Prevalence of antibiotic resistance in Salmonella Typhimurium isolates originating from Iran: a systematic review and meta-analysis

Objective Antibiotic resistance in Salmonella represents a significant global public health concern. Among various serovars, Salmonella enterica serovar Typhimurium is prevalent in multiple countries. This study aims to conduct a systematic review and meta-analysis to evaluate the pattern of antibiotic resistance in S. Typhimurium isolates from diverse sources in Iran. Methods We conducted a comprehensive and systematic search for relevant articles until December 2023 in the following databases: PubMed, Scopus, Web of Science, and SID. The collected data were analyzed using Stata software version 17. Results Eighteen studies examined the pattern of antibiotic resistance in S. Typhimurium for various antibiotics in Iran. Piperacillin and tetracycline exhibited the highest resistance rates, at 79 and 60% respectively, while cefixime and ceftriaxone had the lowest resistance rates at 0%. Conclusion Our findings indicate a high level of antibiotic resistance among the studied antibiotics. This high level of antibiotic resistance raises concerns and underscores the necessity for monitoring the use of antibiotics. Moreover, resistance to these antibiotics was more prevalent in samples isolated from animals compared to other sources. This highlights the importance of animal screening to detect the presence of drug-resistant isolates, with the ultimate goal of reducing antibiotic resistance and preventing the transmission of resistant strains to humans.


Introduction
Salmonellosis is one of the most common food-borne diseases worldwide, causing severe and occasionally deadly infections in humans (1).Based on published data, over 2,500 serotypes of Salmonella have been recognized, with 1,500 serovars linked to human and animal diseases (2).
Salmonella serovars have the ability to infect a diverse array of domestic animals such as sheep, cattle, poultry, and pigs.Infected animals may exhibit varying symptoms, varying from mild gastroenteritis to severe infections that can be fatal (3).Painter et al. ∼17.9% of foodborne illnesses are linked to poultry, with 19% of these poultry-related illnesses attributed to Salmonella enterica (3).
Non-typhoidal salmonellosis is an important enteric infection in humans, particularly in neonates and young children (4).e consumption of contaminated animal-derived foods such as beef, poultry, pork, and lamb is the major route of Salmonella transmission to humans (5).
Non-typhoidal Salmonella causes ∼153 million cases of gastroenteritis and 57,000 deaths annually worldwide (6).Salmonella Typhimurium has been reported as one of the most widespread foodborne pathogens in many countries (7).is serovar is the most common in Europe and can be isolated from humans, pigs, and pork.In the United States, it is one of ve serovars associated with human salmonellosis (7,8).
One of the recent global public health concerns regarding salmonellosis is the emergence and spread of resistant Salmonella strains, including multiple drug-resistant (MDR) strains in both humans and animals (9).
Antibiotics are not commonly used to treat human salmonellosis, as the illness typically resolves in 5-7 days without treatment (10).However, in some cases, antibiotic therapy may be necessary (10).In these instances, appropriate antimicrobial therapy such as cipro oxacin in adults and ceriaxone in children can be used (4,10).Nonetheless, treating these patients can sometimes be challenging due to antibiotic resistance of pathogen (11).
e use of antimicrobial agents in any environment creates pressures that favor the survival of antibiotic-resistant pathogens (12).e routine practice of administering antimicrobial agents to domestic livestock for disease prevention, treatment, and growth promotion is a signi cant factor in the emergence of antibioticresistant bacteria, which are subsequently transmitted to humans through the food chain (13,14).Most infections with antimicrobialresistant Salmonella are acquired by eating contaminated foods of animal origin (15).erefore, this meta-analysis was conducted to investigate the prevalence of antimicrobial resistance of S. Typhimurium isolates in Iran.Additionally, this study provides a better understanding of antibiotic resistance in this bacterium, ultimately helping to choose the most optimal and effective treatment approach.

FIGURE 1
The study Prisma flow diagram.

Search strategy
We conducted a comprehensive search in the PubMed, Web of Science, Scopus, and Scienti c Information Database (SID) databases up to December 2023 to identify potentially relevant studies.e search criteria used were ("Salmonella Typhimurium" OR "S.Typhimurium") AND (Resistan * OR suscep * ) AND (Iran) with their respective Mesh terms.

