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Original article
A five-year antimicrobial resistance pattern observed in
Shigella species isolated from stool samples in Gondar
University Hospital, northwest Ethiopia

Gizachew Yismaw, Challa Negeri, Afework Kassu
Abstract
Background: Shigellosis is a global human health problem and an important public health problem, especially in
developing countries, where substandard hygiene and unsafe water supplies abound. Besides, an increase in resistance
against many different drugs among Shigella isolates has been observed in the last two decades.
Objective: To determine the pattern of antimicrobial sensitivity of shigella species to commonly used antibiotics.
Methods: The antibiotic susceptibility pattern of Shigella species isolated from stool specimens processed over five
years at the bacteriology laboratory of the University of Gondar teaching hospital in northwest Ethiopia was
investigated. Stool specimens were processed in accordance with the standard bacteriological methods and data were
collected in the laboratory log book for bacterial culture, isolation and antimicrobial sensitivity.
Results: From the total of 2,891 stool specimens that were cultured, 214 yielded Shigella species. The overall
sensitivity of Shigella species to the commonly used antibiotics in the area was 92.1% to gentamicin, 91.1% to
ciprofloxacin, 47.2% to chloramphenicol, 26.6% to cotrimoxazole, 20.1% to ampicillin and 14% to tetracycline. About
46% of the isolates were found to be resistant to at least three commonly used drugs, while 1.4% were found to be
resistant to all the commonly used drugs.
Conclusion: The results demonstrate the continued sensitivity of Shigella species to gentamicin and ciprofloxacin and
their widespread resistance against tetracycline, ampicillin and cotrimoxazole. Based on our results, gentamicin and
ciprofloxacin may be used rationally under strict regulation for the treatment of severe cases of shigellosis in case
where other safer and better drugs are unavailable. [Ethiop.J.Health Dev. 2006;20(3):194-198]
Introduction
tetracycline, and from 1.6% to 15.1% for chloram- Shigellosis is a global human health problem. It is still an important public health problem, especially in developing countries, where there is substandard hygiene and unsafe In Ethiopia, strains of Shigella that were resistant to water supplies (1,2). Shigella still accounts for a many commonly used drugs have been reported in significant proportion of bacillary dysentery in many different parts of the country by several studies (12-14). tropical and subtropical countries (3,4). It is the most In the aforementioned Ethiopian study reports, the strains prevalent etiologic agent in childhood diarrhoea in most were found to be most commonly resistant to tetracycline countries (5,6). In Ethiopia, Shigella dysenteriae and (>80%), ampicillin (>65%), and cotrimoxazole (>70%). Shigella flexineri have been identified as the species that Multiple drug resistance to ampicillin, chloramphenicol, account for about 80% of Shigella isolates (2). tetracycline, and streptomycin was also very high in those studies. Belay and his colleagues have reported a The emergence of antimicrobial resistance to members of strain that was resistant to eight drugs out of the nine the Enterobacteriaceae family is posing serious problems in the treatment of outbreaks of infections. Since its first report in studies conducted in the 1950s, multiple-drug Besides the temporal changes in the antibiogram of resistance transmitted by plasmids among Shigella Shigella species, it is well known that antibiotic species has been reported from many countries (6-8). susceptibility patterns in Shigella may differ between Moreover, an increase in resistance against many geographical areas. Such differences are never stable and different drugs has been observed in the last two decades. may change rapidly especially in places where antibiotics In one study, a significant decrease was observed in the are used excessively (particularly in developing susceptibility of the species to ampicillin and countries) (15). This warrants for frequent observation cotrimoxazole from 1988-89 to 1991-92 (9). In another on the change in the pattern of antibiogram for this report, it was shown that cotrimoxazole resistance of Shigella increased from 3% to 40% within ten years time (10). Another study showed that the percentage of To our knowledge, no report exists regarding the resistant Shigella strains in Madrid (Spain) increased antibiotic resistance pattern of Shigella species in Gondar from 39.6% to 97.9% for ampicillin, from 34.4% to region except one in the previous decade (16).This study 96.9% for cotrimoxazole, from 6.3% to 18.0% for was thus carried out to determine the pattern of _______________________________________________________________________________________________ Department of Microbiology and Parasitology, College of Medicine and Health Sciences, University of Gondar, P. O. Box 196 Gondar, Ethiopia A five year antimicrobial resistance pattern of Shigella species isolated from stool 195 _______________________________________________________________________________________ antimicrobial sensitivity of Shigella species to the most (N=53, 24.8%) were from stool specimens collected from commonly used antibiotics in Gondar, northwest in-patients. The distribution of the isolates in the different Ethiopia. years was 45 (20.9%) in 2001, 23 (10.3%) in 2002, 34 (15.8%) in 2003, 85 (39.5%) in 2004, and 27 (14.6%) in This retrospective study was conducted in the bacteriology laboratory of the University of Gondar The in vitro antimicrobial susceptibility pattern of Hospital, Gondar, Northwest Ethiopia, between Shigella isolates identified in the University of Gondar September 2001 and August 2005. The hospital is a Hospital from September 2001-August 2005 is shown in tertiary level teaching and referral hospital currently Table 1. About 46% of the Shigella isolates were found rendering health services for over 4 million rural and to be resistant to at least three commonly used drugs, and urban inhabitants in northwest Ethiopia. 