1. Introduction
Tchoukoutou and Tchapalo are two traditional beers sold as street food throughout Benin and prepared, respectively, from red or brown sorghum (
Sorghum bicolor) and maize [
1,
2]. Aside from their social aspect, since they are used during reunions and traditional ceremonies [
3], selling these beers constitutes an essential source of income, especially for women [
1,
4]. However, during its cooking and sale, a lack of qualitative hygiene conditions of the environment and utensils was reported. Thus, sold as street food, these drinks can cause many cases of food poisoning [
5].
Food poisoning causes more than 200 illnesses, ranging from diarrhea to cancer, with nearly 420,000 deaths yearly worldwide [
6]. During beer manufacturing, microorganism fermentation, one of the essential stages in the production of traditional beers, abounds in diverse microbial communities that strongly influence the sensory quality, the availability of nutrients, and the safety and preservation of these products [
7,
8,
9]. In this microbial community, bacteria, yeasts, and molds come from raw materials, utensils, or the producers themselves [
10,
11].
Even though lactic acid bacteria reduce the level of pathogenic bacteria present in these drinks [
7,
8,
12,
13], it is still observed that resistance of certain bacteria such as
Enterobacter sakazaki,
Klebsiella pneumonia,
Escherichia coli, and
Staphylococcus aureus to the acidity of the fermented medium and the cooking of fermented foods [
14]. Indeed N’tcha et al. [
15] observed the presence of
Enterobacteriaceae in Tchoukoutou. This presence of beer is worrying because it can cause food spoilage [
16,
17] and affect patients with health disorders or habitat disorders such as sepsis, meningitis, endocarditis, peritonitis, or heart disease [
18].
In West African countries, bacterial infections' endemicity has increased with antibiotics consumption [
19,
20]. Due to the misuse and often uncontrolled use of synthetic products, controlling bacterial and fungal infections becomes complex due to the emergence of bacteria and fungi resistant to many conventional antibiotics and antifungals [
21,
22]. This multidrug resistance can be explained by chromosomal mutations of these strains or by acquiring resistance genes [
23]. However, the literature has ignored the species of Enterobacteriaceae and most of the pathogenic bacteria identified in these traditional beers through biochemical and molecular characterization.
Indeed, the lack of hygiene during beer production and the environmental conditions during the sale, accompanied by the poor hygienic quality of the utensils used, can contribute to beer contamination by the pathogenic microorganisms responsible for food poisoning. Thus, the present study aims to characterize the pathogenic bacteria isolated from two traditional beers produced and consumed in Benin.
4. Discussion
The primary source of human infections is ingesting contaminated food [
33]. Indeed, pathogenic bacteria such as staphylococci and
Enterobacteriaceae have been identified in African fermented cereal foods [
34] and traditional fermented drinks [
15]. Our study showed that the percentages of samples contaminated with these microorganisms were 60.64% of
Enterobacteriaceae and 39.36% of staphylococci. This rate of
Enterobacteriaceae contamination is much higher than the 14.4% obtained by Cason et al. [
35] in Sesotho, a traditional beer from South Africa produced from corn or sorghum. The low rate of
Enterobacteriaceae and the absence of staphylococci in Sesotho can be explained by the fact that Sesotho is obtained from two fermentations with the addition of three different ferments (Tomoso, Mmela, and Yomoso) and by the fact that the two studies were not carried out under the same conditions. However, observing the rules of Good Hygiene Practices and Good Preparation Practices can reduce contamination rates in this situation.
