3.1. Enterobacteriaceae in Manure, Soil, and Water in Cattle and Goat Farms
Our results and those of previous studies indicate that animal farms harbor some associates of Enterobacteriaceae family that are foodborne pathogens [
18]. Although other Enterobacteriaceae species were characterized in the current study, emphases were on
E. coli as it is a more specific indicator of fecal contamination than other coliforms [
19]. Overall, our results demonstrated that
Escherichia coli isolates were found most in manure (45.9%), followed by soil (23.6%), runoff water (4.7%), and trough water (2%).
E. coli is extensively found in the guts of animals as commensal microorganism [
20], and ruminants including cattle are considered as the major reservoirs [
21]. According to Kulow et al. [
22],
E. coli in manure is attributed to the cattle intermittent shedding into fecal matter [
23]. Significantly lower rates for other important Enterobacteriaceae, including
Enterobacter cloacae,
Escherichia fergusonii, and
Klebsiella pneumoniae, were identified in manure, soil, and water in cattle and goat farms. Our findings agree with Davin–Regli and Pages [
24] that
Enterobacter cloacae resides in water, soil, and manure in agricultural lands. Although not commonly associated with foodborne diseases,
Enterobacter cloacae is a widely known nosocomial pathogen and third most causative bacteria in hospital acquired infections after
E. coli and
Klebsiella pneumoniae [
25]. In our study,
Escherichia fergusonii demonstrated a low prevalence in manure from cattle farm (CF1), this bacterium has been reported in farm animals [
26].
E. fergusonii is documented to cause severe pneumonia and death in adult cows [
27]. Since
E. fergusonii reside in foods of animal origin, it has a potential risk to food safety and public health [
28].
3.2. Enterobacteriaceae in Raw Cow and Goat Milk
This study showed that Enterobacteriaceae species, such
E. coli,
Pantoea spp.,
Enterobacter spp.,
Escherichia hermannii, and
Klebsiella pneumoniae, were present in cow and goat raw milk. Approximately 23.1% of goat milk samples were positive for
E. coli, as was the case in a previous study [
29]. It is possible that goat milk may have been contaminated during the milking process.
E. coli was not present in cow milk; however, Samet–Bali et al. [
30] and Saba et al. [
31] reported higher incidences in cow milk at 32.5% and 49.3%, respectively.
E. coli is a naturally occurring microorganism in the guts of humans and animals [
20] and is used as indicator of fecal contamination in food and water safety microbiological analysis [
32].
E. coli are commensal bacteria; however, pathogenic
E. coli can result in zoonotic illness that positions as a public health risk.
Pantoea spp., which was displayed in cow milk, is reported to be a naturally occurring organism in the environment and agricultural settings [
33]. It is an opportunistic pathogen that causes bacteremia in immunocompromised individuals [
34]. The presence of
Pantoea spp. in cow milk is a concern, especially if consumed raw, as it is a health risk. Data from this study suggest that raw milk has the potential to carry potentially pathogenic microorganisms, and thus cow and goat milk should not be consumed raw.
3.3. Occurrence of Pathogenic Bacteria in Cattle and Goat Farms
Notably, our findings showed that it is important when detecting pathogenic bacteria from farming environment to enrich environmental samples (manure, soil, water) with recommended supplements. In this study, pathogenic bacteria were only detected when enrichment supplement specific for each bacterium were used.
E. coli O157:H7 was present in manure (0.7%), soil (0.4%), and runoff water (0.4%) in cattle farm (CF1). In CF2,
E. coli O157:H7 was only isolated from manure (0.4%). Our study agrees with previous studies that
E. coli O157:H7 is present in cattle manure [
35,
36]. Notably,
E. coli O157:H7 was not present in trough water; however, it was present in runoff water. This pathogen is zoonotic and is carried by cattle in their gastrointestinal tracts [