1.4% of the Shigella isolates were found to be resistant to all the commonly used drugs. Overall, many different Stool specimens were collected from in- and out-patients patterns of resistance were observed. The predominant during the five year period and were processed following resistance patterns to triple antibiotics were those to the standard bacteriological methods (1). The stool A,T,Sxt (60.3%), A,T,C (46.3%), and A,C,Sxt (41.1%). specimens were inoculated on plates of MacConkey agar The antibiogram resistance patterns for three up to six (DIFCO) and Salmonella-Shigella agar (DIFCO). The antibiotics are depicted in Table 2. plates were incubated at 37oC for 24 hours and suspected colonies were further examined by conventional The highest prevalence of antibiotic resistance was biochemical tests. Antimicrobial sensitivity testing was documented to be against ampicillin 171 (79.9 %), carried out by the standardized agar disk diffusion tetracycline 184 (86 %), and cotrimoxazole 157 (73.4%). techniques on Mueller Hinton agar (DIFCO) using the The least resistance of antibiotics was observed to following antimicrobial agents: ampicillin (A), ciprofloxacin 19(8.9%) and gentamicin 17(7.9%). Over tetracycline (T), cotrimoxazole (SXT), gentamicin (CN), the years from 2001 to 2005, there was no significant chloramphenicol (C), and ciprofloxacin (CIP) (17, 18). increase in resistance to the individual antibiotics tested. Turbidity of the broth was equilibrated to match with 0.5 Table 1: In vitro antimicrobial susceptibility pattern of
Shigella species isolate in University of Gondar
The standard reference strains Escherichia coli ATCC Hospital from September 2001 to August 2005
25922 and Pseudomonas aeruginosa ATCC 27853 were Antibiotic Susceptible
Resistant
tested as controls on the biochemical tests and agar plates including Mueller Hinton with antibiotic discs. Data on age, sex, source of specimens and culture results were collected from the bacteriology log book. In this study, multi-drug resistance was defined as simultaneous resistance to three or more antimicrobial agents. Statistical analysis was made using SPSS version 11.5 software. Ethical clearance was obtained from the
Research and Publication office of the University of Table 2: Multiple drug resistance patterns among
Gondar.
Shigella species isolated in University of Gondar
Hospital, north West Ethiopia, September 2001 to
August 2005.
A total of 2891 stool specimens were received from in- Resistance types
Resistant isolates N (%)
patients (n=2371 (82%)) and out-patients (n=520 (18%)) and processed in the bacteriology laboratory over the five years period. A total of 214 Shigella species were isolated from the stool specimens, while 42 other entries with incomplete data were excluded from the analysis. Specimens cultured from children (up to 15 years of age), adults aged between 16 to 45 years and those above 45 years accounted for 36.4%, 53.3%, and 10.3%, respectively. One hundred fifteen (53.5%) of the isolates were from male patients and the rest 99 (46.5%) were from females. The majority of the Shigella species (N=169, 75.2%) were isolated from specimens collected from patients at the outpatient department and the rest 196 Ethiop.J.Health Dav
______________________________________________________________________________________
Table 3: Comparison of resistance rate of Shigella species to commonly used antibiotics in different regions
(Addis Ababa versus Gondar) and in different periods (1980, 1995, 2001-2005)
Antibiotics 1980
1994-96 (Addis Ababa)
2001-2005 Gondar
(Preset study

Discussion
of gentamicin and related aminoglycosides (e.g., This retrospective study demonstrated a high level of streptomycin) over the past five years (21-23). Since this antimicrobial resistance pattern in Shigella species antibiotic appears to be less commonly used than the isolated from stool samples over a five year period in orally administered antibiotics, the rate of resistance is Gondar, northwest Ethiopia. The fact that the majority of not yet high in this study as well as in other recent studies Shigella isolates are from the pediatric population is from Bangladesh (24) and Sudan (25). Gentamicin and reported in the literature where 70% of all infections ciprofloxacin are the only two commonly available occur in children younger than 15 years (19). In the antibiotics to which the majority of Shigella strains in present work, children accounted for more than a third Gondar area were susceptible as seen from the present (36.4%) of all Shigella positive patients. study. Although ciprofloxacin is contraindicated for those patients below 18 years of age, gentamicin can still be In line with our findings, a low rate of resistance to used in settings where safer drugs are not available. gentamicin and ciprofloxacin was observed in different studies (4, 14). For example, Moez and his colleagues Of the Shigella isolates, 90.8% were found to be resistant observed a 3.1% resistance to ciprofloxacin (4). A recent to one or more antimicrobial agent(s), and 87.8% were