An in vitro method for determining Helicobacter pylori in a biological sample isolated from an individual and for determining the resistance of said Helicobacter pylori to clarithromycin, said method comprising the steps of: I. Purifying (isolating) the DNA from a faecal sample isolated from an individual; and II. Amplifying at least one portion of at least one gene of Helicobacter pylori comprising at least one mutation site responsible for the resistance to clarithromycin, said amplification being performed by real-time PCR using at least one pair of oligonucleotides (pair of primers) and at least two oligonucleotide probes, where the pair of primers hybridizes in the DNA region straddling said mutation site and where each oligonucleotide probe is marked at the 5' and 3' ends with two different marker, and wherein at least one oligonucleotide probe is complementary and specific to at least one gene portion of the wild-type allele of said gene and at least one oligonucleotide probe is complementary and specific to at least one gene portion of the mutated allele of said gene responsible for said antibiotic resistance; - III. Quantifying the amplified wild-type and/or mutated DNA by measuring, preferably at the PCR cycle threshold, the levels of the marker with which said oligonucleotide probes are marked, where the presence of only the marker with which the probe complementary and specific to the at least one gene portion of the wild-type allele is marked defines a normal homozygous genotype and thus the presence of said Hp which is not resistant to clarithromycin; the presence of only the marker with which the probe complementary and specific to the at least one gene portion of the mutated allele of said gene is marked defines a mutated homozygous genotype and hence the presence of said Hp resistant to clarithromycin; and the presence of both markers defines a heterozygous genotype with a wild-type allele and a mutated allele of said gene, and thus the presence of said Hp resistant to clarithromycin, wherein said mutation is selected from: A2143G, A2142C and A2142G for the 23S rRNA gene. I. Purifying (isolating) the DNA from a faecal sample isolated from an individual; and II. Amplifying at least one portion of at least one gene of Helicobacter pylori comprising at least one mutation site responsible for the resistance to clarithromycin, said amplification being performed by real-time PCR using at least one pair of oligonucleotides (pair of primers) and at least two oligonucleotide probes, where the pair of primers hybridizes in the DNA region straddling said mutation site and where each oligonucleotide probe is marked at the 5' and 3' ends with two different marker, and wherein at least one oligonucleotide probe is complementary and specific to at least one gene portion of the wild-type allele of said gene and at least one oligonucleotide probe is complementary and specific to at least one gene portion of the mutated allele of said gene responsible for said antibiotic resistance; - III. Quantifying the amplified wild-type and/or mutated DNA by measuring, preferably at the PCR cycle threshold, the levels of the marker with which said oligonucleotide probes are marked, where the presence of only the marker with which the probe complementary and specific to the at least one gene portion of the wild-type allele is marked defines a normal homozygous genotype and thus the presence of said Hp which is not resistant to clarithromycin; the presence of only the marker with which the probe complementary and specific to the at least one gene portion of the mutated allele of said gene is marked defines a mutated homozygous genotype and hence the presence of said Hp resistant to clarithromycin; and the presence of both markers defines a heterozygous genotype with a wild-type allele and a mutated allele of said gene, and thus the presence of said Hp resistant to clarithromycin, wherein said mutation is selected from: A2143G, A2142C and A2142G for the 23S rRNA gene.