Prevalence, Antimicrobial Susceptibility Pattern, and Associated Health Risks of Foodborne Pathogens in Street Foods Sold in Elementary Schools, Yaounde, Cameroon ()
1. Introduction
Globally, the consumption of unsafe food is estimated to cause 420,000 deaths and 33 million DALYs (disability adjusted life years) each year [1] [2]. Among those affected, children under the age of five years are at high risk due to less developed immune systems to combat pathogenic infections [2]. Specifically, an estimated 1.7 billion cases of childhood diarrhoea occur each year, leading to about 30% of childhood deaths in developing countries [2] [3]. Diarrhoea is an intestinal tract infection, commonly caused by bacterial pathogens such as Escherichia coli, Salmonella spp., Shigella spp., Campylobacter spp., etc. [2] [3]. Infected children could experience 2 - 3 episodes of diarrhoea annually, and each episode can lead to nutrient deprivation, malnutrition, and eventually death [3]. In Cameroon, there is scarcity of data on diarrhoea morbidity and mortality among children, however, epidemiological studies indicate a community-based prevalence of 16 to 23% with common symptoms including stomach ache/cramps, fever, vomiting, and loss of appetite [4]. In fact, the risk of foodborne diarrhoea is high in many African communities, and about 94% of these cases of diarrhoea are attributed to the environment, which includes risk factors such as unsafe drinking water, poor food handling, and hygiene practices [4]-[6].
Street foods are considered nutritious and readily affordable foods that provide a source of income for many people in developing countries [7]. Although they can be consumed by all age groups and are appreciated for their unique characteristics (flavours, taste, convenience, and affordability), their association with microbial pathogens remains a serious threat to public health [8]-[13]. Street foods are prepared and sold under unregulated food safety conditions in public places, including streets, local markets, bus stations, schools, work, and healthcare facilities [13]. In particular, food handling and hygienic practices of these foods across their supply chain, from acquiring raw ingredients, transportation, storage, food preparation, to vending (at the roadside and/or hawking) remain questionable [13]-[15].
In Cameroon, several studies [7] [11] [16]-[19] have highlighted the poor microbiological quality of street foods to include food safety indicators (fecal coliforms, yeast and mould, E. coli, Salmonella, coagulase-positive staphylococci, Bacillus cereus, among others), which could contribute to foodborne diseases. Indeed, on 2 May 2003, the Centre Pasteur du Cameroun (CPC, Cameroon) was notified of a cluster of diarrhoeal illnesses among 90 individuals, who were involved in a party held on 1 May 2003 in Yaounde and included some street food (cold fish and hard boiled eggs with mayonnaise) [20]. This resulted in suspected food contamination with Plesiomonas shigelloides, a rare causative agent in foodborne disease outbreaks [20]. Despite this, the food safety risks of street foods sold within elementary schools that generally enrol children from infants to primary school age have been completely ignored. Foodborne diarrhoea in such settings can be mitigated and even prevented when microbial exposure routes are identified and acted upon [21] [22].
To understand the risk of exposure of vulnerable young children to foodborne pathogens, the purpose of this study was to investigate the prevalence and antibiotic susceptibility patterns of foodborne pathogens in street foods sold within elementary schools in Yaounde, Cameroon.
2. Materials and Methods
2.1. Sample Collection and Preparation
The study was carried out between September and December 2022 in Yaounde. Yaounde is the political capital of Cameroon, and due to socioeconomic conditions (poverty, busy work schedules, changes in tastes and food preferences), several households have been found to primarily consume street foods [7] [11] [16] [17]. In total, 160 samples (n = 20 per street food) were purchased weekly from street vendors who sold these foods within 20 elementary school premises. Of the 5031 elementary schools in the region, these 20 schools were randomly selected based on observed overcrowded and cosmopolitan nature of its pupil’s population [23] [24]. In Cameroon, the education system is divided into two distinct sub-systems: the French and the British colonial model. Although studies in French were popular in the past, English courses are becoming more popular due to the increasing influence of globalisation [24]. In these settings, its education system is made up of two optional years of pre-school (ages 3 - 5), six compulsory years of primary school (ages 6 - 11), and seven years of secondary education (ages 12 - 18) [24]. In this study, we sampled schools that enroled preschool-age children to primary-age children in both the French and the British colonial model. Notably, Nguendo Yongsi [25] isolated at least one pathogenic microorganism among these age groups living within the sampled population; that is, in 59.5% (260/437) of children’s stools with diarrhea. We were interested in two staples (bread, spaghetti) and six sauces (beans, fish, peanuts, eggs, beef, and pepper), based on their availability in all selected schools and since more than 50% of street vendors sold these street foods in Cameroon [17]. These foods were prepared from individual homes either prior to or on the same day and transported to vending school facilities. Upon purchase from street vendors, street food samples were placed aseptically in sterile polythene bags, transported to the laboratory in a cool box between 2˚C and 8˚C, and analysed within one hour.
