Siamak P Yazdankhah

Publications (10)26.17 Total impact

• Article: A New Rapid, On-Site Test for Detection and Major Classification of Bacteria in Milk from Cows with Moderate and Severe Clinical Mastitis

  Bjørn V Herikstad, Henning Sørum, Hans Jørgen S Larsen, Guro Dagfinrud, Ellen A Høegh, Geir Gogstad, Siamak P Yazdankhah
  Acta Veterinaria Scandinavica 04/2012; 44:1-1. · 1.00 Impact Factor
• Article: Development of a Rapid Method for Detection of Gram-Positive and -Negative Bacteria in Milk from Cows with Severe and Moderate Clinical Mastitis

  Siamak P Yazdankhah, Henning Sørum, Hans Jørgen S Larsen, Geir Gogstad
  Acta Veterinaria Scandinavica 04/2012; 44:1-2. · 1.00 Impact Factor
• Article: Does the wide use of quaternary ammonium compounds enhance the selection and spread of antimicrobial resistance and thus threaten our health?

  Kristin Hegstad, Solveig Langsrud, Bjørn Tore Lunestad, Anne Aamdal Scheie, Marianne Sunde, Siamak P Yazdankhah
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  ABSTRACT: Quaternary ammonium compounds (QACs) are widely used biocides that possess antimicrobial effect against a broad range of microorganisms. These compounds are used for numerous industrial purposes, water treatment, antifungal treatment in horticulture, as well as in pharmaceutical and everyday consumer products as preserving agents, foam boosters, and detergents. Resistance toward QACs is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as modifications in the membrane composition, expression of stress response and repair systems, or expression of efflux pump genes. Development of resistance in both pathogenic and nonpathogenic bacteria has been related to application in human medicine and the food industry. QACs in cosmetic products will inevitably come into intimate contact with the skin or mucosal linings in the mouth and thus are likely to add to the selection pressure toward more QAC-resistant microorganisms among the skin or mouth flora. There is increasing evidence of coresistance and cross-resistance between QACs and a range of other clinically important antibiotics and disinfectants. Use of QACs may have driven the fixation and spread of certain resistance cassette collectors (class 1 integrons), currently responsible for a major part of antimicrobial resistance in gram-negative bacteria. More indiscriminate use of QACs such as in cosmetic products may drive the selection of further new genetic elements that will aid in the persistence and spread of antimicrobial resistance and thus in limiting our treatment options for microbial infections.
  Microbial drug resistance (Larchmont, N.Y.) 04/2010; 16(2):91-104. · 1.99 Impact Factor
• Article: Variable number tandem repeat typing of bacteria.

  Siamak P Yazdankhah, Bjørn-Arne Lindstedt
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  ABSTRACT: Analysis of bacterial genomes revealed a high percentage of DNA consisting of repeats, in which DNA motifs existed in multiple copies. Study of these DNA motifs has resulted in the development of variable number tandem repeat (VNTR) or multilocus variant-repeat analysis (MLVA) assays, which have shown to be valuable bacterial typing methods, especially in relation to disease outbreaks. The VNTR-based assay is based on direct PCR amplification of a specific locus, which is well defined. The range and polymorphism index of each locus can be calculated. This chapter describes the VNTR analysis of Neisseria meningitides-based on separation in low resolution media agarose, and VNTR analysis of Salmonella enterica subsp. enterica serovars Typhimurium-based on high resolution capillary electrophoresis.
  Methods in molecular biology (Clifton, N.J.) 02/2007; 396:395-405.
• Article: Fusidic acid resistance, mediated by fusB, in bovine coagulase-negative staphylococci.

