Resumo

BACKGROUND The genus Klebsiella harbors bacteria associated with infections in different hosts. Nosocomial strains are frequently resistant to all β-lactams due to the production of broad spectrum β-lactamases. The bla_SHV gene is constitutive in this species, but is also found in plasmids spread among bacterial species. bla_SHV encodes a Class A β-lactamase that confers resistance to penicillins, especially ampicillin. Depending on bla_SHV allele, the enzyme may recognize a broader spectrum of substrates conferring resistance to all β-lactams. The bla_SHV-28, bla_SHV-110, bla_SHV-121 alleles do not have its resistance spectrum experimentally proven yet. OBJECTIVES This study aimed to determine the resistance spectrum of bla_SHV-28, bla_SHV-110, bla_SHV-121 and other alleles found in K. pneumoniae strains from different Brazilian geographic regions. METHODS Thirty-five clinical and environmental K. pneumoniae isolated between 2000-2006 from Rio de Janeiro, Maranhão and Amazonian region were analyzed. PCR and sequencing were performed to characterize the bla_SHV allele. The different SHV alleles were determined by comparing with the SHV available in the database using blastN and blastP tools. The PCR products corresponding to SHV genes that do not have a resistance spectrum experimentally defined were cloned and expressed in Escherichia coli. The β-lactamase activity spectrum were evaluated by susceptibility test. RESULTS AND DISCUSSION Thirty-five K. pneumoniae were analyzed in order to determine the bla_SHV allele. Twenty-two of these had bla_SHV-11 allele and five harbored the bla_SHV-1 allele, both defined in the literature as restricted spectrum. Strains harboring bla_SHV-28 (n=2), bla_SHV-110 (n=1) and bla_SHV-121 (n=1) were identified. Four strains carried new alleles with an unknown resistance spectrum. The strains harboring the new bla_SHV alleles (n=4) showed resistance to oxyimino-cephalosporins, belonging to the third and fourth generation cephalosporins and monobactams, while strains harboring the bla_SHV-110 and bla_SHV-28 showed resistance to third-generation cephalosporins and aztreonam. The transformants showed resistance to amoxicillin, ampicillin, piperacillin, ticarcillin, and cephalothin, which correspond to a restricted spectrum of resistance. CONCLUSION Here we determined that different bla_SHV alleles, including bla_SHV-28, previously labeled as an extended spectrum β-lactamase (ESBL), and the new ones, had a restricted resistance spectrum to β-lactams.