Virulence factors and clinical patterns of hypermucoviscous Klebsiella pneumoniae isolated from urine

Background: Klebsiella pneumoniae with hypermucoviscosity (HM) phenotype is generally more virulent than HM-negative strains. The aim of this study was to investigate the prevalence of HM phenotype among urinary isolates and to compare the virulence factors, antimicrobial susceptibility patterns and clinical characteristics of HM-positive and -negative K. pneumoniae isolated from urine of hospitalized patients. Methods: From June to October 2013, a total of 81 non-repetitive K. pneumoniae strains were isolated from urine. HM phenotype was determined by a string test. The K1 and K2 genotypes, the allS, kfu, rmpA, rmpA2 and wabG, aerobactin gene were detected by polymerase chain reaction. Results: Of the 81 K. pneumoniae isolates, 12.3% produced a positive string test. The aerobactin (80.0%[8/10] vs. 15.5%[11/71], p=.0001), allS (40.0%[4/10] vs. 9.9%[7/71], p=.009), rmpA (70.0%[7/10] vs. 14.1%[10/71], p=.0001) and rmpA2 (60.0%[6/10] vs. 16.9%[12/71], p=.002) genes were more prevalent in HM positive than in HM negative strains. The K1 (20.0%[2/10) vs. 8.5%[6/71]] and K2 (30.0%[3/10] vs. 4.2%[3/71]) capsular serotypes were more common in HM strains than in non-HM strains (p=.0001). HM-positive K. pneumoniae isolates were more susceptible to amoxicillin/clavulanic acid (p=.02), cefazolin (p=.03), cefotaxime (p=.02) and ciprofloxacin (p=.03) than HM-negative isolates. Multivariate analysis showed that HM phenotype (OR, 23.87; 95% CI, 3.91-145.4, p<.01) and age >60 years (OR, 8.33; 95% CI, 1.25-55.31, p=.03) were significant risk factors for concurrent bacteraemia. Conclusion: Klebsiella pneumoniae with expression of HM phenotype isolated from urine were more likely to be associated with concurrent bacteraemia than isolates without the HM phenotype, and were more susceptible to antibiotics. Physicians have to be aware of the possibility of bacteraemia in patients with K. pneumoniae bacteriuria, especially if strains are HM positive and the patient is >60 years old.