Widespread Multidrug Resistance of Arcobacter butzleri Isolated from Clinical and Food Sources in Central Italy

Abstract

The Arcobacter genus comprises a group of bacteria widely distributed in different habitats that can be spread throughout the food chain. Fluoroquinolones and aminoglycosides represent the most common antimicrobial agents used for the treatment of Arcobacter infections. However, the increasing trend of the antimicrobial resistance of this pathogen leads to treatment failures. Moreover, the test implementation and interpretation are hindered by the lack of reference protocols and standard interpretive criteria. The purpose of our study was to assess the antibiotic resistance pattern of 17 A. butzleri strains isolated in Central Italy from fresh vegetables, sushi, chicken breast, and clinical human samples to provide new and updated information about the antimicrobial resistance epidemiology of this species. Antimicrobial susceptibility testing was carried out by the European Committee on Antimicrobial Susceptibility Testing (EUCAST)'s disc diffusion method. All the strains were multidrug resistant, with 100% resistance to tetracyclines and cefotaxime (third generation cephalosporins). Some differences were noticed among the strains, according to the isolation source (clinical isolates, food of animal origin, or fresh vegetables), with a higher sensitivity to streptomycin detected only in the strains isolated from fresh vegetables. Our data, together with other epidemiological information at the national or European Union (EU) level, may contribute to developing homogeneous breakpoints. However, the high prevalence of resistance to a wide range of antimicrobial classes makes this microorganism a threat to human health and suggests that its monitoring should be considered by authorities designated for food safety.

Keywords: Arcobacter butzleri; chicken breast; disc diffusion method; fresh vegetables; human arcobacteriosis; multidrug resistance (MDR); sushi.

Figure 1

Prevalence of resistance to antimicrobials of all A. butzleri strains (n = 17). Resistant (red), intermediate resistant (yellow), or sensitive (green) strains to the antimicrobials tested. AMC: amoxicillin–clavulanic acid (30 μg); AMP: ampicillin (10 μg); TE: tetracycline (30 μg); CIP: ciprofloxacin (5 μg); E: erythromycin (15 μg); KF: cefalotin (30 μg); CTX: cefotaxime (30 μg); CN: gentamicin (10 μg); NA: nalidixic acid (30 μg); S: streptomycin (10 μg).

Figure 2

Resistance patterns of the tested strains (n=17) according to their origin. Resistant (red), intermediate resistant (yellow), or sensitive (green) strains to the antimicrobials tested. AMC: amoxicillin–clavulanic acid (30 μg); AMP: ampicillin (10 μg); TE: tetracycline (30 μg); CIP: ciprofloxacin (5 μg); E: erythromycin (15) μg; KF: cefalotin (30μg); CTX: cefotaxime (30 μg); CN: gentamicin (10 μg); NA: nalidixic acid (30 μg); S: streptomycin (10 μg).

Figure 3

Distribution of the inhibition zone diameter in the different classes of antimicrobials obtained through the AST on the A. butzleri strains investigated (n = 17). The dotted lines represent breakpoints according to EUCAST [52] or BSAC [53]. Only for CIP and CN, two dotted lines are reported to indicate the intermediate resistance and the resistance cutoff values. Resistant (red), intermediate resistant (yellow), or sensitive (green) strains to the antimicrobials tested. (A) Penicillins: AMC: amoxicillin–clavulanic acid (30 μg) and AMP: ampicillin (10 μg); (B) Tetracyclines: TE: tetracycline (30 μg); (C) Floroquinolones: CIP: ciprofloxacin (5 μg) and NA: nalidixic acid (30 μg); (D) Cephalosporins: KF: cefalotin (30 μg) and CTX: cefotaxime (30 μg); (E) Macrolides: E: erythromycin (15 μg); (F) Aminoglycosides: CN: gentamicin (10 μg) and S: streptomycin (10 μg).