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Original article

Prevalence of Ciprofloxacin Resistance Among Gram-Negative
Bacilli at a Specialist Hospital in Saudi Arabia

Ahmad S
Abstract:
Background: Resistance to antimicrobials of different structural classes including fluoroquinolones has
arisen in a multitude of bacterial species both in the community and the hospitals. This may complicate the
therapeutic management of infections. Decreased susceptibility to fluoroquinolones arises mainly by single-
step mutations in the gyrA and parC genes, which encode the fluoroquinolones targets, the topoisomerase
enzymes, conferring cross resistance to all fluoroquinolones. Accumulation of multiple mutations in sever-
al genes confers increasing level of resistance associated with clinical failure. However, even low level
resistance can generate therapeutic failure. In 1998, some mobile elements with a potential for the horizon-
tal transfer of the quinolone resistance genes were described. The loci which are responsible for this plas-
mid-mediated quinolone resistance, which have been designated as qnrA, qnrB and qnrS, have been identi-
fied in the Enterobacteriaceae species. Aim: To evaluate the susceptibility pattern of the isolates to various
antibiotics and to know the prevalence rate of ciprofloxacin resistance in our hospital. Materials &
Methods: A total of 916 gram-negative bacilli (GNB) were isolated from different clinical specimens over
a period of nine months, were subjected to antibiotic susceptibility testing. Isolates with resistance or with
a decreased susceptibility to ciprofloxacin (£20 mm) were then screened for their minimum inhibitory con-
centration (MIC) by using the E-test. Results: Out of 916 GNB, 321 (35%) isolates were resistant to
ciprofloxacin. The MIC of these isolates ranged from 4 to >32?g/ml. Conclusion: The resistance rate to
ciprofloxacin was 35% in our study. Most of the ciprofloxacin resistant isolates were from urinary tract
infections (UTI). The ciprofloxacin resistance was also closely associated with multi-drug resistance, thus
limiting the treatment options. Ciprofloxacin resistance can be used as a general surrogate marker of mul-
tidrug resistance, thus limiting the already restricted treatment options. The considerably high MIC values
for ciprofloxacin in this study reflected the extent of the treatment problems for these resistant isolates and
a need for the continuous evaluation of the commonly used antibiotics. 

Key Words: Gram-negative bacilli, Fluoroquinolones, Ciprofloxacin, MIC

Introduction:
Fluoroquinolone antimicrobial drugs were a major
therapeutic advance of the 1980s because they have
100-fold greater activity than their parent com-
pound, nalidixic acid 1. Unlike nalidixic acid, which
is used only for urinary infections and occasionally
shigellosis, the fluoroquinolones have a broad range
of therapeutic indications and are given as prophy-
laxis, e.g., for in veterinary medicine fluoro-
quinolones are used as treatment and metaphylaxis
but not as growth promoters. Early researchers
thought that fluoroquinolone resistance was unlikely
to evolve, largely because resistant Escherichia coli
mutants are exceptionally difficult to select in vitro 2
and because plasmid-mediated quinolone resistance
remained unknown even after 30 years of nalidixic
acid usage. Nevertheless, mutational fluoro-

quinolone resistance emerged readily in staphylo-
cocci and pseudomonads, which are inherently less
susceptible than E. coli. More recently, fluoro-
quinolone resistance has emerged in E. coli and
other Enterobacteriaceae, contingent on multiple
mutations that diminish the affinity of its topoiso-
merase II and IV targets in varying ways reduce per-
meability, and up regulate efflux

3
. Plasmid-mediated

quinolone resistance has been reported, but it is
exceptional

4
.

Ciprofloxacin is a broad-spectrum antibiotic which
is active against both gram-positive and gram-nega-
tive bacteria, which belongs to the fluoroquinolone
class 5. Bacterial resistance is a growing therapeutic
problem, both in the community and the hospitals,
involving all the antibiotics, which include fluoro-
quinolones. A decreased susceptibility to fluoro-

Corresponds to: Dr.Shamweel Ahmad, Associate Professor of Medical Microbiology and Consultant
Microbiologist, Department of Medical Laboratory Sciences, College of Medical Sciences, Salman Bin
Abdul Aziz University, Kingdom of Saudi Arabia. E-mail: dshamweel@ksu.edu.sa

Bangladesh Journal of Medical Science Vol. 11 No. 04 Oct’12

317



quinolones arises mainly due to single-step muta-
tions in the gyrA and the parC genes, which encode
the fluoroquinolones targets, the topoisomerase
enzymes

6
. In 1998, some mobile elements which

were responsible for the horizontal transfer of the
quinolone resistance genes were described

7,8
. This

study was undertaken to evaluate the susceptibility
of GNB to various antibiotics and to know the preva-
lence rate of ciprofloxacin resistance in our hospital.

