|Year : 2017 | Volume
| Issue : 4 | Page : 96-101
Prevalence and antimicrobial susceptibility of Shigella species isolates from diarrheal stool of patients in a tertiary health facility in northeastern Nigeria
Ibrahim Y Ngoshe1, Ballah A Denue2, Hauwa S Bello1, Cecilia B Akawu3, Wadzani Gashau2
1 Department of Microbiology, University of Maiduguri, Maiduguri, Borno State, Nigeria
2 Department of Medicine, College of Medical Sciences, University of Maiduguri, Maiduguri, Nigeria
3 Department of Geography, University of Maiduguri, Maiduguri, Borno State, Nigeria
|Date of Web Publication||11-Apr-2018|
Dr. Ballah A Denue
Departments of Medicine, College of Medical Sciences, University of Maiduguri, PMB 1069, Maiduguri, Borno State
Background: Shigella is a frequent cause of bacterial diarrhea especially in sub Saharan Africa region. Antimicrobial chemotherapy is recommended for diarrheal disease due to Shigella species, but the options are limited by emerging resistance.
Aim: To determine the prevalence and antimicrobial susceptibility of shigella species isolated from diarrheal stool of patients in a tertiary health facility in northeastern Nigeria.
Patients and methods: This prospective cross sectional study was conducted in University of Maiduguri Teaching Hospital from 2nd January to 29th December 2013. Diarrheal stool samples were consecutively collected from all consenting patients from Emergency pediatric unit, General out patients and Medical clinics. Shigella species were detected by biochemical and serological tests. Antibiotic sensitivity pattern of these isolates was studied by disk diffusion Method.
Results: A total of 400 diarrheal stool samples were considered, shigella species isolation rate was 32(8%). It consisted of shigella flexneri 15(46.9%), shigella dysenteriae 12(37.5%), shigella sonnei 5(15.6%), no shigella boydii specie was identified. The shigella species were sensitive to Ciprofloxacin, Ofloxacin and Cefuroxime. Resistance to these antimicrobial were as follows: Gentamycin (28.1%), Tetracycline (31.2%) and Amoxycyllin (75%). At least 4 out of every 5 isolates were resistant to Chloromphenicol, Ampicillin and Norfloxacin. The highest resistance of 93.8% was exhibited against Cotrimoxazole.
Conclusion: Shigellosis is a recognized cause of bacterial diarrhea in our setting. In this study, Shigella flexneri was the most commonest isolated species followed by S. dysentriae. There was no resistance against Ciprofloxacin, Ofloxacin, Norfloxacin and Cefuroxime. At least 4 out of every 5 isolates were resistant to Chloromphenicol, Ampicillin and Nitrofurantoin. Cotrimoxazole showed highest resistance pattern.
Keywords: Antimicrobial susceptibility, northeastern nigeria, shigella species
|How to cite this article:|
Ngoshe IY, Denue BA, Bello HS, Akawu CB, Gashau W. Prevalence and antimicrobial susceptibility of Shigella species isolates from diarrheal stool of patients in a tertiary health facility in northeastern Nigeria. Sub-Saharan Afr J Med 2017;4:96-101
|How to cite this URL:|
Ngoshe IY, Denue BA, Bello HS, Akawu CB, Gashau W. Prevalence and antimicrobial susceptibility of Shigella species isolates from diarrheal stool of patients in a tertiary health facility in northeastern Nigeria. Sub-Saharan Afr J Med [serial online] 2017 [cited 2021 Oct 19];4:96-101. Available from: https://www.ssajm.org/text.asp?2017/4/4/96/229757
| Introduction|| |
Diarrheal disease is an important cause of morbidity and mortality, especially in the setting of poor sanitary condition. Globally, it is estimated that 140 million people or more are diseased by Shigella organisms with an estimated 600,000 annual deaths., Most of the global burden of Shigellosis is contributed by developing countries such as Nigeria with the dearth of basic social amenities. Poor personal hygiene, overcrowded living conditions, suboptimal sanitation, and improper sewage disposal are the risk factors for this disease.,,,
Effective antimicrobial therapy for Shigellosis reduces the duration and severity of the dysentery and can also prevent potentially lethal complications. Although there are several reports on Shigella species from Nigeria, most studies that examined the status of drug susceptibility in Shigellosis were conducted outside our region.,,, Since the wake of insurgency attacks on communities in our region in the year 2009, our health facilities have been overwhelmed with diarrheal and other diseases associated with poverty, war, internal displacement, poor sanitation, personal hygiene, and shortage of water supplies. Against this background, we conducted a prospective study to determine the prevalence and antimicrobial susceptibility of Shigella species isolated from the diarrheal stool of patients who presented for care at University of Maiduguri Teaching Hospital, a tertiary health institution from January to December 2013. Information obtained from local study will assist to provide information for use in designing treatment guideline for Shigellosis that will be appropriate for our setting. In addition, the study proposed to add to existing literature on epidemiological information on the resistance patterns of Shigella isolates of public health importance.
