Free range environment in poultry farms, natural diet, and strict bio-security measures might cause the lower prevalence of Salmonella in organic poultry farms. However, the present study’s absence of Salmonella in farm environments might be caused by study design, as including some variables might play a crucial role and may result in different outcomes. Additionally good farm management, bio-security measures and external factors such as proximity to other farms might be potential confounders of not recovering Salmonella in the present study.Generic E. coli were prevalent in 50 out of 70 collected samples, being detected across all sample types except LH cage and egg swab samples. The population of generic E. coli and aerobic bacteria counts are shown in Table 2.1. Both E. coli and aerobic bacteria counts were lower in outwear and boots swabs compared to LH and FH fecal samples . However, both E. coli and aerobic bacteria counts for the FH door swab were not significantly different compared to outwear and boots swab counts . Generic E. coli counts were higher in the fecal samples collected from LH and FH compared to FH door swab samples . Similarly, aerobic bacteria counts were higher in fecal samples from both LH and FH followed by FH door swab samples and LH cage swab while egg swab samples had the lowest counts . Previous studies on E. coli prevalence from poultry farm environmental samples and worker’s samples varied . As mentioned before, the diverse prevalence of recovery of E. coli from farm environments depends on factors such as geographical location, heavy duty propagation trays scale of farms, antimicrobial usage and cleaning and sanitation practices on farms . Counts of E. coli in fecal samples in the present study were similar to the findings of previous studies .

Prior studies reported contaminations of egg surfaces with E. coli . In the present study, LH was cleaned frequently , which might be the reason for the lower bacterial load in LH and possibly caused not discovering E. coli in cage and egg swabs. Isolates from the FH door swab were resistant to 14 drugs, FH fecal sample isolates were resistant to 8 drugs, LH fecal sample isolates were resistant to 5 drugs, outwear swab isolates were resistantto 4 drugs, and of boots swab isolates were resistant to 2 drugs . The E. coli isolates from all types of samples were susceptible to amikacin, piperacillin / tazobactam constant 4, ticarcillin / clavulanic acid constant 2, ceftazidime, gatifloxacin, aztreonam, ciprofloxacin, imipenem, and piperacillin. The highest phenotypic resistance was observed for ampicillin , followed by nitrofurantoin and cefoxitin . A full antibiogram pattern of the antimicrobial susceptibility testing is presented in Table 2. Isolates of E. coli from FH door swabs and worker’s outwear swabs were resistant to the same drugs, such as ampicillin, nitrofurantoin, cefuroxime and trimethoprim/sulfamethoxazole . Isolates from all the environmental sample types and one isolate of boot swab samples were resistant to cefoxitin. All the environmental and worker’s sample types were resistant to ampicillin. Generic E. coli isolates from the FH door swab had a higher prevalence of resistance to at least one drug compared to isolates from the boot swabs . However, there was no difference in the occurence of resistance to at least one drug between the isolates from FH feces , LH feces and outwear swabs. Thirty five percent of all the tested generic E. coli isolates were resistant to at least one drug, nine percent to two drugs, and six percent of isolates were resistant to three or more antimicrobial drugs. Most prevalent non multi-drug resistant pattern was AMP-NIT . Four isolates from FH door swab samples were MDR, one isolate from LH fecal samples, and one outwear sample was MDR .

The present study observed the highest resistance in E. coli isolates for ampicillin and nitrofurantoin . However, these levels of resistance rates are not considered high resistance rate since, in the medical community the, resistance rates 20-30% above are considered as the highest level of resistance in bacteria that raise concern for public health. These antimicrobials are essential for veterinary and human medicine . The resistance prevalence to ampicillin was lower compared to other related previous studies. In most of these studies, the high resistance of ampicillin in E. coli was due to increased use of this prescription drug for treatment and ampicillin is a commonly prescribed antimicrobial to treat a wide range of infections worldwide . Besides, factors such as the horizontal transfer of resistance genes from other bacteria species to E.coli and the production of enzymes degrade or modify ampicillin might be possible reasons for the increased resistance to ampicillin in E. coli . Resistance rates of E. coli for nitrofurantoin in the present study were consistent with findings of previous occupational expose related studies in poultry farming . Nitrofurantoin is not widely used as ampicillin, only to treat urinary tract infections. Therefore, the low prevalence of antimicrobial resistance in E. coli in the present study and previous studies is an expected outcome. Our results showed a high prevalence of AMR in E. coli isolates from FH door swabs and fecal samples, suggesting that the FH environment might be a potential ARB or ARG reservoir and routes of exposure. Moreover, isolates from LH fecal samples and FH samples shared similar antimicrobial resistance patterns with worker’s outwear and boots sample isolates. Previous studies on occupational exposure of poultry farm workers to AMR concluded that ARB could be transmitted from the farm environments to workers . These previous studies compared antimicrobial resistance patterns in E. coli from environmental samples to worker’s urine or stool samples and found that resistance patterns were similar. Additionally, some studies found ARB or resistance genes in farm dust or hand-wash water on farms .

