| Summary: | We investigated the correlation between the polymerase chain reaction (PCR) identification of six virulence genes associated with siderophore activation and the iron-uptake system (iron-acquisition genes; <i>iuc</i>A, <i>ent</i>B, <i>fep</i>A, <i>ybt</i>S, <i>psn</i>, and <i>kfu</i>) in mastitis-associated <i>Klebsiella pneumoniae</i> (<i>K. pneumoniae</i>). The growth of 37 <i>K. pneumoniae</i> isolates from the milk of cows with mild mastitis reared on Japanese dairy farms between October 2012 and December 2014 was examined by incubation in an iron-deficient medium. <i>ent</i>B-, <i>fep</i>A-, or <i>ybt</i>S-positive isolates grew significantly better than <i>ent</i>B-, <i>fep</i>A-, or <i>ybt</i>S-negative isolates after incubating in an iron-deficient medium for three days. Interestingly, the growth of isolates with 0 and ≥4 PCR-positive iron-acquisition genes in the iron-deficient medium were significantly different by day 2, while isolates with 2, 3, and ≥4 PCR-positive iron-acquisition genes grew significantly better than those with no PCR-positive iron-acquisition genes by day 3. Based on the correlation between the results of PCR and iron-deficient incubation tests, iron-deficient incubation for three days can be used to estimate the presence or absence of iron-acquisition genes in mastitis-associated <i>K. pneumoniae</i>.
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