Osteoarticular infections: Blood as a determinant factor in the isolation of Kingella kingae

We assessed the capacity of Kingella kingae to grow in blood culture bottles (BCB), taking into account the concentrations of the microorganism and blood in the culture medium. An initial suspension (McFarland 0.5) of 32 strains of K. kingae was serially diluted. One mL of the initial suspension and 1 mL of the subsequent dilutions were inoculated in two BCB, together with 1 mL of human blood in the 2nd BCB. Also, 1mL serial dilutions of human blood were added to BCBs previously inoculated with 1 mL of K. kingae dilution 1/10⁴. In non-blood-supplemented BCB, 23 strains grew with the initial suspension and only one with the first processed dilution, as compared to all strains with the initial suspension and the 3 first dilutions, 22 with the 4th dilution, and one with the 5th dilution in blood-supplemented BCB. In BCB inoculated with K. kingae dilution 1/10⁴ and decreasing concentrations of human blood, all strains grew with blood dilutions 1/2 and 1/4, 26 with dilution 1/8, 19 with dilution 1/16, 10 with dilution 1/32, and none with dilution 1/64. Increasing time to positivity was observed with both decreasing bacterial (p = .001) and blood concentrations (r = -0.632, p < .0001). The addition of human blood was essential to boost the growth of K. kingae in BCB. If replicated in vivo, these findings would increase the isolation of fastidious K. kingae organisms from pediatric osteoarticular exudates.