| Materials and methods|| |
A total of 400 patients who presented with diarrheal diseases were consecutively recruited from emergency pediatrics unit, general outpatient, and medical clinics in this prospective cross-sectional study. Diarrheal stool samples were collected aseptically into sterile bottles using standard laboratory method. The bacteriological examination of the prepared stool sample was performed, and all suspected colonies of Shigella were further subjected to biochemical analysis and serology. Each stool sample was collected and decontaminated by passing them over a Bunsen burner and then dispensed inside a universal bottle containing 2 ml of selenite-F broth (enrichment medium). It was then incubated at 37°C over 24–48 h. The sample was inoculated into the following media: Salmonella-Shigella Agar, MacConkey Agar, Desoxycholate Citrate Agar, and Xylose-Lysine Desoxycholate Agar (XLD). Positive isolates of Shigella were detected based on their colonial or morphological characteristics, while biochemical characteristics was determined according to standard laboratory techniques. These isolates were subjected to biochemical and serological analysis. Xylose and lactose fermentation, lysine decarboxylation, and hydrogen sulfide production were used to differentiate Shigella species from nonpathogenic bacteria. XLD, a selective differential medium, was used to isolate Shigella from stool specimens. Shigella colonies were identified transparent pink or red smooth colonies measuring 1–2 mm in diameter on XLD.
Biochemical screening test
The identification of Shigella species was done using both biochemical and serological testing. The following biochemical tests were performed: Kligler iron agar and Triple sugar iron agar (TSI), and ureas medium tysine iron agar. They were performed according to the standard procedures. Motility agar was inoculated with a straight inoculating needle, making a single stab about 1–2 cm down into the medium. TSI was also inoculated by stabling the buttt and then streaking the surface by the slant. The culture medium was examined for motility after 24 h incubation at 35–37°C. Shigella species are nonmotile; however, motility which excludes it is indicated by the presence of diffuse growth (appearing as clouding of the medium) away from the line of inoculation.
Serologic identification of Shigella
The genus Shigella is divided into four serogroups, each group consisting of a species that contains distinctive type antigens. The serogroups A, B, C, and D correspond to Shigella dysenteriae, Shigella flexneri, Shigella boydii, and Shigella sonnei, respectively. Serologic identification was performed by slide agglutination with polyvalent somatic (O) antigen grouping sera, followed in some cases, by testing with monovalent antisera for specific serotype identification.
Antimicrobial susceptibility testing
Antimicrobial susceptibility test was performed on Mueller-Hinton (Oxoid, UK) using disc diffusion method for: Ciprofloxacin (5 μg), Ampicillin (10 μg), Tetracycline (50 μg), Amoxycillin (20 μg), Chloramphenicol (10 μg), Cefuroxime (30 μg), Gentamicin (100 μg), Nitrofurantoin (100 μg), Cotrimoxazole (25 μg), and Ofloxacin (5 μg). The susceptibility of all strains was performed using the single disc diffusion technique.