37]. According to Chase-Topping et al. [
38], high levels of shedding by cattle account for most
E. coli O157:H7 in the environmental contamination.
E. coli O157:H7 dispersion from manure/animal feces into soils and runoff water represents a human health concern. Notably,
E. coli O157:H7 was not present in goat farm (GF). Although
E. coli O157:H7 was not detected from manure in goat farm in our study, this pathogen was isolated from goat feces (11.1%) at a USDA-inspected processing plant in the southeastern United States [
39]. It is a public health risk when
E. coli O157:H7 diffuses from manure amended soils to neighboring rivers and streams through water runoff water [
40]. Irrigation of fresh produce with surface water contaminated with
E. coli O157:H7 poses a great risk to consumers, since most fresh produce is consumed raw.
Escherichia coli O157:H7 has a zero tolerance in food products due to its low infectious dose.
E. coli O157:H7 infections may also occur due to direct interactions with animals or contaminated food products of animal origin [
41]. Although several actions are taken during food processing, consumers may not be protected from this pathogen [
42]. Animal handlers in dairy production systems should take extra thoughtfulness when handling livestock, since it is a potential route of infection with
E. coli O157:H7.
Our results showed more prevalence of
Salmonella spp. (10.4%) than
E. coli O157:H7 (1.9%) in the farm environment.
Salmonella spp. was detected in all farms and was present in feces, soil, trough water, and runoff water. Our findings agree with Sobur et al. [
43] that
Salmonella spp. was more prevalent in soil than in water. Although our findings show lower
Salmonella spp. (2.1%) occurrence in goats’ feces, it agrees with previous studies that demonstrated the occurrence of the pathogen at 3. 7% and 3. 4% in the United States [
44] and Ethiopia [
45], respectively.
Salmonella spp. can diffuse via feces from infected livestock to their surrounding environment including soil and water bodies. According to Huston et al., [
46],
Salmonella spp. can persevere in the farm settings for up to six years in animal feces. The main risk for zoonotic salmonellosis from cattle is exposure to contaminated meat through fecal contamination of the carcass during slaughter [
47].
In the present study, 23.4% of environmental samples were positive for
Listeria monocytogenes. This pathogen occurred in all farms and was most prevalent in soil, followed by manure, trough water, and runoff water. According to Vijayakumar and Muriana [
48], this pathogen often occurs in the farm environment including faces, manure, soil, and water sources through which it penetrates the food chain. According to Borucki et al., [
49] and Mohammed et al. [
50], dairy farming environment is considered an important reservoir of
Listeria Monocytogenes, which may be transferred to animal food products, causing listeriosis [
51].
Listeria spp. in animal feces may also be transferred to crops through water used for irrigation and application of manure into agricultural soils [
52], hence it is a major concern in public health.
The study found that
Enterococcus spp. was the most prevalent pathogen at 24.5% and was isolated from manure, soil, water trough water, and runoff water.
Enterococci spp. are ubiquitous organisms that are extensively detected in bovine feces, soil, water, plants, and the gastrointestinal tracts (GI) of humans and animals [
53,
54]. According to Fang, [
55],
Enterococcus spp. is an emerging pathogen that is linked to foodborne illness and cause various infections including nosocomial infections. This pathogen has been used as pointers of microbiological quality of fresh produce [
56] and their presence in water as an indication of fecal contamination [
57]. The presence of
Enterococcus in cattle and goat farms is a suggestion that the dairy production systems are reservoirs of this pathogen.
Overall, our data and other previous studies demonstrate that manure, soil, and water are important sources of
Escherichia coli O157:H7,
Salmonella spp.,
L. monocytogenes, and
Enterococcus spp. [
58,
59,
60,
61]. Occurrence of
E. coli O157:H7 and
Salmonella spp. in dairy farms have been documented [
62,
63]. Although
E. coli O157:H7,
Salmonella spp., and
L. monocytogenes were not isolated from raw milk in our study, they have been associated with the consumption of raw milk from cows and goats [
64,
65]. Nevertheless, pathogenic bacteria may contaminate raw milk via fecal contamination by excretion into the milk.
