In-vitro bactericidal activity of colistin against biofilm-associated Pseudomonas aeruginosa and Acinetobacter baumannii

In-vitro bactericidal activity of colistin against biofilm-associated Pseudomonas aeruginosa and Acinetobacter baumannii

368 Letters to the Editor 2. Munoz-Price LS, Weinstein RA. Acinetobacter infection. N Engl J Med 2008;358:1271e81. 3. Villegas MV, Hartstein AI. Aci...

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Letters to the Editor

2. Munoz-Price LS, Weinstein RA. Acinetobacter infection. N Engl J Med 2008;358:1271e81. 3. Villegas MV, Hartstein AI. Acinetobacter outbreaks, 1977e 2000. Infect Control Hosp Epidemiol 2003;24:284e95. 4. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing. 18th informational supplement. Approved standard; CLSI document M100-S18. Wayne, PA: CLSI; 2008. 5. Jones RN, Ferraro MJ, Reller LB, Schreckenberger PC, Swenson JM, Sader HS. Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp. J Clin Microbiol 2007;45:227e30. 6. Silbert S, Pfaller MA, Hollis RJ, Barth AL, Sader HS. Evaluation of three molecular typing techniques for nonfermentative Gram-negative bacilli. Infect Control Hosp Epidemiol 2004;25:847e51. 7. Patterson JE, Vecchio J, Pantelick EL, et al. Association of contaminated gloves with transmission of Acinetobacter calcoaceticus var. anitratus in an intensive care unit. Am J Med 1991;91:479e83.

S.M. dos Santos Saalfelda,b,* G. Fukita Vianab V.L. Dias Siqueirab C.L. Cardosob L. Botelho Garciab M.C. Bronharo Tognimb a University Hospital, State University of Maringa´, Maringa´, Parana´, Brazil b Department of Clinical Analyses, State University of Maringa´, Maringa´, Parana´, Brazil E-mail address: [email protected] Available online 21 June 2009 * Corresponding author. Address: Laborato ´rio de Microbiologia (Bloco I-90, Sala 114), Departamento de Ana ´lises Clı´nicas, Universidade Estadual de Maringa ´, Avenida Colombo 5790, CEP 87020-900 Maringa ´, Parana ´, Brazil. Tel.: þ55 44 3261 4952; fax: þ55 44 3261 4860. ª 2009 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhin.2009.04.004

In-vitro bactericidal activity of colistin against biofilm-associated Pseudomonas aeruginosa and Acinetobacter baumannii

Madam, Pseudomonas aeruginosa and Acinetobacter baumannii are of concern as nosocomial pathogens and cause a wide spectrum of infection from skin and wound infections to septicaemia.1 In addition, multiple drug-resistant (MDR) strains and even

