Efficacy of two DNA fingerprinting methods for typing Acinetobacter baumannii isolates.

Performance of macrorestriction and repetitive extragenic palindromic DNA sequence-based PCR (REP-PCR) to type Acinetobacter baumannii isolates was quantitatively estimated using a test population of 54 outbreak-related, 29 endemic infection-related and 17 epidemiologically-unrelated isolates. Reproducibility and stability for macrorestriction were 100%, and REP-PCR showed only slightly lower stability. Macrorestriction resolved 18 fingerprints and REP-PCR 10 DNA patterns, forming eight and seven clusters at 75% of similarity level, respectively. Intercluster band variation was > 7 bands for both methods. Although, all endemic isolates, except one, were concordantly grouped by both methods, macrorestriction distinguished a greater number of subtypes over one year study. For outbreaks, the epidemiologic concordance for both methods was 88%. The discriminatory index for macrorestriction and REP-PCR was 0.884 and 0.877, respectively. In conclusion, both methods showed similar efficacy as epidemiological markers, and by concordance, this study demonstrated that for REP-PCR typing, a > or = 7 bands difference seemed an appropriate threshold to identify unrelated strains.

Molecular diversity of live-attenuated prototypic vaccine strains and clinical isolates of Staphylococcus aureus.

Bovine mastitis Staphylococcus aureus isolates and prototypic live-attenuated vaccine strains were analyzed by SmaI pulsed-field gel electrophoresis (PFGE) typing and automated ribotyping. The discriminatory index of these methods was 0.91 and 0.69, respectively. SmaI PFGE typing assigned all laboratory strains into cluster Q, which shared 49% similarity with clusters A and B, and 35% similarity with cluster C. Automated ribotyping placed laboratory strains within ribogroups different from those of bovine isolates. These methods have 70% concordance and permitted identification of the prototypic vaccine background from those of clinical isolates. This information is required before conducting field trials with the vaccine.

Survival of Acinetobacter baumannii on bed rails during an outbreak and during sporadic cases.

Genotypic methods showed Acinetobacter baumannii biotype 9 genotype I to be the epidemic strain on an outbreak in an intensive care unit (ICU) which lasted from January to April of 1996. A cohort was established during March in which hospital personnel were assigned exclusively to A. baumannii infected or colonized patients. New patients were not admitted to the ICU until the last infected patient was discharged. However, strain I was isolated during April and vectors other than human carriage were suspected. The ICU comprised four sections; patients and beds were moved within them according the severity of diseases. Strain I was isolated from a bed rail nine days after the infected patient was discharged. This dry vector may explain the transmission of the epidemic strain between sections. The following July, four new infected patients were identified and three different strains, including the epidemic one, were recovered. The two other strains were also isolated from a bed rail. Although this environmental source does not explain by itself the transmission of an epidemic strain, it illustrates that dry vectors can be secondary reservoirs where A. baumannii can survive.

[Epidemiologic consistency of polymerase chain reaction (PCR) based methods for the study of Acinotobacter baumannii infections]. / Concordancia epidemiológica de los métodos basados en la reacción en cadena de la polimerasa (PCR) para la investigación de las infecciones por Acinetobacter baumannii.

Acinetobacter baumannii is one of the most frequent causative agents of nosocomial infections outbreaks. Consequently, a rapid and specific typing method that can identify epidemic strains is important in preventing their dissemination. To evaluate PCR (polymerase chain reaction)-based methods as epidemiological markers, epidemiologic concordance (EC) and the discriminatory power (D) of two of those methods: 1) arbitrary primed-PCR (AP-PCR), and 2) repetitive extragenic palindrome sequence-based PCR (REP-PCR), were analyzed. The results were compared with that of ribotyping using EcoRI, BglII and ClaI as restriction enzymes. These methods were applied to 69 A. baumannii isolates that included: 15 epidemiological unrelated isolates, 31 recovered from two outbreaks, and 23 obtained from endemic infections. Considering the unrelated isolates, D of ribotyping, AP-PCR and REP-PCR were 0.915, 0.904 and 0.847, respectively. The three methods showed the same EC with respect to the two analyzed outbreaks (100% and 83%, respectively), and the epidemic strains were uniformi differentiated from the co-transferred ones. Ribotyping classified the 23 isolates recovered from endemic infections in 4 different strains, while AP-PCR and REP-PCR identified 3 of them. Although, the 3 methods identified the most frequent disseminated strain. The mayor advantages of REP-PCR versus AP-PCR were reproducibility, and easier optimization. These advantages, in addition to the similar EC of the 3 methods, confirm REP-PCR as an appropriate marker to be used when rapid information about epidemiological A. baumannii infection analysis is required.