Inclusion and exclusion criteria
All original articles that reported the prevalence of antibiotic resistance among S. Typhimurium isolates in Iran were included.Articles were excluded if they were reviews, conference presentations, case reports, studies with unclear results, or written in languages other than English and Persian.

Data extraction
Aer consolidating the articles in the EndNote X20 Citation Manager Soware, duplicate articles were removed before the review process.e citations were then uploaded to Rayyan, a citation classi cation application (16).Two independent reviewers screened the titles and abstracts and removed irrelevant articles.e full texts of potentially relevant articles were collected and reviewed independently by two authors.Data from eligible studies, including the rst author, publication year, source of samples, sample size (total isolates and number of resistances of S. Typhimurium for various antibiotics), were independently extracted by two researchers.Inconsistencies between the reviewers were resolved through discussion to reach a consensus.
Quality assessment of studies e quality of the included studies was assessed using the Joanna Briggs Institute (JBI) checklist (17).Two reviewers independently evaluated and scored the quality of each article included in the review, resolving any disagreements through discussion.

Statistical analysis
e meta-analysis and generation of forest plots for this review were conducted using Stata 17 soware.e I-squared index (I 2 ) was used to assess the possibility of heterogeneity among studies, categorizing the degree of heterogeneity as low, moderate, or high based on I 2 -values (expressed as percentages around 25, 50, and 75, respectively).To evaluate publication bias, Egger and Begg tests were performed; a signi cance level of P < 0.05 indicated statistically signi cant publication bias.e pooled prevalence of S. Typhimurium resistance to the investigated antibiotics, along with corresponding 95% con dence intervals (CIs), was calculated using

Characteristics of the included studies
A total of 841 articles were obtained through a database search.Aer eliminating duplicates, 500 articles remained.Subsequently, 60 publications underwent full-text evaluation.As a result, 42 articles were excluded, and this study included 18 cross-sectional studies that examined the antibiotic resistance of S. Typhimurium (Figure 1).e characteristics of the included studies are presented in Table 1.Additionally, Table 2 contains the results of the quality assessment.

Prevalence of penicillin resistance
e susceptibility to piperacillin was determined in two studies.e prevalence of piperacillin resistance was 79% (95% CI: 70-87%).e susceptibility to ampicillin was determined in 10 studies.e prevalence of ampicillin resistance was 44% (95% CI: 21-68%) with substantial heterogeneity (I 2 = 91.65%,P < 0.01; Figure 3).Furthermore, subgroup meta-analysis of ampicillin resistance based on the source of S. Typhimurium isolation showed that the rate of ampicillin resistance in animal samples was 77% (95% CI: 7-100%), which was higher than in food and human sources (P < 0.01; Figure 4).

Prevalence of fluoroquinolones resistance
e susceptibility to nor oxacin was determined in six studies.e prevalence of nor oxacin resistance was 3% (95% CI: 0-35%) with substantial heterogeneity (I 2 = 93.89%,P < 0.01; Figure 5).e susceptibility to cipro oxacin was determined in ten studies.e prevalence of cipro oxacin resistance was 15% (95% CI: 1-38%) with substantial heterogeneity (I 2 = 91.14%,P < 0.01).Additionally, subgroup meta-analysis of cipro oxacin resistance based on the source of S. Typhimurium isolation showed that the rate of cipro oxacin resistance in animal samples was 20% (95% CI: 0-83%), which was higher than in food sources (P = 0.554; Figure 6).e susceptibility to nalidixic acid was determined in eight studies.e prevalence of nalidixic acid resistance was 46% (95% CI: 16-78%) with substantial heterogeneity (I 2 = 93.89%,P < 0.01).In addition, subgroup meta-analysis of nalidixic acid Youse -Mashouf and Moshtaghi (28 Mehrabian and Jaberi ( 29) Nazer and Safari (33 Total score is from 1 (lowest) to 9 (highest); Q = question; Y = Yes; N = No; U = Unclear.Q1: Was the sample frame appropriate to address the target population?Q2: Were study participants sampled in an appropriate way?Q3: Was the sample size adequate?Q4: Were the study subjects and the setting described in detail?Q5: Was the data analysis conducted with sufficient coverage of the identi ed sample?Q6: Were valid methods used for the identi cation of the condition?Q7: Was the condition measured in a standard, reliable way for all participants?Q8: Was there appropriate statistical analysis?Q9: Was the response rate adequate, and if not, was the low response rate managed appropriately?resistance based on the source of S. Typhimurium isolation showed that the rate of nalidixic acid resistance in animal samples was 90% (95% CI: 83-96%), which was higher than in food sources (P = 0.063; Figure 7).
Furthermore, a subgroup meta-analysis of gentamicin resistance based on the source of S. Typhimurium isolation indicated that the rate of gentamicin resistance in animal samples was 11% (95% CI: 0-47%), which was higher than that in food sources (P = 0.263; Figure 11).e susceptibility to streptomycin was determined in eight studies.e prevalence of streptomycin resistance was 27% (95% CI: 1-66%) with substantial heterogeneity (I 2 = 94.61%,P < 0.01).
Additionally, a subgroup meta-analysis of streptomycin resistance based on the source of S. Typhimurium isolation demonstrated that the rate of streptomycin resistance in animal samples was 48% (95% CI: 0-99%), which was higher than in food sources (P = 0.439; Figure 12).