3.4. Antibiotic Resistance in Enterobacteriaceae
According to our findings, phenotypic screening of antimicrobial resistance among Enterobacteriaceae from cattle and goat farms displayed multi-drug resistance to indispensable antibiotics in both human and animal medicine. Enterobacteriaceae have been associated with higher mortality than other microbes [
66]. Our results showed that all Enterobacteriaceae from soil, manure, and water in cattle and goat farms was highly resistant to novobiocin (100%), erythromycin (100%), and vancomycin (100%). Enterobacteriaceae isolates from runoff water in goat farm and trough water in cattle farm (CF2) were 100% resistant to tetracycline. Kanamycin resistance in all Enterobacteriaceae isolates ranged from 0 to approximately 33.3%. Generally, cefpodoxime and nalidixic acid showed relatively low resistance ranging from 0 to 16.7%. Notably, all Enterobacteriaceae isolates from farm environment were susceptible to imipenem.
Enterobacteriaceae isolates from cow and goat raw milk also showed high (100; 100%) resistance to novobiocin (100; 100%), and vancomycin (100; 100%), tetracycline (100; 100%), and erythromycin (85.7; 100%). Nalidixic acid (42.9; 50%) and kanamycin (0; 33.3%) demonstrated lower of resistance to isolates from cow and goat milk, respectively. None of the Enterobacteriaceae isolates showed resistance to cefpodoxime and imipenem. Our findings suggest that Enterobacteriaceae from farm environment is resistant to common antibiotics used in huma medicine, hence a health risk to consumers.
As indicated in our study, Enterobacteriaceae from goat and cattle farms showed resistance to novobiocin, one of the effective antibiotics used against Gram-negative/Gram-positive microorganisms [
67]. According to Bisacchi and Manchester [
68], novobiocin is frequently used as a penicillin replacement in the treatment of penicillin-resistant
S. aureus. Erythromycin (macrolide) and vancomycin are used for treatment of human campylobacteriosis [
69] and serious Gram-positive bacterial infections [
70], respectively. It is reported that extended use of antibiotics in food animals creates a conducive environment for the development and diffusion of resistant bacteria [
71]. Individuals may attain antimicrobial resistant bacteria via the food chain or contaminated soil, manure, water, and raw milk.
Although low resistance was displayed to cefpodoxime and imipenem in our study, limited studies have recognized the incidence of carbapenemase (CP)-producing bacteria in food-producing animals and surrounding environment [
72]. Even though the incidence of CP microbes in food-producing animals is low, CP bacteria spread from food-producing animals to their derivative products is a risk to consumers and result to severe consequences [
73]. According to Iovleva and Doi [
74], Carbapenem-resistant Enterobacteriaceae (CRE) is on the rise and a major concern to modern medicine.
Multidrug-resistant resistance was demonstrated among the Enterobacteriaceae isolates from manure, soil, and water. A total of four antibiotic resistant patterns were recorded: NOV-ERY-VAN, NOV-TET-ERY-VAN-KAN, and NAL-NOV-TET-ERY-VAN. NOV-TET-ERY-VAN was the most common pattern among the isolates.
E. coli isolates displayed three antibiotic resistant patterns: NOV-TET-ERY-VAN, NOV-TET-VAN, and TET-VAN.
E. coli and
Enterobacter aerogenes displayed resistance to five out of the eight antimicrobials tested. Multidrug-resistant
E. coli is a concern to the public health to the fact that it is an indicator of antimicrobial resistance of Gram-negative bacteria [
75].
Our study presented six (
n = 6) different AMR patterns among Enterobacteriaceae isolate from raw milk. Multidrug resistant Enterobacteriaceae in farm environment and raw milk is a food safety risk, since bacterial species in this family are often resistant to most of the antibiotics that are used against them [
76]. The development of AMR in bacteria may be caused by horizontal gene transfer that originate from bacteria in the environmenta [
77].
