A Review of Listeria and Salmonella: An Update on Description, Characteristics, Incidence, and Antibiotic Susceptibility

| Foodborne pathogens have emerged as a significant public health and food safety concern worldwide. Over the years, the epidemiology of foodborne diseases has drastically changed. The emergence of newly identified foodborne pathogens has significantly added to these changes. Numerous bacteria have the potentials of being significant foodborne pathogens. These include Staphylococcus aureus, Campylobacter jejuni/ coli, Escherichia coli O157: H7, Helicobacter pylori, and Arcobacter butzleri. Others such as Listeria monocytogenes and Salmonella species (spp.) have been known pathogens for several years but have only in the past decades been discovered to be the most common foodborne bacterial pathogens. Their ability and potential to produce toxins causing morbidity or even mortality is enough pointers to the gravity of the situation. This review focuses on Listeria monocytogenes and non-typhoidal Salmonella enterica from vegetables and other food products, with emphasis on their description, characteristics, incidence, and antibiotic susceptibility. The review also explained the impacts and current status of these pathogens. Much progress has been made in these areas, but additional research is needed to control these pathogens.

The survival and proliferation of Listeria genus in an environment are primarily due to its unique tolerance towards the potential of hydrogen (pH), water activity (a w ), salt concentrations and temperature (Sleator et al., 2003;Liu et al., 2005). According to Liu (2006), environmental sources such as agricultural land, soil, sewage, surface water, and animal feeds have been known to be suitable for the multiplication and survival of Listeria species.

Listeria monocytogenes
L. monocytogenes is a ubiquitous bacterium that possesses a mechanism of adaptability, including antibiotic resistance genes (Gandhi and Chikindas, 2007) as well as the formation of biofilm (Da Silva and De Martinis, 2013), which adheres to the surface of food processing equipment and facilities over months and years (Orsi et al., 2008). Due to the formation of biofilm, L. monocytogenes can tolerate ordinary disinfectants, sanitizers, and antimicrobials. This resistance directly causes contamination in food contact surface (Carpentier and Cerf, 2011).
The temperature range for the growth of L. monocytogenes is between -1.5 and 45°C, with the optimal temperature being 30-37°C (Lado and Yousef, 2007). The ability to multiply in a refrigeration temperature enables L. monocytogenes to contaminate food processing environments, such as cutting and chilling room, workers' hands, conveyor belt rollers, and processing equipment (Kerr et al., 1995;Koutsoumanis et al., 2010;Tompkin, 2002). More importantly, L. monocytogenes can be directly transmitted from animals to humans (Nightingale et al., 2005). L. monocytogenes had been found in cooked meat due to cross-contamination, a standard route of transmission of the pathogen from a contaminated L. monocytogenes has been classified at least into four evolutionary genetic lineages (Lineages I-IV) based on its flagellar (H) and somatic (O) antigens (Doumith et al., 2004). Lineage I (serovars 1/2a, 3b, 4b, 4d, 4e and 7) is highly pathogenic and is more commonly associated with human outbreak cases, whereas Lineage II (serovars 1/2a, 1/2c, 3c, 3a) is very prevalent in foods, farm and natural environments, which causes cases of human and animal listeriosis. Lineage III serotypes 4b, 1/2a, 4a and 4c and Lineage IV (serovar 4a, 4c) are usually animal pathogens and less pathogenic, which rarely cause human diseases (Doumith et al., 2004;Haase et al., 2014).
Three of the 13 recognised L. monocytogenes serovars 1/2a, 1/2b, and 4b were accountable for over 95% of human listeriosis cases (Doumith et al., 2004;Kasper et al., 2009). Serovar 1/2a accounts for almost over 50% of the L. monocytogenes isolated from the environment and foods. On the other hand, most of the human listeriosis cases globally have been caused by Lineage I serotype 4b isolates (Kathariou, 2002;Chemaly et al., 2008).
Over the years, several virulence factors have been known to be involved in the cellular mechanism as well as cytosolic proliferation, which are a vital process in the intracellular parasitic life cycle of L. monocytogenes (Vázquez-Boland et al., 2001). The existence of Listeria pathogenicity island1 (LIPI-1), which harbours numerous essential virulence genes, has contributed immensely to the pathogenicity of these serotypes (Lim et al., 2016). The LIPI-1 comprised of six genes that play a dominant role in the pathogenicity of L. monocytogenes and are vital for phagosomal abscond (hly, plcA, plcB, mpl), movement and cell-to-cell spread (act), and gene regulation (prfA) (Vázquez-Boland et al., 2001). Several strains of L. monocytogenes display wideranging virulence and pathogenicity, whereas some strains are known to be naturally virulent causing severe human listeriosis, while others are avirulent and unable to produce an infection in the mammalian host (Liu et al., 2003a;da Silva et al., 2017). A number of multiple virulence factors exist in L. monocytogenes, which significantly regulate the pathogenicity, such as surface internalin (inlA, inlC, inlJ), invasion-associated protein (iap) actin (actA), phosphatidylinositol-phospholipase C (plcA), listeriolysin O (hlyA), and virulence regulator (prfA) (Vázquez-Boland et al., 2001;Liu et al., 2007). From the varieties of putative virulent markers identified in L. monocytogenes, the internalins surface protein is known to perform a significant function in the pathogenesis of human clinical listeriosis (Hadjilouka et al., 2016). Furthermore, internalin inlA and inlB genes that are carried by L. monocytogenes help in adherence and invasion of mammalian cells (Bierne et al., 2007). The broad families now consist of at least nine additional members, namely inlC, inlC2, inlD, inlE, inlF, inlG, inlH, inlI, and inlJ. These internalin genes are clearly demonstrated to be essential in the invasion of host epithelial cells and virulence (inlA and inlB), cell-to-cell spread (inlC), adherence (inlF and inlJ), and autophagy evasion (inlK) (Bierne et al., 2007;Dortet et al., 2011;Kirchner and Higgins, 2008).
According to Goldfine and Shen (2007), gene expression by transcriptional regulation plays an essential function in bacterial acclimatisation to its new environment. Another study by Glaser et al. (2001) stated that a bioinformatics study of the L. monocytogenes genome sequence has identified over 200 putative transcriptional regulators. Decisive regulatory factor A (PrfA) has an essential and central role in controlling the expression of virulence gene products. Moreover, PrfA was initially known as a regulatory factor that is relevant for hly transcription, and it has since been shown to regulate the expression of a growing number of bacterial gene products that are directly associated with virulence (Wang et al., 2017).

