Selection of colistin-resistant Acinetobacter baumannii isolates in postneurosurgical meningitis in an intensive care unit with high presence of heteroresistance to colistin Rodriguez Carlos Hernan ⁎ , Bombicino Karina, Granados Gabriela, Nastro Marcela, Vay Carlos, Famiglietti Angela Laboratorio de Bacteriología, Departamento de Bioquímica Clínica, Hospital de Clínicas José de San Martín, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, 1120 Buenos Aires, Argentina Received 7 March 2009; accepted 31 May 2009 Abstract Colistin heteroresistance in Acinetobacter baumannii (Ab) has been reported, but the clinical impact and the antimicrobial treatment have not been established yet. We observed the selection intratreatment with colistin of Ab colistin-resistant strains from a colistin-heteroresistant isolate in one patient with postneurosurgical meningitis. The presence and the genetic relationship of heteroresistant Ab isolates from intensive care units (ICUs) obtained in the same period of the case report were analyzed. Twenty-eight isolates from patients admitted to the ICUs of an Argentinian university hospital during June to December 2004 were evaluated. Genomoespecie was determined by amplified ribosomal DNA restriction analysis, and genetic similarity among the strains was determined by pulsed-field electrophoresis. Colistin heteroresistance was observed in 46, 4% of these isolates. The majority belonged to clones previously identified as I and III. © 2009 Published by Elsevier Inc. Keywords: Acinetobacter; Colistin; Heteroresistance to colistin 1. Introduction Acinetobacter baumannii (Ab) are opportunistic patho- gens with growing relevance in nosocomial infections (Bergogne-Bérézin & Towner, 1996). Although the carba- penems have retained excellent in vitro and clinical activity against susceptible strains of Ab, an increasing number of reports have documented resistance to antibiotics (Peleg et al., 2008; Perez et al., 2007). A recent Argentinian collaborative study showed an alarming elevated percentage of resistance to imipenem in Ab (Bantar et al., 2007). Because of this, nontraditional agents, including poly- myxin B, colistin, and tetracycline, have been used to treat patients infected with multiresistant Ab (Applemann et al., 2000). Currently, only sporadic cases of colistin resistance have been documented in the literature (Koo et al., 2007; Reis et al., 2003). Heteroresistance to colistin has been recently described (Li et al., 2006), but the clinical impact had not been reported until today. The aims of the present study were to report the selection intratreatment with colistin of Ab colistin-resistant strains from a colistin-heteroresistant isolate in one patient with postneurosurgical meningitis and to investigate the presence and the genetic relationship of heteroresistant Ab isolates from an intensive care unit (ICU) obtained in the same period of the case report. 2. Case report A 22-year-old male underwent surgery for meningioma. After surgery, he developed multiple complications, includ- ing fever and rise of CSF. Therapy with intravenous ceftriaxone was started. After 3 days of treatment, Ab86 was recovered from CSF cultures. This isolate was susceptible to colistin (MIC, 0.5 mg/L) and minocycline but resistant to ampicillin–sulbactam, cefepime, ciprofloxa- Available online at www.sciencedirect.com Diagnostic Microbiology and Infectious Disease 65 (2009) 188 – 191 www.elsevier.com/locate/diagmicrobio ⁎ Corresponding author. Tel.: +54-11-45028597; fax: +54-11-5950-8694. E-mail address: carlos_hernanrodriguez@hotmail.com.ar (R.C. Hernan). 0732-8893/$ – see front matter © 2009 Published by Elsevier Inc. doi:10.1016/j.diagmicrobio.2009.05.019