  Siamak P Yazdankhah, Anette W Asli, Henning Sørum, Hanne Oppegaard, Marianne Sunde
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  ABSTRACT: The aim of this study was to determine the occurrence of fusidic acid resistance, mediated by the fusB gene, among coagulase-negative staphylococci (CoNS) isolated from bovine mastitis. A total of 113 CoNS isolates were screened for susceptibility to fusidic acid by using a disc diffusion method. The fusB gene was detected by using PCR and subsequent DNA sequencing. The localization of fusB was determined by hybridization. The fusB gene was detected in 3 of 11 fusidic acid-resistant bovine CoNS isolates. The organization of the fusB downstream region on a 40 kb plasmid in a Staphylococcus haemolyticus isolate (288/96) was highly similar to the previously reported organization of fusB on plasmid pUB101 from a Staphylococcus aureus isolate of human origin. The fusB gene was chromosomally located in the remaining two isolates. Fusidic acid resistance mediated by fusB is not the dominant resistance mechanism in fusidic acid-resistant CoNS studied in this work. The similarity between the organization of the fusB downstream region in S. haemolyticus (isolate 288/96) and on plasmid pUB101 from an S. aureus isolate of human origin indicates a common ancestral origin of these genes.
  Journal of Antimicrobial Chemotherapy 01/2007; 58(6):1254-6. · 5.07 Impact Factor
• Article: Triclosan and antimicrobial resistance in bacteria: an overview.

  Siamak P Yazdankhah, Anne A Scheie, E Arne Høiby, Bjørn-Tore Lunestad, Even Heir, Tor Øystein Fotland, Kristine Naterstad, Hilde Kruse
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  ABSTRACT: Triclosan is a widely used biocide that is considered as an effective antimicrobial agent against different microorganisms. It is included in many contemporary consumer and personal health-care products, like oral and dermal products, but also in household items, including plastics and textiles. At bactericidal concentrations, triclosan appears to act upon multiple nonspecific targets, causing disruption of bacterial cell wall functions, while at sublethal concentrations, triclosan affects specific targets. During the 1990s, bacterial isolates with reduced susceptibility to triclosan were produced in laboratory experiments by repeated exposure to sublethal concentrations of the agent. Since 2000, a number of studies have verified the occurrence of triclosan resistance amongst dermal, intestinal, and environmental microorganisms, including some of clinical relevance. Of major concern is the possibility that triclosan resistance may contribute to reduced susceptibility to clinically important antimicrobials, due to either cross-resistance or co-resistance mechanisms. Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials.
  Microbial Drug Resistance 02/2006; 12(2):83-90. · 2.15 Impact Factor
• Article: Variable-number tandem repeat analysis of meningococcal isolates belonging to the sequence type 162 complex.

  Siamak P Yazdankhah, Konstantinos Kesanopoulos, Georgina Tzanakaki, Jenny Kremastinou, Dominique A Caugant
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  ABSTRACT: Thirty-one meningococcal isolates from carriers and disease cases belonging to the sequence type (ST) 162 complex, isolated in Greece in 1999 and 2000, were studied by the use of variable-number tandem repeat analysis. Our study demonstrated that the isolates belonging to the ST-162 clonal complex were a heterogeneous group. Based on this heterogeneity, it is unlikely that the disease-associated isolates represent an outbreak.
  Journal of Clinical Microbiology 10/2005; 43(9):4865-7. · 4.15 Impact Factor
• Source

  Available from: ncbi.nlm.nih.gov

  Article: Use of variable-number tandem repeats to examine genetic diversity of Neisseria meningitidis.