pan-resistant strains are evolving and spreading, while few new antibacterial agents are being developed in parallel.2 As a result, a re-evaluation of polymyxins has taken place and these agents may be a last resort for MDR Gram-negative infections, even though their use in clinical practice was discontinued due to adverse renal and neurological effects in a large number of patients. Biofilm is one of the important mechanisms of persistence of drug-resistant organisms and both P. aeruginosa and A. baumannii can form typical biofilms.3,4 Therefore, we evaluated the in-vitro bactericidal activity of colistin against different stages of biofilms of these two species. Minimum inhibitory concentration (MIC) data of colistin for P. aeruginosa clinical isolate (PA 2201), A. baumannii (AB 2306) as well as P. aeruginosa wild type PAO1 were determined by the microdilution method. PA 2201 and AB 2306 were both resistant to piperacillin, piperacillin/tazobactam, ticarcillin/clavulanate, imipenem, meropenem, minocyline, ciprofloxacin and SMZ-TMP. PA 2201 was sensitive to amikacin and levofloxacin, whereas AB2306 was susceptible to ceftazidime and cefepime. MICs of colistin for each strain were 0.25 mg/mL (PAO1), 0.5 mg/mL (PA 2201) and 0.125 mg/mL (AB 2306), respectively. Biofilm inhibitory concentrations were conducted with 72 h colony biofilms of PA 2201, AB 2306 and PAO1. Colistin MICs of 0.5 to 4 mg/mL showed little effect on the three strains after 24 h exposure. When MICs reached 8 mg/mL, viable counts in biofilms of all three strains showed obvious reduction (about 2e4 log) compared with control groups (without colistin treatment) (data not shown). Then an MIC of 8 mg/mL was chosen in the next time-kill studies and the greatest decrease was observed at 8 h for each strain treated by colistin an MIC of 8 mg/mL (data not shown). The effect of colistin on PA2201, AB2306 and PAO1 in 24 h, 48 h and 72 h colony biofilms was evaluated 8 h after treatment with colistin MIC 8 mg/mL (Figure 1). For 24 h biofilms, a slight decrease was observed between control and colistin treatment groups (P > 0.05; Figure 1), and significant decreases were noted in both 48 and 72 h biofilms (P < 0.05; Figure 1). These results may have some implications for colistin in clinical use. First, the initial concentration of colistin must reach a certain level to eradicate biofilm-associated P. aeruginosa and A. baumannii, especially for MDR strains. Second, colistin was more effective on mature biofilm than on initial stage biofilm. Finally, Haagensen et al. showed that colistin preferentially killed cells forming the core/stalk of the PAO1 mushroom

Letters to the Editor


14 24 h control 12 24 h colistin 48 h control 10

48 h colistin

log10 cfu/cm2

72 h control 8

72 h colistin *



* *









Figure 1 Bactericidal activities of colistin MIC 8 mg/mL on 24 h, 48 h and 72 h colony biofilms after 8 h treatments. Error bars denote SD. *P < 0.05 compared with the control group of the same stage of biofilm.

structures, which were less active than the capforming subpopulation.5 This may partly explain why colistin was more effective on mature biofilm, in which most cells were in an inactive stage; colistin has excellent bactericidal activity against cells in a quiescent stage. So the combination of colistin and antibiotics with good bactericidal activity against strains in an active stage might be a good choice for biofilm-associated infection and maintain the efficacy of colistin.

Acknowledgements We thank Y. Luo of Department of Microbiology of the PLA General Hospital for providing the P. aeruginosa and A. baumannii clinical strains and E.P. Greenberg of University of Washington School of Medicine for providing P. aeruginosa PAO1. Conflict of interest statement None declared. Funding sources None.

References 1. Navon-Venezia S, Ben-Ami R, Carmeli Y. Update on Pseudomonas aeruginosa and Acinetobacter baumannii infections in the healthcare setting. Curr Opin Infect Dis 2005;18: 306e13. 2. Kwa AL, Tam VH, Falagas ME. Polymyxins: a review of the current status including recent developments. Ann Acad Med Singap 2008;37:870e83. 3. Sauer K, Camper AK, Ehrlich GD, Costerton JW, Davies DG. Pseudomonas aeruginosa displays multiple phenotypes during development as a biofilm. J Bacteriol 2002;184: 1140e54. 4. Cevahir N, Demir M, Kaleli I, Gurbuz M, Tikvesli S. Evaluation of biofilm production, gelatinase activity, and mannoseresistant hemagglutination in Acinetobacter baumannii strains. J Microbiol Immunol Infect 2008;41:513e8. 5. Haagensen JA, Klausen M, Ernst RK, et al. Differentiation and distribution of colistin and sodium dodecyl sulfate tolerant cells in Pseudomonas aeruginosa biofilms. J Bacteriol 2007; 189:28e37.