2.2. Microbiological Analyses of Street Food Samples
Each sample was thoroughly mixed, and 25 g was homogenised in 225 mL of maximum recovery diluent. Serial dilutions were prepared, and then 50 µL of each diluent was plated and incubated on the respective agar and growth conditions. Total viable count (TVC) and total coliforms (TC) were plated on plate count agar and violet red bile agar, respectively, and incubated at 30˚C for 48 h. Yeast and mould on Dichloran Rose-Bengal Chloramphenicol agar and incubated at 25˚C for 5 days. Skirrow Campylobacter selective agar with SR0069 as a supplement was used for Campylobacter spp. and incubated at 42˚C for 48 h, under microaerophilic conditions. For E. coli, Salmonella spp., Listeria monocytogenes, Staphylococcus aureus and Yersinia enterocolitica, Eosin Methylene Blue, xylose lysine desoxycholate, Palcam, Baird Parker, and MacConkey agars were used, respectively, and incubated at 37˚C for 24 h. Other Enterobacteriaceae were qualitatively identified using the RapIDTM ONE System (Thermofisher, USA), according to the manufacturer’s guidelines. Growth colonies were presumptively identified by Gram staining, catalase, oxidase tests, and using API 20E and API Listeria kits (Biomerieux, France), to characterise Enterobacteriaceae, Listeria, Staphylococcus, Campylobacter, non-fermenters, and anaerobes.
2.3. Antibiotic Susceptibility Testing for Selected Bacterial
Pathogens
Antibiotic susceptibility tests were carried out based on Kirby-Bauer agar disk diffusion method, to determine which antimicrobials could inhibit the growth of the bacteria isolates. Here, 3 - 5 of the cultured-confirmed bacteria isolates were transferred to 3 mL of nutrient broth, mixed, and then adjusted to 0.5 McFarland standards using normal saline. The suspension was spread uniformly on solidified Mueller-Hinton agar. For fastidious bacterial isolates, 5% defibrinated sheep blood was supplemented [26]. Subsequently, five broad-spectrum antibiotic-impregnated discs, namely, ciprofloxacin (5 μg), tetracycline (30 μg), gentamicin (30 μg), chloramphenicol (30 μg) and vancomycin (30 μg), were placed aseptically in agar media, and sterile discs impregnated with 50 µL distilled water served as negative control. The plates were incubated at 37˚C for 18 h, and the results were interpreted as susceptible, intermediate, or resistant according to the CLSI breakpoint criteria [26]. All growth media and antibiotic-impregnated discs were obtained from Oxoid Limited, United Kingdom.
2.4. Statistical Analysis
All experiments were carried out in triplicate and analysed using SPSS (v26). The results were expressed as mean ± standard deviation and one-way ANOVA was used to compare the means. Duncan’s multiple range test was used, where the mean difference was considered significant at p < 0.05. Additionally, we calculated the percentages of bacteria prevalence in each type of street food.
3. Results
The total viable count for the bread and spaghetti staples, as well as for the fish and beef sauces, was not statistically different (p > 0.05) (Table 1). Also, total coliforms, yeast and mould counts were high, and ranged between 1.77 log10cfu/g (spaghetti) and 6.42 log10cfu/g (pepper sauce), and 1.27 log10cfu/g (beef) and 7.28 log10cfu/g (bread), respectively.
Table 1. Total viable count and total coliforms (log10cfu/g) of street food samples.
