Using major outer membrane protein typing as an epidemiological tool to investigate outbreaks caused by milk-borne Campylobacter jejuni isolates in California

Abstract

We describe using major outer membrane protein (MOMP) typing as a screen to compare the Campylobacter jejuni porA gene sequences of clinical outbreak strains from human stool with the porA sequences of dairy farm strains isolated during two milk-borne campylobacteriosis outbreak investigations in California. The genetic relatedness of clinical and environmental strains with identical or closely related porA sequences was confirmed by multilocus sequence typing and pulsed-field gel electrophoresis analysis. The first outbreak involved 1,644 C. jejuni infections at 11 state correctional facilities and was associated with consumption of pasteurized milk supplied by an on-site dairy (dairy A) at a prison in the central valley. The second outbreak involved eight confirmed and three suspect C. jejuni cases linked to consumption of commercial raw milk and raw chocolate colostrum at another central valley dairy (dairy B). Both dairies bottled fluid milk on the farm and distributed the finished product to off-site locations. Altogether, C. jejuni was isolated from 7 of 15 (46.7%) bovine fecal, 12 of 20 (60%) flush alley water, and 1 of 20 (5%) lagoon samples collected on dairy A. At dairy B, C. jejuni was cultured from 9 of 26 (34.6%) bovine fecal samples. Environmental strains indistinguishable from the clinical outbreak strains were found in five flush alley water samples (dairy A) and four bovine fecal samples (dairy B). The findings demonstrate that MOMP typing is a useful tool to triage environmental isolates prior to conducting more labor-intensive molecular typing methods.

Fig 1

Phylogenetic tree comparing the porA sequence of the Campylobacter jejuni clinical outbreak strain (sequence type 21) from dairy A with those of related isolates from our strain collection. The sequences of two clinical outbreak isolates (outbreak) and three flush alley water isolates (dairy) identified through major outer membrane protein screening are displayed. *, sequence and clonal type 21 strains. The scale bar represents the number of nucleotide changes per site.

Fig 2

Phylogenetic tree comparing the porA sequences of representative Campylobacter jejuni and Campylobacter coli strains isolated from dairy A environmental samples with that of the clinical outbreak strain (outbreak 1, 2006 to 2007). *, clinical outbreak strain. Dairy strains with the identical porA and multilocus sequence typing alleles and indistinguishable SmaI and KpnI patterns are underlined. The scale bar represents the number of nucleotide changes per site.

Fig 3

Phylogenetic tree comparing the porA sequences of representative Campylobacter jejuni and Campylobacter coli strains isolated from dairy B environmental samples with that of the clinical outbreak strain (outbreak 2, 2007). *, clinical outbreak strain. Dairy strains with the identical porA and multilocus sequence typing alleles and indistinguishable SmaI and KpnI patterns are underlined. The scale bar represents the number of nucleotide changes per site.