Y. Cai R. Wang* B.-B. Liang M.-M. An Department of Clinical Pharmacology, PLA General Hospital,


Letters to the Editor Beijing, People’s Republic of China E-mail address: [email protected] Available online 13 May 2009

* Corresponding author. Address: Department of Clinical Pharmacology, PLA General Hospital, 28 Fu Xing Road, Beijing 100853, People’s Republic of China. Tel.: þ86 10 6693 7908; fax: þ86 10 8821 4425. ª 2009 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jhin.2009.03.013

Successful control of norovirus outbreak in an infirmary with the use of alcohol-based hand rub

Madam, Norovirus is recognised as an important cause of gastroenteritis outbreaks. A short incubation period of one to two days, prolonged survival on both hands and environmental surfaces and relatively poor sensitivity to disinfectants, frequently result in outbreaks with high attack rates. Here, we describe the successful containment of a norovirus outbreak in an infirmary facility, with emphasis on the use of directly observed hand hygiene using World Health Organization (WHO) formulation alcohol-based hand rub (AHR). An outbreak of norovirus-associated gastroenteritis occurred in an infirmary ward of Tung Wah Hospital, an extended care hospital containing 633 beds. The index patient, a man aged 71 years, developed watery diarrhoea on 12 July 2006. Within the next two days, three more patients staying in the same ward became symptomatic with watery diarrhoea. The infection control team was informed at this stage and closed the ward to admissions and discharges from the following day. Contact tracing and collection of stool samples for norovirus reverse transcriptione polymerase chain reaction (RTePCR) were performed. Thorough environmental cleaning and disinfection with sodium hypochlorite 1000 ppm were implemented. Due to geographical constraints, symptomatic cases were cohorted in a designated area within the same ward with contact precautions instituted. AHR in both a bedside preparation with 500 mL per bottle and pocketsized bottles with 100 mL each was provided. Staff were educated on the proper use of AHR (each time obtaining 3 mL AHR and continuously

rubbing all hand surfaces for 30 s until the hands are dry). The infection control nurse monitored the staff compliance to hand hygiene and performed directly observed hand hygiene practice especially during high risk procedures such as changing of diapers and patients’ feeding, as described previously.1 During the outbreak period, 33 inpatients and 22 ward-based staff (13 nurses, six ward assistants, two physiotherapists, and one medical officer) were followed up in this ward. Overall, in addition to the index case, six more patients (aged between 48 and 85 years) and one visitor developed gastroenteritis. The stool samples of the symptomatic patients were confirmed to be positive for norovirus by RTePCR. All symptomatic patients were fed by either nasogastric tube or percutaneous endoscopic gastrotomy. It was concluded the norovirus was most likely transmitted during assisted feeding by healthcare workers. Norovirus is a non-enveloped RNA virus, which is resistant to common disinfectants. As norovirus is considered as non-cultivable, feline calicivirus is often used as a surrogate for in-vitro or in-vivo testing for different preparations of disinfectants.2,3 Although the virucidal efficacy of alcohol against feline calicivirus is inferior to that of povidone-iodine, it is greatly variable depending on the different formulations, concentrations and contact time used. In one study, only 0.5e1 log10 reduction of virus titre could be achieved after exposure to ethanol (62e99.5%) for 30 s.2 Another study showed that a 2 and 3 log10 reduction in virus titre was achieved when ethanol (80%) was used for 30 s and 1 min respectively.3 In the WHO formulation AHR, formula I preparation contains ethanol (80% v/v) which, based on the above studies, may possess reasonable virucidal activity for norovirus when the contact time is prolonged for up to 30 s. Therefore, we applied the principle of directly observed hand hygiene practice as described previously to ensure the compliance of hand hygiene during the outbreak period and successfully controlled further spread of norovirus within the hospital.1 In 2006, there was an upsurge of nosocomial outbreaks of norovirus due to an epidemic strain, a new genogroup II4 variant in Hong Kong.4 This new variant also caused a prolonged outbreak with a high clinical attack rate as recently reported.5 Based on our previous experience, we were able to control the outbreak within two days and limit the clinical attack rate to <15% with directly observed hand hygiene practice using the AHR.1 Conflict of interest statement None declared.