Distribution of Kingella kingae Capsular Serotypes in France Assessed by a Multiplex PCR Assay on Osteoarticular Samples

Abstract

K ingella kingae is the leading pathogen of osteoarticular infection (OAI) in Ͻ4-yearold children in different countries where improved culture methods and nucleic acid amplification assays are routinely employed (1). The oropharynx is recognized as the portal of entry for K. kingae, which can penetrate the bloodstream and invade distant organs, facilitated by several virulence factors, such as a recently described polysaccharide capsule (2). From an international collection of 150 invasive and carriage isolates from 10 countries, Porsch et al. (2) have described four capsule types using a multiplex PCR approach. Over 95% of invasive isolates in the collection were types a or b, while capsule types c and d were more commonly observed among carriage isolates (2, 3). This distribution was described based on K. kingae isolates; however, K. kingae is a fastidious bacterium, and whether strains harboring capsule types a or b can be more easily cultivated from clinical samples is unknown. Such differences may lead to biased epidemiological results. Moreover, among this collection, 30 invasive isolates were from France, mainly isolated from 2010 to 2013 (n ϭ 24/30, date range 1972 to 2013). To our knowledge, no more recent data are available yet, and whether the epidemiology has changed remains to be determined. We aimed to describe the K. kingae capsule serotypes using a multiplex PCR protocol, as recently described (4), on a fraction of our collection of osteoarticular samples, which were positive with the K. kingae specific real-time PCR used as routine in our laboratory (5). From July 2013 to April 2018, we found 115 K. kingae-positive osteoarticular samples from 105 patients (1 to 3 samples per patient). Sample origins were joint fluid (95/105; 90.5%), synovial biopsy specimen (8/105; 7.6%), bone abscess (1/105; 0.9%), and subcutaneous collection (1/105; 0.9%). Capsular PCR allowed unambiguously identification of a capsule type in all of these 115 samples (Fig. 1). Among the 105 patients, the PCR results showed 71 (67.6%) type a capsules, 33 (31.4%) type b capsules, 1 (0.9%) type c capsule, and no type d capsules. When multiple samples were available for one patient, the results were identical for each sample. There were no significant variations between distribution of type a and b

Kingella kingae Virulence Factors and Insights into Pathogenicity

“…As polysaccharide capsules in multiple bacterial pathogens, including Haemophilus influenzae type b, Streptococcus pneumoniae , and N. meningitidis , were successfully incorporated into highly effective glycoconjugate vaccines, it is interesting to speculate that this approach could be applied to K. kingae . As only two capsule types (types a and b) make up >95% of invasive disease isolates in all collections examined to date [ 26 , 29 , 30 ], a glycoconjugate vaccine containing these two polysaccharides could potentially prevent the vast majority of invasive K. kingae disease.…”

“…Interestingly, there is a difference in capsule type representation in strains collected from healthy carriers versus strains collected from patients with invasive K. kingae disease. While type c and type d capsules combined make up ~30% of healthy carrier isolates, they only make up <5% of invasive disease isolates, suggesting that strains that express the type a and type b capsules have greater pathogenic potential [ 26 , 29 , 30 ].…”

Pathogenic determinants of Kingella kingae disease

“…In contrast, the type c and type d capsules are disproportionally present in carrier isolates (43). Analysis of an international collection of isolates from the United States, Canada, Iceland, France, Switzerland, Spain, and New Zealand also revealed dominance of the type a and type b capsule types among invasive isolates (48)(49)(50). Whether the type a and type b capsules directly confer greater pathogenicity or are instead associated with other virulence determinants is an active area of investigation.…”