RESEARCH ARTICLE

Antimicrobial Resistance of Shigella Isolates in Alanya, Turkey

Haluk Erdogan • Askin Erdogan

Received: 21 September 2013 / Revised: 31 December 2013 / Accepted: 5 March 2014

� The National Academy of Sciences, India 2014

Abstract Shigella spp. were isolated from stool samples

and stored at -80 �C for antimicrobial susceptibility.

Antimicrobial susceptibility was determined according to

the Clinical and Laboratory Standards Institute criteria. The

antimicrobials tested against Shigella spp. included ampi-

cillin, trimethoprim–sulfamethoxazole, tetracycline, chlor-

amphenicol, ciprofloxacin, ceftriaxone and azithromycin.

Minimum inhibitory concentration of ceftriaxone and

azithromycin were determined by E-test. Quality control

was ensured by testing Escherichia coli ATCC 25922 and

Staphylococcus aureus ATCC 29213. A total of 33 Shigella

isolates (17 S. sonnei, 9 S. flexneri, 5 S. dysenteriae and 2 S.

boydii) were assessed for their antimicrobial susceptibility

patterns. The resistance to trimethoprim–sulfamethoxazole,

ampicillin, tetracycline, chloramphenicol, ceftriaxone and

azithromycin were found to be 66.7, 45.5, 57.6, 9.1, 9.1 and

3 %, respectively. S. sonnei showed higher resistance than

S. flexneri to trimethoprim–sulfamethoxazole, but resis-

tance to ampicillin was more common in S. flexneri than S.

sonnei. Minimum inhibitory concentration values were in

the following ranges: azithromycin 0.75–16 lg/mL and

ceftriaxone 0.002 to [32 lg/mL. Minimum inhibitory

concentration that inhibit 90 % of the strains for azithro-

mycin and ceftriaxone were 6 and 0.47 lg/mL, respec-

tively. The resistance to ceftriaxone and azithromycin may

be a cause for concern.

Keywords Diarrhea � Shigellosis � Shigella �Antimicrobial resistance

Introduction

Diarrhea is a major cause of morbidity and mortality in

children and adults worldwide. Shigella spp. remains one of

the most frequently isolated bacteria from the stool samples

of diarrhea patients. Antimicrobial therapy has been shown

to decrease the duration of the fever and diarrhea, as well as

the spread of the disease. The highest global rates of anti-

microbial drug resistance of all Shigella spp. have been

reported in relation to ampicillin, trimethoprim–sulfa-

methoxazole and chloramphenicol [1–4]. According to The

World Health Organization guidelines for the control of

shigellosis, ciprofloxacin, pivmecillinam, azithromycin and

ceftriaxone are the antimicrobial agents that are effective

for the treatment of multidrug-resistant strains of Shigella

[5]. However, extended-spectrum beta lactamase-producing

Shigella have been reported from different regions of the

world [6, 7]. Fluoroquinolone resistance in Shigella spp. has

also been reported [8]. There is not sufficient information on

pivmecillinam, azithromycin or ceftriaxone susceptibility

patterns of Shigella isolates in Turkey. Because antimi-

crobial resistance among Shigella strains is a common

finding that has increased over time, the aim of the present

study was to evaluate the antimicrobial susceptibility

The part of the study has presented as a poster at the Digestive

Disease Week (DDW), Orlando, 2013.

H. Erdogan

Department of Infectious Disease and Clinical Microbiology,

Faculty of Medicine, Baskent University, Ankara, Turkey

A. Erdogan

Department of Gastroenterology, Faculty of Medicine,

Baskent University, Ankara, Turkey

H. Erdogan (&)

Baskent Universitesi Alanya Arastırma ve Uygulama Merkezi,

Saray m, Kizlarpinari cd, No. 1, Alanya 07400, Antalya, Turkey

e-mail: erdoganhaluk@hotmail.com

123

Proc. Natl. Acad. Sci., India, Sect. B Biol. Sci.

