Acquired carbapenemase-encoding genes among Gram-negative isolates in USA medical centres: report from the MYSTIC Program (2007)

Abstract number: P1514

Mendes R., Rhomberg P., Castanheira M., Deshpande L., Jones R.

Objective: To evaluate the occurrence of acquired carbapenemase-encoding genes among Gram-negative patient isolates recovered from USA MC in the 2007 MYSTIC Program.

Methods: 1,392 Enterobacteriaceae (ENT), 133 Acinetobacter spp. (ASP) and 465 Pseudomonas spp. (PSP) clinical isolates from 15 USA MC were susceptibility tested by CLSI reference broth microdilution method. ENT and PSP isolates showing MIC values 2 mg/L and 16 mg/L, respectively, for imipenem and meropenem were screened for KPC- and metallo-b-lactamase (MBL)-encoding genes. ASP isolates showing MIC values 16 mg/L for imipenem and meropenem were screened for MBL- and OXA-encoding genes. Presence of ISAba1 upstream of the blaOXA-51 and clonality were also investigated by PCR and PFGE, respectively. Additionally, ASP isolates from previous MYSTIC Program years were tested for OXA genes.

Results: 42 (3.0% of the total) ENT isolates were screened and 35 (2.5%) isolates from MC located in New York (24/35; 68.6%), New Jersey (10/35; 28.6%) and Ohio (1/35; 2.8%) harboured blaKPC. This gene was found in C. freundii (2), E. coli (1), E. cloacae (3), K. oxytoca (1) and K. pneumoniae (28). Among 133 ASP, 50 (37.6%) isolates were screened and blaOXA-23 was detected in 10 isolates from MC in New York (3), Kentucky (3), Arkansas (2) and Colorado (2), while blaOXA-24 was detected in 5 isolates from New Jersey. ISAba1 was associated with blaOXA-51 in 76.5% of the cases and clonal dissemination of blaOXA-carrying ASP within MC was noted. In the retrospective sample of ASP collected from 1999 to 2006, 42 (6.8%) isolates were screened for blaOXA. blaOXA-23 was observed in 2 isolates from Tennessee (2004) and one isolate each from Kentucky and Washington (2005). Among the 36 (7.7%) PSP isolates screened, no carbapenemases were detected. MBL-encoding genes were not observed.

Conclusions: Although the results presented here document an alarming presence of blaKPC, the rate (2.5%) was lower when compared with the previous MYSTIC year (4.5%; P = 0.0063; OR = 1.80, CI 95% 1.15–2.82). However, the KPC gene has spread among several different ENT species, while it was detected only in Klebsiella spp. in the previous year. blaOXA genes have been detected in several MYSTIC Program MC within the USA; first detected in 2004. blaOXA genes were only observed in consecutive years in Kentucky, suggesting a sporadic appearance in ASP, overall. MBL-encoding genes are still quite rare in the MYSTIC Program.