Disc diffusion method
Peptone water was prepared according to the manufacturer’s instruction. Two milliliters peptone water was dispensed into each bijou bottles. With the help of sterile inoculating wire loop, the top of three or four individual colonies were smeared and transferred into the peptone water; this procedure was repeated for all the isolates. They were all emulsified to avoid lumps and allowed to stand for about 15 min. Each inoculum was then poured on a nutrient agar plate making sure it covers the entire surface of the media and the excess inoculums drained off. The lids of the plates were left open for about 5 min to allow any excess moisture to be absorbed before applying disks. The disks were then placed on the agar surface with the aid of sterile forceps to ensure adequate contact with the agar surface. The plates were then incubated at 37°C for 16–18 h and the diameter of inhibition zones measured in millimeter using a caliper. The interpretation of the measurement as sensitive, intermediate, and resistant was made according to a standard zone size interpretive chart.
| Result|| |
Of the 400 diarrheal stool samples considered for this study, 32 (8%) had Shigella species isolated from them. The isolation rate was 17 (8.5%) in males and 15 (7.5%) in females. The isolates rate of 15.3% obtained from the diarrheal stools of children aged 0–9 years was the highest, followed by 11.0% among adults aged 40–49 years. The age and sex distribution of studied patients with Shigella species positive stools is presented in [Table 1]. The distribution of Shigella serogroup is depicted in [Figure 1]. S. flexneri was the predominant serogroup in this study, and it constituted 15 (47%), followed by S. dysenteriae 12 (37%), while S. sonnei was implicated in 5 (16%) of cases seen, and no case of S. boydii was identified. The stratification of Shigella serogroup across defined age group is as depicted in [Table 2]. There is no uniformity in the distribution of the serogroups based on age groups. As shown in [Table 3], there was no gender variation in the distribution of the Shigella serogroups across the defined age group.
|Table 1: Age and sex distribution of patients with Shigella positive stools|
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|Table 2: Distribution of isolated Shigella serogroups by defined age group|
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[Table 4] shows the antimicrobial susceptibility of the isolated Shigella species. The isolated Shigella species were sensitive to Ciprofloxacin, Ofloxacin, Norfloxacin, and Cefuroxime. At least four out of every five isolates were resistant to Chloramphenicol, Ampicillin, and Norfloxacin. Almost all the isolated strain was resistant to Cotrimoxazole. Resistance patterns against the antimicrobials considered are as follows: Gentamicin (28.1%), Tetracycline (31.2%), Amoxycillin (75%), Chloramphenicol (81.3%), Ampicillin (84.4%), Nitrofurantoin (87.5%), and Cotrimoxazole (93.8%).
|Table 4: Antimicrobial susceptibility of the Shigella species isolated from the stool samples of patients in University of Maiduguri Teaching Hospital (UMTH)|
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| Discussion|| |
Shigellosis, a diarrheal disease due to the members of the bacterium genus Shigella, is a severe and occasionally life-threatening enteric infection. Shigella is highly adapted to lumen, with humans and primates as the only natural hosts. Its burden is greatest in the impoverished population of developing countries than industrialized countries because of the lack of basic social amenities, overcrowding, poor personal hygiene, and immunological defects resulting from poor nutrition and background infections.,, The isolation rate of Shigella species of 8% from diarrheal stool obtained from this study is similar to the previous report of 7.7% from south western Nigeria. Our finding from both northeastern and southwestern Nigeria is in agreement with results obtained from similar studies conducted in northern Ethiopia, Trinidad, Iran, and Nepal. Similar studies conducted in southwestern Ethiopia and India reported higher prevalence rates. Conversely, similar studies conducted in Europe and north America reported the lower prevalence rate of Shigella species.,
The presence or otherwise of basic social amenities such as access to safe drinking water, personal hygiene, housing, sewage disposal, socioeconomic status, and research methodologies (sample size, study population, and design) may be responsible for the variation of the prevalence within the same region or among population with similar level of socioeconomic development. The geographical repartition of the four pathogenic Shigella species (S. dysenteriae, S. flexneri, S. boydii, and S. sonnei) is dynamic. The species diversity of Shigella has been documented in the same country.,, S. flexneri constituted almost half (47%) of the Shigella isolates. S. dysenteriae and S. sonnei were isolated in 37% and 16% cases, respectively, while no boydii was isolated in study. Our finding of S. flexneri as the predominant subgroup followed by S. dysenteriae is in agreement with similar previous studies conducted in other regions of Nigeria (Egah et al., North Central; Enabulele et al., South South Nigeria; Abdulrasheed et al. and Ogunlesi et al.; South Western Nigeria). The observation of S. flexneri as the predominant strain implicated as a causative agent in diarrheal diseases due to Shigellosis has been corroborated by other workers from other African countries of Kenya,, Ethiopia, and Ghana. This is in contrast with prevalence data from developed countries that shows S. sonnei as the major cause of Shigellosis. The frequency of S. flexneri, S. sonnei, S. boydii, and S. dysenteriae of 60, 15, 6, and 6%, respectively has been documented from studies conducted in developing countries. Conversely, the corresponding frequency was 16, 77, 2, and 1%, respectively has been reported from developed countries.,, Over the past decades in developed countries, significant changes of the major culprit of Shigellosis among the subgroups have been seen, evolving from S. dysenteriae to S. flexneri, to S. sonnei. S. sonnei subgroup is the dominant strain in developed countries; the decrease in the proportion of the more virulent S. flexneri and S. dysenteriae observed over the few decades has been attributed to general improvement in sanitary conditions. This suggests that the more virulent Shigella species decreases with improvement in hygiene and sanitary condition. On the other hand, the persisting virulent species (S. flexneri and S. dysenteriae) in developing countries is a reflection of the absence or decimal improvement of socioeconomic and living condition.
