Antimicrobial susceptibility pattern of Helicobacter suis strains

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Bacterial Pathogenesis

Background:

• Helicobacter suis is a difficult-to-culture gastric pathogen in pigs, posing zoonotic risks.
• Standard antimicrobial susceptibility testing methods are unsuitable for H. suis due to its fastidious growth requirements and acidic pH preference.

Purpose of the Study:

• To develop and validate a novel in vitro assay for determining the antimicrobial susceptibility of Helicobacter suis isolates.
• To evaluate the activity of nine different antimicrobial agents against H. suis.

Main Methods:

• A combined agar and broth dilution method was employed for antimicrobial susceptibility testing.
• Microaerobic incubation for 48 hours followed by software-assisted calculation of bacterial growth to determine minimal inhibitory concentrations (MICs).

Main Results:

• The developed assay successfully determined MICs for nine H. suis isolates against nine antimicrobial agents.
• A bimodal distribution of enrofloxacin MICs was observed, indicating acquired resistance in one isolate.
• The resistant H. suis strain exhibited an AGT→AGG substitution at codon 99 of the gyrA gene.

Conclusions:

• The novel assay is suitable for assessing the antimicrobial susceptibility of H. suis.
• Enrofloxacin resistance can emerge in H. suis, linked to specific gyrA mutations.
• The activity of acid-sensitive antimicrobials against H. suis may be underestimated by standard MIC endpoints.