The biochemical characterization of the enterobacteria and staphylococci isolated strains gave us more precision on the species in these traditional beers. We noted the presence of
Klebsiella terrigena (2.28%),
Enterobacter aerogens (6.82%),
Providencia rettgeri (9.09%),
Chryseomonas luteola (11.36%),
Serratia rubidae (25%) and
Enterobacter cloacae (45.45%) for
Enterobacteriaceae. As for the
Staphylococcus genus, we noted the presence of 13.51% of coagulase-positive staphylococci (probably
Staphylococcus aureus) and 86.48% of coagulase-negative staphylococci (
Staphylococcus spp). Certain pathogenic microorganisms and alterations of traditional beers observed in Sesotho, namely, the genus
Chryseobacterium,
Enterobacter, and
Klebsiella [
35], were also present in our samples. These strains have also been isolated in other traditional beers prepared from raw materials, such as rice for Chicha, a Brazilian fermented drink [
36], and cactus juice for pulque, a Mexican alcoholic beverage [
37]. The high proportion of
Enterobacter cloacae (45.45%) observed in these traditional beers could be due to its habitat, which remains the environment. The results of our study corroborate those of several studies [
35,
36,
37] by highlighting the presence of unusual species such as
Serratia rubidae,
Providencia rettgeri, and
Staphylococcus aureus in our samples. Indeed,
Serratia rubidae and
Providencia rettgeri have been found in stool [
38] and fly [
39], respectively.
Staphylococcus are ubiquitous bacteria ubiquitous in nature, i.e., air, water, soil, food, furniture, and equipment [
18,
40]. The presence of these different species can be explained by their contamination of the beer production process, raw materials, the sales environment, lack of supervision, or non-compliance with the hygiene rules.
During bacterial infections, the way of life developed by bacteria is biofilm production [
41]. The production of biofilm is one of the defense mechanisms of bacteria. Biofilm formation is a default lifestyle for staphylococci and
Enterobacteriaceae [
42,
43]. The high rate of biofilm production observed in
Enterobacter aerogens and
Klebsiella terrigena during our research can be explained by the fact that they are Gram-negative thermotolerant bacilli of food origin. Regarding staphylococci, the low rate observed in Coagulase Negative Staphylococci (15.35%) was also found in the work of Ahouandjinou et al. [
44], with a respective proportion of biofilm production of 28% for
Staphylococcus lugdunensis and 20%
S. warneri on food Coagulase Negative Staphylococcus (CNS) strains. Indeed, some CNSs, such as
Staphylococcus epidermidis, adhere more quickly to the stainless steels of food industry equipment [
45]. Therefore, these CNSs can easily comply with the kitchen utensils involved in producing these traditional beers. Therefore, properly cleaning these equipment and kitchen utensils could justify the low rate observed in the CNS. As for
S. aureus (60%), the high rate observed can be explained by the fact that they adhere and quickly develop biofilm in contact with the food surface [
46]. This lifestyle facilitates the adhesion of bacteria to food surfaces creating a public health problem [
47]. In short, in these beers, the high rate of contamination observed with
Providencia rettgeri,
Enterobacter aerogens,
Klebsiella terrigena, and
Staphylococcus aureus can be explained by the fact that they can produce biofilm, which provides specific adhesion characteristics allowing their persistence and their adaptation to bad conditions. The production of biofilm is potentially a risk of poisoning for the consumer.
Gentamicin and nalidixic acid had shown efficacy in almost all strains isolated except
Enterobacter cloacae. Our results corroborate those of Hama et al. [
48] and Anago et al. [
49], who qualify gentamicin as having excellent efficacy against staphylococci and ESBL-producing strains of enterobacteria, respectively. This effectiveness of gentamicin, accompanied by nalidixic acid, can be explained by the fact that aminoglycosides (gentamicin) act on the bacterial ribosome and induce the synthesis of erroneous proteins [
50]. As for quinolones (nalidixic acid), they exert their action at the time of DNA replication by acting on DNA gyrase and topoisomerase IV, which regulate the topology of DNA to allow replication [
51]. The inhibition of DNA gyrase leads to the suppression of the positive supertowers of DNA.
