Antimicrobial susceptibility profile ofAcinetobacterspecies isolated from blood cultures in two Japanese university hospitals

Acinetobacter spp. bloodstream infection in hematological patients: a 10-year single-center study

PURPOSE

This study investigated the clinical and antimicrobial characteristics of Acinetobacter spp. bloodstream infection (BSI) in hematological patients. Risk factors for 30-day mortality and carbapenem-resistant Acinetobacter spp. (CRA) BSI acquisition were also identified.

METHODS

We reviewed forty hematological patients with Acinetobacter spp. BSI in a large Chinese blood disease hospital between 2013 and 2022. The remaining CRA isolates were subjected to whole-genome sequencing.

RESULTS

The 30-day mortality rate was high at 35%. Hematological patients with Acinetobacter spp. BSI often presented with severe conditions and co-infections at multiple sites. All strains were colistin-susceptible and 40.0% were CR. Multivariate analysis identified several risk factors associated with CRA BSI acquisition, including previous exposure to carbapenems within 30 days and CRA colonization. Very severe aplastic anaemia, tetracycline-resistant Acinetobacter spp. BSI, and unresolved neutropenia after infection were closely associated with 30-day mortality. Non-survivors often presented with higher median PCT and CRP levels and severe complications, such as intracranial infection, cardiac dysfunction, respiratory failure, and severe sepsis or septic shock. Our study also identified inappropriate empirical antibiotic therapy as an independent predictor of 30-day mortality (OR: 11.234, 95% CI: 1.261-20.086, P = 0.030). This study was the first to report A. oleivorans as a human pathogen, and to identify its unique oxacillinase, OXA-325.

CONCLUSION

An environment-originated non-pathogenic species can become pathogenic when the body's immunity is compromised. Our results also highlighted the importance of improving neutropenia after infection, treating severe organ dysfunction, and administering appropriate empirical antibiotic therapy to reduce mortality in this patient population.

Characteristics of invasive Acinetobacter infection: A multicenter investigation with molecular identification of causative organisms

We examined microbiological and clinical characteristics of invasive Acinetobacter infection occurring in four hospitals located in the Minami-Ibaraki Area. Glucose-non-fermentative Gram-negative bacilli isolated from the blood and the cerebrospinal fluid in independent cases between 2001 and 2014 were consecutively collected and those possibly to be Acinetobacter species were re-identified using molecular methods. Of 158 strains identified as Acinetobacter species, 155 were classified into 16 officially designated species, including 42 Acinetobacter pittii and 40 Acinetobacter baumannii. Imipenem non-susceptibility was detected only in 4 strains, none of which demonstrated multidrug resistance. Retrospective analyses of 154 cases for which medical records were fully available showed that the most common cause of infection was primary bloodstream infection (134 cases), of which 128 were related to intravascular catheter use. The mortality on day 28 after the onset was independently associated with cerebrovascular disease, moderate to severe renal disease, the Pitt bacteremia score, and infection other than primary bloodstream infection but not with appropriate empiric antimicrobial therapy. Isolation of A. baumannii was significantly associated with septic shock but not with the 28-day mortality. These findings, obtained in a region where drug-resistant Acinetobacter strains were much less prevailing, indicated that non-baumannii Acinetobacter species were common pathogens, that the most predominant cause of invasive Acinetobacter infection was intravascular catheter-related infection, that virulence of A. baumannii might be higher than those of other species but its association with mortality was unclear, and that administration of broad-spectrum antibiotics targeting Acinetobacter species might be deferrable in a certain situation.

Blood stream infections caused by Acinetobacter baumannii group in Japan - Epidemiological and clinical investigation

Acinetobacter calcoaceticus-Acinetobacter baumannii complex, especially A. baumannii, Acinetobacter pittii and Acinetobacter nosocomialis, constitutes an important group of nosocomial pathogens; however, epidemiological or clinical characteristics and prognosis is limited in Japan. From 2009 to 2013, 47 blood stream infection cases resulting from A. baumannii group were reviewed at the National Defense Medical College, an 800-bed tertiary hospital. To determine the genospecies, further comparative nucleotide sequence analyses of the RNA polymerase b-subunit (rpoB) gene were performed. Sequence analysis of rpoB gene showed that 25 (49.0%), 17 (33.3%) and 5 (9.8%) cases were caused by A. baumannii, A. pittii and A. nosocomialis, respectively. The 30-day and in-hospital mortality rates of A. baumannii were 8.5% and 25.5%, respectively, and there were no significant differences between Acinetobacter species. Clinical characteristics were statistically insignificant. Multidrug-resistant Acinetobacter species were detected in 3 cases (5.9%) with same pulsed-field gel electrophoresis (PFGE) pattern and A. baumannii was less susceptible to amikacin and levofloxacin. In this study, the mortality and clinical characteristics were similar among A. baumannii group isolate cases despite some showing drug resistance. However, identification of Acinetobacter species helps to initiate appropriate antibiotic therapy in earlier treatment phase, because A. baumannii shows some drug resistance.