Acinetobacter baumannii in intensive care unit: A novel system to study clonal relationship among the isolates

Department of Experimental Medicine and Biochemical Sciences, Tor Vergata University of Rome, Via Montpellier 1, 00133 Rome, Italy.
BMC Infectious Diseases (Impact Factor: 2.61). 02/2008; 8(1):79. DOI: 10.1186/1471-2334-8-79
Source: PubMed


The nosocomial infections surveillance system must be strongly effective especially in highly critic areas, such as Intensive Care Units (ICU). These areas are frequently an epidemiological epicentre for transmission of multi-resistant pathogens, like Acinetobacter baumannii. As an epidemic outbreak occurs it is very important to confirm or exclude the genetic relationship among the isolates in a short time. There are several molecular typing systems used with this aim. The Repetitive sequence-based PCR (REP-PCR) has been recognized as an effective method and it was recently adapted to an automated format known as the DiversiLab system.
In the present study we have evaluated the combination of a newly introduced software package for the control of hospital infection (VIGI@ct) with the DiversiLab system. In order to evaluate the reliability of the DiversiLab its results were also compared with those obtained using f-AFLP.
The combination of VIGI@ct and DiversiLab enabled an earlier identification of an A. baumannii epidemic cluster, through the confirmation of the genetic relationship among the isolates. This cluster regards 56 multi-drug-resistant A. baumannii isolates from several specimens collected from 13 different patients admitted to the ICU in a ten month period. The A. baumannii isolates were clonally related being their similarity included between 97 and 100%. The results of the DiversiLab were confirmed by f-AFLP analysis.
The early identification of the outbreak has led to the prompt application of operative procedures and precautions to avoid the spread of pathogen. To date, 6 months after the last A. baumannii isolate, no other related case has been identified.