In contrast, that of topoisomerase IV leads to the accumulation of daughter replicons, thus disrupting this replication. In addition to gentamicin and nalidixic acid, we note that some antibiotics, such as doxycycline, trimethoprim-sulfamethoxazole, remain active on enterobacteria and streptomycin on staphylococci. A study conducted by Kadja et al. [
52] on combining tetracycline and trimethoprim sulfonylurea on strains from dairy farming corroborated our results with an efficacy of 62% and 67%, respectively. As for β-lactams and others, the
Enterobacteriaceae were all resistant (100%). Previous work corroborates our results on the sensitivity of
Enterobacteriaceae strains isolated to the antibiotics tested [
53,
54]. In addition, some work has shown that vancomycin, penicillin G, and macrolides are effective against food-borne
S. aureus strains [
52,
55]. Globally, the resistance of
Enterobacteriaceae and staphylococci isolates to β-lactams can be explained by the production of β-lactamase, which hydrolyzes these antibiotics or the reduction of the structure of the pores by the antibiotics which pass [
56]. The development of resistance to other antibiotics can be explained by the fact that these strains have already been in contact with different families of antibiotics. Particularly for staphylococci, resistance to ceftriaxone implies resistance to almost all β-lactams currently available [
57] and the development of resistance to many antibiotics widely used to control infections such as food poisoning [
58,
59]. The multidrug resistance of the isolates could be explained by self-medication and excessive and uncontrolled use of antibiotics accompanied by a selection of resistant bacteria [
60,
61]. This selection could be due to acquiring resistance genes such as erm,
msr,
mef, and
mph [
56] or virulence genes such as
fimA and
cnf1 [
62].
Our study only revealed a shallow presence of
fimA and ermB genes in
Enterobacteriaceae (
Enterobacter cloacae) and staphylococci (CNS). The work of Le Trong [
63] showed the
fimA gene's presence in many
Enterobacteriaceae species. In 2020, Soria-Bustos et al. [
64] isolated
Enterobacter cloacae with virulence properties in the appearance of extra-intestinal infections. Thus, the biofilm production capacity of
E. cloacae could be explained by the fimA gene, which codes for the synthesis of adhesin, an essential protein in biofilm formation. As for the cnf1 gene, its absence can be explained by the fact that it is mainly produced by
E. coli [
65]. Regarding staphylococci, a study on the transferability of antibiotic resistance genes between bacteria carried out during food fermentation of milk showed that
Staphylococcus aureus and potentially pathogenic coagulase-negative staphylococci are carriers of macrolide resistance genes [
66,
67].
However, the low proportion of
ermB genes with a complete absence of
mefA genes, even though staphylococci were phenotypically resistant to erythromycin in our study, can be explained by the fact that these staphylococci could develop other resistance mechanisms through the acquisition of other genes such as
msr,
mph and
ere, encoding for macrolides resistance. Apart from the addition of genes, the multidrug resistance of strains can be explained by forming a biofilm that protects bacteria from antibacterial molecules [
68]. There is a correlation between the ability to form biofilms and antibiotic resistance. This antibiotic resistance can be explained by the diffusion of drugs in the biofilm [
69]. After exposure to these agents, a small surviving population can repopulate the surface immediately and become more resistant to antimicrobial treatment. Food contaminated with bacteria resistant to antibiotics and carrying genes for resistance or virulence are dangerous germs that could threaten public health.
Author Contributions
Conceptualization, NC, HS, and L.B-M.; methodology, BB, RA, and DNB; software, DNB and RA; validation, NC, HS, AA, IMSH, and L.B-M.; formal analysis, DNB, IMSH, and HS; investigation, NC and BB; resources, OOB and L.B-M.; data curation, NC, BB, and HS; writing—original draft preparation, NC and DNB; writing—review and editing, JF-M; OOB and L.B-M.; visualization, HS; supervision, JF-M; OOB and L.B-M..; project administration, AA. HS and LB-M.; funding acquisition, OOB; AA; HS All authors have read and agreed to the published version of the manuscript.