Listeria monocytogenes in foods, epideMioloGy, and incidences
Regarded as the most important bacterial pathogen causing food contamination, food poisoning, and sporadic outbreaks, Listeria is a facultative anaerobic foodborne pathogen widely distributed in soil, sewage and foods. It is also found on the body of humans and animals (Marian et al., 2012). Fresh plant produce and food products of animal origin are well known to play a vital role in harbouring varying numbers of L. monocytogenes (Leong et al., 2015). Many studies and food survey conducted in Malaysia have reported findings of L. monocytogenes in numerous categories of foods, including raw leafy vegetables, burger patties, vegetarian burger patties, poultry and poultry product, seafood, and ready to eat (RTE) foods (Ponniah et al., 2010b;Adzitey et al., 2012b;Marian et al., 2012;Wong et al., 2012;Budiati et al., 2013). However, no study has been done on Salmonella and Listeria on varieties of leafy vegetables and chicken processing environment in Malaysia.
Although the pathogen can be killed via heat treatment during food processing (Muriana et al., 2002), food products can be re-contaminated during food handling, packaging and distributing (Lekroengsin et al., 2007). Outbreaks of listeriosis are mainly reported in developed countries as compared to developing countries due to the differences in diagnosis and reporting systems of listeriosis (WHO,

prevalence and antibiotic resistance of Listeria monocytogenes isolated froM veGetables
There is a variation in the prevalence of L. monocytogenes in vegetables based on several studies, as revealed in Table  1. The prevalence among the surveys ranged from 0.6% to 34.4%. A prevalence of greater than 10% was reported in countries such as Malaysia, Nigeria, Turkey, Poland, and Spain. In another study, 4.1% L. monocytogenes was detected from vegetable samples collected in Nigeria (Bello et al., 2013). Lettuce in Spain (10.0%) and Norway (10.0%) had similar contamination rates. Also, L. monocytogenes were isolated from 3/90 (3.3%) raw vegetable samples (lettuce and sweet basil) in Thailand (Stonsaovapak et al., 2010). On the other hand, watercress RTE (ready-to-eat) and escarole (0.6%) from Brazil were the least contaminated sources Maistro et al., 2012). A study in Malaysia on the incidence of L. monocytogenes in a variety of vegetables obtained from retail markets indicated that winged bean had the highest contamination (34.4%), followed by parsley (25%), Indian pennywort (25%), carrot (24%), and cabbage (21.9%) (Ponniah et al., 2010a). While a study in Nigeria by Ajayeoba et al. (2016) showed that lettuce (19.67%) and cabbage (28.28%) were the most contaminated (Table 1). Table 1 have shown a relatively significant trend of L. monocytogenes in different countries, which is most likely due to several factors, such as minimal control programs and safety inspection of fresh produce (Harris, 2003), differences in agricultural practices, and growing international trades (Cabedo et al., 2008). Moreover, leafy vegetables are very prone to the contamination that originates from the irrigation water, soil, animal manures, and vegetation, due to their growing conditions (FAO/ WHO, 2008), which will likely cause L. monocytogenes contamination in the main food chain (Ivanek et al., 2006). Other factors could be pre-harvest and postharvest, such as processing, packaging, transportation, distribution, and marketing of vegetables, have the potential for multiplication and contamination (Brackett, 1994). Likewise, seasonal variation and climate, as well as geographical variations, such as longitude and latitude are also significant factors liable for the contamination of vegetables by pathogens (Matthews et al., 2014;Liu et al., 2013). Others may well be associated with crosscontamination as these vegetables are combined at retail points or even washed from the same water source (Bello et al., 2013).