  Siamak P Yazdankhah, Bjørn-Arne Lindstedt, Dominique A Caugant
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  ABSTRACT: Repetitive DNA motifs with potential variable-number tandem repeats (VNTR) were identified in the genome of Neisseria meningitidis and used to develop a typing method. A total of 146 meningococcal isolates recovered from carriers and patients were studied. These included 82 of the 107 N. meningitidis isolates previously used in the development of multilocus sequence typing (MLST), 45 isolates recovered from different counties in Norway in connection with local outbreaks, and 19 serogroup W135 isolates of sequence type 11 (ST-11), which were recovered in several parts of the world. The latter group comprised isolates related to the Hajj outbreak of 2000 and isolates recovered from outbreaks in Burkina Faso in 2001 and 2002. All isolates had been characterized previously by MLST or multilocus enzyme electrophoresis (MLEE). VNTR analysis showed that meningococcal isolates with similar MLST or MLEE types recovered from epidemiologically linked cases in a defined geographical area often presented similar VNTR patterns while isolates of the same MLST or MLEE types without an obvious epidemiological link showed variable VNTR patterns. Thus, VNTR analysis may be used for fine typing of meningococcal isolates after MLST or MLEE typing. The method might be especially valuable for differentiating among ST-11 strains, as shown by the VNTR analyses of serogroup W135 ST-11 meningococcal isolates recovered since the mid-1990s.
  Journal of Clinical Microbiology 05/2005; 43(4):1699-705. · 4.15 Impact Factor
• Source

  Available from: Martin C J Maiden

  Article: Distribution of serogroups and genotypes among disease-associated and carried isolates of Neisseria meningitidis from the Czech Republic, Greece, and Norway.

  Siamak P Yazdankhah, Paula Kriz, Georgina Tzanakaki, Jenny Kremastinou, Jitka Kalmusova, Martin Musilek, Torill Alvestad, Keith A Jolley, Daniel J Wilson, Noel D McCarthy, Dominique A Caugant, Martin C J Maiden
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  ABSTRACT: The distribution of serogroups and multilocus sequence types (STs) in collections of disease-associated and carried meningococci from the period 1991 to 2000 in three European countries (the Czech Republic, Greece, and Norway) was investigated. A total of 314 patient isolates and 353 isolates from asymptomatic carriers were characterized. The frequency distributions of serogroups and clone complexes differed among countries and between disease and carrier isolate collections. Highly significant differentiation was seen at each housekeeping locus. A marked positive association of serogroup C with disease was evidenced. The ST-11 complex was strongly positively associated with disease; associations for other clone complexes were weaker. The genetic diversity of the clone complexes differed. A single ST dominated the ST-11 clone complex, while the ST-41/44 complex exhibited greater levels of diversity. These data robustly demonstrated differences in the distribution of meningococcal genotypes in disease and carrier isolates and among countries. Further, they indicated that differences in genotype diversity and pathogenicity exist between meningococcal clone complexes.
  Journal of Clinical Microbiology 12/2004; 42(11):5146-53. · 4.15 Impact Factor
• Article: Neisseria meningitidis: an overview of the carriage state.

  Siamak P Yazdankhah, Dominique A Caugant
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  ABSTRACT: During periods of endemic disease, about 10 % of the general population harbour Neisseria meningitidis in the nasopharynx. Since N. meningitidis is a strict human pathogen and most patients have not been in contact with other cases, asymptomatic carriers are presumably the major source of the pathogenic strains. Most carrier isolates are shown to lack capsule production. The capsule deficient state of meningococcal strains in the nasopharynx may aid evasion of the human immune defence and hence be selected to survive nasopharyngeal colonization. Carriage itself can be an immunizing process resulting in systemic protective antibody responses. Frequent nasopharyngeal colonization with related bacteria like Neisseria lactamica improves natural immunity to meningococci by the formation of cross-reacting antibodies. While most meningococcal strains recovered from patients belong to a limited number of clonal groups worldwide, strains isolated from carriers comprise numerous genotypes, with only a small proportion of the strains representing invasive clones. During the carriage state, co-colonization with other pathogenic and non-pathogenic bacteria may lead to genetic exchange, which may result in the emergence of new meningococcal clones. The high diversity of meningococcal carrier strains, compared with hypervirulent strains, supports the idea that transmissibility, not invasion, is essential in the life cycle of N. meningitidis.
  Journal of Medical Microbiology 10/2004; 53(Pt 9):821-32. · 2.50 Impact Factor