Pattern Of Polymicrobial Isolates And Antimicrobial Susceptibility From Blood

Objective: To determine the pattern of polymicrobial isolates in blood cultures and antimicrobial susceptibility in a tertiary care hospital of Karachi. Study Design: Cross-sectional study. Place and Duration of Study: Sindh Institute of Urology and Transplantation (SIUT), Karachi, Pakistan, from September to November 2014. Methodology: Blood culture samples were received from patients, which were processed by BACTEC 9240 system (Becton Dickinson). All positive blood samples were further analyzed. Susceptibility to antimicrobial agents was determined according to the Clinical and Laboratory Standards Institute (CLSI) criteria of the year. Identification of growth was based on Gram staining, colony morphology and appropriate biochemical tests. Antibiotic susceptibility was done as per Clinical and Laboratory Standards Institute (CLSI) recommendations. Results: Out of the 7251 samples submitted, 2931 (40.42 percent) were positive for growth, 2389 (81.5 percent) samples were monomicrobial, whereas 542 (18.5 percent) samples were polymicrobial. Among the polymicrobial isolates, 468 (86.34 percent) blood culture samples yielded two, 66 (12.17 percent) yielded three, and 8 (1.47 percent) yielded four organisms. Gram positive isolates were 281 (51.84 percent) and Gram negative were 261 (48.15 percent). The most frequent isolates in polymicrobial blood stream infection were Acinetobacterspp. (51/542, 9.4 percent) and Coagulase negative Staphylococcus(84/542, 15.5 percent), respectively. Staphylococcus aureus isolates, which were resistant to Methicillin, accounted for 24.65 percent. Third generation Cephalosporins resistance in Klebsiella spp. and Eschericia (E.) coli was found to be 63.6 percent and 58 percent, respectively. Carbapenem resistance was seen in 5.9 percent of Pseudomonas aeruginosa and 17.6 percent Acinetobacter spp. Conclusion: Gram positive bacteria were more commonly involved in polymicrobial blood stream infections with Coagulase negative Staphylococcus being the most common Gram positive isolate. Methicillin-resistant Staphylococcus aureus accounted for one-fourth of isolates. Higher resistance to third generation Cephalosporins was seen in Klebsiella spp. and E.coli isolates. Resistance of Pseudomonas aeruginosa and Acinetobacter species to Carbapenems was found out to be on the lower side. (author)