Antimicrobial Resistance in Swiss Laying Hens, Prevalence and Risk Factors

Evolution of the Antibiotic Resistance Levels, Multi-Resistance Patterns, and Presence of Antibiotic Resistance Genes in E. coli Isolates from the Feces of Breeding Hens during the Rearing Period

The food chain acts as an entry point for antibiotic resistance to reach humans and environment. Because of the importance of the poultry sector, we investigated the prevalence and evolution of antibiotic resistance in Escherichia coli isolates from a series of 14,500 breeding hens and their farm environment during the rearing period. Samples included meconium from one-day-old breeders and fecal samples and boot swabs from the breeding sheds of pullets and adult hens. All E. coli isolates from one-day-old chicks, 77% from feces and 61% from boot swabs, were resistant to at least one antibiotic. Cefotaxime and multi-drug resistance in fecal isolates decreased during the rearing period from 41.2% and 80.8% in one-day-old chicks to 3.8% and 33.8% in adults. All genes studied were detected in E. coli from feces and boot swabs, the most common being blaTEM (75%), blaSHV (72%), and qnrB (67%). blaCMY-2 was detected in 100% of one-day-old breeders. The combination of at least one cephalosporin and one quinolone resistance gene was detected in 68.7% of fecal and boot swab isolates. Our results highlight the need to monitor the prevalence of antibiotic resistance on farms and to take appropriate measures to reduce the risk to public and environmental health.

Dosage Optimisation of Trimethoprim and Sulfamethoxazole for the Treatment of an Avian Pathogenic Strain of Escherichia coli in Broiler Chickens

Based on pharmacokinetic studies carried out according to the methodologies defined by the European Medicines Agency (EMA) using mass spectrometry analysis, a new formulation of a veterinary drug for the treatment of broiler chickens is proposed. Currently, the traditional trimethoprim-sulfamethoxazole drug used for broilers is applied in a 1:5 ratio, and the recommended dose is 45 mg kg-1 of live weight administered at 24 h intervals for 3 to 5 days. In this study, we propose a novel combination containing similar active substances in a newly established ratio of 1:4, with a recommended dosage of 20 mg kg-1 of live weight administered at 24 h intervals for 3 to 5 days. With this method, the currently recommended dose of the traditional trimethoprim-sulfamethoxazole drug used for broilers can be reduced by more than half. The efficacy of the newly designed formulation and dosage of the drug was verified in a bioassay for the treatment of broilers experimentally infected with an avian pathogenic strain of Escherichia coli. In the experiment, we compared the newly designed dosage with the traditional dosage in terms of efficacy and dosage. There were no statistically significant differences between the two drugs in efficacy regarding the survival of chickens after experimental infection or changes in their health status. The experimental results suggest that a significant reduction in the recommended daily dose of drugs containing trimethoprim and sulfamethoxazole for the treatment of bacterial infections in broilers is possible and can support the prudent use of antimicrobials, including the limitation of their overuse.

Pathotypes and Phenotypic Resistance to Antimicrobials of Escherichia coli Isolates from One-Day-Old Chickens

The aim of this work was to describe the pathotypes of Escherichia coli strains isolated from one-day-old chickens, as well as the occurrence of resistance and multidrug resistance (MDR) in these strains. A total of 429 mixed swabs from 4290 one-day-old chicks were examined between August 2021 and July 2023 (24 months) during routine point-of-destination inspections at 12 poultry farms in the Czech Republic. All samples were processed via cultivation methods using meat-peptone blood agar and Mc Conkey agar under aerobic conditions at 37 ± 1 °C for 18-24 h. The identification of the strains was performed using MALDI-TOF mass spectrometry. All confirmed strains of E. coli were screened via single or multiplex PCRs for the presence of genes encoding the virulence-associated factors iroN, cvaC, iss, felA, iutA, frz and tsh. Antimicrobial susceptibility tests were performed using the minimal inhibitory concentration (MIC) method, focusing on ampicillin, cefotaxime, tetracycline, doxycycline, enrofloxacin, florfenicol, amoxicillin with clavulanic acid and trimethoprim with sulfamethoxazole. A total of 321 E. coli strains (prevalence of 74.8%) were isolated, and 300 isolates were defined as avian pathogenic strains of E. coli (APEC) via multiplex PCR. Based on the defined virulence genes, the isolates were classified into 31 pathotypes. A total of 15.9% of the tested isolates were susceptible to all the tested antimicrobials. On the other hand, 20.5% of the isolates were identified as multidrug-resistant (8.7% of isolates were resistant to three antimicrobials, 7.3% to four antimicrobials, 3.6% to five antimicrobials and 0.9% to six antimicrobials). Monitoring pathogenic strains of E. coli in different animals and in the environment makes it possible to understand their spread in animal and human populations and, at the same time, reveal the sources of virulence and resistance genes.