Street food |
Total viable count |
Total coliforms |
Yeast and mould |
Bread |
7.89 ± 0.02a |
2.04 ± 0.02d |
7.28 ± 1.61a |
Spaghetti |
8.21 ± 0.90a |
1.77 ± 0.04e |
4.32 ± 1.08b |
Beans |
3.70 ± 0.02f |
3.56 ± 0.04c |
2.44 ± 0.00b |
Fish |
6.42 ± 0.03b |
5.63 ± 0.02a |
5.61 ± 0.12b |
Peanut |
5.83 ± 0.02c |
4.44 ± 0.04b |
2.89 ± 0.00d |
beef |
6.55 ± 0.77b |
5.56 ± 0.24a |
1.27 ± 0.88d |
Eggs |
5.34 ± 0.08d |
5.84 ± 0.99a |
1.69 ± 0.61d |
Pepper |
5.25 ± 0.04e |
6.42 ± 0.31a |
3.79 ± 0.51c |
Mean |
6.13 ± 0.64 |
4.40 ± 0.50 |
3.64 ± 1.11 |
cfu: colony forming units, n = 20 per street food, results are expressed in mean ± standard deviation of three replicates, different superscripts (a, b, c….) within the same column are significantly different at p < 0.05.
In Table 2, at least one bacteria pathogen was identified in each street food. Fish sauce was the most contaminated, containing 13 of the 16 bacteria isolates, and pepper sauce was the least contaminated, with six of the 16 bacteria pathogens. Furthermore, E. coli was the most prevalent 47.50% (76/160) in all street food samples, particularly in beef sauce 80% (16/20), bread 65% (13/20), and pepper sauce 55% (11/20). S aureus was the second most prevalent bacteria pathogen 39.37% (63/160) and was largely isolated in bread 85% (17/20), fish sauce 55% (11/20), and peanut sauce 40% (10/20). Other bacterial pathogens such as Salmonella spp. 32.50% (52/160), Shigella spp. 23.75% (38/160), Campylobacter spp. 14.37% (23/160) and E. aerogenes 14.37% (23/160) were highly prevalent in beans 75% (15/20), pepper 40% (8/20), eggs 35% (7/20) and beef 60% (12/20) sauces, respectively. E. cloacae 20.62% (33/160) was highly isolated in fish, beef, and pepper sauces at 40% (8/20). In all food samples, P. penneri 5% (8/160) and C. freundii 3.12% (5/160) were the least identified.
Table 2. Prevalence of bacterial pathogens in street food samples.
Bacterial pathogens |
Bread n (%) |
Spaghetti n (%) |
Beans n (%) |
Fish n (%) |
Peanut n (%) |
Beef n (%) |
Eggs n (%) |
Pepper n (%) |
Overall prevalence N (%) |
E. coli |
13 (65) |
4 (20) |
10 (50) |
7 (35) |
9 (45) |
16 (80) |
6 (30) |
11 (55) |
76 (47.50) |
Salmonella spp. |
7 (35) |
5 (25) |
15 (75) |
8 (40) |
0 |
2 (10) |
12 (60) |
3 (15) |
52 (32.50) |
Campylobacter spp |
1 (5) |
0 |
2 (10) |
5 (25) |
0 |
5 (25) |
7 (35) |
3 (15) |
23 (14.37) |
L. monocytogenes |
4 (20) |
3 (15) |
0 |
2 (10) |
2 (10) |
4 (20) |
0 |
2 (10) |
17 (10.62) |
Y. enterolitica |
2 (10) |
