Characterization of novel exotoxins in an Enterobacter aerogenes clinical strain responsible for urinary tract infection.

GARCÍA VÉSCOVI, ELEONORA; ENRIQUE, RAMÓN; BALAGUÉ, CLAUDIA

New Orleans, Lousiana

Congreso; 104º General Meeting of American Society for Microbiology; 2004

American Society for Microbiology

Enterobacter cloacae and Enterobacter aerogenes, are increasingly important nosocomial pathogens responsible for a variety of infections, including bacteremia, endocarditis, osteomyelitis, septic arthritis, and lower respiratory and urinary tract infections. The main risk factors to acquiring Enterobacter infections are prolonged hospital stay in intesive care units and the prior use of antimicrobial agents. Apart from the raising frecuency in acquisition of resistance to antibiotics, no other pathogenicity traits have been extensively studied in these emerging pathogens. We carried out a phenotypic characterization of a two-year Enterobacter strain collection isolated from clinical specimens of patients from the Hospital Provincial del Centenario, Rosario, Argentina. Among these strains 50% corresponded to Enterobacter aerogenes and out of them, 40% were recovered from urinary tract infections. From this last group, we focused in the analysis of E. aerogenes RM66262 strain, that exhibited extracellular citolytic activity was Ca2+-independent, Zn2+-inhibited, termolabile, and it displayed a saturable cholesterol-inhibited binding, suggesting this last molecule to be the recognition target in the host cells. By plate and liquid media assays, we determined the lipolytic activity to be a lipase rather than an esterase or phospholipase. It showed an estimated molecular weight of 26 KDa, Ca2+ and Mg2+ dependence, and preference for long-chain fatty acid-containing substrates. By mini-Tn5 random mutagenesis we selected for lipase null mutant strains. BALB/c mice were challenged with these mutants in an intra-urethra infection model. The mutants were rapidly cleared from urine and severely attenuated for their ability to persist in the bladder and to ascend to kidney. These results show that the E. aerogenes lipase is a pathogenicity factor involved in the urinary tract infection.