Pseudomonas aeruginosa infection of avian origin: Zoonosis and one health implications

Zoonotic diseases are diseases that are transmitted from animals to humans and vice versa. Pseudomonas aeruginosa (P. aeruginosa) is a pathogen with zoonotic nature. Commercial poultry could be infected with P. aeruginosa, especially at young ages with great losses. Infection of embryos with P. aeruginosa induced death in the shell, while infection of chicks led to septicemia, respiratory and enteric infections, and high mortality. Humans are also highly susceptible to P. aeruginosa infection, and the disease is associated with severe lung damage, especially in immunocompromised patients. Chicken carcass and related poultry retail products play an important role in the transmission of P. aeruginosa to humans, especially after processing in abattoirs. Treatment of P. aeruginosa infection is extremely difficult due to continuous development of antibiotic resistance. The transfer of antibiotic-resistant genes from poultry products to humans creates an additional public health problem. Accordingly, this study focused on avian pseudomonad, especially P. aeruginosa, with respect to infection of poultry, transmission to humans, and treatment and antibiotic resistance.

Prevalence, Persistence, and Antimicrobial Resistance of Campylobacter spp. from Eggs and Laying Hens Housed in Five Commercial Housing Systems

Husbandry practices for laying hens in commercial egg production is a topic of interest from a social, economic, and regulatory standpoint. Animal welfare concerns regarding the use of conventional cages have arisen and consumer perceptions of hen welfare have led to a higher demand for cage-free eggs. The aim of this study was to assess the impact of housing systems on prevalence, persistence, and antimicrobial resistance (AMR) of Campylobacter from laying hens and shell eggs. A total of 425 samples were collected over a 10-month period from the North Carolina Layer Performance and Management Test and Campylobacter isolates were identified by serological, biochemical, and molecular tests. Genetic variability was evaluated using pulsed-field gel electrophoresis (PFGE) and AMR testing was performed. Prevalence of Campylobacter spp. ranged from 11.1% in the enrichable cages to 19.7% in the conventional systems. A greater prevalence of Campylobacter was found in the fecal swab samples from free-range birds compared with those of birds housed in the more intensive housing systems (p > 0.05). Overall, 72 isolates were confirmed as Campylobacter spp. by PCR. More than 90% of the isolates (n = 66) were identified as Campylobacter jejuni, followed by Campylobacter coli (n = 6). C. jejuni isolates displayed high levels of resistance to tetracycline (67%). Genetic variability of Campylobacter was high, with more than 20 PFGE patterns identified. Pattern "a" comprised 42% of isolates from all housing systems and was also the most persistent. This study suggests that housing systems of laying hens used for commercial shell egg production may impact the rate of Campylobacter shedding by layers. Isolation rates and tetracycline resistance levels of this pathogen are still of concern, emphasizing the need for well-implemented biosecurity measures on the farm.

