IN ANIMAL HEALTH

Annet Heuvelink1*, Jobke van Hout1, Thijs Derkman1, Marieke Augustijn1, Els Broens2, Maaike Gonggrijp1 1Royal GD, Deventer, the Netherlands, 2Utrecht University, Utrecht, the Netherlands, * Presenting author

Assessing the representativeness and reliability of antimicrobial sensitivity testing (AST) results available for Salmonella Dublin (SDU) and Salmonella Typhimurium (STY) from clinical samples from Dutch veal calves.

Methods

Conclusions

The low number of isolates does lead to less representative and reliable AST results. Therefore, effort should be made to increase the number of isolates from veal calves.

AST results (Minimal Inhibitory Concentrations (MICs)) and additional data (e.g., location of the farm and the associated veterinary practice) were extracted from the Laboratory Information Management System of Royal GD, from 2016 - 2020. After validation of the data, multilevel mixed-effects logistic regressions were carried out (STATA 15.1) to study associations between AST results and different parameters.

Results

Low numbers of isolates

• After validation of the data, 202 unique SDU and 316 STY isolates remained available for analyses (Table 1).

• Because of the relatively low numbers of SDU and STY, the determined resistance percentages were less precise, especially when results of only one year were presented, with 95% confidence intervals ranging up to 30%.

• The number of STY isolates even decreased during the study period.

Positive trend antimicrobial susceptibility

• The MIC distributions for SDU and STY are shown in Table 2.

• Results showed a positive trend for antimicrobial susceptibility of SDU and STY from 2016 to 2020, with decreasing odds for resistance for the majority of included antimicrobials.

Antimicrobial Salmonella Dublin 2016 − 2020 (n=202) Salmonella Typhimurium 2016 − 2020 (n=316) MIC values (µg/mL) MIC50 MIC90 S R R CI MIC values (µg/mL) MIC50 MIC90 S R R CI 0.25 0.5 1 2 4 8 16 32 64 128 (μg/ mL) (μg/ mL) (%) (%) (%) 0.25 0.5 1 2 4 8 16 32 64 128 (μg/mL) (μg/mL) (%) (%) (%) Ampicillin 3.5 51.0 21.8 4.0 0.5 0.0 0.0 0.0 19.3 0.5 >32 80.7 19.3 14.1-25.4 0.0 5.1 41.1 7.0 0.6 0.0 0.0 0.3 45.9 2 >32 53.8 46.2 40.6-51.9 Apramycin 100.0 0.0 0.0 ≤8 ≤8 - - - 99.7 0.3 0.0 ≤8 ≤8 - -Cefepime 99.5 0.5 0.0 0.0 0.0 0.0 0.0 ≤1 ≤1 99.5 0.5 0.0-2.7 100.0 0.0 0.0 0.0 0.0 0.0 0.0 ≤1 ≤1 100.0 0.0 0.0-1.2 Cefotaxime 100.0 0.0 0.0 0.0 ≤1 ≤1 100.0 0.0 0.0-1.8 99.7 0.3 0.0 0.0 ≤1 ≤1 99.7 0.3 0.0-1.8 Colistin 1.0 13.9 10.9 73.3 0.5 0.0 0.5 4 4 99.5 0.5 0.0-2.7 76.6 20.3 2.5 0.3 0.0 0.0 0.3 ≤0.5 1 - -Enrofloxacin 99.5 0.5 0.0 0.0 0.0 ≤0.25 ≤0.25 - - - 97.8 0.6 0.6 0.9 0.0 ≤0.25 ≤0.25 - -Florfenicol 23.3 54.0 3.5 19.3 4 >8 - - - 1.9 54.1 2.5 41.5 4 >8 - -Flumequine 95.5 0.5 2.0 2.0 0.0 ≤2 ≤2 95.5 4.5 2.1-8.3 96.8 0.3 0.9 1.6 0.3 ≤2 ≤2 96.8 3.2 1.5-5.7 Gentamicin 83.7 1.0 1.5 13.9 ≤2 >8 84.7 15.3 10.7-21.1 67.4 0.3 3.2 29.1 ≤2 >8 67.7 32.3 27.2-37.7 Neomycin 93.6 0.0 0.5 5.9 ≤4 ≤4 93.6 6.4 3.5-10.8 94.9 0.3 0.3 4.4 ≤4 ≤4 94.9 5.1 2.9-8.1 Streptomycin 15.8 28.2 31.2 4.5 1.5 0.0 18.8 8 >64 79.7 20.3 15.0-26.5 1.6 2.8 3.2 2.2 5.7 27.5 57.0 >64 >64 9.8 90.2 86.4-93.2 Tetracycline 0.5 8.4 62.9 6.4 0.0 0.0 0.0 21.8 1 >16 78.2 21.8 16.3-28.1 0.0 0.0 3.5 1.9 0.6 0.0 1.9 92.1 >16 >16 6.0 94.0 90.8-96.3 Trim/Sulfaa 79.2 1.0 0.0 0.0 0.0 19.8 ≤0.25 >4 80.2 19.8 14.5-26.0 80.7 5.7 0.0 0.0 0.0 13.6 ≤0.25 >4 86.4 13.6 10.0-17.9

Representativeness a.heuvelink@gdanimalhealth.com www.gdanimalhealth.com

• The distribution of SDU and STY isolates across the Netherlands was similar to the population density of veal calves (Figure 1).

• The individual provinces did not have significant different odds for isolates being resistant.

• Isolates originating from farms associated with the same veterinary practice were more alike than isolates originating from farms associated with different veterinary practices.

Funding by The Netherlands Organisation for Health Research and Development (ZonMw); Dossier number: 541003007.