1887

Abstract

One hundred and twenty-four isolates were selected for antimicrobial susceptibility testing with anti-pseudomonal agents, MIC determination for polymyxin B and metallo-beta-lactamase detection (genes , , and ). According to the imipenem and/or meropenem susceptibility profile, a set of randomly selected isolates (12 isolates carbapenem-susceptible and 12 isolates carbapenem-resistant) were evaluated for heteroresistance to polymyxin B. Heteroresistance testing was performed by plating the isolates onto increasing concentrations of polymyxin B (from 0 to 8.0 mg l). The population analysis profile (PAP) was defined as the ratio of the number of colony-forming units on the plate with the highest concentration of polymyxin B at which bacterial growth occurred against the number of colony-forming units on the plate without antibiotic. Isolates presenting subpopulations that exhibited growth at polymyxin B concentrations ≥2 mg l were considered heteroresistant. Isolates containing subpopulations that grew at polymyxin B concentrations at least twice as high as the original MIC but <2 mg l were considered heterogeneous. Antimicrobial susceptibility testing results indicated a variable degree of susceptibility: high levels of resistance to gentamicin (30.6 %) and imipenem (29.0 %); low levels of resistance to aztreonam (1.6 %) and ciprofloxacin (4.8 %). All isolates were susceptible to polymyxin B: MIC and MIC were 1 mg l and 2 mg l, respectively. Thirty-seven isolates (30 %) were carbapenem-resistant. Four isolates resistant to carbapenems were positive for . There were no heteroresistant subpopulations in the carbapenem-susceptible group, but three isolates presented heterogeneous subpopulations. The PAP frequency ranged from 2.1×10 to 6.9×10. In the carbapenem-resistant group, one isolate was heteroresistant. Six isolates in this group presented heterogeneous subpopulations. In the resistant population, the PAP frequency ranged from 2.1×10 to 2.6×10. In this study, polymyxin B heteroresistance in was uncommon and occurred in only one carbapenem-resistant isolate, despite the fact that several isolates presented heterogeneous subpopulations with increased polymyxin B MICs.

Loading

Article metrics loading...

/content/journal/jmm/10.1099/jmm.0.059220-0
2013-08-01
2024-11-04
Loading full text...

Full text loading...

/deliver/fulltext/jmm/62/8/1184.html?itemId=/content/journal/jmm/10.1099/jmm.0.059220-0&mimeType=html&fmt=ahah

References

  1. Arakawa Y., Shibata N., Shibayama K., Kurokawa H., Yagi T., Fujiwara H., Goto M. 2000; Convenient test for screening metallo-β-lactamase-producing gram-negative bacteria by using thiol compounds. J Clin Microbiol 38:40–43[PubMed]
    [Google Scholar]
  2. CLSI (2011 Performance Standards for Antimicrobial Susceptibility Testing; Vol. 31, no. 1, 21st Informational Supplement M100-S20. Wayne, PA: Clinical and Laboratory Standards Institute
  3. Hawley J. S., Murray C. K., Jorgensen J. H. 2008; Colistin heteroresistance in Acinetobacter and its association with previous colistin therapy. Antimicrob Agents Chemother 52:351–352 [View Article][PubMed]
    [Google Scholar]
  4. Ikonomidis A., Neou E., Gogou V., Vrioni G., Tsakris A., Pournaras S. 2009; Heteroresistance to meropenem in carbapenem-susceptible Acinetobacter baumannii. J Clin Microbiol 47:4055–4059 [View Article][PubMed]
    [Google Scholar]
  5. Li J., Rayner C. R., Nation R. L., Owen R. J., Spelman D. K., Tan K. E., Liolios L. 2006; Heteroresistance to colistin in multidrug-resistant Acinetobacter baumannii. Antimicrob Agents Chemother 50:2946–2950 [View Article][PubMed]
    [Google Scholar]
  6. Martins A. F., Zavascki A. P., Gaspareto P. B., Barth A. L. 2007; Dissemination of Pseudomonas aeruginosa producing SPM-1-like and IMP-1-like metallo-beta-lactamases in hospitals from southern Brazil. Infection 35:457–460 [View Article][PubMed]
    [Google Scholar]
  7. Monteiro J., Widen R. H., Pignatari A. C., Kubasek C., Silbert S. 2012; Rapid detection of carbapenemase genes by multiplex real-time PCR. J Antimicrob Chemother 67:906–909 [View Article][PubMed]
    [Google Scholar]
  8. Plipat N., Livni G., Bertram H., Thomson R. B. Jr 2005; Unstable vancomycin heteroresistance is common among clinical isolates of methicillin-resistant Staphylococcus aureus. J Clin Microbiol 43:2494–2496 [View Article][PubMed]
    [Google Scholar]
  9. Poole K. 2011; Pseudomonas aeruginosa: resistance to the max. Front Microbiol 2:1–13 [View Article][PubMed]
    [Google Scholar]
  10. Pournaras S., Ikonomidis A., Markogiannakis A., Maniatis A. N., Tsakris A. 2005; Heteroresistance to carbapenems in Acinetobacter baumannii.. J Antimicrob Chemother 55:1055–1056 [View Article][PubMed]
    [Google Scholar]
  11. Pournaras S., Ikonomidis A., Markogiannakis A., Spanakis N., Maniatis A. N., Tsakris A. 2007; Characterization of clinical isolates of Pseudomonas aeruginosa heterogeneously resistant to carbapenems. J Med Microbiol 56:66–70 [View Article][PubMed]
    [Google Scholar]
  12. Pournaras S., Ikonomidis A., Neou E., Kantzanou M., Maniatis A. N., Tsakris A. 2008; Piperacillin/tazobactam-heteroresistant Pseudomonas aeruginosa from urinary infection, successfully treated by piperacillin/tazobactam. J Antimicrob Chemother 61:757–758 [View Article][PubMed]
    [Google Scholar]
  13. Rinder H. 2001; Hetero-resistance: an under-recognised confounder in diagnosis and therapy?. J Med Microbiol 50:1018–1020[PubMed]
    [Google Scholar]
  14. Tomasz A., Nachman S., Leaf H. 1991; Stable classes of phenotypic expression in methicillin-resistant clinical isolates of staphylococci. Antimicrob Agents Chemother 35:124–129 [View Article][PubMed]
    [Google Scholar]
  15. Yamazumi T., Pfaller M. A., Messer S. A., Houston A. K., Boyken L., Hollis R. J., Furuta I., Jones R. N. 2003; Characterization of heteroresistance to fluconazole among clinical isolates of Cryptococcus neoformans.. J Clin Microbiol 41:267–272 [View Article][PubMed]
    [Google Scholar]
  16. Yau W., Owen R. J., Poudyal A., Bell J. M., Turnidge J. D., Yu H. H., Nation R. L., Li J. 2009; Colistin hetero-resistance in multidrug-resistant Acinetobacter baumannii clinical isolates from the Western Pacific region in the SENTRY antimicrobial surveillance programme. J Infect 58:138–144 [View Article][PubMed]
    [Google Scholar]
  17. Zavascki A. P., Goldani L. Z., Li J., Nation R. L. 2007; Polymyxin B for the treatment of multidrug-resistant pathogens: a critical review. J Antimicrob Chemother 60:1206–1215 [View Article][PubMed]
    [Google Scholar]
/content/journal/jmm/10.1099/jmm.0.059220-0
Loading
/content/journal/jmm/10.1099/jmm.0.059220-0
Loading

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error