The Risk Factors And Mechanism Of Drug Resistance In Pathogens Of Secondary Peritonitis

Objective:To investigate the current changes in bacterial distribution and the factors that cause the changes in aerobic pathogens distribution and drug resistance in order to guide the rational use of antibiotics.To study the drug-resistance mechanism of an Enterobacter cloacae isolated from ascitic fluid, which showed multiple drug resistance and low susceptibility to imipenem.Materials and Methods:This retrospective study, conducted at the surgical department of the First Affiliated Hospital of Anhui Medical University from 2002 to 2008, included 104 patients diagnosed with secondary peritonitis whose ascitic fluid bacterial culture was positive. To analysis the changes and influence factors in bacterial spectrum and resistance spectrum of the aerobic pathogens, and to study the risk factors of multidrug-resistant bacteria. Reviewed the previously report of 222 cases with secondary peritonitis in our hospital, the changes in bacterial spectrum have been analyzed.A further research has been done on the multiresistant E. cloacae which showed low susceptibility to imipenem. M-H agar dilution method and disk diffusion method were used to determine MICs of antimicrobial agents against the clinical isolate. The types of enzymes were identified by the three-dimensional test of AmpCβ-lactamase, and the confirmation test of ESBLs and Cabapenems. The genotypes of these enzymes were confirmed by Specific PCR and DNA sequencing. Moreover, the specific structural gene of integron was detected by PCR amplification.Results:One hundred and nineteen aerobic strains were isolated from 104 different ascitic fluid specimens. The main causative organisms was Gram-negative bacteria (66.4%), but shown a significant declined trend (P=0.001) in recent years. The majority of gram positive bacteria were Enterococcus instead of Staphylococcus aureus. The isolated rate of fungus were rising (P=0.001). The proportion of Gram-positive bacteria were increased with the extension of the length of hospital stay (≥5 days) and the use of empirical antimicrobial therapy(P=0.003;P=0.009). The former were significantly associated with the resistance spectrum of Gram-negative bacteria and the presence of multidrug-resistant bacteria.A strain of E. cloacae was isolated from ascitic fluid, which showed low susceptibility to imipenem. According to the drug-sensitivity results, the isolate is only sensitive to amikacin, and was intermediary resistant to Ciprofloxacin, Levofloxacin, Imipenem and Meropenem, and was resistant to the rest of antibiotics. The EBC type AmpCβ-lactamase, CTX-M and TEM type ESBLs, and IMP type Cabapenems were detected. When compared with the GenBank, DNA sequence analyses revealed that the genotypes were MIR-1, TEM-1b, CTX-M-22, and IMP-26, respectively. The class 1 integron was detected in the bacteria, and the coding gene of PSE-1/CARB-2β-lactamase had been found, which caused the resistant to ampicillin and carbenicillin.The blaIMP-26 gene, coding the IMP-26 enzyme, has been described in a Pseudomonas aeruginosa in 2009. To date, the blaIMP-26 gene has not been reported in E. cloacae. The sequence for blaIMP-26 was submitted to GenBank under the accession number HQ685900.1. Conclusions:The current changes in bacterial distribution should be taken into account in antibiotic therapy. The influence of the length of hospital stay and empirical treatment in bacterial spectrum and resistance spectrum should also be thinking about. Early bacterial cultivation is advantageous for the clinical diagnosis and the treatment of secondary peritonitis.The E. cloacae strains, showing low susceptibility to carbapenem antibiotic, have emerged in our area. They are frequently multiple-drug bacteria and the production ofβ-lactamases is the main resistance mechanisms. In clinical practice, the spread of this enzyme should be given sufficient attention, and must be noticed in the examination and control.