I- Intermediate susceptibility to the drug; S- Susceptibility to the drug; 0- No inhibition zone of inhibition around the antibiotic
disk; Amp- ampicillin; Tet- tetracycline; Cot- cotrimoxazole; Gen- gentamicin; Str- streptomycin; Nal- nalidixix acid; Nit- nitrofurantoin; Col- colistin.
of bacterial resistance and the development of resistance
to antimicrobial agents (Mincey and Parkulo, 2001). For
most bacteria, there is evidence that increased usage of
a particular antimicrobial correlates with increased levels
of bacterial resistance (Granizo et al., 2000).
Over 50% susceptibility of E. coli to gentamicin and
streptomycin observed in this study might be due to their
requirement for parenteral administration which hinder
their misuse and abuse. Resistance to the
aminoglycosides by E. coli is also not new (Ngwai et al.,
2005; Mordi and Erah, 2006; Olaitan, 2006). The ob-
servation that some isolates were resistant to
streptomycin but not to gentamicin could be explained by
the fact that gentamicin, in addition to binding to a
specific S12 protein in the 30S ribosome, also binds to
the L6 protein of the 50S ribosome to inhibit protein
synthesis (Tripathi, 2003). Hence, a possible alteration of
the S12 protein target alone in the streptomycin-resistant
isolates is incapable of affecting its action.
The high level multiple resistances observed is
probable indication of an earlier exposure of the MAR
isolates to these drugs. This is suggested by the high
MAR indices observed. An MAR index (a tool that reveals
the spread of bacterial resistance in a given population)

188 Afr. J. Microbiol. Res.
Table 3. Susceptibilities of the unclassified coliforms to common antibiotics.
Isolate
Source
Antibiotic inhibition zone diameters (mm)
Amp Tet Cot Gen Str Nal Nit Col
R I S R I S R I S
R I S R I
S R I S R I S
R I S
C2 Male 1 3 2 10 10
2 18
8
C3 Male 21 4 14 18
17
3 10 2
C4 Female 1 1 1 17 3
0 17
9
C5 Female 3 9 0 14
17
15
14
0
C6 Female 0 0 0 9 0
0 11 8
C7 Female 0 0 0 8 8
0 3 8
C8 Female 0 0 0 14
0
9 0 1
C9 Female 0 0 0 9 0
18
0 10
C10 Female 10
0 0 11 0
12
0 8
C11 Female 0 3 0 6 0
0 0 7
C12 Female 0 5 0 0 0
10
0 11
C13 Female 0 1 0 11 0
0 5 8
C14 Female 0 0 0 2 6
7 9 11
C15 Female 7 11
11 13
17
19
18
5
C16 Female 1 0 0 9 0
11
0 8
*Interpretation was based on the standard interpretation chart updated according to the M2-A9 (9th edition) CLSI (formerly NCCLS) Standard;
C- unclassified coliforms (pink colonies from MacConkey agar which did not produce metallic sheen growth on eosin methylene blue [EMB]
agar); R- Resistance to the drug; I- Intermediate susceptibility to the drug; S- Susceptibility to the drug; 0- No inhibition zone of inhibition
around the antibiotic disk; Amp- ampicillin; Tet- tetracycline; Cot- cotrimoxazole; Gen- gentamicin; Str- streptomycin; Nal- nalidixix acid; Nit-
nitrofurantoin; Col- colistin.
Table 4. Percentage susceptibilities of E. coli and unclassified coliforms to antibiotics.
Antibiotics Disk content (µg)
Number (%) susceptible to drugs
E.
coli
(n = 31)
Coliforms (n = 15)
Ampicillin (Amp) 25 9 (29) 1 (6.7)
Tetracycline (Tet) 25 7 (22.6) 0 (0)
Cotrimoxazole (Cot) 25 11 (35.5) 2 (13.3)
Gentamicin (Gen) 10 20 (64.5) 5 (33.3)
Streptomycin (Str) 25 17 (54.8) 3 (20)
Nalidixic acid (Nal) 30 13 (41.9) 3 (20)
Nitrofurantoin (Nit) 200 15 (48.4) 4 (26.7)
Colistin (Col) 25 14 (45.2) 4 (26.7)
Table 5. Distribution of the E. coli and unclassified coliforms into resistance phenotypes.
Resistance phenotypes Number (%) of isolates with corresponding phenotypes
E. coli (n = 31) Coliforms (n = 15)
Na 1 (3.2) 0 (0)
AT 1 (3.2 0 (0)
AC 1 (3.2) 0 (0)
CtN 1 (3.2) 0 (0)
ATC 1 (3.2) 1 (6.7)
ATN 1 (3.2) 0 (0)
TGNa 1 (3.2) 0 (0)
TNaC 1 (3.2) 0 (0)
NaNC 2 (6.5) 0 (0)
ATCtS 1 (3.2) 0 (0)
ATCtC 0 (0) 1 (6.7)

