Species identification within Acinetobacter calcoaceticus-baumannii complex using MALDI-TOF MS

Acinetobacter baumannii, one of the more clinically relevant species in the Acinetobacter genus is well known to be multi-drug resistant and associated with bacteremia, urinary tract infection, pneumonia, wound infection and meningitis. However, it cannot be differentiated from closely related species such as Acinetobacter calcoaceticus, Acinetobacter pittii and Acinetobacter nosocomialis by most phenotypic tests and can only be differentiated by specific, time consuming genotypic tests with very limited use in clinical microbiological laboratories. As a result, these species are grouped into the A. calcoaceticus-. A. baumannii (Acb) complex. Herein we investigated the mass spectra of 73 Acinetobacter spp., representing ten different species, using an AB SCIEX 5800 MALDI-TOF MS to differentiate members of the Acinetobacter genus, including the species of the Acb complex. RpoB gene sequencing, 16S rRNA sequencing, and gyrB multiplex PCR were also evaluated as orthogonal methods to identify the organisms used in this study. We found that whilst 16S rRNA and rpoB gene sequencing could not differentiate A. pittii or A. calcoaceticus, they can be differentiated using gyrB multiplex PCR and MALDI-TOF MS. All ten Acinetobacter species investigated could be differentiated by their MALDI-TOF mass spectra

Human neutrophils phagocytose and kill Acinetobacter baumanii and A. pittii

Acinetobacter baumannii is a common cause of health care associated infections worldwide. A. pittii is an opportunistic pathogen also frequently isolated from Acinetobacter infections other than those from A. baumannii. Knowledge of Acinetobacter virulence factors and their role in pathogenesis is scarce. Also, there are no detailed published reports on the interactions between A. pittii and human phagocytic cells. Using confocal laser and scanning electron microscopy, immunofluorescence, and live-cell imaging, our study shows that immediately after bacteria-cell contact, neutrophils rapidly and continuously engulf and kill bacteria during at least 4 hours of infection in vitro. After 3 h of infection, neutrophils start to release neutrophil extracellular traps (NETs) against Acinetobacter. DNA in NETs colocalizes well with human histone H3 and with the specific neutrophil elastase. We have observed that human neutrophils use large filopodia as cellular tentacles to sense local environment but also to detect and retain bacteria during phagocytosis. Furthermore, co-cultivation of neutrophils with human differentiated macrophages before infections shows that human neutrophils, but not macrophages, are key immune cells to control Acinetobacter. Although macrophages were largely activated by both bacterial species, they lack the phagocytic activity demonstrated by neutrophils

Evaluation of a new chromogenic medium, chromID OXA-48, for recovery of carbapenemase-producing Enterobacteriaceae from patients at a university hospital in Turkey

The purpose of this study was to evaluate a new chromogenic medium, chromID OXA-48, for the isolation of carbapenemase-producing Enterobacteriaceae (CPE) directly from rectal swabs. chromID CARBA and chromID OXA-48 are two chromogenic media that have been commercialized for the isolation of CPE directly from clinical samples. Both media were evaluated alongside a broth enrichment method recommended by the CDC for isolation of CPE, with rectal swabs from 302 unique hospitalized patients at the Hacettepe University Hospital, Ankara, Turkey. A total of 33 patients (11 %) were found to be colonized with CPE using a combination of all methods, and all CPE produced OXA-48 carbapenemase. Klebsiella pneumoniae was by far the most dominant species of CPE and was isolated from 31 patients. Culture on chromID OXA-48 offered the highest sensitivity (75.8 %) for detection of CPE compared with the other two methods (sensitivity for both other methods was 57.6 %) and also offered the highest specificity (99.3 %). However, a combination of methods (either chromID OXA-48 plus CDC method or chromID OXA-48 plus chromID CARBA) was necessary to achieve an acceptable sensitivity (90.9 %). For isolation of CPE, in a setting where OXA-48 carbapenemase is the dominant type of carbapenemase, chromID OXA-48 is a highly useful medium but using a combination of methods is optimal for adequate detection. The combined use of two chromogenic media offered acceptable sensitivity (90.9 %) and the highest specificity (98.5 %) and also allowed for isolation of CPE within 18–20 h