Evaluation of Chromogenic Medium for Selective Isolation of Yersinia

Yersinia pseudotuberculosis Infection Complicated with Bacteremia in a 10-Month-Old Boy

Yersinia pseudotuberculosis (Y. pseudotuberculosis) infection complicated with bacteremia rarely occurs. Y. pseudotuberculosis infection is also known to produce various symptoms similar to Kawasaki disease (KD) due to the production of Y. pseudotuberculosis-derived mitogen (YPM), an exotoxin with superantigen activity. Moreover, it causes terminal ileitis and is responsible for appendix swelling. Here, we report a case of Y. pseudotuberculosis infection in a 10-month-old boy who was brought to our hospital due to fever, watery stool, and poor vitality. Abdominal echocardiography revealed wall thickening of the entire colon and appendix swelling; therefore, he was admitted and treated with antibiotics for bacterial enteritis or appendicitis. After the antibiotic administration, facial skin rashes and hand and foot edema developed. However, he had 5/6 major symptoms of KD and was diagnosed with Y. pseudotuberculosis infection because of its presence in the blood and stool cultures. Thereafter, antibacterial therapy improved his symptoms and increased the inflammatory response. After his hospital discharge, the skin on his fingers showed desquamation like that of KD. Y. pseudotuberculosis infection should be considered as a differential disease in KD, terminal ileitis, and appendicitis. Furthermore, its infection route and culture methods should also be carefully considered.

Prevalence of human pathogenic Yersinia enterocolitica in Swedish pig farms

BACKGROUND

Pigs are the most important reservoir for human pathogenic Yersinia enterocolitica. We investigated the herd prevalence of human pathogenic Y. enterocolitica in Swedish pig farms by analysing pen faecal samples using a cold enrichment of 1 week and thereafter subsequent plating onto chromogenic selective media (CAY agar).

RESULTS

Pathogenic Y. enterocolitica was found in 32 (30.5%) of the 105 sampled farms with finisher pigs. Bioserotype 4/O:3 was identified at all but one farm, where 2/O:9 was identified. Pen-prevalence within the positive herds varied from 1/4 to 4/4 pens. The calculated intra-class correlation coefficient ICC (0.89) from a model with a random effect for grouping within herd indicated a very high degree of clustering by herd. None of the explored risk factors, including herd size, herd type, pig flow, feed type, access to outdoors, evidence of birds and rodents in the herd, usage of straw, number of pigs in sampled pen and age of pigs in pen were significantly associated with Y. enterocolitica status of the pen. The use of high pressure washing with cold water was significantly associated with Y. enterocolitica in the pen (OR = 84.77, 4.05-1772). Two culture methods were assessed for detection of Y. enterocolitica, one of which included the use of a chromogenic agar (CAY agar) intended for detection of human pathogenic Y. enterocolitica. The chromogenic media was found equal or superior to traditional methods and was used in this study. The isolates obtained were characterised by biotyping, serotyping, mass spectrometry (MALDI-TOF) and PCR. Characterisation by MALDI-TOF gave identical results to that of conventional bioserotyping. All porcine isolates were positive for the ail and inv genes by PCR, indicating that the isolates were most likely pathogenic to humans.

CONCLUSIONS

Human pathogenic Y. enterocolitica was found in nearly one-third of the Swedish pig farms with finisher pigs. The use of high pressure washing with cold water was associated with the presence of Y. enterocolitica in the pen. A modified culturing method using a chromogenic agar was efficient for detection of pathogenic Y. enterocolitica in pig faeces. The use of masspectrometry for identification and subtyping was in agreement with conventional biotyping and serotyping methods.

Fast methods of fungal and bacterial identification. MALDI-TOF mass spectrometry, chromogenic media

MALDI-TOF mass spectrometry is now a routine resource in Clinical Microbiology, because of its speed and reliability in the identification of microorganisms. Its performance in the identification of bacteria and yeasts is perfectly contrasted. The identification of mycobacteria and moulds is more complex, due to the heterogeneity of spectra within each species. The methodology is somewhat more complex, and expanding the size of species libraries, and the number of spectra of each species, will be crucial to achieve greater efficiency. Direct identification from blood cultures has been implemented, since its contribution to the management of severe patients is evident, but its application to other samples is more complex. Chromogenic media have also contributed to the rapid diagnosis in both bacteria and yeast, since they accelerate the diagnosis, facilitate the detection of mixed cultures and allow rapid diagnosis of resistant species.