Original Article

Ahmad Khorshidi, Ph.D.*,

Hossein Akbari, M.Sc.**

*Department of Microbiology & Immunology, Kashan University of Medical Sciences, P.O. Box 87155.111, Kashan, Iran.

**Department of Statistics, Kashan University of Medical Sciences and Health Services, Kashan, Iran.

Received for publication: September 12, 2005.

Reprint request: Ahmad Khorshidi, Ph.D., Department of Microbiology & Immunology, Kashan University of Medical Sciences, P.O. Box:

87155.111, Kashan, Iran.

E-mail: khorshidi-ha@yahoo.com

Keywords: multidrug resistance, Shigella, acute diarrhea

Emergence of Multidrug-Resistant Shigella in Iran

15

INTRODUCTION

Acute infectious diarrhea is a major cause of

morbidity and mortality, especially in developing

countries.1-4 The use of oral rehydration therapy has

markedly decreased the mortality, but antimicrobial

agents are usually employed to treat acute bloody

ABSTRACT

Acute infectious diarrhea is a major cause of morbidity and mortality in Iran especially during the

warm season, with shigellosis recognized as a particular causes of acute bloody diarrhea. In view of increasing

antibiotic resistance, this study was conducted to determine the prevalence of multidrug-resistant (MDR)

Shigella in Kashan Hospital, Kashan, Iran.

The prevalence of multidrug-resistant (MDR) Shigella in Kashan Hospital, Kashan, Iran. The

study was performed in 734 patients with acute diarrhea who were treated from 2002 to 2003. After

admission and registration of demographic characteristics, the fecal specimens were studied by culturing and

serotyping according to the recommendation of the National Committee for Clinical Laboratory Standards

(NCCLS). The antibiotic susceptibility was done by the disk diffusion method (Kirby-Bauer). The results

were presented by a descriptive analysis. The prevalence of shigellosis was reported as 7.6 percent (56 of

734). Thirty-four (60%) of the isolates belonged to Shigella flexeneri, 14.3 percent were S. dysenteria, 25

percent were S. boydii. The highest rate of antibiotic resistance were found in cephalothin (78.6%), followed

by sulfamethoxazole-trimethoprim (SXT) (58.9%), and ampicillin (38.9%). Furthermore, the results showed

that 21 (61.6%) of S. flexneri were resistant to cephalothin and (SXT), 3 (8.8%) resistant to three antibiotics

(cephalothin, SXT, and ampicillin), and 2 (5.9%) resistant to four antibiotics (cephalothin, SXT, ampicillin, and

chloramphenicol). In conclusion, these results confirm that MDR strains of Shigella are present in Kashan,

Iran and emphasize the importance of maintaining this surveillance in order to determine the local susceptibility

patterns for appropriate empirical antibiotic treatment in patients with acute infectious diarrhea. (J Infect

Dis Antimicrob Agents 2006;23:15-9.)

16 J INFECT DIS ANTIMICROB AGENTS Jan.-Apr. 2006

diarrhea, as occurs with shigellosis, to the decrease the

duration of the episode and the period of infectiousness,

as well to prevent the complications and death.5

An appropriate use of antimicrobials in patients with

bloody diarrhea depends on the physician’s knowledge

of the relative frequency of enteropathogens and

their susceptibility to these drugs.6 Accordingly,

a continous surveillance of the resistance patterns of

enteropathogens is needed to select the appropriate

antimicobial agent.5-7 Unfortunately, in Kashan, Iran,

limited financial and laboratory resources generally

preclude the use of accurate stool cultures and

antimicrobial drug susceptibility testing to guide the

empirical therapy. Hence, an empirical therapy is often

used without supporting data, and a decision usually

depends on the clinical experience of the physician.

Sulfamethoxazole-trimethoprim (SXT) and

ampicillin are less expensive antimicrobial agents, and

are widely available for the treatment of bloody diarrhea

at Iranian hospitals and health care centers at no cost

to patients. However, an antibiotic treatment of patients

with suspected shigellosis, especially in children, has

been complicated by the occurrence of drug resistance

since the 1940, when strains of Shigella resistant to

SXT were first recognized in Japan8, and later in other

parts of the world.9-12 Thus, the traditional theraputic

agents such as ampicillin and SXT have lost much of

their effectiveness over the last decade7-15, because the

resistance patterns are changing constantly and vary

among different parts of the world.

