Antimicrobial susceptibility pattern of Helicobacter suis isolates from pigs and macaques. Antimicrobial susceptibility pattern of Helicobacter suis

Helicobacter suis colonizes the stomach of pigs, humans, and non-human primates. Infection in humans has been associated with gastritis, peptic ulceration, and low-grade mucosa-associated lymphoid tissue lymphoma, which are generally treated with a combination of a proton pump inhibitor and 2 or 3 antibiotics. However, few data is available on the antimicrobial susceptibility and prevalence of acquired resistance of H. suis isolates. Moreover, since H. suis only grows in a biphasic medium with an acidic pH, standard assays cannot be used to determine antimicrobial susceptibility. Here, we determined the antimicrobial susceptibility of a collection of H. suis isolates from pigs and non-human primates. A combined agar and broth dilution method was used to analyze the activity of 15 antimicrobial agents against 20 and 15 H. suis isolates obtained from pigs and macaques, respectively. After 48h microaerobic incubation, minimal inhibitory concentrations (MICs) were determined by software-assisted calculation of bacterial growth as determined by quantitative real-time PCR.A monomodal distribution of MICs was seen for β-lactam antibiotics, macrolides, gentamicin, neomycin, doxycycline, metronidazole, and rifampicin. Presence of a bimodal distribution of MICs indicated that 2 porcine isolates did not belong to the wild type population for fluoroquinolones. This was also the case for 1 porcine isolate for tetracycline, 1 porcine and 2 primate isolates for lincomycin, and 1 primate isolate for spectinomycin. MICs of ampicillin and tetracyclines (i.e. tetracycline and doxycycline) were higher for porcine H. suis isolates compared to primate isolates. Single nucleotide polymorphisms (SNPs) were present in the gyrA gene of the 2 H. suis isolates not belonging to the wild type population for fluoroquinolones and in ribosomal protein genes of the porcine and primate H. suis isolate not belonging to the wild type population for tetracycline and spectinomycin, respectively. SNPs were also detected in penicillin binding protein and ribosomal protein genes of porcine H. suis isolates with higher MICs of ampicillin and tetracyclines (i.e. tetracycline and doxycycline) compared to primate H. suis isolates, respectively. This study indicates that acquired resistance occasionally occurs in H. suis isolates. For treatment of H. suis infections, potential acquired resistance to fluoroquinolones, spectinomycin, lincomycin, and tetracycline should be taken into consideration. The clinical significance of higher MICs of ampicillin and tetracyclines in porcine isolates is not yet clear.