Prevalence and Antimicrobial Susceptibility of Zoonotic <em>Salmonella</em> Species Isolated from Water Bodies in Bukombe District

Research Article

J Bacteriol Mycol. 2018; 5(3): 1070.

Prevalence and Antimicrobial Susceptibility of Zoonotic Salmonella Species Isolated from Water Bodies in Bukombe District

Anatory YS1* and Machang’u RS2

¹Department of Microbiology and Parasitology, Mwalimu Julius K. Nyerere University of Agriculture and Technology, Tanzania

²Department of Microbiology and Parasitology, Sokoine University of Agriculture, Tanzania

*Corresponding author: Anatory YS, Department of Microbiology and Parasitology, Mwalimu Julius K. Nyerere University of Agriculture and Technology, Tanzania

Received: May 10, 2018; Accepted: June 18, 2018; Published: June 25, 2018


A study on zoonotic Salmonella in water bodies was carried out between November 2016 and April 2017 in rural areas of Bukombe district, Tanzania. A total of 10 wards of Bukombe district were involved in the study. The main objective of the study was to estimate the burden of zoonotic Salmonella species (serovars Typhimurium and Enteritidis) as well as the antimicrobial resistance profile of isolates obtained from water bodies in Bukombe district. The specific objectives were to establish prevalence of zoonotic Salmonella spp from water, establish the antimicrobial resistance and to compare the prevalence of zoonotic Salmonella spp of multipurpose with single purpose water bodies in Bukombe district, Tanzania. A total of 240 water samples were examined for Salmonella contamination of which 50% were from multipurpose and the rest were from single purpose water bodies. Salmonella species were identified in 1.3% (3/240) of the 240 water samples. Multipurpose water bodies had a prevalence of 1.6% (2/120) while the single purpose water showed prevalence of 0.8% (1/120). The definitive confirmation by polymerase chain reaction (PCR) showed 1.3% isolates were positive for Salmonella. Based on biochemical test by lysine reaction 4.2% of the isolates were identified as Salmonella spp. The study observed that all isolated Salmonella spp. were resistant to penicillin (ampicillin) and cephalosporins (cephalexin), but were sensitive to floroquinolones (ciprofloxacin) and aminoglycosides (gentamicin).

Abbreviations and Symbols

Spp: Species; PCR: Polymerase Chain Reaction; Var: Serovar; Subsp: Subspecies; n: Number of samples; rpm: Rotation per minute; DNA: Deoxyribose Nucleic Acid; Bp: Base pair; Min: Minute; sec: Second; V: Voltage; BSL: Biosafety Level: MDR: Multidrug Resistant; UK: United Kingdom; DWAF: Department of Water Affairs and Forestry in South Africa; HIV: Human Immunodeficiency Virus; WHO: World Health Organization; TBE: Tris-Borate-EDTA


Background information

Water bodies in Tanzania: Most of the water bodies in Tanzania are poorly sanitized and protected which makes them potential sources of infections such as zoonotic Salmonella. The scarcity of water has also led people and animals to share the water body which increases chances of salmonellosis transmission in humans and animals [1]. As of 2012 only 40.6% of the households have access to improved drinking water sources such as piped water, tube wells and protected springs. The remaining percentage uses non-improved drinking water sources [2].

Zoonotic salmonella: Salmonella species are gram-negative, rodshaped bacteria with broad host spectrum, including most animal species: mammals, birds and reptiles. Currently there are more than 2600 serotypes (serovars) of Salmonella classified into two species; Salmonella enterica and Salmonella bongori. S. enterica subsp. enterica I is divided into serotypes, for example serotypes enteriditis, typhimurium, typhi and choleraesuis [3]. Serotypes S. typhi and S. paratyphi A are referred to as typhoidal salmonella the rest are called non-typhoidal or zoonotic Salmonella species.

Epidemiology of zoonotic Salmonella: Salmonellosis ranks high in causing bacterial enteric illness in humans and animals. Zoonotic Salmonella spreads by direct or indirect means from infected animals through contaminated feed and water supplies. Water is among the main transmission routes for diseases such as salmonellosis in humans and animals [4]. It is among the common causes of illness and death among the poor populations in developing countries. Individuals infected with Salmonella spp. shed the organism in their faeces, which may contaminate drinking water sources through rain runoff [5]. Infection can still occur even if concentration of Salmonella in water is low, because the organism escapes the natural host defense mechanisms due to rapid passage of water through the stomach into the intestines without stimulating digestion.

Status of zoonotic Salmonella: The prevalence of salmonellas is varies slightly from one country to another. For example in Nepal 42 out of 300 drinking water samples were positive, with a total of 54 isolates identified to genus level by PCR detection of the virulence genes invA and spvC. The predominant serotypes were Salmonella typhimurium, followed by Salmonella typhi, Salmonella paratyphi A and Salmonella enteritidis [6,7].