Data from
The emergence of antibiotic resistance Listeria is a significant health concern all over the world. A study performed in Nigeria showed salad vegetables exhibited a resistance of 92.9% to ampicillin followed by 85.7% to oxacillin, the least resistance of 14.3% to ciprofloxacin and 21.4% to gentamicin. The antimicrobial resistance pattern displays that most isolates were resistant to at least one antimicrobial agent, but about 64.3% of the isolates were resistant to more than four antimicrobial agents (Bello et al., 2013). This survey showed that there is a lack of study or literature in response to the vegetables L. monocytogenes isolates to the antibiotic found. In Brazil, all L. monocytogenes isolated from RTE vegetables were susceptible to ciprofloxacin, oxacillin, vancomycin, cefoxitin, streptomycin, and erythromycin, but only two isolates exhibited resistance to tetracycline and penicillin G (Byrne et al., 2016).

prevalence and antibiotic resistance of Listeria monocytogenes froM other food sources
The increasing occurrence of antibiotic-resistant Listeria species among animals and other food samples have been reported (Abatcha, 2017;Abatcha et al., 2020). According to a study by Marian et al. (2012) in Central Malaysia where a total of 140 raw and RTE food samples were tested for L. monocytogenes was detected in 8.57% of the food samples.
The study found L. monocytogenes in 33.3%, 25%, and 13.3% of burgers, minced meat, and sausages, respectively. The isolates exhibited high resistance to ampicillin and penicillin G (100%), while high susceptibility was displayed toward streptomycin (100%). Between 2009 to
A two-year study in China aimed at investigating the incidence of L. monocytogenes isolates from retail RTE foods revealed that the average prevalence of L. monocytogenes was 6.87% (Shi et al., 2015). L. monocytogenes were detected in 8/31 (25.8%) of cold vegetable dishes in sauce, 9/131 (6.9%) of roast poultry, 4/62 (6.5%) of cooked meat, 2/32 (6.25%) of cold noodles in sauce and 2/84 (2.4%) of dairy product (Shi et al., 2015). Also, 80 isolates of L. monocytogenes from retail RTE foods in China were susceptible to mezlocillin and penicillin, with the highest resistance of 51.25% to clindamycin, followed by 23.75% to cephalothin and 12.5% to ampicillin (Shi et al., 2015). Twenty-seven isolates were sensitive to all 14 antibiotics tested with 17 strains resistant to more than two antibiotics, including six multi-resistant strains, that are resistant to more than ten antibiotics (Shi et al., 2015).  (Lotfollahi et al., 2017).
In another study by Wieczorek et al. (2012), a total of 812 bovine hides and carcasses were examined for the presence of L. monocytogenes. The isolates of L. monocytogenes found were 10.8% from the hide and 2.5% from carcasses. The isolate serotypes were (87.0%) 1/2a serotype, and 4 were 1/2c (Wieczorek et al., 2012). All the 54 L. monocytogenes strains obtained from bovine hide and carcasses by Wieczorek et al. were susceptible to trimethoprim-sulfamethoxazole, gatifloxacin, levofloxacin, penicillin, ampicillin, vancomycin, rifampin, and streptomycin (Wieczorek et al., 2012). Furthermore, many of the isolates were resistant to oxacillin (72.2%), clindamycin (37.0%), and ceftriaxone (13.0%) (Wieczorek et al., 2012). The summary of the prevalence of Listeria spp. in other foods from various countries is presented in Table 2.