The aim of the present study was to determine

the antimicrobial resistance patterns of 56 Shigella

strains isolated from patients with acute diarrhea in

Kashan University Hospital, Iran.

MATERIAL & METHODS

Patients and bacterial isolates

From 2002 to 2003, 56 Shigella strains were

isolated from patients with acute diarrhea who were

treated at Kashan University Hospital, Kashan, Iran.

Freshly excreted fecal specimens were collected from

each patient, inoculated into the Cary Blair medium,

and transported to the Central Laboratory of Kashan

within three hours of the inoculation. Slides of fecal

specimens were stained with Gram stain and methylen

blue, and were examined for fecal leukocytes using light

microscopy. All strains were isolated from unrelated

cases of acute diarrhea. Isolation, identification, and

serotyping of Shigella species were performed according

to the standard procedures.10

Antimicrobial Agents

Nine antimicrobial agents including SXT, ampicillin,

cephalothin, ceftriaxone, ceftizoxime, chloramphenicol,

nalidixic acid, ciprofloxacin, gentamycin were obtained

from Patan Tab Company, Iran.

Suceptibility testing methods

Susceptibility test was done by the disk diffusion

method (Kirby-Bauer).11 The resultes were presented

by a descriptive analysis.

RESULTS

The prevalence of shigellosis in patients with

acute diarrhea was reported as 7.6 percent (56 of 734),

with 34 (60.7%) of the isolates belonging to Shigella

flexeneri, 8 (14.3%) belonging to S. dysenteriae, and

14 (25%) belonging to S. boydii. The results show

that all of Shigella were susceptible to ciprofloxacin,

gentamycin, ceftizoxime, and were mostly resistant to

cephalothin (78.6%) and SXT (58.9%) (Table 1).

The antimicrobial resistance phenotypes of

Shigella included a resistance to two antibiotics

(cephalothin and SXT) in 35 (62.21%), a resistance to

three antibiotics (cephalothin, SXT, and ampicillin) in 9

(61.1%), and a resistance to four antibiotics (cephalothin,

Vol. 23 No. 1 17 Emergence of Multidrug-Resistant Shigella in Iran:- Khorshidi A & Akbari H.

SXT, ampicillin, and chloramphenicol) in 4 (7.1%)

isolates.

All eight isolates of S. dysenteriae were

susceptible to all nie antibiotics tested. Of 34 S. flexneri,

27 (79.2%) were resistant to two antibiotics (cephalothin

and SXT), 3 (8.8%) to three antibiotics (cephalothin,

SXT, and ampicillin), 4 (11.8%) to four antibiotics

(cephalothin, SXT, ampicillin, and chloramphenicol). Of

14 S. boydii, 8 (57.1%) were resistant to two antibiotics,

6 (42.9%) were resistant to three antibiotics (Table 2).

DISCUSSION

In our study, the prevalence of shigellosis was

7.6 percent, and the frequently isolated species were

S. flexneri (60.7%), followed by S. dysenteriae

(14.3%), and S. boydii (25%). Multidrug-resistant

(MDR) Shigella has been reported in several parts of

the world.5,6,9-12 Our study also demonstrates a high

prevalence of Shigella with resistance to the first-line

therapeutic agents including cephalothin, SXT, and

ampicillin, as reported in Bulgaria1, the United States13,

Canada7, and in several other countries6,7 Shahid and

colleagues9 as well as Tauxe and colleaguse5 have found

that an increased resistance to SXT is directly related

to an extensive use of this drug. In Iran, SXT is

frequently prescribed as an empirical therapy for

shigellosis and other diarrhea of suspected bacterial

origin. It is probable that its extensive use would lead

Table 1. Antimicrobial susceptibility results of all 56 isolates of Shigella.

