Background
Poultry is one of the world’s fastest growing sources of meat, and its share in the world meat production has increased from 15 % to 30 % [
1]. The modern production unit can produce market ready broiler chicken in less than six weeks. This development arose from genetic selection, improved feeding and health management practices involving use of antibiotics as therapeutic agents [
2,
3]. Antibiotics have improved poultry performance effectively and economically [
3,
4] but an increase in numbers of antibiotic-resistant bacterial strains [
5] such as
E. coli [
6‐
8],
Salmonella spp. [
9] and
Pseudomonas spp. [
10] continue to occur [
4,
11].
The high incidence and rising frequency of antibiotic resistance among the bacteria populating poultry chicken presents a public health hazard [
5]. These antibiotic resistant bacteria can be transmitted from poultry to humans through the food chain with serious consequences on public health [
5,
12]. This, therefore, necessitates a need for better antimicrobial drugs. Plants have been documented as one of the sources that possesses antimicrobial traits which are chiefly synthesized during secondary metabolism [
13‐
15]. Plant based antimicrobial compounds have great therapeutic potentials as they can serve the purpose without any side effects associated with synthetic drugs [
16]. The inherent utility and practical applications of plant extracts such as garlic, cinnamon, tulsi, ginger, turmeric, lemon, neem, yucca, thyme and rosemary have been explored for improving poultry health as well as production with fruitful results [
17,
18]. Though, it has been reported that some plant based chemotherapeutic agents may be ineffective on emerging resistant bacterial strains [
19,
20], therefore, further work still needs to be done to search for more effective plant based chemotherapeutic agents especially for poultry chicken management.
Generally, plants contain bioactive components [
21,
22], that are less toxic and environmentally friendly [
23]. Their antibacterial activity have been documented against methicillin-resistant
Staphylococcus aureus and a variety of other bacteria [
24,
25] such as
Escherichia coli,
Klebsiella pneumonia [
26],
Pseudomonas aeruginosa,
Proteus mirabilis [
27],
Brevibacterium ammoniagenes,
Streptococcus mutans and
Propionibacterium acnes [
28]. Despite the fact that global interest has been shifted to plant based antimicrobials [
29], many plants still remain largely untapped against antibiotic resistant bacterial isolates. This study therefore investigated not only susceptibility of isolated bacteria to different antibiotics but also antibacterial activity (in vitro) of plant extracts on selected antibiotic resistant bacterial isolates. These isolates were obtained from water, feed, crop, gizzard, and faeces of poultry layer chicken. The isolates were characterized and assayed as multi-antibiotic resistant bacteria and then subjected to different plant extracts. Apart from
Mangifera indica (Mango), other plant extracts used have not previously been evaluated on the antibiotic resistant bacterial isolates from poultry chicken.
Discussion
Interest in poultry bacteria specifically those that threaten public health motivated this study. Based on phenotypic antibiotic susceptibility test, the level of resistance exhibited by the test isolates on selected antibiotics is alarming. This is an indication that indiscriminate use of conventional antimicrobials has led to a steady increase in the antibiotic resistance and the low-income countries which are home to the majority of the world’s population are particularly affected by this phenomenon [
14]. With the exception of
K. oxytoca, the antibacterial activity of plant extracts was centred on
E. coli, S. enteritidis and
P. aeruginosa because of their high MAR.
Apart from the occurrence of
E. coli in the crop, gizzard and faeces of poultry chickens, their resistance to antibiotics is a great concern. This shows that preventive medications are still given to chicken in order to reduce mortality [
43]. The application of antibiotics will not only increase the resistance in pathogenic strains but can also lead to resistance in the endogenous flora of humans and animals [
44]. Following the consumption of poultry meat specifically chicken, MAR bacterial strains may spread to the human population, which can lead to the transfer of genes coding for resistance [
45]. Our observation shows that the resistance rate of
E. coli to Amoxicillin, Erythromycin, Cefuroxine, Ceftazidine and Cloxacillin presents a serious cause for concern considering the fact that the uninformed farmers may continue to use increasing level of ineffective antibiotics in the management of infection in farms with possible residues in poultry meat, eggs and other products meant for human consumption [
46].