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Available from: Carla Fontana
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    • "Acinetobacter baumannii (A. baumannii) is an important opportunistic pathogen responsible for a nosocomial infections, such as pneumonia, urinary tract infections, bacteraemia and meningitis [1] [2] [3] . Its clinical significance is due to its rapid acquisition of a wide variety of antibiotic resistance genes so it has caused difficulties in the control [4] . "
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    ABSTRACT: To investigate the antibiotic resistance genes inserted into class 1 and class 2 integrons in Acinetobacter baumannii (A. baumannii) isolates obtained from nine different cities in Turkey. A collection of 281 A. baumannii clinical isolates were collected from nine diferent state hospitals in Turkey and were confirmed as A. baumannii by conventional biochemical, API testing and bla -OXA-51 specific PCR. The isolates were examined by PCR for existence of class 1 and 2 integron gene cassettes. They were characterized by antimicrobial susceptibility testing and the highest resistance rates were determined for piperacillin (90.03%), ciprofloxacin (87.54%), cefepime and trimethoprim/sulfamethoxazole (81.13%). The lowest resistance rates was for cefotaxime (3.55%). class I integrons were detected in 6.4% (18/281) of A. baumannii strains and no class 2 integron was detected. The gene cassettes of class 1 integrons AacC1-AAC(3)I-aadA1, AacC1-aadA1, AAC(3)-I, AAC(3)-I -AAC(3)-I -aadA1, TEM-1, AAC(3)-I-aadA1 - AAC(3)-I -AAC(3)-I, AAC(3)-I -AAC(3)-I -AAC(3)-I -aadA1, AAC(3)-I - aadA1, AAC(3)-I-AAC(3)-I, AAC(3)-I-aadA1- AAC(3)-I-aadA1, AAC(3)-I- AAC(3)-I- aadA1-AAC(3)-I-aadA1 were detected in eighteen strains. The aac genes family were most frequently found integrated into the class 1 integrons and it was followed by aadA genes and TEM-1 genes. This is an extensive study on the distribution of class 1 integron among A. baumannii in Turkey. In addition to these, two new alleles were observed. Their percentage rates of similarity to other cassettes are 95% aadA1 ( TKA18) and 89% aadA1 (ANKA3).
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    • "Regarding the molecular fingerprinting of isolates, rep-PCR was used instead of PFGE, which is viewed as the gold-standard method for molecular epidemiology. However, recent reports indicated that rep-PCR was a reliable and fast molecular-fingerprinting method for hospitals and had satisfactory resolution, compared to amplified fragment-length polymorphism and PFGE [16], [29], [30], [31]. With respect to the mathematical model, all patients were assumed to have the same risk of acquiring or transmitting MDRAB. "
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    ABSTRACT: Infections caused by multidrug-resistant bacteria are a major concern in hospitals. Current infection-control practices legitimately focus on hygiene and appropriate use of antibiotics. However, little is known about the intrinsic abilities of some bacterial strains to cause outbreaks. They can be measured at a population level by the pathogen's transmission rate, i.e. the rate at which the pathogen is transmitted from colonized hosts to susceptible hosts, or its reproduction number, counting the number of secondary cases per infected/colonized host. We collected data covering a 20-month surveillance period for carriage of multidrug-resistant Acinetobacter baumannii (MDRAB) in a surgery ward. All isolates were subjected to molecular fingerprinting, and a cluster analysis of profiles was performed to identify clonal groups. We then applied stochastic transmission models to infer transmission rates of MDRAB and each MDRAB clone. Molecular fingerprinting indicated that 3 clonal complexes spread in the ward. A first model, not accounting for different clones, quantified the level of in-ward cross-transmission, with an estimated transmission rate of 0.03/day (95% credible interval [0.012-0.049]) and a single-admission reproduction number of 0.61 [0.30-1.02]. The second model, accounting for different clones, suggested an enhanced transmissibility of clone 3 (transmission rate 0.047/day [0.018-0.091], with a single-admission reproduction number of 0.81 [0.30-1.56]). Clones 1 and 2 had comparable transmission rates (respectively, 0.016 [0.001-0.045], 0.014 [0.001-0.045]). The method used is broadly applicable to other nosocomial pathogens, as long as surveillance data and genotyping information are available. Building on these results, more epidemic clones could be identified, and could lead to follow-up studies dissecting the functional basis for variation in transmissibility of MDRAB lineages.
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    • "Rep- PCR libraries can therefore be easily assembled to enable, for example, the comparison of strains over time and probably across laboratories, with a view to charting the epidemiology of isolates. Outbreaks of Acinetobacter baumannii have been extensively studied using DiversiLab rep-PCR typing (Carretto et al., 2008;Fontana et al., 2008;Kohlenberg et al., 2009;Yan et al., 2010;Perez et al., 2010). Using DiversiLab, a snapshot emerged of the global epidemiology of carbapenem-resistant A. baumannii, where it was found that almost half of 492 isolates from a worldwide collection belonged to a single clonal lineage that clustered with European clone II (Higgins et al., 2010;Dijkshoorn et al., 1996). "
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    ABSTRACT: We have investigated the reproducibility of DiversiLab rep-PCR fingerprints between two laboratories with the aim of determining if the fingerprints and clustering are laboratory-specific or portable. One-hundred non-duplicate Acinetobacter baumannii isolates were used in this study. DNA isolation and rep-PCR were each performed separately in two laboratories and rep-PCR patterns generated in laboratory A were compared with those from laboratory B. Twelve A. baumannii isolates processed in laboratory A showed ≥98 % pattern similarity with the corresponding 12 isolates tested in laboratory B and were considered identical. Sixty-four isolates showed 95-97.9 % similarity with their corresponding isolates. Twenty-three isolates showed 90-94 % similarity with the corresponding isolates, while one isolate showed only 87.4 % similarity. However, intra-laboratory clustering was conserved: isolates that clustered in laboratory A also clustered in laboratory B. While clustering was conserved and reproducible at two different laboratories, demonstrating the robustness of rep-PCR, interlaboratory comparison of individual isolate fingerprints showed more variability. This comparison allows conclusions regarding clonality to be reached independent of the laboratory where the analysis is performed.
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