Antibiotics resistance and the carbapenems-resistant mechanisms in Serratia marcescens

Abstract

Objective To find out the antimicrobial resistance of clinical sequential isolates of Serratia marcescens, investigate the primary antimicrobial resistant mechanism of Serratia marcescens to β-lactams antibiotics. Methods Review the antimicrobial resistance data of 247 Serratia marcescens isolates collected sequentially from different clinical wards during 2007 to 2010 in the First Hospital of Ningbo, which their antimicrobial susceptibility testing was got by using Vitek2-Compact system and matching products of gram-negative susceptibility card (GNS). The antimicrobial resistant genes of 20 carbapenems resistant isolates were detected by PCR. Results The Serratia marcescens resistant rates to ceftriaxone, aztreonam and ciprofloxacin in our hospital were 70.4%(174/247)，64.8%(160/247)，57.4%(142/247), respectively, the resistant rates were lower to amikacin, gentamicin, imipenem and meropenem, which were 3.5%(8/229),5.4%(13/241),5.9%(14/237),8.1%(20/247), respectively.PCR experiment showed that the expression levels of the AmpC gene in 4 strains were higher than that of the negative reference strains.The expression levels were 98.3, 102.3, 121.5, 87.3 times compared to the negative reference strains, respectively.Twelve strains (strain no.2, 3, 5, 6, 9, 10, 14, 15, 16, 17,18 and 19) produce both blaCTX-M and blaKPC-2 enzymes.Highly deteced blaCTX-M of Serratia marcescens in our hospital included CTX-M1,CTX-M2,CTX-M9.Isolates no.7 and 18 were carrying blaSHV gene, Isolates no.8 and 13 were carrying blaSME, Isolates no.11 and 20 were carrying blaTEM.There were 5 strains (no.3, 4, 5, 7 and 16) lose the outer membrane protein (OMP) genes ompC and ompF.Two strains(no.1 and 12) lose OMP gene ompF only, and one strain (no.20) was lose OMP gene ompC only. Conclusions The cause of β-lactam antibiotics resistance of Serratia marcescens was complicated, and the most important mechanism is producing β-lactams and loss of OMP.Understanding the evolution and drug resistant mechanisms will help for best use of antibiotics and reducing the selection of antibiotics to resistant isolates.（Chin J Lab Med,2012,35:625-629） Key words: Serratia marcescens; Drug resistance，bacterial; Carbapenems; Polymerase chain reaction