3 (10) |
5 (25) |
0 |
0 |
1 (35) |
0 |
0 |
11 (6.87) |
S. aureus |
17 (85) |
5 (25) |
1 (5) |
11 (55) |
8 (40) |
9 (45) |
5 (25) |
7 (35) |
63 (39.37) |
Y. pseudotuberculosis |
1 (5) |
7 (35) |
0 |
7 (35) |
0 |
4 (20) |
3 (15) |
8 (40) |
30 (18.75) |
E. aerogenes |
2 (10) |
2 (10) |
0 |
2 (10) |
1 (5%) |
12 (60) |
4 (20) |
0 |
23 (14.37) |
E. cancerogenus |
0 |
0 |
1 (10) |
4 (20) |
0 |
5 (25) |
3 (15) |
0 |
13 (8.12) |
E. cloacae |
0 |
0 |
2 (10) |
8 (40) |
7 (35) |
8 (40) |
0 |
8 (40) |
33 (20.62) |
Shigella spp. |
4 (20) |
7 (35) |
7 (35) |
6 (30) |
5 (25) |
0 |
1 (5) |
8 (40) |
38 (23.75) |
K. pneumoniae |
1 (5) |
5 (25) |
0 |
3 (15) |
2 (10) |
0 |
0 |
2 (10) |
13 (8.12) |
P. penneri |
0 |
0 |
4 (20) |
1 (5) |
3 (15) |
0 |
0 |
0 |
8 (5) |
P. oryzihabitans |
2 (10) |
6 (30) |
0 |
4 (20) |
1 (5) |
5 (25) |
0 |
0 |
18 (11.25) |
P. luteola |
1 (5) |
0 |
0 |
0 |
4 (20) |
0 |
1 (5) |
3 (15) |
9 (5.62) |
C. freundii |
0 |
0 |
2 (10) |
0 |
0 |
1 (10) |
3 (15) |
0 |
5 (3.12) |
0 = not detected in street food samples.
Table 3. Antibiotic resistance pattern of foodborne pathogens.
Bacteria isolates |
Ciprofloxacin n (%) |
Tetracycline n (%) |
Gentamicin n (%) |
Chloramphenicol n (%) |
Vancomycin n (%) |
Salmonella spp. (n = 37) |
S |
21 (56.75) |
7 (18.91) |
28 (75.67) |
31 (83.78) |
4 (10.81) |
I |
16 (43.24) |
11 (27.72) |
4 (10.81) |
6 (16.21) |
10 (27.02) |
R |
0 |
19 (51.35) |
5 (13.51) |
0 |
23 (62.16) |
Campylobacter spp. (n = 23) |
S |
16 (69.56) |
3 (13.04) |
18 (78.26) |
12 (52.17) |
3 (13.04) |
I |
7 (30.43) |
1 (4.34) |
5 (21.73) |
11 (47.82) |
11 (47.82) |
R |
0 |
19 (82.60) |
0 |
0 |
9 (39.13) |
L. monocytogenes
(n = 17) |
S |
13 (76.47) |
8 (47.05) |
7 (41.17) |
2 (11.76) |
15 (88.23) |
I |
4 (23.52) |
5 (29.41) |
1 (5.88) |
4 (23.53) |
2 (11.76) |
R |
0 |
3 (13.63) |
9 (52.94) |
11 (64.70) |
0 |
S. aureus (n = 63) |
S |
55 (87.30) |
33 (52.38) |
28 (44.44) |
0 |
62 (98.41%) |
I |
7 (11.11) |
19 (30.15) |
15 (23.80) |
6 (9.52) |
1 (1.58) |
R |
1 (1.58) |
11 (30.56) |
20 (31.74) |
57 (90.47) |
0 |
Y. enterocolitica
(n = 11) |
S |
10 (90.90) |
9 (81.81) |
5 (81.81) |
10 (90.09) |
0 |
I |
1 (9.09) |
3 (27.72) |
5 (45.45) |
1 (9.09) |
2 (18.18) |
R |
0 |
0 |
1 (9.09) |
0 |
9 (81.81) |
E. coli (n = 76) |
S |
53 (69.73) |
36 (47.36) |
1 (1.31) |
11 (14.47) |
17 (22.36) |
I |
16 (21.05) |
27 (35.52) |
13 (17.10) |
35 (46.05) |
30 (39.47) |
R |
7 (9.21) |
13 (17.10) |
62 (81.57) |
10 (13.15) |
49 (64.47) |
S = Susceptible, I = Intermediate, R = Resistant.
