Epidemiologic surveillance of multidrug-resistant bacteria in a teaching hospital: A 3-year experience.

BACKGROUND: The objective of this prospective study was to verify the effectiveness of a multidisciplinary surveillance program that was implemented in a teaching hospital in southern Brazil, to prevent and control the spread of multidrug-resistant organisms. METHODS: The program implemented involved establishment of prevention guidelines, hand-hygiene promotion, isolation of patients colonized or infected by such organisms, enforced contact precautions, and terminal cleaning and disinfection of isolation rooms. A microbiology service, previously provided by an external laboratory, was established in the hospital. Detection of bacteria-resistant genes and molecular typing were performed also. RESULTS: Statistically significant differences were observed between the pre- and post-intervention periods (P = .00198). Control measures were effective in blocking the dissemination of a previously endemic clone of Acinetobacter baumannii. Changes were observed in the dissemination pattern, from a monoclonal to a polyclonal mode. The incidence of vancomycin-resistant Enterococcus during the surveillance period was low. Only 2 isolates of BLAKPC-positive Klebsiella pneumoniae (distinct profiles), and 5 isolates of BLASPM-positive Pseudomonas aeruginosa (a single cluster), were detected. CONCLUSIONS: These results indicate that the surveillance program implemented was effective in preventing the spread of multidrug-resistant organisms in the hospital.

What does the susceptible-dose dependent interpretive category for cefepime in ESBL-producing bacteria?

In this study, we investigated the frequency of isolates included in the susceptible-dose dependent (SDD) category, according to the Clinical and Laboratory Standards Institute guidelines, carrying blaTEM, blaSHV and blaCTX genes among 92 Klebsiella pneumoniae and 80 Enterobacter cloacae clinical isolates. The presence of one or more extended-spectrum ß-lactamases (ESBLs) genes was observed in 64% K. pneumoniae and 69% E. cloacae isolates. Nineteen isolates were included in SDD interpretive category criteria, of which 15 carried ESBL genes (seven K. pneumoniae and eight E. cloacae). Considering the high proportion of ESBL gene-containing isolates included in the SDD category (79%), we recommend that physicians exercise caution in the use of cefepime for treatment of infections caused by these isolates, reducing possible therapeutic failure, particularly in cases of ESBL-producing bacterial strains.

Strategies for the treatment of polymyxin B-resistant Acinetobacter baumannii infections.

In this study, the activity of meropenem (MEM), fosfomycin (FOF) and polymyxin B (PMB), alone and in combination, was analysed. In addition, optimisation of the pharmacodynamic index of MEM and FOF against six isolates of OXA-23-producing Acinetobacter baumannii (including three resistant to PMB) that were not clonally related was assessed. Antimicrobial combinations were evaluated by chequerboard analysis and were considered synergistic when the fractional inhibitory concentration index (FICI) was ≤0.5. Pharmacodynamic analyses of the MEM and FOF dosing schemes were performed by Monte Carlo simulation. The target pharmacodynamic index (%ƒT>MIC) for MEM and FOF was ≥40% and ≥70%, respectively, and a probability of target attainment (PTA) ≥0.9 was considered adequate. Among the PMB-resistant isolates, combinations of PMB+MEM and PMB+FOF+MEM showed the highest synergistic activity (FICI ≤0.125); isolates that were previously PMB-resistant were included in the susceptible category using CLSI interpretive criteria. Pharmacodynamic evaluation found that for a FOF minimum inhibitory concentration (MIC) of ≤16µg/mL, treatment both by bolus dosing and prolonged infusion achieved adequate PTA, whilst for MIC=32µg/mL only infusion achieved adequate PTA. For a MEM MIC of 4µg/mL, only the bolus treatment scheme with 1.5g q6h and the infusion schemes with 1.0g q8h, 1.5g q6h and 2.0g q8h achieved PTA ≥0.9. Results of antimicrobial and pharmacodynamic analyses can assist in treating infections caused by multidrug-resistant A. baumannii. However, in vivo clinical studies are essential to evaluate the true role of these compounds, including intravenous antimicrobial FOF therapy.

ISAba1/blaOXA-23: A serious obstacle to controlling the spread and treatment of Acinetobacter baumannii strains.

This study demonstrated a direct correlation between Acinetobacter baumannii clusters carrying the ISAba1/blaOXA-23 gene and increased minimal inhibitory concentrations for carbapenems and greater clonal diversity. Our findings showed that clusters carrying ISAba1 are widely distributed in our hospital, further complicating the treatment and control of infections caused by A baumannii.

Can ampicillin/sulbactam resistance in Acinetobacter baumannii be predicted accurately by disk diffusion?

The objective of this study was to compare the performance of disk diffusion and agar dilution for the determination of susceptibility to ampicillin/sulbactam (SAM), ceftazidime, cefepime, imipenem, meropenem, polymyxin B and tigecycline of 121 Acinetobacter baumannii clinical isolates. The antimicrobial susceptibility testing methods were performed as recommended by the Clinical and Laboratory Standards Institute (CLSI). For SAM, in addition the Etest method was performed according to the manufacturer's instructions. The error rates for the antimicrobial agents for 121 isolates tested were within the acceptable ranges established by the CLSI, with the exception of SAM and polymyxin B. For polymyxin B, there were 1.7% very major errors and for SAM there were 15% comparing disk diffusion with agar dilution. The very major error rate of SAM comparing the Etest with agar dilution was 10%. These high observed rates of very major error cast doubt on the disk diffusion and Etest techniques as appropriate methods for detecting resistance to SAM.