Taxonomic studies of Acinetobacter species based on the electrophoretic analysis of enzymes

Acinetobacter radioresistens as a silent source of carbapenem resistance for Acinetobacter spp

Carbapenem resistance results mostly from the expression of acquired carbapenem-hydrolyzing oxacillinases in Acinetobacter baumannii. The bla OXA-23 oxacillinase gene is increasingly reported worldwide and may represent an emerging threat. Our goal was to identify the progenitor of that carbapenemase gene. A collection of 50 Acinetobacter sp. strains corresponding to several Acinetobacter species was screened for bla(OXA-23)-like genes by PCR and hybridization techniques. Five Acinetobacter radioresistens isolates that were susceptible to carbapenems harbored chromosomally encoded bla OXA-23-like genes. A similar plasmid backbone was identified in several bla OXA-23-positive A. baumannii and A. radioresistens isolates, further strengthening the vectors of exchanges for these bla OXA-23-like genes. Therefore, A. radioresistens, a commensal bacterial species which is identified on the skin of hospitalized and healthy patients (a property shared with A. baumannii), was identified as the source of the bla OXA-23 gene.

Radiation sensitivities of Acinetobacter strains isolated from clinical sources

For twelve clinical strains genetically grouped together with Acnetinobacter radioresistens FO-1T, the radiation sensitivity was measured. Their D10 values in gamma-ray irradiation under N2-equilibrium were 0.24 to 0.93 kGy and about 1/10 to 1/3 of that of the radiation-resistant strain FO-1. The results showed that the genospecies A. radioresistens contained some radiation-sensitive strains.

The identification and classification ofAcinetobacter strains exhibiting variations in phosphate accumulation by SDS-PAGE and numerical analysis

The limitation of phosphate concentrations in effluents is of international concern because of the risk of eutrophication.Acinetobacter spp. have often been isolated from activated sludge plants exhibiting enhanced phosphate removal. The ability to remove phosphate from mixed liquor byAcinetobacter isolates and reference strains was, therefore, determined. The ability to remove phosphate was found to vary among theAcinetobacter strains. The taxonomic relationships among these various strains were elucidated by SDS-PAGE and numerical analysis, and the correlation between their taxonomy and phosphate uptake ability was determined. The ability to remove large amounts of phosphate was found to be strain specific rather than species specific. The classification ofA. haemolyticus andA. baumannii as separate species is questioned.

Serotyping of clinical isolates of Acinetobacter: serovars of genospecies 3

A total of 156 clinical isolates of genospecies 3, the second most commonly encountered member of the genus Acinetobacter at our institution, were identified with carbon source utilization tests among 400 Acinetobacter isolates. Checkerboard tube agglutination tests and reciprocal cross-absorption studies with polyclonal rabbit immune sera against heated (100 degrees C, 1 h) cells of serovar candidate strains of genospecies 3 permitted identification of 13 serovars. Minor one-way crossreactions were noted between serovars 10 and 8 and between serovars 2 and 12, respectively. Isolates of serovar 13 cross-reacted extensively one-way with serovar 2 and less so with serovars 4 and 12. Genospecies 3 serovars 3, 7, 8, and 9 cross-reacted with Acinetobacter baumannii serovars 19, 21, 6, and 15, respectively.