Total (%) of Total (%) of Total (%) of

Antimicrobical agents S. dysenteriae S. flexeneri S. booydii Total (%)

(N=8) (N=34) (N=14)

Ciprofloxacin 8 (100) 34 (100) 14 (100) 56 (100)

Cephalothin 8 (100) 4 (11.8) - 12 (21.4)

Gentamicin 8 (100) 34 (100) 14 (100) 56 (100)

Nalidixic acid 8 (100) 32 (94.1) 14 (100) 96.4 (54)

Ceftizoxim 8 (100) 34 (100) 14 (100) 56 (100)

Sulfamethoxazole-trimethoprim 8 (100) 4 (11.8) 11 (78.6) 23 (41.1)

Chloramphenicol 8 (100) 26 (76.5) 14 (100) 48 (85.7)

Ampicillin 8 (100) 25 (73.5) - 33 (58.9)

Ceftriaxone 8 (100) 34 (100) 11 (78.6) 53 (94.6)

Table 2. Number of resistant frequency of multidrug resistance according to the species of Shigella.

S. dysenteriae S. flexeneri S. boydiiAntimicrobial agents Total (%) N (%) N (%) N (%)

0 8 (14.3) 8 (100) 0 0

2 35 (62.5) 0 27 (79.2) 8 (57.1)

3 9 (16.1) 0 3 (8.8) 6 (42.9)

4 4 (7.1) 0 4 (11.8) 0

18 J INFECT DIS ANTIMICROB AGENTS Jan.-Apr. 2006

the emergence of resistant Shigella in our hospital. A

study in Caracas reported that 86 percent of Shigella

isolated from patients with diarrhea in two health care

centers, were resistant to SXT.14 This finding is in

accordence with our study.

It is important to note that the resistance to

ampicillin among Shigella has grown steadily over the

past 25 years, along with an indiscriminate use of this

drug.2,5,6,11 Indeed, 38.9 percent of the total isolates of

Shigella in our study were resistant to ampicillin, which

in accordence with a study of Flores and coleaguse.16

The high resistance rates of Shigella to cephalothin,

SXT, and ampicillin are shown in our study, in accordance

with others sties in Iran.17,18 No resistance to nalidixic

acid among Shigella was observed in our study, and its

use in controlled clinical trials has been shown to be

effective against shigellosis, mainly in terms of clinical

response. Nalidixic acid is not readily available in

Kashan, Iran and is thus used occasionally in clinical

practice. Its use should be promoted, rather than SXT

or ampicillin, as the first-line agent for the empirical

treatment of patients with suspected shigellosis.

All Shigella isolates in our study were susceptible

to ciprofloxacin, a 4-fluoroquinolone. Other studies

have confirmed an excellent in vitro activity of 4-

fluoroquinolone against Shigella.5,13,16,17,19,20 It has been

recommended as an alternative therapeutic choice

for pediatric patients with shigellosis, because all

quinolones are contraindicated due to their potential

chondrotoxicity.5,14 The broad-spectrum of cephalosporin

may be another therapeutic option. It has recently been

suggested that ceftriaxone may be used in children with

Shigella dysentery.21 Varson and colleagues compiled

the results from eleven studies which demonstrated that

ceftoriaxone was active against more than 500 Shigella

isolates tested worldwide.22 The results obtained in our

study indicated that ceftriaxone is very active in vitro

against Shigella.

MDR strains of Shigella are now considered

a public health problem6,7,10,22, and the results

obtained in our study support this statement.

According to the susceptibility of Shigella isolated

in our community, it is clear that cephalothin, SXT,

and ampicillin are not good choice for the empirical

treatment. Physicians should be aware of the

increasing antimicrobial resistance of Shigella.

Because the resistance patterns vary according to

the specific location, routine antimicrobial resistance

monitoring is mandatory and thus becomes an

essential part of any diarrhea control program that

advocates empirical antimicrobial therapy.

We conclude that MDR strains of Shigella are

circulating in Kashan, Iran. We emphasize the

importance of keeping these strains under surveillance

in order to evaluate the local susceptibility patterns. At

the same time, the empirical antibiotic treatment for

patients with suspected shigellosis should be changed

accordingly.

ACKNOWLEDGEMENT

We gratefully acknowledge Kashan University of

Medical Sciences and Health Services for their financial

support of this work.

We thank Mrs.Afshin Salehi and Mr.Hassan Rasa

for assistance in the laboratory.

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