Materials and Methods:
A total of 916 gram-negative bacilli were isolated
from different clinical specimens i.e., urine, pus,
sputum, blood etc, received in the Microbiology
Laboratory over a period of nine months were sub-
jected to the study. Specimens were processed using
different media like MacConkey’s agar, Cystein
Lactose Electrolyte Deficient (CLED) Agar, Sheep
Blood Agar and Chocolate Agar. All isolates were
identified using standard biochemical tests

9
. In addi-

tion commercially available biochemical kits, API
20E (Analytic Profile Index system, La Balme les
Grottes, France) were also used for the identification
of enteric pathogens.

Antibiotic sensitivity testing was performed using
the disc diffusion method on 85 mm Mueller-Hinton
agar (Oxoid) plates with agar depth of 4 mm. The
bacterial suspension that was prepared for antibiotic
sensitivity testing on Mueller-Hinton agar was
adjusted to the recommended turbidities for all
species

10
.

The antibiotics tested on each disc were Ampicillin
25 µg, Amoxicillin-Clavulanic Acid (20/10 µg),
Trimethoprim-Sulphamethoxazole (1.25/23.75 µg),
Cephalothin 30 µg, Cefuroxime 30 µg, Cefotaxime
30 µg, Ciprofloxacin 5 ?g, Norfloxacin 30 µg (for
urinary isolates), Nalidixic Acid 30 µg (for urinary
isolates), Nitrofurantoin 300 µg (for urinary iso-
lates), Gentamicin 10 µg, Amikacin 30 µg and
Imipenem 30 µg.

The Clinical Laboratory Standards Institute (CLSI)
break points were used for interpretation of suscep-
tibility patterns as sensitive or resistant

11
. Isolates

with resistance or with decreased susceptibility to
Ciprofloxacin (?20mm) were subjected to further
study. This study design and protocol was approved
by ‘Research and Ethics Committee’ of the institute.
E-Test

The resistance to ciprofloxacin was confirmed by
breakpoint minimum inhibitory concentration (MIC
in ?g/ml) by using E-test strips. The isolates with
MIC value ?4 ?g/ml were defined as resistant iso-
lates, as outlined by CLSI guidelines

11
.

Results:Escherichia coli (29.4%) was the most pre-
dominant isolate which was found among the GNB,
followed by Klebsiella pneumoniae (26.2%)
Pseudomonas aeruginosa (25.0%) and Proteus
species (12.9%) as shown in Table I. 
Table I: Total number of Gram-negative Bacilli
isolated from different  clinical specimens
(n=916)

Out of 916 gram-negative bacilli, 321 (35%) isolates
were resistant to ciprofloxacin. High rates of resist-
ance were observed for Ampicillin and Amoxicillin-
Clavulanic Acid, followed by Cephalothin,
Trimethoprim-Sulphamethoxazole, and cefotaxime,
while low levels of resistance were observed for
nitrofurantoin, nalidixic acid, amikacin and nor-
floxacin, as shown in Table II.
Table II: Antibiotic Susceptibility pattern of the
isolates to various antibiotics (n=916)

Prevalence of Ciprofloxacin resistance among Gram-Negative Bacilli

318

Percentage 

(%) 

Total 

number 

isolated 

Organism                                                         

 
S. 

No.  

29.4% 269 Escherichia coli 1. 
26.2% 240 Klebsiella 

pneumoniae 
2. 

25.0 229 Pseudomonas  
aeruginosa 

3. 

12.9% 118 Proteus species 4. 
5.3% 49 Acinetobacter  

species 
5. 

1.2% 11 Citrobacter  
species 

6. 

100.0%  Total  

Total no of 

Resistant 

isolates 

(%) 

Total no of 

Sensitive 

isolates 

(%) 

Antibiotics                                                        

 
S. 

No. 

  

724 
(79%) 

192 
(21%) 

Ampicillin 1. 

687 
(75%) 

229 
(25%) 

Amoxicillin-
Clavulanic Acid 

2. 

549 
(60%) 

367 
(40%) 

Trimethoprim-
Sulphamethoxazole 

3. 

559 
(61%) 

357 
(39%) 

Cephalothin 4. 

237 
(26%) 

679 
(74%) 

Cefuroxime 5. 

541 
(59%) 

375 
(41%) 

Cefotaxime 6. 



The lowest level of resistance was observed for
imipenem (4%). The resistance rate for
ciprofloxacin was 35%. The MIC of ciprofloxacin
for these isolates ranged from 4 to >32 ?g/ml (Table
III).

Table III: MIC values of the resistant Gram
Negative Bacilli to Ciprofloxacin (n=321)

The isolated bacteria showed wide differences in
their susceptibility to ciprofloxacin. A high rate of
resistance to ciprofloxacin was observed among
Pseudomonas aeruginosa, Klebsiella pneumoniae,
Acinetobacter sps.,  and Proteus  sps. followed by E.
coli.

