Additionally, the loss of HV-phenotype also impaired the anti-phagocytosis ability, as the intracellular survival of KPG6 was lower in GANT61 Raw264.7 macrophages than that of 1112 (Table 1). These results suggest that the HV-phenotype was a virulence determinant for the HV-positive strain 1112. Table 1 Virulence characteristics of K. pneumoniae 1112, KPG6, and 1084.

Characteristics K. pneumoniae mTOR inhibitor drugs strains   1112 KPG6 1084 Hypermucoviscosity Positive Negative Negative Serum killing a Resistant Sensitive Resistant Oral LD50 b 6.9 × 106 > 109 9 × 106 Intracellular survival (%) in Raw264.7 cell c 60.29 ± 5.04 46.77 ± 1.61 57.82 ± 2.42 Note. a If the bacteria examined showed a reduction of 2 log10 in the surviving counts after serum incubation, this strain was defined as serum-sensitive. If the viability of a strain remain > 90% after 30 min-treatment, the strain was defined as serum-resistant. b Five 8 wk old male AZD5153 BALB/c mice of a group were orally inoculated with bacterial culture of a particular K. pneumoniae strain in 10-fold steps graded doses. The 50% lethal doses, based on the number of survivors after one week, were calculated by the method of Reed and Muench

[29] expressed as colony forming units (CFU). c A particular K. pneumoniae strain was used to infect Raw264.7 cells with m.o.i. = 100. After stringent washes, the number of adherent and intracellular K. pneumoniae was determined before and after gentamicin treatment. The intracellular survival rate was calculated as 100% × (number of intracellular bacteria after gentamicin treated for 3 h/number of adherent bacteria before gentamicin treatment). Discussion

A capsule-associated mucopolysaccharide web, also known as the hypermucoviscosity (HV) phenotype, was previously considered a characteristic associated with pyogenic K. pneumoniae infections [14, 15]. Nevertheless, the prevalence of K. pneumoniae negative for HV-phenotype in our pyogenic cases (49%; 46/94) suggests (-)-p-Bromotetramisole Oxalate that HV-negative strains have emerged as etiologic in the formation of tissue abscesses. HV-negative-associated infections were related to diabetic conditions, as diabetic patients suffering from pyogenic infections were more frequently associated with HV-negative strains than with HV-positive strains (70% vs. 56%). Therefore, in this study, we aimed to assess how essential the HV-phenotype is for K. pneumoniae pathogenesis by comparing the virulence of clinically isolated strains that were naturally HV-positive or -negative. Because K1 is the predominant serotype in KLA cases, we selected two K1 strains, 1112 and 1084, which have relatively high genetic similarity among our clinical isolates. Not surprisingly, the HV-positive strain 1112 demonstrated greater virulence than the HV-negative strain 1084 in either a pneumonia or KLA infection model in naïve mice.