A study conducted in Tunisia reported that antimicrobial-resistant Campylobacter was found in 3% of chicken farm workers boot samples, but researchers did not recover the bacteria from worker’s outwear . To our best knowledge, the present study is the first study characterizing antimicrobial resistance patterns of E. coli in a poultry facility environment and comparing these patterns with farm worker’s outwear and footwear. The present study shows the importance of using personal protective equipment in reducing the spread of ARB or ARG from farm environments to workers. Additionally, the high prevalence of antimicrobial-resistant E. coli in door handles could suggest a potential risk of AMR transmission to farm workers. Because workers might touch their face or mouth after touching the door handles, we noticed that workers did not wear gloves, which might expose them to ARB. Therefore, wearing gloves and frequently sanitizing door handles is an important measure to minimize the risk of transmission of ARB or ARG, as bio-security measures have been proven to play a crucial role in minimize the transmission of pathogens in farms . Different sample matrices yield different prevalence outcomes. For example, fecal samples might have higher bacteria prevalence compared to surface swab samples, affecting overall prevalence significantly in a study. Additionally, in the present study, birds and workers did not receive antibiotics before and during the sample collection period, and consequently, overall resistance prevalence was low , and our results support the findings of Tang et al. where authors systematically reviewed 181 studies and found out that restriction of antimicrobials in food-producing animals are associated with reduced ARB in these animals. However, previous research has shown that ARB can still be present and transmitted in facilities with no antimicrobial drug use ; and our study found that the poultry facility might be a reservoir of AMR in which workers may be exposed to ARB. The present study cannot imitate intensive poultry production, vertical cannabis where antibiotics are usually used to prevent, control the disease, and treat birds. However, antibiotic usage in food animals in Western countries, including the U.S., has changed over the years. Implementing the Veterinary Feed Directive in the U.S. restricted certain antibiotics, and medically necessary antibiotics are allowed only with veterinary oversight and prescription. Additionally, there might be differences in population density and management practices between small-scale and intensive large-scale poultry production. In the U.S., a surveillance program, NARMS, was established in 1996 to monitor antimicrobial resistance in hospitals, retail meats, and food animals . However, currently, there is a lack of systematic surveillance of AMR in farmworkers. Additionally, there is a lack of awareness or education among the public and policymakers about the risks of AMR affecting farmworkers in livestock production . Moreover, a large body of previous and current AMR studies and regulatory efforts mainly focused on food safety from farm to retail and have considered pathogens as a food safety issue .

The above mentioned facts might explain the scarcity of research or data related to occupational exposure of animal farmworkers in the U.S. Therefore, more research is needed to identify possible ARB routes from the farm environment to workers in order to raise awareness of farmworkers and producers to avoid the risk of occupational exposure to AMR.The development of antibiotics in the 20th century was a groundbreaking advancement in medicine and one of the most significant advances in modern science . However, after a few decades, this great achievement has been compromised by the emergence and spread of antimicrobial resistance . AMR is the ability of microorganisms to protect themselves from the effects of antimicrobial agents via different mechanisms such as enzymatic inactivation, alteration of target sites, efflux pumps, reduced intake, horizontal gene transfer and formation of biofilms . Nowadays, AMR is a major global threat to public health . For example, AMR causes 2.6 million infections and 44,000 deaths each year in the U.S., while costing around 20 billion USD in healthcare and 35 billion USD in lost productivity annually . Overuse and misuse of antimicrobials in humand medine and food animal production have been considered as major contributors to the emergence of AMR around the globe. Moreover, the World Health Organization acknowledged the usage of antibiotics in food animal production as one of the leading causes of the development and spread of AMR . Many studies have shown the assosiation between the usage of antibiotics in food animal production and the emergence of Antimicrobial-resistant bacteria . ARB with their genetic determinants can be transmitted from food animal production to humans via various pathways such as direct contact with animals, environmental and air routes, cross-contamination, water and the food chain, and global trade . Among these transmission pathways, food chain is considered as critical. Previous studies documented that among animal food products, meat is a major reservoir of ARB and AMR in enteric bacteria such as Campylobacter, Eschericchia coli and Salmonella is a serious threat . Non-typhoidal Salmonella is a common and widespread pathogen that causes foodborne infections and outbreaks in the U.S. and around the world . AMR in Salmonella, especially multidrug resistance has become a serious health concern. For example, Salmonella resistance to critically important drugs such as extended spectrum cephalosporins, fluoroquinolones, and carbapenems limits treatment options and heightens the risk of morbidity and mortality among the patients to an estimated 40% . California is a highly populous and demographically diverse state in the U.S. with almost 40 million people which constitutes a major consumer market for retail meat products. Hence, research on the prevalence, distribution and AMR patterns of major foodborne pathogens such as Salmonella is integral to ensuring food safety and public health. The perpetual nature of bacterial populations to evolve over time highlights the importance of continuous monitoring of the trends of pathogens circulating in the food supply chain. Previously, we have characterized AMR of Salmonella from retail meat collected in California in 2018 . The aim of the current study was to characterize the AMR profiles of Salmonella isolated from retail meats in California using samples collected by NARMS routine surveillance in 2019. The specific objectives of the study were to assess the prevalence and phenotypic and genotypic AMR in various Salmonella serovars, to identify the resistance patterns of Salmonella, and to assess the correlation between Salmonella AMR phenotypes and genotypes.Fresh retail meat samples were collected twice a month from January to December 2019 as a part of the NARMS Retail Meat Surveillance. A total of 849 samples were purchased from randomly selected grocery stores in Northern and Southern California.