Comparison of eight phenotypic methods for subspecies characterization of thermophilic Campylobacter spp. isolated from pig liver

Abstract

Four hundred pork livers from bacon pigs (37 herds) obtained at six pig-processing plants were studied to assess the Campylobacter contamination rate. Deep tissue areas were sampled immediately after evisceration. Approximately 6% of livers were infected with Campylobacter spp., including Campylobacter coli (67%), Campylobacter jejuni (30%), and Campylobacter lari (3%). The 60 resulting isolates (39 C. coli isolates, 19 C. jejuni isolates, and 2 C. lari isolates) employed in this study were characterized at the subspecies level in a comparison of eight phenotyping schemes, including four biotyping, two serotyping, and two phage-typing schemes. The Skirrow-Benjamin biotyping scheme produced two biotypes for C. jejuni, i.e., biotype 2 (95%) and biotype 1 (5%). The Lior biotyping scheme subdivided C. coli into biotype 1 (41%) and biotype 2 (59%), while biotype 4 was the dominant type (95%) for C. jejuni. The Roop scheme allowed further differentiation of C. coli into three biovars, i.e., biovar 1 (57%), biovar 2 (40%), and biovar 3 (3%), and it subdivided C. jejuni into two biotypes, i.e., biovar 1 (95%) and biovar 2 (5%). Preston biotyping produced the largest degree of subspecies differentiation, with 18 C. coli biotypes and 7 C. jejuni biotypes being identified. The most common were biotypes 2650 and 6030, representing 18 and 42% of all C. coli and C. jejuni isolates, respectively. The Penner-Hennessy serotyping scheme successfully serotyped 89% of the isolates, with 10 serotypes being identified; 30% of the serotypeable isolates were accounted for by Penner 23, followed by Penner 20 (16%) and Penner 39 (14%). The Lior serotyping scheme successfully serotyped only 45% of the strains, and eight serogroups were identified, with Lior 36 (31%), Lior 20 (23%), and Lior 5 being the most frequent. The Preston scheme and the Khakhria-Lior phage-typing scheme were able to type 16 and 25% of the isolates, respectively. The Preston scheme produced three phage groups, i.e., 69 (56%), 90 (22%), and 116 (22%), and the Khakhria-Lior scheme also produced three phage types, i.e., 44 (40%), 27 (33%), and 37 (20%), as well as atypical lysis patterns (7%). The results of this study demonstrate the role of Preston biotyping in the phenotyping of isolates, particularly in diagnostic laboratories that have no access or limited access to molecular typing equipment.