Antibiotic susceptibility pattern of Campylobacter sp. isolated from human stool samples including comparison of ellipsoid test and broth microdilution for meropenem

Abstract

Foodborne campylobacteriosis is the most common cause of bacterial gastroenteritis in Germany. Due to increasing antibiotic resistance in Campylobacter, data of isolates of human origin are published by the European Center for Disease Control and Prevention (ECDC)/European Food Safety Authority (EFSA). However, data on susceptibility to meropenem, an antibiotic of last resort, is not included. Therefore, the minimal inhibitory concentration (MIC) for meropenem was measured in 125 Campylobacter jejuni (Cj) and 57 Campylobacter coli (Cc) isolates isolated from human stool samples between 2020 and 2023, comparing ellipsoid test and broth microdilution. Additionally, we determined the susceptibility of 249 Cj and 84 Cc strains isolated between 2018 and 2023 to erythromycin, ciprofloxacin and oxytetracycline by disk diffusion according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST). For meropenem, the MIC results of 5% Campylobacter isolates were interpreted as resistant. Erythromycin resistance was found in none Cj versus 9 (11%) Cc isolates that were resistant to all three substances. Ciprofloxacin and oxytetracycline resistance were detected in 72 and 41% Cj, and 67 and 70% Cc isolates, respectively. Only 24% Cj and 13% C c isolates were susceptible to all three substances. The dual resistance of ciprofloxacin and oxytetracycline was the most common resistance pattern, observed in 37% Cj and 38% Cc isolates, respectively. None of the isolates was resistant to all four tested substances. Our data underline the need for susceptibility testing of Campylobacter to alternatively used antimicrobial substances in clinical laboratories. The ellipsoid test provides a good alternative for meropenem MIC testing, although borderline isolates should be confirmed using microdilution.

Keywords: Campylobacter; meropenem; resistance; susceptibility testing.

Table 1. Major and very major errors, categorical agreement and Cohen’s Kappa for the interpretation as sensitive or resistant for the determination of meropenem MIC by ellipsoid test compared to broth microdilution of Campylobacter jejuni and coli

Table 2. Essential agreement for ellipsoid test compared to broth microdilution (reference) for determination of meropenem MIC by ellipsoid test compared to broth microdilution of Campylobacter jejuni and coli

Table 3. Distribution of single and combined resistance of C. jejuni and C. coli isolates to erythromycin, ciprofloxacin and oxytetracycline

Figure 1. Numbers of stool samples and annual detection rates of Campylobacter spp. during the observation period 2018 to 2023 in comparison to previous years from the laboratory of the TLV

* Species not specified

Figure 2. Meropenem MIC distribution in Thuringian Campylobacter jejuni and Campylobacter coli isolates between 2020 and 2023. MIC was determined using the ellipsoid test.

Figure 3. Resistances of Campylobacter jejuni and Campylobacter coli isolates to erythromycin (ERY), ciprofloxacin (CIP), and oxytetracyclin (OTC): (A) Thuringian human isolates collected between 2018 and 2023; (B) Resistance data of German human Campylobacter isolates adapted from the ECDC/EFSA “European Union Summary Report on Antimicrobial Resistance in zoonotic and indicator bacteria from humans, animals and food 2021 to 2022” [7]; (C) Resistance data of European human Campylobacter isolates adapted from the ECDC/EFSA Report [7]; (D) Combined resistance data of German isolates from animal origin adapted from the BVL Zoonoses Monitoring Reports 2021 and 2022 [2], [3]

* Consisting of 120 broiler isolates, 140 turkey isolates, 3 pig isolates and 133 calve/heifer isolates ** Consisting of 31 broiler isolates, 148 turkey isolates, 258 pig isolates and 41 calve/heifer isolates