Furthermore, Table 3 presents the antimicrobial susceptibility pattern of six bacteria pathogens, namely, Salmonella spp., Campylobacter spp., Listeria monocytogenes, Staphylococcus aureus, Yersinia enterocolitica E. coli. All bacteria isolates were resistant to at least one antibiotic and highly susceptible to ciprofloxacin. With the exception of Campylobacter spp. and Salmonella spp., all other bacteria isolates were largely susceptible to tetracycline. Specifically, Yersinia enterocolitica was the most susceptible to ciprofloxacin 90.90% (10/11), tetracycline 81.81% (9/11), gentamicin 81.81% (5/11), and chloramphenicol 90.09% (10/11). E. coli was the most resistant, particularly to gentamicin 81.57% (62/76), and vancomycin 64.47% (49/76). Staphylococcus aureus and Campylobacter spp. were highly resistant to chloramphenicol 90.47% (57/63) and tetracycline 82.60% (19/23), respectively.
4. Discussion
The results showed that all street foods were contaminated with various levels of microorganisms and only the bean sauce (total viable count = 3.70 log10cfu/g) was within acceptable limits (total viable count <105 cfu/g) for human consumption [27]. Similarly, total coliforms were apparent in all food samples examined. Djoulde et al. [16] and Zokou et al. [28] respectively reported a similar unsatisfactory bacterial count ranging between 5.1 and 7.3 log10cfu/g, and 2.56 and 4.48 log10cfu/g in street-vended meat and egusi pudding sold in Cameroon. Although total coliforms might not mean that the street food samples were a potential risk to human health, their presence (including fecal coliforms and E. coli) indicated some exposure to animals and/or human faeces, thus, suggesting contamination with enteric pathogens. Within the same studied population in Yaounde, several unhygienic street food practices were reported [7] [11], such as the use of dirty utensils and hands to prepare and/or serve food, and the use of plastic packaging that was opened by blowing with the mouth. Moreover, the poor food safety quality and microbial contamination of street food in this research could have occurred at any point, for example, from uncontrolled temperatures during cooking and food storage and the fact that food was sold unpackaged, and stalls did not have protective coverings against environmental contaminants (dusts, flies, rodents, dirt, and soil debris). Similarly, Compaore et al. [29] reported that street foods (bread, pasta, rice with sauce, beans and milk) in five different localities in Burkina Faso were sold in related retailing conditions; on pushcarts, bicycles, baskets or balance poles, and stalls that do not have four permanent walls.
Additionally, the results indicated significant public health concerns in street food consumption, as at least one foodborne pathogen was isolated in each street food. Specifically, credible outbreaks of foodborne diarrhoea have been reported among related street food handlers and schoolchildren in Ghana [30] and Indonesia [15]. In the same region, our previous published investigations [31] [32] reported a high prevalence of Listeria spp. (86%), Campylobacter spp. (75%), Yersinia spp. (71%), Salmonella spp. (69%), and Shiga toxin-producing E. coli (57%) in edible land snails, and STEC (20%), Yersinia enterolitica (13%), Campylobacter spp. (21%), Listeria monocytogenes (15%), and Salmonella spp. (15%) in locally consumed leafy vegetables. Ngueugang et al. [17] also enumerated S. aureus (93.3%), Salmonella spp. (60.7%), Shigella spp. (57.4%) Citrobacter freundii (23.4%), E. coli (18.0%), Enterobacter aeruginosa (5.2%) and Klebsiella pneumoniae (6.6 %) in street foods sold in Douala, Cameroon. Likewise, Nicholas et al. [18] identified E. cloacae (31.57%), Salmonella spp (10.52%), C. freundii, and K. pneumonia (15.78%) in street-vended pepper sauces in Buea, Cameroon. Although Enterobacteriaceae are typically a normal flora in the human intestinal tract, their presence at high levels (>104 cfu/g) in cooked foods is an indicator of several risks factors resulting from cross-contamination, and inadequate cooking. In addition, Enterobacteriaceae could indicate an increased risk of the presence of foodborne pathogens as well as the potential formation of histamine in scombroid fish (scombrotoxin) [27] [33]. For example, the presence of E. coli in street foods indicated poor hygiene or faecal contamination [33], and C. freundii indicated mild to severe foodborne infections. In particular, C. freundii contamination of green butter was reported to cause 152 cases of gastroenteritis and eight haemolytic uremic syndromes among nursery school pupils in Germany [34].
