Polymyxin B Heteroresistance and Adaptive Resistance in Multidrug- and Extremely Drug-Resistant Acinetobacter baumannii.

Acinetobacter baumannii is an emerging pathogen associated with nosocomial infections and multidrug resistance. Polymyxin B has been used to treat infections caused by multidrug-resistant (MDR) A. baumannii but an increase in polymyxin B resistance has been observed. We aimed to determine the diversity, antimicrobial susceptibility, presence of polymyxin B heteroresistance and adaptive resistance in 72 A. baumannii clinical isolates from two public hospitals in Rio de Janeiro. The isolates were identified by sequencing of rpoB gene. Determination of the genetic diversity of isolates was performed by pulsed-field gel electrophoresis and oxacillinases genes were detected by polymerase chain reaction. The polymyxin B heteroresistance was analyzed by population analysis profile and adaptive resistance was evaluated after serial daily passages of isolates in broth containing increasing polymyxin B concentrations. The results showed that 49% of the isolates were collected from respiratory system and 62% were MDR, while 35% were extensively drug resistant. Additionally, all the isolates carried blaOXA-23-like, blaOXA-51-like genes and ISAba1, while 1% had blaOXA-24-like gene. The association of ISAba1-blaOXA-23 was found in 96% of the isolates. Polymyxin B heteroresistance was found in 36% of the isolates and polymyxin B adaptive resistance was not found in the isolates. Our study demonstrated the high resistance to antimicrobials used in clinical practice and the spread of oxacillinases genes and insertion sequence (IS). We also reported the presence of heteroresistance to polymyxin B used as a last-resort therapy for MDR A. baumannii.

Staphylococcus haemolyticus disseminated among neonates with bacteremia in a neonatal intensive care unit in Rio de Janeiro, Brazil.

Oxacillin-resistant Staphylococcus haemolyticus (ORSH) was found as the most prevalent (77.5%) species of coagulase-negative staphylococci associated with bacteremia in neonates making use of intravenous catheters in an intensive care unit of a Brazilian teaching hospital. Thirty-one blood isolates were confirmed as S. haemolyticus by sequencing of the 16S and clustered in 6 pulsed-field gel electrophoresis types (with 58% of the strains belonging to 2 predominant types B and D). S. haemolyticus was mostly oxacillin-resistant (90.3%) displaying multiresistance profiles (70.4%). However, the mecA gene was undetected in 22.6% strains. ORSH exhibited slime production on Congo-Red agar (67.7%), adherence to polystyrene (96.7%), and glass (87%) surfaces. Interestingly, ica-operon was detected in 58% strains, mostly belonging to the B, D, and F genotypes, which is a significantly higher percentage when compared to other studies conducted at different parts of the globe. Data indicated that ica operon and biofilm-forming ORSH are endemic in Brazilian nosocomial environment.