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A prospective study of tigecycline susceptibility of bacteria isolated from complicated intra-abdominal as well as skin and soft tissue infections in a large UK hospital
Abstract number: 1733_1526
Oliver L., Watson E., Hovenden J., Budai I., Marodi C.
Objectives: Tigecycline (TIG) is a glycylcycline antibiotic with expanded activity licensed in the UK for the treatment of complicated intraabdominal (cIAI) and skin/soft tissue infections (cSSTI) in 2006. No data have been available about its activity against regional isolates. TIG had not been used in our hospital prior to this study. We aimed to collect information about the TIG sensitivity of isolates from cIAI/cSSTI in our hospital. Methods: Isolates from cIAI (infections that spread beyond the hollow viscus of origin into the peritoneal space associated with abscess formation/peritonitis) and cSSTI (infections involving deeper soft tissue/requiring surgical intervention) from both in- and outpatients, processed in line with the UK laboratory and local guidelines, were collected over 1 month. In polymicrobic infections, each isolate was tested. No duplicate isolates were included. Pseudomonads and anaerobic bacteria were not included in this study. TIG sensitivity was tested using the standard E-test method on Isosensitest or Columbia blood agar (BSAC). MICs were read after an incubation of approximately 20 hours at 35–37°C on air or at 5% CO2 atmosphere (BSAC). Results: Altogether 97 isolates were tested (21 from cIAI's, 76 from cSSTI's). See Table for results. Two ESBL-producing E. coli were isolated with TIG MICs of 0.19 and 0.38 mg/L respectively. We found two AmpC positive Enterobacteriaceae, an E. cloaceae and an S. marcescens, with MICs of 3.0 and 4.0, respectively. Table 1. Tigecycline sensitivity of clinical isolates recovered from intra-abdominal and skin/soft tissue | Isolates | n | Breakpoints (mg/L) | MIC (mg/L) | Sensitive |
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| S >= | R < | Range | MIC50 | MIC90 | No. | (%) | | |
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| Streptococcus beta haemolytic | 10 | 0.25 | 0.5 | 0.047–0.190 | 0.064 | 0.094 | 10 | 100 | | Enterococcus faecalis | 1 | 0.25 | 0.5 | 0.125 | NA | NA | 1 | NA | | MSSA | 37 | 0.5 | 0.5 | 0.047–0.47 | 0.125 | 0.19 | 37 | 100 | | MRSA | 11 | 0.5 | 0.5 | 0.125–0.250 | 0.19 | 0.25 | 11 | 100 | | Total Staphylococcus aureus | 48 | 0.5 | 0.5 | 0.047–0.47 | 0.125 | 0.19 | 48 | 100 | | Escherichia coli | 13 | 1 | 2 | 0.125–1.5 | 0.25 | 0.5 | 12 | 92.3 | | Enterobacter spp. | 5 | 1 | 2 | 0.5–3 | 0.75 | 0.75 | 4 | 80 | | Klebsiella spp. | 7 | 1 | 2 | 0.380–3.0 | 0.75 | 0.75 | 6 | 85.7 | | Proteus mirabilis | 2 | 1 | 2 | 1.5–3.0 | NA | NA | 0 | NA | | Serratia marcescens | 4 | 1 | 2 | 2.0–4.0 | NA | NA | 0 | NA | | Citrobacter koseri | 3 | 1 | 2 | 0.380–0.50 | NA | NA | 3 | NA | | Total Enterobacteriaceae | 34 | 1 | 2 | 0.125–4.0 | 0.5 | 3 | 25 | 73.5 | | Sphingomonas paucimobiIis | 1 | 0.25 | 0.5 | 0.32 | NA | NA | 1 | NA | | Acinetobacter baumannii | 3 | NA | NA | 0.19–0.5 | NA | NA | NA | NA | | Total isolates | 97 | NA | NA | 0.032–4.0 | 0.19 | 2 | NA | NA | | S, sensitive; R, resistant; n, number; NA, not applicable. |
Conclusions: Our Gram-positive isolates were universally sensitive to TIG with generally low MIC50 and MIC90, although MRSA strains had slightly higher MICs than the MSSAs. Among Gram-negative isolates sensitivity was not universal; with only 73.5% of Enterobacteriaceae being susceptible. Despite the short study period, it was shown that Gram-negatives are frequently isolated in both cIAIs and cSSTIs. We can conclude that despite its excellent activity against regional Gram-positive isolates TIG cannot be used universally in cIAI and cSSTI because of the significant number of Gram negatives tested as resistant. The excellent activity against MRSA makes TIG a good candidate for outpatient intravenous antibiotic treatment for MRSA infected chronic ulcers and pressure sores. At present the use of TIG is restricted in our hospital and can only be prescribed on the advice of a Consultant Microbiologist or Infectious Disease Physician.
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