Furthermore, antimicrobial resistance (AMR) of bacteria isolates in street foods could be devastating to public health, and its associated health risks have been emphasized in spoiled vegetables [35] and healthy pigs [36]. In 2019, Cameroon was rated the 31st highest age-standardized mortality rate per 100,000 population worldwide, due to 5600 attributable and 24,600 associated deaths from AMR [37]. Specifically in Yaounde, Cameroon, antibiotic susceptibility testing over a three-year period demonstrated high resistance of Gram-negative bacteria such as E. coli (30.5%) and K. pneumoniae (24.2%), to penams and cephems, and low resistance to carbapenems [38]. Recognising that AMR is a natural process primarily due to antibiotic overuse, other contributing socioeconomic determinants, such as poor community hygiene, poor infection control in hospitals and clinics, and the accumulation of antibiotics in the environment due to mishandling, could further lead to fatal diseases [36]. The high prevalence of S. aureus, 39.37% (63/160), especially in beef sauce at 45% (7/20), indicated a high risk of enterotoxin production [27] [32] [39], and, as shown, the isolates were highly resistant to chloramphenicol 90.47% (57/63) and gentamicin 31.74% (20/63). In the United States, for example, the five main isolated enteric pathogens in this research caused 291,162 illnesses in children under five years of age, which resulted in 102,746 physician visits, 7830 hospitalisations, and 64 deaths [39]. In these foodborne disease outbreaks, non-typhoidal Salmonella was the most prevalent (42%), followed by Campylobacter spp. (28%), Shigella spp. (21%), Y. enterocolitica (5%) and E. coli O157 (3%) [40]. Among the studied population, Nguendo Yongsi [25] isolated foodborne-related microorganisms in children aged 6 - 59 months, particularly Enteric adenovirus (2.7%), Salmonella spp. (9.6%), Campylobacter spp. (8.8%), E. coli enteropathogenic (4.2%), Shigella spp. (7.3%), Ascaris lumbricoides (17.8%), Giardia lamblia (13.2%), Trichuris Trichiura (10.7%), and Entamoeba (8.4%). Moreover, it should be noted that foodborne diseases are not only limited to gastroenteric symptoms (diarrhoea, vomiting), but also short-to-long term systemic infections [38]. As such, the presence of Campylobacter spp. and Y. enterocolitica that were highly resistant to tetracycline 82.60% (19/23) and vancomycin 81.81% (9/11) indicated bloody and chronic diarrhoea that could develop into Guillain-Barré syndrome [41], Graves’ disease, and reactive arthritis [42], respectively.
Although salmonellosis is common in foods such as meat, eggs, and milk; however, foodborne diseases have also been reported in bread [43] [44] and peanut butter [45]. Salmonella spp. in ready-to-eat foods and its resistance to tetracycline and vancomycin are considered harmful to health regardless of their level of contamination, especially in children where irritable bowel syndrome could develop later in life [27] [34]. In the study area, high levels of Salmonella spp. were previously attributed to inadequate refrigeration due to constant power shortages, and the ancestral practice of insufficient heating or reheating of food in Cameroon [17]. In fact, Salmonella spp. and Listeria monocytogenes in the selected street foods (25g of food) should be considered capable of causing disease [33].
5. Conclusion
This research examined the presence of foodborne pathogens in street foods sold within elementary school facilities in Yaounde, Cameroon. At least one foodborne pathogen was present in each street food examined (bread, beans, fish, peanut butter, eggs, minced meat, pepper, and spaghetti). The findings indicated that street food handlers and vulnerable young children are significantly at risk of foodborne diseases in such local food handling, vending and consumption practices. Although further research could be carried out to 1) investigate the genomic virulence gene profiles of these isolates to reveal bacterial strains that are not associated with foodborne diseases, 2) determine the different routes of street food contamination between street vendors and elementary schools, and 3) establish any incidence of foodborne disease outbreak among the studied population, there is an urgent need to mitigate these identified health risks, such as through local government initiatives and effective food safety implementation programmes in nursery and primary schools across Cameroon.
Acknowledgements
The authors thank placement students at the Wonet-bioscience laboratory of the Women’s Network of Biodiversity and Food Science, Yaounde, Cameroon, for their assistance with sample collection.