Listeria immunohistochemistry now available at the AHL 

Josepha DeLay

The AHL has recently validated an immunohistochemical (IHC) test for Listeria monocytogenes in formalin-fixed, paraffin-embedded tissue sections.  This test is very helpful in cases with histologic lesions typical of listeriosis, but for which fresh tissue is not available for bacterial culture.

The beauty of IHC lies in the ability to co-localize staining for infectious antigens and histologic lesions, enhancing the value of test results (Figure 1).   

Listeria antigen (brown staining) within a focus of necrosuppurative hepatitis.  Calf with septicemic listeriosis.

Speciation of coagulase-negative Staphylococcus spp. isolated from milk samples  

Durda Slavic

There are over 40 coagulase-negative Staphylococcus spp. (CNS) recognized to date.  Among them, 3 species (Staphylococcus chromogenes, S. simulans, S. epidermidis) are predominantly isolated from milk samples.  In contrast to the other species of CNS, these species persist in mammary glands during lactation resulting in a moderate increase in somatic cell counts associated with subclinical mastitis.  Recently it has been also shown that S. simulans can resist phagocytosis and killing by macrophages more successfully than other species of CNS, and comparable to S. aureus.  With the growing body of evidence supporting significance of these species in mastitis, the AHL mastitis laboratory started reporting these 3 species of CNS as individual species in January 2014.  All other CNS species will be reported as CNS, and further speciation within this group will be attempted as more research data in this field becomes available.   

Enteritis associated with Campylobacter jejuni and rotavirus A in a 3-day-old calf  

Murray Hazlett, Durda Slavic, R Bryan Hicks

One of 3 calves ranging in age from 2 days to 1 week that had died from scours was submitted to the AHL for postmortem examination.  The owner had noted some blood in the stool of some calves.

The submitted calf was 3 days old and when submitted was notably dehydrated with loose feces staining the perineal region.  The rumen and abomasum were distended with clotted milk, and mucoid yellow-brown content was present in the small intestine, with pasty feces in the colon.  Microscopic examination of tissues showed occasional neutrophils in crypts in small intestine and colon, and in ileum there was ulceration with an outpouring of neutrophils, fibrin and cellular debris, with bacterial colonies enmeshed.

Routine bacteriological cultures for enteropathogenic E. coli, Salmonella spp. and Yersinia spp. were negative.  Based on histological findings, Campylobacter spp. culture was requested, and large numbers of Campylobacter jejuni (4+) were isolated.  In addition, the colon content was positive on PCR testing for rotavirus A.  PCR tests for BVDV and bovine coronavirus were negative.

C. jejuni can be commonly isolated from feces in healthy cattle.  However, there are anecdotal reports of it being associated with enteritis in young ruminants; we are not aware of disease being reproduced by this organism in any controlled studies.  Although C. jejuni culture is not usually done for cases of calf diarrhea, it was done in this case because of the absence of other pathogens and in view of the lesion seen.  Because of the microscopic lesions seen, the failure to isolate other bacterial pathogens, and the large numbers of C. jejuni isolated, it appears that C. jejuni contributed to the enteritis in this case.  It is likely that C. jejuni played a role of opportunistic bacterial pathogen following rotavirus A infection.

C. jejuni is a zoonotic agent, and a common cause of enteritis in humans.