3.5. Antimicrobial Drug Resistance in Pathogenic Bacteria
Our findings demonstrated
E. coli O157:H7 and
Salmonella spp. resistance to erythromycin (7%) and vancomycin (7%). Contrary to our study, Sobur et al. [
43], noted in their findings that high
E. coli O157:H7 resistance to erythromycin (88.9%) and tetracycline (89.4%).
E. coli O157:H7 and
Salmonella spp. in our study presented three (
n = 3) and five (
n = 5) AMR patterns, respectively. Our findings support the Chang et al. [
16] study which demonstrated that dairy cows are reservoirs of antimicrobial resistant
E. coli O157:H7 and
Salmonella spp. These pathogens may be transmitted to humans through interaction with animals, contaminated soil, manure, and water, or milk [
16]. Antimicrobial use in food-animal farming has been assumed to be a source for the emergence and dissemination of antimicrobial resistant
Salmonella spp. [
78]. In our study, imipenem was effective for both
E. coli O157:H7 and
Salmonella spp. and agrees with findings [
43].
L. monocytogenes isolates in cattle and goat farms demonstrated multidrug resistance to most antibiotics tested, such as cefpodoxime (27.9%), kanamycin (27.9%), tetracycline (25.6%), and nalidixic acid (25.6%). Our results display that
Listeria spp. displayed the most AMR patterns (
n = 10). The most common of the 10 patterns were TET-CEF-KAN-NAL, displayed by one soil, and two manure isolates. Of the 10 patterns, one isolate from manure displayed resistance to seven of the eight antimicrobials used: TET-VAN-CEF-NOV-KAN-ERY-NAL.
L. monocytogenes are generally susceptible to antibiotics that are used for treatment of listeriosis [
79] Healthy cattle are reservoirs of
Listeria spp. and through shedding of feces and can potentially contaminate the soil, water sources, milk, and meats [
80]. The movement of animals and farm worker within and between farms could also result to the dispersion of
monocytogenes in the farm environment [
81]. Multidrug resistance of
Listeria spp. strains has also been detected in food and environmental sources [
82]. Since
Listeria spp. is present in all aspects of the environment and a challenge to control [
7], the implementation and application of Good Agricultural Practices (GAPs) and Good Management Practices (GMPs) can mitigate the occurrence of antimicrobial resistant
Listeria spp. in food animal production systems.
Enterococcus spp. from cattle and goat farms showed 32.6%, 30.2%, 30.2%, 7% resistance to vancomycin, novobiocin, erythromycin, and tetracycline, respectively. Although antibiotic resistance was at a lower rate in our study, our findings agree with [
83] report that stated vancomycin (98%) and erythromycin (82%) resistance to
Enterococcus spp. from dairy cattle.
Enterococcus spp. presented six (
n = 6) AMR patterns. Our study indicates that
Enterococcus spp. isolates were resistant to Vancomycin. VRE has previously been isolated from manure contaminated feedlot soils [
84] and in cattle fecal samples [
85]. According to Foka and Ateba [
83], VRE is the most widespread multidrug resistant strain of
Enterococcus spp.
Enterococcus spp. resistance to both imipenem and cefpodoxime was lowest at 4.7%.
Enterococcus spp. have been reported to colonize the guts of cattle and humans [
86] and are known to survive in varying environments where they cause serious infections [
87].
Enterococci spp. are reported to have the potential to transfer their antimicrobial resistant genes to other microbes [
88], hence their prevalence in cattle and goat farms is a public health concern. According to Simner et al. [
89], occurrence of multidrug resistant
Enterococcus spp. has been attributed to the widespread use and misappropriation of antimicrobials in animal agriculture.
Generally, our study demonstrated that Enterobacteriaceae isolates from manure, soil, water, and raw milk were resistant to the same antibiotics to some extent. Overflow of antibiotic-resistant bacteria from the animal farming settings to the neighboring environment is creating a potential public health risk throughout the world [
3]. Although the understanding on the spread of AMR within farming environments and from animals to humans is limited, food animals are responsible in the propagation of AMR into the environment [
90].