Salmonellosis is an important but neglected disease in sub Saharan Africa, where food or fecal-oral associated transmissions are the primary causes of infections. The role of water-borne transmission is unclear, although significant prevalence has been demonstrated. For example, 6.5% of Salmonella spp was detected in dug wells in a rural area of Ghana [8]. A study by [9], showed the presence of Salmonella in water supplies to a slum and densely populated communities and a prevalence of 86 to 98.6% was reported in river Nile water in Egypt [10]. In Dar es salaam, Tanzania Salmonella spp. reported from different water bodies were; Salmonella ser. Paratyphi A (96.9%), and Salmonella choleraesuis serovar Choleraesuis (99.5%).

Problem statement and justification

Tanzania faces a serious lack of potable water which forces people to share surface water sources with animals (livestock and wild) on a day-to-day basis [11]. Water bodies are therefore areas where zoonotic diseases, including salmonellosis, may arise. Bukombe district possess a number of livestock, which at some point share same water bodies with humans. At these water bodies infected animals may shed the bacteria through faeces. Also, humans contaminate the water while carrying out different activities including: Bathing, swimming, fishing and irrigation. These situations justify establishing the magnitude of water-borne zoonotic Salmonella species in both multi-purpose water bodies (with high human-animal interaction) and singlepurpose water bodies (for humans use only) in communities such as Bukombe. So far limited studies have been conducted to address this concern in Bukombe district. This study aims at establishing the prevalence of zoonotic Salmonella spp. (serovars Typhimurium and Enteritidis) in the water bodies. Furthermore, the study determined the prevalence of antimicrobial resistance among Salmonella spp. isolated from the water bodies in Bukombe district.


General objective: To estimate the burden of zoonotic Salmonella species (serovars Typhimurium and Enteritidis) in water bodies and establish antimicrobial resistance profile of the bacteria isolated from water bodies in Bukombe district.

Specific objectives:

1. To estimate prevalence of zoonotic Salmonella species from single and multi-purpose water bodies in Bukombe district.

2. To establish the antimicrobial resistance profile of zoonotic Salmonella species obtained from water bodies.

3. To compare the prevalence of zoonotic Salmonella spp of multipurpose versus single purpose water bodies in Bukombe district.

Research questions:

1. What is the prevalence of zoonotic Salmonella species in single and multi-purpose water bodies in Bukombe district?

2. What is the antimicrobial resistance profile of zoonotic Salmonella species obtained from the water bodies?

3. Is there any difference in the prevalence of zoonotic Salmonella species in multipurpose and single purpose water bodies?

Literature Review

Zoonotic Salmonella

Salmonella spp. comprise over 2600 serotypes and colonize range of animal hosts such as mammals, amphibians, reptiles, birds and insects [12]. The bacterial genus Salmonella causes a huge global burden of morbidity and mortality. With regard to human disease, salmonellae are divided into typhoidal serotypes (Salmonella enteric var Typhi) and Salmonella enteric var Paratyphi A) and thousands of non-typhoidal Salmonella serotypes [13]. Non-typhoidal Salmonella serotypes affect a wide range of hosts including human hence zoonotic, examples of these zoonotic Salmonella are S. Typhimurium and S. Enteritidis.

Epidemiology of zoonotic Salmonella

Water-borne diseases are a major public health concern worldwide, not only by the morbidity and mortality that they cause, but by the high cost associated with their prevention and treatment [14,15]. There has been increased number of epidemics in sub-saharan Africa, with the tendency towards more typhoid-like with regard to patterns of transmission and virulence [16]. Salmonella enterica var. Typhimurium, ST313 and Salmonella enteritidis are far more important in sub-Saharan Africa. HIV infections in adults, malaria and malnutrition in children have been identified as important risk factors [12].

A distinct genotype of Salmonella entericavar Typhimurium, ST313, has emerged as a new pathogenic clade in sub-Saharan Africa. This genotype might have adapted to cause invasive disease in humans [12]. According to [17], predominant serotypes have been shown to be Salmonella enterica serotype Typhimurium (54.9%) and Salmonella enterica serotype Enteritidis (64; 33.2%). It is estimated that 93.8 million cases of gastroenteritis due to Salmonella species occur globally each year, causing 155,000 deaths [18].