saLmoneLLa description and characteristic of saLmoneLLa species
The genus Salmonella is an enteric Gram-negative, facultative anaerobic and non-spore forming bacillus with cell diameters ranging from 0.7 to 1.5 μm and lengths from 2 to 5 μm, belonged to the family Enterobacteriaceae (Tindall et al., 2005;Todar, 2008). They are chemotrophs and mostly have peritrichous flagella except for S. Gallinarum and S. Pullorum, which are severely pathogenic to poultry and are non-motile (Bhunia, 2008). Salmonella can grow and multiply at various environmental conditions outside a living host cell and are non-fastidious (Pui et al., 2011). They grow at temperatures ranging from 7-48°C, with the lowest a w at 0.995 and pH ranges are between 6.5 to 7.5 (Pui et al., 2011). Salmonella is relative heat sensitive and is killed at 60˚C in 15 to 20 minutes at milk pasteurisation temperatures (Adams and Moss, 2008;Forsythe, 2011). The genus Salmonella comprised of two

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November 2020 | Volume 8 | Issue 11 | Page 1237 species based on the sequence analysis differences, which are Salmonella enterica and Salmonella bongori. The latter group is divided into six subspecies (Adams and Moss, 2004). S. enterica contains more than 2500 serovars, and about 80 are commonly associated with Salmonellosis in animals and humans (de Freitas Neto et al., 2010). Among the S. enterica, S. Typhimurium, S. Enteritidis, S. Hadar, S. Newport, S. Heidelberg, and S. Javiana are the most frequently reported serotypes related with human foodborne illnesses in the United States (Suresh et al., 2006). On the other hand, S. bongori consists of 20 serotypes and is commonly associated with cold-blooded animals, but it can infect humans too (Bhunia, 2008).
The clinical pattern of human salmonellosis has been classified into four, namely typhoid fever, gastroenteritis, bacteremia, and chronic carrier state (Darby and Sheorey, 2008). The signs and symptoms of human salmonellosis comprise of vomiting, abdominal cramps, nausea, diarrhoea (or constipation), fever (> 37.5°C to 41.5°C), chills, headache, body aches, and blood in the stool or none (Bhunia, 2008). The symptoms of the infection most often appear around an incubation time of one week or longer after consumption of contaminated food and last for 1-7 days (Crump et al., 2008). The Salmonella infectious dose is ranging from 1 to 10 10 CFU/g depending on the strain. A single food source outbreak shows that 10 10 cells can cause salmonellosis (Yousef and Carlstrom, 2003;Bhunia, 2008).
Host factors, such as age, immune status, underlying illness, and condition of the intestinal tract control susceptibility to Salmonella infection (Pui et al., 2011). Nontyphoidal salmonellosis, which is a self-limited illness, is distributed worldwide and is the most commonly reported Salmonella infection. On the other hand, enteric fever caused by typhoidal Salmonella are remarkably related to high morbidity and mortality rates and frequently occur in low income developing nations (Hardy, 2004).