Genotypic analysis of Staphylococcus aureus from milk of dairy cows with mastitis in Argentina.

Staphylococcus aureus is the most prevalent pathogen causing mastitis of dairy ruminants. This study was developed to ascertain the genotypes and genealogical relationship among strains isolated from milk of bovines with mastitis in Argentina. Molecular epidemiological analysis of S. aureus was performed on 112 isolates from 21 districts. Clonality was assessed by SmaI pulsed-field gel electrophoresis (PFGE) typing, automated EcoRI ribotyping and restriction enzyme analysis of plasmid (REAP) DNA profiles. A total of 22 band patterns distributed in four clusters were found by SmaI PFGE analysis. The similarity of clusters 2, 3 and 4 with cluster 1 was 0.73, 0.69 and 0.33, respectively, and 101 of 112 isolates belonged in cluster 1. PFGE band patterns from 42 isolates within cluster I were indistinguishable from each other (type A). The second largest group of isolates with indistinguishable PFGE band patterns was subtype A11, which was composed of 19 isolates. Automated ribotyping assigned the 112 isolates into 13 ribotypes. Among these, the most prevalent ribotypes I and VI were composed of 49 and 35 isolates respectively. Although there was certain correspondence between PFGE genotypes and ribotypes, further discrimination was achieved by combining both methods. REAP DNA profile analysis was useful to provide even further discrimination between isolates with identical PFGE genotype and ribotype. The most prevalent S. aureus strains A/I and A11/VI were widely distributed in the country and were not restricted to individual nearby locations. Prevalence of these two strains varied consecutively within a period of 8 years. Whether the shift in type prevalence was due to selection of a phenotypic trait remains undisclosed.

Concordancia epidemiológica de los métodos basados en la reacción en cadena de la polimerasa (PCR) para la investigación de las infecciones por Acinetobacter baumannii. / [Epidemiologic consistency of polymerase chain reaction (PCR) based methods for the study of Acinotobacter baumannii infections]

Acinetobacter baumannii is one of the most frequent causative agents of nosocomial infections outbreaks. Consequently, a rapid and specific typing method that can identify epidemic strains is important in preventing their dissemination. To evaluate PCR (polymerase chain reaction)-based methods as epidemiological markers, epidemiologic concordance (EC) and the discriminatory power (D) of two of those methods: 1) arbitrary primed-PCR (AP-PCR), and 2) repetitive extragenic palindrome sequence-based PCR (REP-PCR), were analyzed. The results were compared with that of ribotyping using EcoRI, BglII and ClaI as restriction enzymes. These methods were applied to 69 A. baumannii isolates that included: 15 epidemiological unrelated isolates, 31 recovered from two outbreaks, and 23 obtained from endemic infections. Considering the unrelated isolates, D of ribotyping, AP-PCR and REP-PCR were 0.915, 0.904 and 0.847, respectively. The three methods showed the same EC with respect to the two analyzed outbreaks (100

and 83

, respectively), and the epidemic strains were uniformi differentiated from the co-transferred ones. Ribotyping classified the 23 isolates recovered from endemic infections in 4 different strains, while AP-PCR and REP-PCR identified 3 of them. Although, the 3 methods identified the most frequent disseminated strain. The mayor advantages of REP-PCR versus AP-PCR were reproducibility, and easier optimization. These advantages, in addition to the similar EC of the 3 methods, confirm REP-PCR as an appropriate marker to be used when rapid information about epidemiological A. baumannii infection analysis is required.