Detection methods for Arcobacter

Owing to only fairly recent interest in Arcobacter there are only a limited number of detection methods and a standardised method does not yet exist (Johnson and Murano, 1999b). Although Arcobacter strains are capable of aerobic growth, the optimum growth condition for primary isolation is micro-aerophilic (3-10% oxygen). Several different methods using both aerobic and micro-aerophilic conditions have been proposed based on media for Campylobacter and Leptospira (Mansfield and Forsythe, 2000; Phillips, 2001).

CAT agar was shown to support a wider range of arcobacters than mCCD agar and the sub-optimal growth on mCCD agar was considered to be due to the synergistic interaction between deoxycholate and cefoperazone (Corry and Atabay, 1997). A pre-enrichment stage in either CAT broth or Arcobacter enrichment broth together with a filter method onto mCCDA or CAT agar has been suggested for optimum isolation from chicken carcasses (Phillips, 2001). Another combination of pre-enrichment (in an Arcobacter selective broth) and plating onto a semi-solid Arcobacter selective medium has been used and in this case an isolation temperature of 24 °C was employed and piperacillin was added to prevent the outgrowth of Pseudomonas spp. from raw meats (Phillips, 2001).

The productivity of an Arcobacter enrichment medium (AM) [Oxoid] was compared with two Campylobacter enrichment media (Preston broth, Oxoid; LabM broth) (Atabay and Corry, 1998). Twenty strains of Arcobacter and Campylobacter were tested for growth. None of the Campylobacter spp. grew in AM and the medium supported good growth of all strains of Arcobacter.

An agar medium (JM agar) containing a basal nutrient mix along with 0.05% thioglycolic acid, 0.05% sodium pyruvate and 5% sheep's blood (pH 6.9 ± 0.2) was found to be the most effective formulation for the growth of A. butzleri, A. cryaerophilus and A. nitrofigilis (Johnson and Murano, 1999a). In addition to superior growth characteristics, a deep red colour around the colonies was also observed with this formulation. The use of an aerobic pre-enrichment in JM broth prior to plating on JM agar was subsequently found to be more effective at isolating arcobacters from broiler chicken samples than two existing methods (Johnson and Murano, 1999b).

Rapid method development for Arcobacter has centred on PCR-based methods. A multiplex PCR assay to identify Arcobacter isolates, and to distinguish A. butzleri from other arcobacters, has been developed (Harmon and Wesley, 1997). Upon PCR amplification all the Arcobacter isolates yielded a 1233 bp (base pair) product, whereas the A. butzleri exhibited an additional 686bp product. It was claimed that the assay was specific, rapid and easy to interpret. A multiplex PCR method has also been developed to specifically detect both C. jejuni and A. butzleri in the same reaction tube (Winters and Slavik, 2000). The organisms were differentiated by 159 bp and 1223 bp products, respectively, and the method has been evaluated in a range of spiked foods.

Methods that have been used, or proposed, for the identification and characterisation of Arcobacter isolates have included: biochemical profiling, antimicrobial resistance testing, serotyping based on heat-labile antigens, SDS-PAGE of whole cell proteins, fatty acid profiles, PCR-based assays and ribotyping (Harrass et al., 1998; Mansfield and Forsythe, 2000; Phillips, 2001). It has been suggested that some of these methods might represent valuable tools for epi-demiological analyses of Arcobacter isolates. However, reliable commercially available tests are lacking. For example, the API Campy, although effective for the differentiation of Campylobacter spp., does not allow similar identification of Arcobacter at species level (Phillips, 2001).

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