saLmoneLLa virulence Genes
As been known for a long time, virulence factors are produced by bacteria and other organisms, which add to their efficiency and allow them to achieve specific functions, such as attachment to cells, avoidance of the host's immune response, entrance into and exit out of the cells and obtaining nutrition from the host (Ibarra et al., 2009). Most Salmonella carries a different set of virulence factors, such as invasion capability and adhesion and the formation of toxin whose activation in the infected host will determine their pathogenic potentials (Tenor et al., 2004). The status of the host and that of the bacterium mostly determine the outcome of Salmonella infection. While the ability of an individual to come down with disease is primarily determined by host factors, such as genetic, environmental and age, at the same time, the pathogenicity of the bacterium is determined by virulence gene or virulence factor (Ahmer et al., 1999). For Salmonella spp. to attain full virulence, it requires numerous genes, as it reflects a complex set of interactions within its host (Lhocine et al., 2015). For most of the genes, distinct regions on the chromosomal clusters, known as 'Salmonella pathogenicity islands' (SPIs) were found (Karunasagar et al. 2012;Que et al., 2013).
The essential virulence factors are encoded by genes located within the highly conserved Salmonella pathogenic islands (SPIs), while others are encoded by the genes located on a chromosome or virulence plasmid (pSLT) (Fàbrega and Vila, 2013). According to Fàbrega and Vila (2013) within the chromosome of Salmonella enterica, there are five most essential pathogenicity islands (SPI-1, SPI-2, SPI-3, SPI-4, and SPI-5), while Salmonella bongori possesses only four (SPI-2 is absent). The pathogenicity islands SPI-1 and SPI-2 genes code for proteins regulating the T3SS (Type Three Secretion System), which enabled the carriage of S. enterica proteins from the bacterial cell straight into the cytosol of host cells (Farhad, 2013). For T3SS to operate appropriately, it requires five distinct types of proteins, such as effector, translocator, chaperone, a transcriptional regulator, and apparatus protein (Portaliou et al., 2016). There is also a structural component of T3SS called Injectisome, preserved among diverse pathogenic T3SSs and looks like flagellar T3SS (Galán and Collmer, 1999; Cornelis et al., 2000). Most often, the virulence genes that are linked to the intestinal phase of infection are located in the pathogenicity islands (SPI-1 and SPI-2) and the remnant SPIs are needed for essential functions, such as magnesium and iron uptake, fimbrial expression, intracellular survival, the development of systemic infections and multiple antibiotic resistance (Almeida et al., 2013;Campioni et al., 2012;Siriken, 2013).
Some virulence genes are encoded on prophages that are incorporated into the Salmonella chromosome. Virulence genes grvB, which encodes a translocated effector protein, is harboured by Prophage Gifsy-1 (Coombes et al., 2005). Similarly, Gifsy-2 plays a significant role in virulence through sodCI, which encodes Cu/Zn periplasmic superoxide dismutase involved in the protection against oxidative stress, and gtgE, encoding a protein of unknown function (De Groote et al., 1997;Ho et al., 2002). The spvR ABCD genes, encoded in the Salmonella virulence plasmid, are necessary for systemic infection (Guiney et al., 1995), with SpvB functioning as a mono-ADP-ribosyl transferase involved in actin depolymerisation (Lesnick et al., 2001). The slyA (transcriptional regulator) is being involved in the resistance to macrophage survival, oxidative stress, and virulence in the mouse model .