Discussion
Recently, there have been reports of an increase in the prevalence of Salmonella strains that are resistant to antimicrobial agents (36).is surge in prevalence poses a signi cant public health concern (27).erefore, acquiring epidemiological information on drug resistance can assist physicians and healthcare professionals in selecting appropriate antimicrobials and averting treatment failure.Given that serovar Typhimurium is among the prevalent Salmonella serovars in numerous countries, we utilized a metaanalysis approach to gather pertinent published data on the antibiotic resistance patterns of S. Typhimurium isolates in Iran.
Our results showed that piperacillin, tetracycline, doxycycline, nalidixic acid, and ampicillin had the highest resistance rates in S. Typhimurium isolates in Iran, with 79, 60, 59, 46, and 44%, respectively.e high rate of antibiotic resistance for these antibiotics may be the result of improper use or misuse of these antibiotics in human clinical treatment and animal food production  (37).Improper use of antibiotics may lead to exposure of bacteria to antibiotics, which increases the possibility of antibiotic-resistant bacteria (12).In general, the increase in the antibiotic resistance levels of S. Typhimurium isolates may contribute to the further spread of the serovar (38), which highlights the importance of establishing targeted surveillance throughout the country to obtain more information about the antibiotic resistance of this bacterium in order to take appropriate measures to reduce its prevalence in different sources.
While ce xime, ceriaxone, imipenem, and nor oxacin antibiotics were the most effective against S. Typhimurium with  Forest plot showing the prevalence of ciprofloxacin resistance of S. Typhimurium in Iran from different sources.0, 0, 2, and 3% resistance, respectively.erefore, these drugs could be applied as treatment options against illness caused by this microorganism.
In a study conducted by Tai et al. on Salmonella samples isolated from raw meat in Vietnam, the highest antibiotic resistance observed in S. Typhimurium was against tetracycline (86.4%), followed by streptomycin (81.8%) and nalidixic acid (77.3%) (39).In a study by Zeng et al., S. Typhimurium isolated from human clinical samples in China showed the highest resistance to ampicillin (81.6%), cipro oxacin (81.6%), and tetracycline (82.4%) (40).ese ndings demonstrate the variation in S. Typhimurium resistance  across different countries, highlighting the importance of resistance screening in each nation.
In the meta-analysis, Tadesse et al. indicated that certain strains of Salmonella found in farm animals in Ethiopia exhibit resistance to drugs commonly used for treating human salmonellosis, posing a potential risk of human exposure to drug-resistant Salmonella (41).ung et al. conducted a study in Malaysia to investigate the presence of Salmonella, speci cally S. Enteritidis and S. Typhimurium, in uncooked chicken meat (42).eir analysis of 120 chicken meat samples revealed that the prevalence of Salmonella and S. Typhimurium was 20.80 and 2.50%, respectively.Notably, all isolates exhibited resistance to erythromycin, penicillin, and vancomycin, with relatively lower resistance rates observed for nalidixic acid (9.09%) and streptomycin (9.09%).e study 10.3389/fvets.2024.1388790ndings underscore the potential for chicken meat to serve as a reservoir of antibiotic-resistant Salmonella.Meanwhile, Talukder et al. conducted a meta-analysis focusing on the prevalence and antimicrobial resistance patterns of Salmonella strains isolated from human, animal, and environmental samples in South Asia (43).eir analysis revealed a lower prevalence of salmonella in humans (5.81%) compared to animals (22.66%) and the environment (27.81%).Salmonella strains displayed high resistance levels to nalidixic acid (74.25%) and tetracycline (37.64%), whereas lower resistance rates were observed for ceriaxone (1.07%) and ce xime  (1.24%).We categorized the origins of isolates into human, animal (such as poultry, livestock, and dogs), and food samples (including processed foods, meat, and eggs) for ampicillin, cipro oxacin, nalidixic acid, tetracycline, gentamicin, and streptomycin.In all these antibiotics, the level of resistance in the samples isolated from animals was higher than in other sources.is emphasizes the importance of animal screening to check for the presence of drug-resistant isolates and the signi cance of controlling antibiotic consumption in animals to reduce antibiotic resistance and prevent the transmission of resistant strains to humans.
In general, third-generation cephalosporins and uoroquinolones are considered the most effective and commonly used antibiotics for treating S. Typhimurium infections (44).e study ndings revealed that among third-generation cephalosporins, ce xime, and ceriaxone exhibited the lowest 10.3389/fvets.2024.1388790 Forest plot showing the prevalence of chloramphenicol resistance of S. Typhimurium in Iran.

