Salmonella prevalence in south east asia and China strategies to reduce bacterial load
Salmonella is one of the most common foodborne pathogenic bacteria. It causes salmonellosis in humans and animals, a major public health burden that has a significant cost worldwide. Poultry is one of the main sources of Salmonella which can infect humans trough the food chain.There are multiple serotypes of Salmonella, and they can be classified by host-specificity, where S. pullorum and S. gallinarum are able to infect poultry and cause a disease and numerable economic losses...
Salmonella is one of the most common foodborne pathogenic bacteria. It causes salmonellosis in humans and animals, a major public health burden that has a significant cost worldwide. Poultry is one of the main sources of Salmonella which can infect humans trough the food chain.
There are multiple serotypes of Salmonella, and they can be classified by host-specificity, where S. pullorum and S. gallinarum are able to infect poultry and cause a disease and numerable economic losses, while there are other serotypes, like S. Enteritidis and S. Typhimurium, which have non-specific hosts and can infect either poultry and humans, accounting for the most Salmonella infections in humans in both developed and developing countries.
Therefore, the control of this bacterium and the reduction of its prevalence is key to reduce the economic impact of the disease either in the poultry industry and also in Public Health.
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Prevalence of salmonell in poultry of south east asia
Several publications assessing the prevalence of Salmonella revealed its important presence throughout the food chain in South East Asia, the high number of strains resistant to one or more antibiotics, and the Public Health problem it supposes.
In Thailand, an epidemiology study that lasted for 8 years (Whistler et al., 2018) revealed that Salmonella was detected in 18.05% of broiler isolates. Most common serovars were Kentucky and Thyphimurium, while antibiotic resistance found was commonly against nalidixic acid, amplicillin, amonxicilin clavulanate, tetracycline and ciprofloxacin.
An study conducted in retail markets with fresh chicken meat (Zaw Moe et al., 2017) in Yangon showed that Salmonella was recovered from 97.9% of the samples, and the most frequent isolated serovars were Albany (38%), Kentucky (11%), Braenderup (10%) and Indiana (8). The most frequent resistance was found to trimethoprim-sulfamethoxazole (70.3% of isolates), tetracycline (54.3%), streptomycin (49.3%), and ampicillin (47.1%). 52.2% of the isolates were resistant to three or more antimicrobial agents.
In Vietnam, Trung et al. (2017), investigated the prevalence of Salmonella in backyard farms, farmers and individuals not exposed to chicken farming, and the prevalence was of 45.6%, 4.4% and 2.6%, respectively. S. Weltevreden was the predominant serovar and 20-40% of the isolates showed resistance to tetracycline, chloramphenicol, sulfamethoxazole-trimethoprim and ampicillin.
An study made in retail outlets (Abu Bakar et al., 2017) showed that 40.4% of the chicken meat samples were positive for Salmonella. Highest presence of Salmonella was detected from wet market samples (35.4%), followed by supermarket (26.9%) and butcher shop (21.3%). Most common Salmonella serovars identified were S. Enteritidis (40.3%) and S. Hadar (24.2%).
An study made in retail markets in the Philippines (Elumba et al., 2018), found a 18% Salmonella prevalence on retail chicken meat in Valencia city markets. 100% of those isolates were resistant to amoxicillin, 88.88% to amoxicillin and ampicillin.
Prevalence of salmonella in China
Several publications assessing the prevalence of Salmonella revealed its important presence throughout the food chain in China, the high number of strains resistant to one or more antibiotics, and the Public Health problem it supposes.
A 6-year study made in Shenzhen (Shen et al., 2020), found a prevalence of 5.7% positive samples for Salmonella in sampled human stools, with a broad range of serotypes, being the most common ones S. Thypimurium (39.7%) and S. Enteritidis (23.9%). High antibiotic resistance was found in the positive samples, where 95.3% of the S. Typhimurium isolates were resistant to ampicillin and tetracyclin, and 93,1% of the S. Enteritidis isolates were resistant to nalixidic acid, while around 70% of the isolates of S. Thypimurium and S. Enteritidis were resistant to 5 or more antimicrobial agents.
Talking about the prevalence in poultry, an study made at Shandong province (Yang et al., 2019) in large-scale breeder farms identified Salmonella in 15.4% of the samples collected, where all the isolates were S. Enteritidis serovar resistant to nalixidic acid and streptomycin (100%), while ampicillin resistance appeared in 98.4% of the cases and erythromycin in 93.7%.
Another study performed in retail markets with fresh chicken meat (Zeng et al., 2019), revealed that Salmonella was found in 28 of the 196 samples (14.28%), being the serotypes isolated S. Enteritidis (42.8%), Indiana (32.1%) and Thypimurium (7.1%). High antimicrobial resistance was found to the following antibiotics: trimethoprim-sulfamethoxazole (96.4%), carbenicillin (67.8%), amoxicillin-clavulanic acid and piperacillin (50%), tetracycline (46.4%) and Streptomycin (42%).
Those publications in reveal the high prevalence of Salmonella throughout the food chain in China and South Eat Asia, both at farm level and at markets, and also the potential public health risk that implies, which demonstrates the need of implementing strict protocols and strategies to reduce the incidence of Salmonella in the poultry industry and prevent it from entering the food chain.
The high rate of antimicrobial resistance that was found reflects the misuse of antimicrobials in the livestock production, including for growth promotion, even though China has banned this application on July this year. This finding underlines the need to reinforce the measures to be taken by the authorities to monitor the production methods and control the presence of this bacteria. Alternative solutions should be implemented to reduce bacterial prevalence and the presence of resistant strains.