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saLmoneLLa in foods; epideMioloGy and incidence
Most of Salmonella spp. is capable of colonising a broad range of hosts and all the main livestock species (poultry, cattle, pigs, dogs, cats and reptiles) and is often asymptomatic (Newell et al., 2010;Abatcha et al., 2013;Abatcha et al., 2014c). More importantly, Salmonella cells are easily transferred to chicken carcasses through faecal contamination during transportation to slaughterhouses. A more spread of cells may occur during processing stages, leading to cross-contamination (Carrasco et al., 2012). Poultry and eggs are the primary reservoirs for Salmonella, and both singly or in combination have been documented as essential causes of salmonellosis (Altekruse et al., 1997). If already infected, the live chicken can harbour and spread the Salmonella cells to other birds using lateral transmission, mainly through faeces, water, soil, dust, litter, feeds, and feathers (Carrasco et al., 2012). Furthermore, the transovarian infection does occur, and chicks hatching from these infected eggs might excrete the bacterium, infecting other chicks (Rabsch et al., 2003).
Fresh produce grown in developing nations where animal manures are commonly used as natural fertilisers might add to the contamination of pathogens to the field, and run-off waters can contaminate water meant for irrigation (Heaton and Jones, 2008). Handling processes from storage and rinsing to cutting are also potential causes of contamination. Also, insects are possible contamination sources, as contaminated flies are a potential vector of Salmonella spp. to fruits (Heaton and Jones, 2008).
Nontyphoidal Salmonella (NTS) causes an estimated 93.8 million incidents of gastroenteritis, with 155,000 deaths. While typhoidal Salmonella causes about 22 million typhoid fever incidents, with 210,000 typhoids feverrelated fatality and 5.4 million episodes of paratyphoid fever worldwide (Buckle et al., 2012;Majowicz et al., 2010). In developed countries, cases of typhoid fever are sporadic, yet, it is an essential disease in developing countries (Buckle et al., 2012). NTS, on the other hand, are the second most commonly recorded causes of human zoonotic diseases, after campylobacteriosis (Majowicz et al., 2010;Abatcha et al., 2014aAbatcha et al., , 2014bGoni et al., 2017).
In the United States, salmonellosis is the most common infection recorded (8,256 diseases; 17.6 illness per 100,000 persons) and lead to the most significant number of hospitalisations (2,290) and deaths (450) (Cummings et al., 2012). Similarly, Salmonella is also one of the most commonly recorded causes of foodborne diseases in Europe, with approximate 108, 614 reported human case in 2009 (23.7 cases per 100,000 populations) (Duggan et al., 2012). Salmonellosis is a notifiable disease in Australian and New Zealand with an incidence rate of 49 and 24 cases per 100,000 population in the years 2012 and 2011, respectively (Lal et al., 2012;Stephen et al., 2017). The estimated incidence of Salmonella infection in Germany, Japan, and the Netherlands was 120, 73, and 16 cases per 100,000 population, respectively (Thorns, 2000). Often, there is a lack of official Salmonella surveillance data in much of the developing countries, although it is estimated that 22.8 million cases occur yearly with 37,600 deaths (Majowicz et al., 2010).
The estimated economic burden due to salmonellosis is USD 210 per outpatient, USD 5,797 per inpatient with enteric illness, USD16, 661 per inpatient with invasive infection and USD 4.63 million per premature death (Adhikari et al., 2004). Moreover, the estimated countrywide economic burden of Salmonellosis stood at USD 3.7 billion for the year 2013, according to the Economic Research Unit Agency (ERS) of USDA.

prevalence and antibiotic resistance of saLmoneLLa species in veGetables
Over the years, the prevalence of Salmonella has drastically increased worldwide. The prevalence of Salmonella spp. in vegetables among several studies is presented in Table  3. The incidence ranges from 0.4% to as high as 97.9% (Sant'Ana et al., 2011;Najwa et al., 2015). The highest prevalence rate of 97.9 % was found in leafy green vegetables in Malaysia (Najwa et al., 2015), followed by 28%, 27% and 21.5% from a similar country (Salleh et al., 2003;Nillian et al., 2011;Abatcha et al., 2018). From these findings, it is quite clear that vegetables from Malaysia were the highest contaminated with Salmonella spp., followed by Iran (

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November 2020 | Volume 8 | Issue 11 | Page 1240 Different countries also reported a variety of serovars in this survey. For instance, S. Typhimurium and S. enteritidis were said to be the main Salmonella serovars in Malaysia (Najwa et al., 2015;Nillian et al., 2011), Iran (Mehrabian et al., 2009, and Nigeria (Bagudo et al., 2014). Interestingly, three studies reported the presence of strains originating from human in vegetables, this is quite worrisome because it causes invasive typhoid fever (S. Typhi) and paratyphoid fever (S. Paratyphi A, B, C), whereas, some serovars cause gastroenteritis symptoms primarily without systemic invasion (Bagudo et al., 2014;Abakpa et al., 2015;Abatcha et al., 2018). Similarly, Quiroz-Santiago et al. (2009) in Brazil detected a poultry host-related Salmonella serovars, Pullorum, and Gallinarum in leafy vegetables, which may perhaps be as a result of using untreated animal manure as fertiliser in vegetable production or attributable to the quality of wastewater used in farming.