DOI 10.1007/s40011-014-0341-8

against Shigella spp. in Alanya, a town that accounted for

13 % of the total number of tourists in Turkey in 2004, and

also to review the pertinent literature [9].

Material and Methods

The study was carried out between 2004 and 2012 years.

Shigella spp. were isolated from stool samples at Baskent

University Alanya Research and Medical Center and stored

at -80 �C. Fecal samples were cultured on Eosine methy-

lene blue agar and Hektoen enteric agar for the isolation of

Shigella spp., which were identified biochemically by the

standard methods and grouped serologically by slide

agglutination with specific antisera (Denka Saiken, Tokyo,

Japan). Antimicrobial susceptibility was determined by the

Kirby–Bauer disk diffusion method according to the

guidelines of the Clinical and Laboratory Standards Insti-

tute (CLSI) [10]. The antimicrobials tested against Shigella

spp. included ampicillin, trimethoprim–sulfamethoxazole,

tetracycline, chloramphenicol, ciprofloxacin and ceftriax-

one(BD BBL, Sensi-Disc).Minimum inhibitory concentra-

tion (MIC) of ceftriaxone and azithromycin was determined

by E-test (Liofilchem� s.r.l., Italy).Quality control was

ensured by testing Escherichia coli ATCC 25922 and

Staphylococcus aureus ATCC 29213. In the present study,

multidrug resistance is defined as the presence of resistance

to three or more classes of antimicrobial agents.

Results and Discussion

Shigella was detected in 33(0.9 %) of 3,422 stool samples

and assessed for their antimicrobial susceptibility patterns.

Out of 33 patients from whom Shigella strains were iso-

lated, 24 (72.7 %) were female and 9 (27.3 %) were male.

Fifty-five percent of the patients were of 15 years or older.

The species were distributed as follows: 17 S. sonnei

(46.2 %), 9 S. flexneri (30.8 %), 5 S. dysenteriae (15.4 %)

and 2 S. boydii (7.7 %). These strains showed high per-

centage of resistance to trimethoprim–sulfamethoxazole

(66.7 %), ampicillin (45.5 %), tetracycline (57.6 %) while

64 % were multidrug-resistant. S. flexneri strains were

resistant to ampicillin in 88.8 % of cases, to trimethoprim–

sulfamethoxazole in 44.4 %, to tetracycline in 44.4 %, to

chloramphenicol in 33.3 % and to ceftriaxone in 11.1 %. S.

sonnei strains were found to be resistant to trimethoprim–

sulfamethoxazole (88.2 %), tetracycline (70.6 %), ampi-

cillin (23.5.7 %), ceftriaxone (11.8 %), but these strains

were not resistant to chloramphenicol (Fig. 1).Three iso-

lates of 5 S. dysenteriae were resistant to ampicillin, tri-

methoprim–sulfamethoxazole and tetracycline. One isolate

of 2 S. boydii was only resistant to ampicillin.

Antimicrobial susceptibility testing is essential for the

management of the patients with suspected shigellosis.

Shigella isolates resistant to ampicillin, tetracycline, tri-

methoprim–sulfamethoxazole and chloramphenicol are of

growing concern [2–5]. Surveillance for the antimicrobial

susceptibility of Shigella isolates from 1999 to 2002 by the

National Antimicrobial Resistance Monitoring System of

the United States demonstrated that Shigella isolates were

highly resistant to ampicillin (78 %) and trimethoprim–

sulfamethoxazole (46 %) [4]. In various regions of Turkey,

the levels of antibiotic resistance against Shigella strains

were reported as follows: trimethoprim–sulfamethoxazole

resistance, 69–74 %; ampicillin resistance, 20–50 %; tet-

racycline resistance, 66–71 %; and chloramphenicol

resistance, 20–40 % [1, 7, 11–15]. In the present study, the

levels of ampicillin, tetracycline, trimethoprim–sulfa-

methoxazole and chloramphenicol resistance were found to

be high, in comparison to other studies. As shown in the

present study, the resistance rates reported in Turkey for S.

sonnei and S. flexneri were not similar. Ozmert et al. [1]

reported that out of the S. sonnei isolates, which repre-

sented 87 % of the 238 Shigella isolates sampled between

2003 and 2009, 31.4 % were resistant to ampicillin, and

71.6 % were resistant to trimethoprim–sulfamethoxazole.