Colistin use and colistin resistance in bacteria from animals

Colistin has been used in veterinary medicine for decades, mainly for the prevention and treatment of Enterobacteriaceae infections. However, data regarding colistin resistance in bacteria from animals and food of animal origin are relatively scarce, partly because there are methodological difficulties hampering the analysis of susceptibility to colistin. Most data regarding clinical isolates are related to enteropathogenic Escherichia coli and Salmonella. The resistance percentages are sometimes high for pathogenic strains, and the mcr-1 gene has been detected in pathogenic E. coli isolates from pigs, cattle and poultry in different countries. The prevalence of colistin resistance in Salmonella from healthy animals is usually low but depends on the proportion of intrinsically colistin-resistant serotypes. For indicator E. coli, the resistance levels are often very low, although higher levels have been observed in Asia. The mcr-1 gene has been detected in indicator E. coli from pigs, cattle, poultry and their products. Thus, there is an urgent need to re-assess the use of colistin in livestock throughout the world to ensure a global strategy for preserving this last-resort antimicrobial.

Susceptibility of avian pathogenic Escherichia coli from laying hens in Belgium to antibiotics and disinfectants and integron prevalence

Avian pathogenic Escherichia coli (APEC) causes huge annual losses in the poultry industry worldwide. Multiresistance against antibiotics of APEC strains is increasingly seen in broilers, although much is still unknown about strains from laying hens where use of antibiotics is limited. Disinfection can reduce the infection burden. However, little is known about the presence of resistance against these products. Ninety-seven APEC strains were isolated from Belgian laying hens. The resistance to different classes of antibiotics was determined as well as the minimum inhibitory concentrations (MIC; agar and broth dilution) and minimum bactericidal concentrations (MBC) of five disinfectants most often used in the poultry industry (formaldehyde, glutaraldehyde, glyoxal, hydrogen peroxide, and a quaternary ammonium compound). The presence of integrons was determined by PCR Resistance to ampicillin (35.1%), nalidixic acid (38.1%), sulfonamides (SULFA, 41.2%), and tetracycline (TET, 53.6%) was high but resistance to other tested antibiotics was low. Nevertheless, two extended spectrum beta-lactamase producers were found. The MIC of the disinfectants for the APEC strains showed a Gaussian distribution, indicating that there was no acquired resistance. MBCs were similar to MICs via the broth dilution method, showing the bactericidal effect of the disinfectants. Twenty-one strains (21.6%) were found positive for class 1 integrons and a positive association between integron presence and resistance to trimethoprim, SULFA, and TET was found. No association could be found between integron presence and phylogenetic group affiliation. Susceptibility of APEC strains from laying hens to antibiotics is, in general, very high. Phenotypic resistance to commonly used disinfectants could not be found, indicating that the current use of disinfectants in the laying hen industry did not select for resistance.

Comparison of antimicrobial resistance patterns in enterococci from intensive and free range chickens in Australia

Resistance to antimicrobials in enterococci from poultry has been found throughout the world and is generally recognized as associated with antimicrobial use. This study was conducted to evaluate the phenotypic and genotypic profile of enterococcal isolates of intensive (indoor) and free range chickens from 2008/09 and 2000 in order to determine the patterns of antimicrobial resistance associated with different management systems. The minimum inhibitory concentrations in faecal enterococci isolates were determined by agar dilution. Resistance to bacitracin, ceftiofur, erythromycin, lincomycin, tylosin and tetracycline was more common among meat chickens (free range and intensive) than free range egg layers (P<0.05). Isolates were evaluated by polymerase chain reaction for bacitracin (bcrR), tylosin (ermB), tetracycline (tet(L), tet(M), tet(O), tet(S), and tet(K)), gentamicin (aac6-aph2), vancomycin (vanC and vanC2), ampicillin (pbp5) and integrase (int) genes. Resistance to bacitracin, erythromycin and tetracycline were found to be correlated with the presence of bcrR, ermB, and tet genes in most of the isolates collected from meat chickens. Most bacteria encoding ermB gene were found to express cross-resistance to erythromycin, tylosin and lincomycin. No significant difference was found in these resistance genes between isolates sampled in 2000 and 2008/09 (P<0.5). Unlike the enterococcal strains sampled in 2000, the 2008/09 isolates were found to be susceptible to vancomycin and virginiamycin. This study provides evidence that, despite strict regulation imposed on antibiotic usage in poultry farming in Australia, antimicrobial resistance is present in intensively raised and free range meat chickens.