Clinical signs in humans and poultry
In humans, Salmonella usually causes self-limiting gastroenteritis. The disease-derived costs are relatively high despite the severity is low. However, there are groups of risk, like children (<5 years-old), old and immunosuppressed people, where the disease may evolve to focal infection, septicemia and death.
In the case of poultry, clinical signs may not be visible in adult animals, although it may cause a drip in the mortality and the appearance of greenish faeces. Affected animals may show cachexia and small crest. In addition, bacteria can contaminate the eggshell and can also move to internal organs, like the liver, causing spotted greenish lesions, and colonise the reproductive system and be transmitted to the progeny. Infected ovules may show a darker-greenish colour (pictures 1 and 2).
Vertically infected one-day-old chicks show some characteristic lesions (tryad): enlarged greenish yolk and liver, green content in the gizzard, and greenish and gaseous content in the ceca (picture 3).
Pictures 1 and 2. Salmonella lesions: greenish spots in the liver (left picture) and greenish ovules (right picture).
Picture 3. Characteristic lesions in yolk, gizzard, liver and ceca caused by Salmonella in day-old chicks.
Useful tools to reduce bacterial load and risk of food-borne salmonella infectons
Control measures along the food chain should be stablished, from farm to fork. There is the need to implement a proper hygiene and disinfection measures in poultry farms, slaughter plants and processing sites, as well as to inform consumers on the proper storage and cooking conditions.
From our side, we recommend that farming activities should be focused on reducing the pathogen prevalence by:
-Implementing a proper plan of cleaning and disinfection of the poultry houses with strict biosecurity measures
-Identifying and eliminating the sources and contamination sites at farm by performing a continuous assessment of the presence of bacteria in the animals.
- Birds with compatible signs should be separated from healthy ones and tested.
- “Healthy” carriers should be detected by agglutination techniques.
- Monitor day-old chicks and the relative weight of the yolk. Vertical infection will show a higher relative yolk weight.
– Vaccination plan with an auto-vaccine can be stablished for the rearing pullets.
– Continuous use of the natural antimicrobial cimenol ring as a tool to eliminate the pathogenic bacteria, such as Salmonella, from the digestive tract and avoid an outbreak.
Cimenol Ring: Key tool to reduce salmonella prevalence
Cimenol ring is a molecule of botanical origin with demonstrated bactericidal and fungicidal activity. Its action is potentiated when combined with citric acid thanks to the synergy between both compounds.
The effectivity of the blend of cimenol ring and citric acid against Salmonella is corroborated through different in vitro trials: in culture plates (Picture 4) and in contaminated raw materials (table 1). In addition, this solution is also effective against other microorganisms such as Fusarium, Candida, E. coli and Clostridium perfringens.
Picture 4. Salmonella culture in agar plate with different concentrations of cimenol ring. Reddish colour in the culture indicates Salmonella growth, while yellowish medium is indicative of no Salmonella growth.
Table 1. Evaluation of CFU count in artificially contaminated corn with Salmonella (~106CFU/g) which received cimenol ring and organic acids.
Therefore, the inclusion of cimenol ring plus citric acid in feed and/or drinking water can reduce the presence of Salmonella in feed and in the digestive tract and decrease the public health risk that this bacterium may suppose.
The use of such natural antimicrobial in the strategy against Salmonella is a great innovative tool that can be used for conventional and organic production. Compared to other products used for the same purpose, cimenol ring compounds are non-corrosive and non-toxic, which means they are safe for handlers and animals, and have a long-term efficacy (demonstrated up to 6 months), while they are available in liquid and powder form.
As it is a natural solution, it does not cause the development of resistances, and it does not require a withdrawal period because no residues are left in animal products. These are advantages in front of antibiotics, added to great problem of resistances to most common antibiotics present in Salmonella strains isolated in South East Asia.
Salmonellosis is a major foodborne disease present in animals and humans. A high prevalence has been found in chicken meat (97.9% of the samples were positive in a trial in Myanmar, 40.4% in an study in Malaysia, while 18% in the Philippines), as well a high antimicrobial resistance (in the case of Myanmar, more than 50% of the isolates were resistant to three or more antimicrobials).
The economic impact of the different serotypes in Public Health and also on the poultry industry, demonstrate that Salmonella should be a prior topic of concern and the need to implement strict measures to reduce the prevalence of Salmonella in the poultry industry.
An innovative tool to avoid the presence of Salmonella in food chain is the use of cimenol ring with citric acid, an effective natural antimicrobial combination against Salmonella and other microorganisms, with demonstrated effectivity to eliminate the pathogen from feed and reduce the bacterial load in the intestine.
The superiority of cimenol ring to other products marketed for the same purpose, like organic acids, is demonstrated in multiple trials, since cimenol ring is able to obtain higher reduction percentages for Salmonella (95.9% vs 93.3%) maintained in time at a four times lower dosage. Compared to antibiotics, cimenol ring does not develop resistances, does not create residues and does not need a withdrawal period.
Cimenol ring has been researched, developed, manufactured and marketed by Biovet S.A. under the commercial name “Alquermold Natural”.
Alquermold Natural is a patented product, available in premix and liquid presentation, intended for feed preservation and control of pathogenic digestive microorganisms. It can be sprayed on raw materials and mixed with feed and drinking water.