Discussion:
Evolution of reduced susceptibility to the quinolones
is causing concern following rapidly rising rates of
fluoroquinolone- resistant E. coli in many parts of
the world

12
. The Surveillance Network database

(http://www.mrlworld.com) shows resistance trends
(with intermediate counted as resistant) in blood-
stream isolates from 250 U.S. hospitals as follows:
E. coli, 1.8% in 1996 and 4.3% in 1999; Klebsiella
spp., 7.1% in 1996 and 6.7% in 1999; Enterobacter
spp., 6.6% in 1996 and 6.5% in 1999; and P.
mirabilis, 5.7% in 1996 and 12.7% in 1999. Much
higher rates are reported from Barcelona, Spain,
where 17% of E. coli isolates from community
infections were ciprofloxacin resistant

13
, and India,

where up to 50% of hospital E. coli are reported
resistant

14
. High rates in E. coli may reflect contam-

ination via the food chain: the Spanish study found

quinolone-resistant E. coli in 90% of chicken feces
and noted similar fecal carriage rates of resistant E.
coli in children and adults. There is a small set of
drugs commonly used to treat P. aeruginosa infec-
tion, including ciprofloxacin, tobramycin, gentam-
icin, ceftazidime, and imipenem. While P. aerugi-
nosa has developed various levels of resistance to
each of these, its response to ciprofloxacin is of par-
ticular interest because the drug is initially very
effective, but P. aeruginosa rapidly acquires high-
level resistance, rendering the drug impotent. In clin-
ical isolates, approximately 30% of strains now pres-
ent high-level ciprofloxacin resistance

15
.

The resistance rate for ciprofloxacin was 35% in our
study. Most of the ciprofloxacin resistant isolates
were obtained from UTI samples. This may be
because fluoroquinolones are preferred as the initial
agents for empiric therapy in UTI, because of their
excellent activity against the pathogens which are
commonly encountered in UTI

16
. This emphasises

the importance of the re-assessment of the antibi-
otics which are used in the empiric treatment of
UTIs. Most of the isolates from UTIs were suscepti-
ble to nitrofurantoin, nalidixic acid, amikacin and
imipenem. This was in agreement with the finding of
a study reported by Astal ZE, 2005

17
.

These data suggest that nitrofurantoin can still be
successfully used in the treatment of UTI. The
ciprofloxacin resistance was also closely associated
with multi-drug resistance, thus making the treat-
ment options limited

18
. Ciprofloxacin resistance can

be used as a general surrogate marker of multi-drug
resistance. Hence, it severely limits the already
restricted treatment options. This finding was in
accordance with the finding of a study which was
conducted by Paterson et al

19
. The high resistance

pattern which was seen in our study was probably
due to the inappropriate prescribing of antibiotics,
lack of antibiotic policy and the poor infection con-
trol strategies. But the antibiotic history could not be
properly elicited from the patients in this study.

Ciprofloxacin remains a potent antibiotic; but the
slow accumulation of resistant Enterobacteriaceae
is disturbing, not least because resistance is a class
effect, affecting all fluoroquinolones. Ultimately,
this resistance may be partly overcome by inhibiting
the efflux pumps that contribute to the resistance 

20
,

Ahmad S

319

( )( )
321 

(35%) 
595 

(65%) 
Ciprofloxacin 7. 

 
(23%) 

247 
(77%) 

Norfloxacin(for 
urinary 
isolates=321 GNB) 

8. 

67 
(21%) 

254 
(79%) 

Nalidixic Acid(for 
urinary 
isolates=321 GNB) 

9. 

64 
(20%) 

257 
(80%) 

Nitrofurantoin (for 
urinary 
isolates=321 GNB) 

10. 

284 
(31%) 

632 
(69%) 

Gentamicin 11. 

174 
(19%) 

742 
(81%) 

Amikacin 12. 

37 
(4%) 

879 
(96%) 

Imipenem 13. 

>32μg/
ml 

32μg/
ml 

16μg/
ml 

8μg/
ml 

4μg/
ml 

Ciprofloxacin 

MIC values 
112  
(35%) 

 51 
(16%) 

39  
(12%) 

42  
(13%) 

77  
(24%) 

Total No. of 

isolates 



but this strategy is still several years from fruition. In
the interim, the best approach lies in the prudent use
of fluoroquinolones in humans and animals, coupled
with an emphasis on preventing patient-to-patient
spread of resistant strains. 

The antibiotic which showed maximum activity
against most of the isolates was imipenem. Though
carbapenems remain the final options for treating
these infections, there is a possibility that the
increasing use of carbapenems may lead to a rapid
emergence of carbapenem resistance.

Conclusion:
The considerably high MIC values for ciprofloxacin
in this study reflect the limited treatment options
which are available for these resistant isolates and a
need for the continuous evaluation of the commonly
used antibiotics. Repeated surveillance, the formula-
tion of an antibiotic policy, the prudent prescription
of antibiotics and the recycling of antibiotics are the
possible routes which can be used to curb the rapid
emergence and the spread of these resistant isolates.

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Ahmad S

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