Ngwai et al. 189
Table 5. cont.
Resistance phenotypes Number (%) of isolates with corresponding phenotypes
E. coli (n = 31) Coliforms (n = 15)
ANaNC 1 (3.2) 0 (0)
ATCtSC 2 (6.4) 0 (0)
TNaNC 0 (0.0) 1 (6.7)
ATCtNaN 1 (3.2) 0 (0)
ATCtSNa 0 (0) 1 (6.7)
ATNaNC 1 (3.2) 0 (0)
TCtGNC 1 (3.2) 0 (0)
ATCtGSNa 4 (12.9) 0 (0)
ATCtGSN 1 (3.2) 1 (6.7)
ATCtSNC 1 (3.2) 0 (0)
ATCtSNaC 1 (3.2) 0 (0)
ATCtNaNC 2 (6.5) 0 (0)
TCtGSNaN 1 (3.2) 0 (0)
ATCtGSNaC 0 (0) 1 (6.7)
ATCtGSNaN 0 (0) 2 (13.3)
ATCtSNaNC 0 (0) 1 (6.7)
ATCtGSNaNC 3 (9.7) 6 (40.0)
A = ampicillin; T = tetracycline; Ct = co-trimoxazole; G = gentamicin; S = streptomycin; Na = nalidixic acid; N
= nitrofurantoin; C = colistin.
Table 6. Multiple antibiotic resistance (MAR) in E. coli and unclassified coliforms.
Number of antimicrobial agents isolate is resistant to Number (%) of isolates with multiple resistance
E. coli (n = 31) Coliforms (n = 15)
3 6 (19.4) 1 (6.7)
4 2 (6.5) 2 (13.3)
5 5 (16.1) 1 (6.7)
6 10 (32.3) 1 (6.7)
7 0 (0) 4 (26.7)
8 3 (9.7) 6 (40)
above 0.2 implies that the strains of such bacteria
originate from an environment where several antibiotics
are used (Krumpermann, 1983).
Conclusion
Although in a small sample size, E. coli appears to be
more prevalent in the asymptomatic male than female
student population of Niger Delta University investigated.
In addition, isolates from the female students pose
greater risk of antimicrobial resistance owing to their
lower susceptibility to antimicrobials compared with those
from their male counterparts. The prior exposure of
isolates to antimicrobial agents as suggested by their
high MAR indices provides justification for continuous
monitoring of bacterial susceptibility to antibiotics before
prescription in order to ensure adequate treatment of
infections arising from urinary pathogens and reduction in
the spread of bacteria resistant strain. The emergence
and spread of antimicrobial resistance is an important
public health issue.
ACKNOWLEDGEMENT
We thank the technical staff of Pharmaceutical
Microbiology and Biotechnology laboratory at the Niger
Delta University’s Faculty of Pharmacy for the technical
assistance.

190 Afr. J. Microbiol. Res.
Table 7. Multiple antibiotic resistance index (MAR-I) of E. coli and unclassified coliforms.
Isolates Source Number of antibiotics isolate is resistant to (a) Number of antibiotics tested (b) MAR-I (a/b)
EC2 Male 5 8 0.63
EC3 Male 5 8 0.63
EC5 Male 3 8 0.38
EC6 Male 6 8 0.75
EC7 Male 3 8 0.38
EC8 Male 5 8 0.63
EC9 Male 8 8 1.00
EC10 Male 6 8 0.75
EC11 Male 5 8 0.63
EC12 Male 5 8 0.63
EC13 Male 4 8 0.50
EC14 Male 6 8 0.75
EC15 Male 4 8 0.50
EC17 Male 6 8 0.75
EC18 Male 6 8 0.75
EC20 Male 6 8 0.75
EC24 Male 6 8 0.75
EC22b Female 3 8 0.38
EC25 Female 3 8 0.38
EC26 Female 3 8 0.38
EC27 Female 6 8 0.75
EC28 Female 8 8 1.00
EC29 Female 8 8 1.00
EC30 Female 6 8 0.75
EC31 Female 6 8 0.75
EC32 Female 3 8 0.38
C2 Male 7 8 0.88
C3 Male 4 8 0.50
C4 Female 5 8 0.63
C5 Female 4 8 0.50
C6 Female 8 8 1.00
C7 Female 8 8 1.00
C8 Female 7 8 0.88
C9 Female 6 8 0.75
C10 Female 8 8 1.00
C11 Female 8 8 1.00
C12 Female 7 8 0.88
C13 Female 8 8 1.00
C14 Female 7 8 0.88
C15 Female 3 8 0.38
C16 Female 8 8 1.00
EC- E. coli; C- unclassified coliforms.
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