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November 2020 | Volume 8 | Issue 11 | Page 1241 NB: (not tested). According to Abakpa et al. (2015), all Salmonella spp. isolated from vegetables in Nigeria were multidrug resistance (MDR). The emergence of MDR Salmonella isolates suggests that these isolates may have originated from areas where antibiotics are commonly misused or used as therapeutic, prophylaxis and growth promoters in livestock production (Singh et al., 2013;Abatcha et al., 2015).

prevalence and antibiotic resistance of saLmoneLLa species froM other foods
Over the decades, the prevalence of antibiotic-resistant Salmonella from other food sources have been on the rise. In China, out of the 539 RTE food products collected and examined from July 2011 to May 2014, 19 (3.5%) were positive for Salmonella, (Yang et al., 2016). Among the isolates, ten distinct serovars were identified includes S. Derby, S. Meleagridis, S. Enteritidis, and S. Senftenberg were the most prevalent serovars (Yang et al., 2016). Moreover, among the isolates identified, 74.0% were resistant to at least one antimicrobial, while 42.0% were resistant to more than three antimicrobials. High rates of resistance were observed for tetracycline (56.0%), ampicillin (38.0%), and streptomycin (34.0%) (Yang et al., 2016).
In Ethiopia, a cross-sectional study was conducted between 2014-2015 on 384 food items of animal origin to assess the prevalence and antimicrobial-resistant profiles of Salmonella isolates using the standard bacteriological methods (Ejo et al., 2016). The overall prevalence rate of Salmonella was 5.5% (21/384) from food items of animal origin. The Salmonella isolates were found to be relatively resistant to tetracycline (42.6%), sulfamethoxazoletrimethoprim (28.6%), and ampicillin (14.3%), respectively, while 9.5%-19% were resistant to ampicillin, cephalothin, amoxicillin, nitrofurantoin and tetracycline (Ejo et al., 2016).
Salmonella is one of the most commonly reported foodborne pathogens around the world, and an increase in antimicrobial-resistant Salmonella could limit the therapeutic options for clinical cases that necessitate antimicrobial therapy. There is a need for precautionary measures to reduce the spread of Salmonella contamination in food sources. More importantly, the maintenance of effective food hygiene and water sanitation remains the cornerstone. Additional steps, such as restriction of the indiscriminate use of antibiotics in food animals, are essential. The summary of the prevalence of Salmonella spp. in other foods from various countries is presented in Table 5.

MonitorinG and control of Listeria
and saLmoneLLa based on international recoMMendation Building a baseline of projects to ensure the monitoring and control of enteric pathogens such as Listeria and Salmonella need advance support and strengthening projects through a multisectoral, One Health approach. Creating a multisectoral, One Health approach to be prosperous in countries requires an understanding of existing national infrastructure, capacity and resources for addressing zoonotic diseases, and in particular, existing mechanisms for collaboration across sectors and

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November 2020 | Volume 8 | Issue 11 | Page 1243 disciplines. Similarly, ensuring sustainable and equitable financing among all relevant sectors is critical for ensuring continuity of programmes to decrease risks from zoonotic diseases from the WHO, FAO and OIE. Resources are required for both emergencies (e.g. outbreak investigation, laboratory surge capacity, quarantine) and routine activities (e.g. core workforce, routine surveillance, routine animal and human control programmes) (OIE, 2019).
In concussion, the pathogenic foodborne bacteria stated here will remain a cause of outbreaks and mortality worldwide because no possible interferences have eliminated them from fresh produce and other foodstuffs. Additional study is necessary to strengthen practical approaches against these foodborne bacteria, and these strategies can be a mixture of practices and technologies earlier developed or those being in the pipeline. The presence of L. monocytogenes and Salmonella in vegetables and other food products is of great public health concern.
There is an urgent need to enhance the microbiological monitoring of the production and processing chains of the foods, to ensure health safety.