Although no S. boydii was isolated in this study, it was, however, reported as the most common species from a study conducted in Jos, north central Nigeria. An isolation rate of S. boydii of 18.6 and 17.7% was also reported by workers in Ile Ife and Lagos, respectively, both in south Western Nigeria. This suggests that S. boydii, although not as common as S. flexneri and S. dysenteriae, is implicated in several human diseases in the developing countries. Furthermore, in a Canadian study, a steady increase of S. boydii was recorded from patients with travel history to the developing countries such as Ethiopia, India, Cuba, Guatemala, and Mexico.
Antimicrobial therapy is the goal standard of treatment of Shigellosis, because it shortens the severity and duration of the illness. It also reduces the shedding of the organisms and prevents subsequent infection by contacts. However, mild cases can be managed solely with rehydration and supportive care. It may, therefore, be reasonable to reserve antimicrobial agents for only severe cases to avoid the development of antimicrobial resistance. The guiding principle for the choice of antimicrobial in developing countries includes the availability of the drug, cost, and pattern of resistance in the locality.
In this report, the Shigella isolates were sensitive to Ciprofloxacin and Ofloxacin. Our finding was corroborated by previous study conducted among both children and adults in southwestern Nigeria. Studies conducted in Iran, Kuwait, and Ethiopia also reported no resistance against Ciprofloxacin. The World Health Organization (WHO) recommends the use of Ciprofloxacin as a drug of choice for bloody diarrhea, especially in resource-limited settings, irrespective of age. Although there are concerns about arthropathy and chondrotoxicity, reports suggest the safety of fluoroquinolones for pediatric usage. However, several reports from both developing and developed countries including United states suggest the evolution of Ciprofloxacin resistance. Resistance to Ampicillin, a common antibiotic used for bloody diarrhea in our environment, was high at 84.4%. Similar high resistance to Ampicillin (78.0%) was reported by National Antimicrobial Resistance Monitoring System in United States and other studies. Higher resistances to Chloramphenicol, Ampicillin, and Norfloxacin and almost total resistance against Cotrimoxazole seen in at least one out of four isolates in this study is worrisome. Worldwide, in the last decade, there has been an increased proportion of isolates resistance to drugs that were known to be effective against Shigella isolates such as Ampicillin, Chloramphenicol, Cotrimoxazole, and Tetracycline. The WHO, therefore, no longer recommends empirical therapy for Shigellosis.,,,,
| Conclusion|| |
Shigellosis is a common cause of diarrhea in our environment. S. flexneri was the most common isolated species followed by S. dysenteriae. The high prevalence of antimicrobial resistance among Shigella isolates observed in this study limits treatment options for Shigellosis. Empirical therapy, therefore, requires the knowledge of the susceptibility pattern in a locality.
The study of antimicrobial resistance pattern to Shigellosis is desirable to provide a guide for clinical case management and control spread of the diseases. This study indicates that Quinolone antibiotic is effective against Shigella species. The treatment guidelines derived from antimicrobial studies need to be updated regularly.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]