FIGURE 14
Forest plot showing the prevalence of imipenem resistance of S. Typhimurium in Iran.levels of resistance, making them favorable treatment options for infections caused by this bacterium.Additionally, within the uoroquinolone class, nor oxacin demonstrated the least resistance compared to other antibiotics in this category, suggesting its potential as a treatment of choice for this bacterium in Iran.Furthermore, the resistance rate to imipenem in this bacterium was found to be 2%, indicating the potential usefulness of this antibiotic in managing MDR bacteria.
One limitation of the present study was the relatively high heterogeneity between studies.We employed subgroup analysis to identify sources of heterogeneity and mitigate its impact on the results.

Conclusion
A high level of resistance to most of the studied antibiotics was observed.e highest antibiotic resistance was observed against piperacillin, tetracycline, doxycycline, nalidixic acid, and ampicillin, while ce xime, ceriaxone, imipenem, and nor oxacin were the most effective treatment options for S. Typhimurium.Management and monitoring of antibiotic use, as well as screening to check the presence of drug-resistant isolates in animals, are recommended.

FIGURE 2 Forest
FIGURE 2Forest plot showing the prevalence of cephalosporin family resistance of S. Typhimurium in Iran.

FIGURE 3 Forest
FIGURE 3Forest plot showing the prevalence of penicillin family resistance of S. Typhimurium in Iran.

FIGURE 4 Forest
FIGURE 4Forest plot showing the prevalence of ampicillin resistance of S. Typhimurium in Iran from different sources.

FIGURE 5 Forest
FIGURE 5Forest plot showing the prevalence of fluoroquinolones family resistance of S. Typhimurium in Iran.

FIGURE 7 Forest
FIGURE 7Forest plot showing the prevalence of nalidixic acid resistance of S. Typhimurium in Iran from different sources.

FIGURE 8 Forest
FIGURE 8Forest plot showing the prevalence of tetracycline family resistance of S. Typhimurium in Iran.

FIGURE 9 Forest
FIGURE 9Forest plot showing the prevalence of tetracycline resistance of S. Typhimurium in Iran from different sources.

FIGURE 10 Forest
FIGURE 10Forest plot showing the prevalence of aminoglycoside family resistance of S. Typhimurium in Iran.

FIGURE 11 Forest
FIGURE 11Forest plot showing the prevalence of gentamicin resistance of S. Typhimurium in Iran from different sources.

FIGURE 12 Forest
FIGURE 12Forest plot showing the prevalence of streptomycin resistance of S. Typhimurium in Iran from different sources.

FIGURE 15 Forest
FIGURE 15Forest plot showing the prevalence of SXT resistance of S. Typhimurium in Iran.

TABLE 2
Quality score of included studies.