prospective study conducted in southern Ethiopia showed multi-drug resistant. The most common resistance was to a high sensitivity of Shigella isolates to gentamicin (14). tetracycline (73.5%) and cotrimoxazole (70.4%) as was observed by other authors (4, 14). A high rate of Resistance to cotrimoxazole, one of the drugs used in the resistance of Shigella species was also observed for treatment of shigellosis was first reported in Ethiopia in cotrimoxazole (87.75%) and ampicillin (55.5%) in 1981 (20). Prior to this period, all strains isolated in Pakistan and Nigeria (3, 26). On the contrary, Khan- Addis Ababa were found to be sensitive to cotrimoxazole Mohammed and his coworkers have found a low level of and gentamicin (20). However, Belay and his colleagues resistance to the above antibiotics as only 8.1% of the (14) demonstrated a 55% resistance of Shigella strains to isolates exhibited resistance to ampicillin, 2.7% to cotrimoxazole. Although Khan-Mohammed et al (5) chloramphenicol, and 2.7% to cotrimoxazole (5). showed a 2.7% resistance rate in Trinidad, our finding of a 73% resistance rate of the isolates to this antibiotic was In this study, multiple drug resistance to as many as five in agreement with observations from Pakistan (3) and and six antibiotics was observed. Similar findings were Iran (4) where a resistance rate of 70.4% and 87.8%, seen in other studies from other localities in Ethiopia (12- respectively, by Shigella species to cotrimoxazole was 14, 20). Shigella isolates from Sudanese patients with diarrhoea also showed high resistance rates against the commonly used antimicrobial agents: ampicillin, In northwest Ethiopia, the resistance of Shigella species chloramphenicol, tetracycline, cotrimoxazole, and to cotrimoxazole is high and has slightly increased in sulfonamide (25). Another study conducted in six comparison to the previous report (16) (Table 3). countries in the East African region also showed Unfortunately, the drug is still commonly prescribed and resistance of Shigella isolates to the commonly used used by the community for diarrhoeal diseases, antibiotics except for nalidixic acid (27). A WHO particularly in children, and on the bases of self scientific working group had reported a high prevalence prescription from private pharmacies (21-23). Therefore, of resistance to A, C, T and Sxt in developing countries the fact that the majority of Shigella isolates were because of the very high consumption of antibiotics from resistant to cotrimoxazole is depressing since this drug is the open market in these countries (15). Similarly, this one of the drugs of choice in many countries (19) antibiogram was also common in our setting accounting including Ethiopia. for 40% of the isolates (Table 2). Yet, the current treatment of choice for shigellosis are still co- Compared to a previous report from Gondar (16), a four trimoxazole, ampicillin and ciprofloxacin (19,28). fold increase in resistance to gentamicin was observed in the present study (from 2% to 7.9%) (Table 3). This Shigella are notorious for the rapid emergence and spread increase might be because of the relatively increased use of multiple drug resistance among strains and resistance A five year antimicrobial resistance pattern of Shigella species isolated from stool 197 _______________________________________________________________________________________ patterns observed among strains of any one species in a single area may be numerous (16, 29) as also noted in our 9. Dan M. Marked decrease in susceptibility of Shigella findings. The measures suggested to delay the to ampicillin and cotrimoxazole in Israel. Eur J Clin development of resistance to cotrimoxazole in the days when it was a potent drug against the then prevalent 10. Heikkila E, Siitonen A. Increase of trimethoprim strains hold true for fluoroquinolones and gentamicin resistance among Shigella species. J Infect today. Unfortunately, the orally administered fluoroquinolones are sold at private pharmacies without 11. Lopez BM and Collado L. Increasing antimicrobial prescription in the region and the urban community has resistance of Shigella sonnei. J. Antimicrob become well-acquainted with those antibiotics for the treatment of common infections. Unless the unrestricted 12. Afeworki G and Lirneneh Y. Multiple drug use of these antibiotics is stopped in the area, the time resistance within Shigella serogroups. Ethiop Med J that these antibiotics become ineffective in the treatment of severe shigellosis (such as cotrimoxazole and 13. Senait K, Abera G, Sileshi L, KidaneMariam M. chloramphenicol) is not far. Clinical profile and drug susceptibility pattern of Shigella strains isolated from children in Addis The pitfalls in the study include the fact that we could not Ababa. Ethiop Med J.1993; 37:19-29. control the bacteriological methods and the data 14. Belay R, Solomon W, Shiferaw T, Nina L. collection. There were only six antibiotic discs used for Antimicrobial susceptibility pattern of Shigella the sensitivity testing and antibiotic discs such as isolates in Awassa. Ethiop J Health Dev. nalidixic acid, cephalosporins and norfloxacin were not included in the battery. Important data such as the nature 15. Leslie C, Albert B, Max S. Escherichia and Shigella. of the diarrhoea (whether dysenteric, persistent or acute In: Topley & Wilson’s Microbiology and Microbial watery) could not be obtained. Such measures as Infections. 9th edtion. Arnold Press, Great Britain. incidence of shigellosis could not also be calculated from 16. Assefa A, Gedlu E, Asmelash T. 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