However, out of the S. flexneri samples, 72 % were resis-

tant to ampicillin, and 58.3 % were resistant to trimetho-

prim–sulfamethoxazole. In another study from June 2002

to December 2002 Karacan et al. [16] reported that in S.

sonnei out of 198 clinical isolates 8.5 % were resistant to

ampicillin and 96.4 % were resistant to trimethoprim–sul-

famethoxazole. Among the sampled S. flexneri strains,

60 % showed ampicillin resistance and 70 % showed tri-

methoprim–sulfamethoxazole resistance.

Ciprofloxacin, ceftriaxone and azithromycin are cur-

rently the antimicrobial agents of choice for the treatment of

multidrug-resistant strains of Shigella. However, fluoro-

quinolone resistance in Shigella spp. has also been recently

reported. Ciprofloxacin resistant Shigella first emerged in S.

dysenteriae serotype 1 and later in S. flexneri [17, 18]. In the

present study, quinolone resistance was not detected. To the

best of the knowledge, quinolone resistance has only been

reported by Birengel et al. [14] in one case in Turkey.

Ceftriaxone is recommended for the treatment of patients

with suspected ciprofloxacin-resistant infections. Cefixime

may be considered as an oral alternative therapy for chil-

dren [19, 20]. However, Shigella species that produce

extended spectrum beta lactamase have been reported from

different regions of the world at the rates of approximately

2–5 % [2–6]. Taneja et al. [21] reported a higher percentage

of cephalosporin-resistant isolates (15.1 %) of S. flexneri in

India. To the best the knowledge, only Acikgoz et al. [7]

reported 5 (3.2 %) S. sonnei isolates with ceftriaxone

resistance in 153 clinical isolates and Karacan et al. [16]

H. Erdogan, A. Erdogan

123

reported 3 (2 %) strains that were resistant to ceftriaxone

out of 198 clinical isolates in Turkey. Ceftriaxone resistance

was found in 9.1 % of the Shigella isolates in the present

study (MIC range, 0.002 to[32 lg/mL; MIC50, 0.002 lg/

mL; MIC90, 0.47 lg/mL). Centers for Disease Control and

Prevention has recently reported thatShigella sonnei has a

decreased susceptibility to azithromycin in the United

States [22]. Azap et al. [23] reported that 23 Shigella strains

were tested against azithromycin using the agar dilution

method in Turkey. Both the MIC50 and MIC90 values were

8 mg/L (MIC range 4–16 mg/L). None of these strains was

shown to be susceptible to azithromycin. In the present

study, MIC of azithromycin was determined by E-test.

The MIC range, 0.75–16 lg/mL; MIC50 3 lg/mL;

MIC90, 6 lg/mL were found. Azithromycin resistance

(MIC C 8 lg/mL) was found in 3 % of the Shigella isolates

and many isolates (50 %) were intermediate susceptible

(MICs, 2–8 lg/mL) to azithromycin.

Conclusion

S. sonnei is discovered to be the predominant pathogenic

species responsible for shigellosis. The prevalence of

resistance to ampicillin, tetracycline and trimethoprim–

sulfamethoxazole among Shigella isolates is high. The

ceftriaxone and azithromycin resistance of these isolates

are troubling, while quinolone resistance was not found.

This study suggests that ciprofloxacin, azithromycin and

ceftriaxone can be used as empirical therapies in severely

ill patients and in patients with predisposing factors to

severe infection with suspected shigellosis and a history of

travel to Alanya, Turkey. However, the ceftriaxone and

azithromycin resistance of Shigella spp. should be closely

monitored.

Acknowledgments The authors thank Burcu Dobrisan and Sibel

Ozturk for their assistance in collecting and working with the samples.

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