One of the ways to handle antibiotic resistant
E. coli is to develop new and novel antimicrobial agents specifically from plant origin. From this study, the methanol extract of
Mangifera indica Julie cultivar leaves demonstrated antibacterial effectiveness on antibiotic resistant
E. coli [
47]. This is an indication that the leaves of
Mangifera indica contain inhibitory substances active against
E. coli [
48] in comparison to
Euadenia trifoliata that was ineffective. This observation is similar to that of
Euadenia eminens root extract evaluated against
E. coli by Dickson et al. [
49] but contrary to that of Amole et al. [
50]. The resistance of
E. coli to the extracts [
51] is similar to what was obtained for Amoxicillin, Erythromycin, Cefuroxine, Ceftazidine and Cloxacillin. Although, in this case, the crude extract used may not be active enough as potency of each phytoactive components may have been affected by each other. This suggests that further work still needs to be done to evaluate the specific phytoactive compound present in all the tested plant extracts so as to ascertain their efficacy on this antibiotic resistant
E. coli.
S. enteritidis occurrences in faeces of poultry chicken may be as a result of improperly disposed poultry wastes [
52]. With reference to Nigeria, wastes from commercial poultry farms are not properly disposed and most rural farmers use these wastes as manure, which are often kept at the backyards before moving them to the farm. These poultry wastes may serve as source of enteric organisms that habour novel resistance factors for birds, including chicken that feed on such wastes. The isolated
S. enteritidis was generally resistant to Gentamycin, Amoxicillin, Cloxacillin, Erythromycin, Cefuroxime and Ceftazidine. The observed high resistance against these antibiotics probably reflects the high usage of the drugs in the study sites. This could be because these antibiotics are readily available and farmers see them as first point of contact broad-spectrum to treat their chickens [
53,
54]. As a result of this, these drugs may have become seriously compromised and probably are currently ineffective.
The high rates of antibiotic resistance in
S. enteritidis may be more difficult to treat with synthetic antibiotics alone, but rather needs the touch of nature such as bioactive components in plants. Evaluated plant extracts inhibited the growth of
S. enteritidis in vitro. Extracts from
Euadenia trifoliata leaves and
Euadenia trifoliata stem-bark demonstrated antibacterial activity against
S. enteritidis. This corroborated the work of Amole et al. [
50] using
petroleum ether, ethyl acetate and methanol fractions of Euadenia trifoliata leaves against
S. typhi. Osundiya et al. [
55] also reported similar observation using
root extracts of
Burkea africana and
Combretum adenogonium against
S. typhi. The antibacterial activity of methanol extract of
Mangifera indica - Julie cultivar leaves on
S. enteritidis is in agreement with the work of De and Pal [
48] who also used
aqueous young leaves extract of Mangifera indica against
S. typhi. This suggests that
Euadenia trifoliate and
Mangifera indica possesses antibacterial compounds which are active against
Salmonella species.
The occurrence of
P. aeruginosa in feed [
56] and water [
10,
57] is not new however, our work re-established it.
P. aeruginosa exhibited resistance to Erythromycin, Amoxicillin, Cloxacillin, Cefuroxime, Ceftazidine and Gentamycin which corroborated with the work of Kibret and Abera [
58].
Pseudomonas species are naturally resistant to many antibiotics due to the permeability barriers afforded by its outer membrane composed of lipopolysaccharide [
27]. Resistance of
P. aeruginosa to Gentamycin, is unique because it has been documented that
P. aeruginosa used to be resistant to certain antibiotics [
59] but not Gentamycin, however this may be peculiar to our study site. This suggests that poultry chicken farmers (especially the untrained) in the study site may have indirectly abused Gentamycin as a broad spectrum antibiotic [
53,
54] to treat poultry chicken diseases.
P. aeruginosa was resistant to more than 70 % of the antibiotics, but sensitive to more than 80 % of the extracts evaluated. This shows that one of the methods to reduce the resistance of
P. aeruginosa to synthetic antibiotics is by using antibiotic resistant inhibitors from plant origin [
60,
61]. The effectiveness of the plant extracts is in agreement with Abid et al. [
62] who also emphasized that the most sensitive bacterium to tested plants is
Pseudomonas. In this study, activity of
Euadenia trifoliata [
50],
Euadenia eminens [
49] and
Mangifera indica was evident against
P. aeruginosa [
62]. Interestingly, methanol extracts of
Mangifera indica (MJLM) showed more activity against
P. aeruginosa [
47] in comparison to other extracts. This suggests that
Mangifera indica possesses potent and specific inhibitory substance (s) against
P. aeruginosa.
Acknowledgements
The authors hereby acknowledge the technical support of Okunlola Idowu, Akande Akinwumi, Olusola Olumide, Akanji Abolade, Dibiagwu Theresa and Ologun Olusanya. We also appreciate the Poultry Association of Nigeria (PAN), Ilora chapter for their cooperation.