According to the WHO, the mortality of water associated diseases exceeds five million people per year with 50% of these deaths being microbial intestinal infections. Salmonella enterica subsp. Enterica serovar Enteritidis is the most frequently isolated serovar from humans all over the world. Humans can carry the bacteria in the gut without showing signs of disease for considerable periods of time [19]. Water-borne Salmonella spp is becoming a big problem. A study by [20], detected a relatively low contamination frequency of Salmonella spp in ground water around burial sites of culled animals in South Korea. Some studies have revealed high numbers of water-borne pathogens, including 6% Salmonella spp in harvested rainwater, which is gaining acceptance among many countries such as Australia, Germany, and South Africa [21]. Salmonella species loads in borehole water in South Africa were higher than the WHO threshold, which suggests that water from these sources may pose serious health risks if consumed without treatment [22]. It is the aim of this study therefore to estimate the magnitude of zoonotic Salmonella spp in single and multipurpose water bodies in Bukombe district.

Mode of infection and clinical signs

Most human Salmonella infections result in gastroenteritis, and are caused by Salmonella enteric serovar Typhimurium or Salmonella enteric serovar Enteritidis acquired from contaminated food and water. Apart from humans, other animals can also be infected with Salmonella Typhimurium. Some Salmonella spp are important pathogens that can be transmitted to people via food and water and can cause diseases characterized by mild to severe enteric and systemic illness [11]. Salmonella spp can arise from direct or indirect animal contact via an environment contaminated by clinically affected animals that exhibit a higher prevalence of shedding than apparently healthy animals, or transmission can occur through contaminated food and water to humans [23].

Diagnostic methods of Salmonella species

Several diagnostic methods currently in use for Salmonella species; bacterial culture by using selective culture media such as Xylose Lysine Deoxycholate (XLD) and Salmonella Shigella Agar (SSA). However, this method is time consuming and laborious [24].

PCR technology is widely used in detecting the presence of specific Salmonella species by amplification of a specific fragment of nucleic acid, genes such as invA, fliC are frequently targeted [25].

Serological methods are also used for the detection of Salmonella serotypes, one of them is ELISA, which may be indirect or double antibody-blocking assays using a range of antigens such as lipopolysaccharide, flagella and SEF14 fimbrial antigen [26].

Materials and Methods

Study area description

This study was conducted in Bukombe district which is located in the southern part of Geita region at the coordinates 03028’S 031054’E. The district has a total area of 8,055.59 km2. According to the 2012 census, the district has 75,668 cattle, 70,810 goats and 17,000 sheep and a human population of 224,542 individuals. The district is bordered to the East by Mbogwe District (Shinyanga), to the North by Chato District Geita), to the North-west by Biharamulo (Kagera) to the West by Kibondo District (Kigoma) and to the South by Urambo District (Tabora). The district eastern part constitutes Bugelenga, Bukombe, Butinzya, Ushirombo, and Lyamba mgongo wards whereas the western part consists of Namonge, Runzewe Mashariki, Runzewe Magharibi, Igulwa and Ng’anzo. The eastern part of Bukombe has a large number of livestock keeper’s as compared to the western part of the district.

As of 2012 only 40.6% of the households have access to improved drinking water sources such as piped water, tube wells and protected springs. The remaining percentage uses non-improved drinking water sources [2,26]. Prevalence of Salmonella spp and Escherichia coli in raw milk value chain in American Journal of Research Communication.

Study design and sampling techniques

cross-sectional study was done to estimate the prevalence of zoonotic Salmonella species in water bodies followed by the assessment of antimicrobial resistance of Salmonella isolates found in these water bodies in Bukombe district, Tanzania.

Sample size

The sample size was calculated based on the prevalence of the variables of interest with 0.05 sampling proportion assumed to have safe water with the least desired level of precision

n=z2 .p.qe2

Where: n= sample size, Z=standard normal deviation, set at 1.96 corresponding to 95% confidence level, p=proportion in the target population estimate; taken at 0.5

q=1.0-p =0.5, e=degree of precision desired, set at 0.05. Therefore the sample size calculated was as follows:

n=1.962x0.5x0.5/0.052=384 samples

Due to the small number of water bodies in the study area, only 240 water samples were examined, of which 120came from singlepurpose water bodies and the other 120 samples from multi-purpose water bodies.

Sampling and data collection methods

The study was undertaken in 10 wards of Bukombe district namely:Bugelenga, Bukombe, Butinzya, Igulwa, Lyambamgongo, Namonge, Ng’anzo, Runzewe Mashariki, Runzewe Magharibi, and Ushirombo. In each ward two villages were purposively selected based on the number of livestock, making a total of 20 villages. Four water bodies were selected from each village based on the purpose of each water body (single or multipurpose). Water bodies were checked for evidence of human activities and/or livestock depending on the purpose of the water body (Figure 1). Then three water samples were taken from three different water layers of each water body (at the bottom, middle, and surface).