Research Shows Surveillance Culture Screening for MDRGNs Insufficiently Sensitive

   Understandably, multidrug-resistant gram-negative bacteria (MDRGN) have been found to cause greater illness and risk of death than their antibiotic-susceptible counterparts. One strategy to control these organisms is to identify which patients harbor them asymptomatically using surveillance culture screening (SC) with perianal swabs.

   However, research presented at the 50th Interscience Conference on Antimicrobial Agents and Chemotherapy in Boston shows that the sensitivity of SC in detecting MDRGN colonization in the gastrointestinal tract is suboptimal in that it fails to detect 21% of colonized patients.

   Graham Snyder, MD, and colleagues at Beth Israel Deaconess Medical Center in  Boston performed perianal SC on consecutive patients with positive clinical cultures (CC) for MDRGN, as identified by microbiology records. Multiple drug resistance was defined as resistance to three or more of extended-spectrum penicillins, carbapenems, 3d- or 4th-generation cephalosporins, quinolones, and aminoglycosides. To determine potential factors associated with false negative SC, demographic and clinical data were collected from medical charts. Pulsed-field gel electrophoresis (PFGE) was performed on CC and SC isolates.

   Thirty-five patients with positive CC (55% urine, 23% sputum, 10% blood, 7% bile/peritoneum, 5% other) for 38 MDRGN isolates were enrolled. The patients’ average age was 66 years, average Charlson score 4.3, transplant recipient 9%, antibiotic exposure in previous two weeks 94%, diarrhea in the preceding week 23%, and urinary incontinence 20%. The use of SC identified colonization with the same MDRGN species and similar PFGE profiles among 30 (79%) MDRGN CC isolates. There were no differences in factors potentially associated with false negative SC. The MDRGN species associated with a false negative SC were Morganella morganii 1/1 (100%), Proteus mirabilis 1/2 (50%), Klebsiella pneumoniae 2/9 (22%), Escherichia coli 3/17 (18%), Pseudomonas aeruginosa 1/7 (14%), and Enterobacter cloacae 0/2.

   As noted,  the sensitivity of SC in detecting MDRGN colonization in the study was suboptimal in that it failed to detect 21% of colonized patients. According to Dr. Snyder, as MDRGNs “represent a significant public health threat and continue to spread globally” more sensitive methods of detection are called for.