Assessment of hypermucoviscosity as a virulence factor for experimental Klebsiella pneumoniaeinfections: comparative virulence analysis with hypermucoviscosity-negative strain

Table 1 Virulence characteristics of K. pneumoniae 1112, KPG6, and 1084.

Characteristics	K. pneumoniaestrains
	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. ^aIf 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. ^bFive 8 wk old male 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). ^cA 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).

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