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Background and aims: Over the past two decades in Taiwan, pyogenic liver abscess has usually been caused by a single microorganism, Klebsiella pneumoniae, and is frequently associated with the serious complication of endophthalmitis, especially in diabetic patients. However, the relationship between the clinical presentation and bacterial factors remains unclear. The aim of this study was to investigate the clinical features of patients and the serotype and ribotype of K pneumoniae liver abscess. Methods: From July 1991 to June 1998, a total of 134 cases of K pneumoniae liver abscess with 248 K pneumoniae isolates from the same patients were collected from two large medical centres in northern Taiwan. Clinical data were collected from medical records. Serotyping and ribotyping were performed using the countercurrent immunoelectrophoresis method and automated Riboprinter. Results: Serotyping revealed that the most common serotypes were K1 (63.4%) and K2 (14.2%). K1 isolates occurred at a significantly higher frequency (p<0.01) than all other serotypes. Among 134 patients, 105 (78.4%) had suffered from diabetes mellitus for 3-15 years. Fourteen patients (10.4%) had metastatic infection to the eye causing septic endophthalmitis. Liver aspirates, and blood and vitreous pus cultures yielded the same serotype of K pneumoniae in all patients. Among patients with septic endophthalmitis, 92.3% (13/14) were diabetic, and 85.7% (12/14) of the isolates belonged to serotype K1. For molecular typing, different degrees of genetic polymorphism among isolates with the same K1 serotype suggested no particular prevalence of any one strain in K pneumoniae liver abscess. Conclusion: K pneumoniae serotype K1 was significantly associated with liver abscess and the complication of endophthalmitis, especially in diabetic patients. Physicians should request an immediate report of serotyping and susceptibility test results simultaneously if a diagnosis of pyogenic liver abscess has been made so that early and appropriate management for possible complications will not be delayed. The use of ceftriaxone because of its higher concentration in the aqueous humor is suggested to decrease the chance of septic endophthalmitis.

OmpK35 and OmpK36 are the major outer membrane porins of Klebsiella pneumoniae. In this study, a virulent clinical isolate was selected to study the role of these two porins in antimicrobial resistance and virulence. The single deletion of ompK36 (⌬ompK36) resulted in MIC shifts of cefazolin, cephalothin, and cefoxitin from susceptible to resistant, while the single deletion of ompK35 (⌬ompK35) had no significant effect. A double deletion of ompK35 and ompK36 (⌬ompK35/36) further increased these MICs to high-level resistance and led to 8-and 16-fold increases in the MICs of meropenem and cefepime, respectively. In contrast to the routine testing medium, which is of high osmolarity, susceptibility tests using low-osmolarity medium showed that the ⌬ompK35 mutation resulted in a significant (>4-fold) increase in the MICs of cefazolin and ceftazidime, whereas a ⌬ompK36 deletion conferred a significantly (4-fold) lower increase in the MIC of cefazolin. In the virulence assays, a significant (P < 0.05) defect in the growth rate was found only in the ⌬ompK35/36 mutant, indicating the effect on metabolic fitness. A significant (P < 0.05) increase in susceptibility to neutrophil phagocytosis was observed in both ⌬ompK36 and ⌬ompK35/36 mutants. In a mouse peritonitis model, the ⌬ompK35 mutant showed no change in virulence, and the ⌬ompK36 mutant exhibited significantly (P < 0.01) lower virulence, whereas the ⌬ompK35/36 mutant presented the highest 50% lethal dose of these strains. In conclusion, porin deficiency in K. pneumoniae could increase antimicrobial resistance but decrease virulence at the same time.