First report of blaOXA-181-mediated carbapenem resistance in Aeromonas caviae in association with pKP3-A: Threat for rapid dissemination.

OBJECTIVES: Carbapenemase-producing Aeromonas spp. are of great concern in healthcare settings and are also known to acquire clinically relevant resistance genes. In this study, carbapenem-non-susceptible Aeromonas isolates were characterised for their molecular mechanisms of resistance. METHODS: Among 180 Aeromonas isolates, 10 carbapenem-non-susceptible isolates were selected based on their antimicrobial susceptibility profile. Carbapenemase production was investigated by the CarbaNP test. ESBL-, AmpC- and carbapenemase-encoding genes were screened by PCR. Isolates VBF557 and VBF856 with high MICs for imipenem were selected for whole-genome sequencing (WGS). Conjugation experiments were performed to determine the transmissibility of resistance. RESULTS: WGS remarkably revealed the presence of class D ß-lactamases (AmpS/AmpH), class C ß-lactamases and class B2 metallo-ß-lactamase (cphA3) in VBF557. In contrast, VBF856 had multiple resistance genes coding for aminoglycoside, sulphonamide, carbapenem (blaOXA-181 class D ß-lactamase), macrolide, fluoroquinolone, rifampicin, phenicol, tetracycline and trimethoprim resistance. This is the first global report of blaOXA-181 in Aeromonas spp. Interestingly, blaOXA-181 was identified in association with transposon Tn2013 in plasmid pKP3-A. Additionally, an IncQ2 plasmid with qnrS2 was identified. Among the tested isolates, VBF1116 and VBF888 possessed blaNDM and blaVEB, respectively, by PCR. None of the other isolates harboured any tested ß-lactamase genes. The resistance gene was transmissible in the presence of imipenem. CONCLUSIONS: Presence of such resistance genes in plasmids further adds complexity for control of spread of carbapenem resistance. This study reveals the emergence of carbapenem resistance among Aeromonas spp. and the importance of mobile genetic elements such as plasmids in interchanging resistance determinants between species.

Molecular Characterization of Invasive Carbapenem-Resistant Acinetobacter baumannii from a Tertiary Care Hospital in South India.

INTRODUCTION: Acinetobacter baumannii is an important opportunistic pathogen responsible for causing nosocomial infections. Carbapenems are considered to be the drug of choice to treat infections caused by multidrug-resistant A. baumannii. The prevalent mechanism of carbapenem resistance in A. baumannii is enzymatic degradation by ß-lactamases. Therefore, the aim of the study is to determine the prevalence and distribution of molecular determinants among the clinical isolates of carbapenem-resistant A. baumannii. METHODS: A total of 103 consecutive, non-duplicate carbapenem-resistant A. baumannii isolated from blood and endotracheal aspirates (ETAs) were included in the study. The CarbAcineto NP test was performed for the screening of carbapenemase production. Polymerase chain reaction (PCR) was performed to detect extended spectrum ß-lactamases (ESBLs), metallo-ß-lactamases (MBLs) and oxacillinases (OXAs). PCR was done for the detection of ISAba1 elements, and mapping PCR was performed to identify the position of ISAba1 with respect to the OXA-23-like gene. RESULTS: Among the 103 A. baumannii isolates, 94 were phenotypically identified as carbapenemase producers. blaPER was the most common among the ESBLs. Among MBLs, blaNDM was predominant followed by the blaVIM gene. blaOXA-51 and blaOXA-23 were the most common and present in all 103 isolates. Almost 80% of the isolates had ISAba1 upstream blaOXA-23 gene. CONCLUSION: The blaOXA-23 and blaNDM genes are the most common type of oxacillinases and metallo ß-lactamases, respectively, and contribute to carbapenem resistance in clinical isolates of A. baumannii. The presence of ISAba1 upstream of the blaOXA-23 gene suggests that the insertion element acts as a promoter for its increased expression. FUNDING: Indian Council of Medical Research, New Delhi, India (ref. no. AMR/TF/54/13ECDHII dated 23 October 2013).

A Pilot Study on Carbapenemase Detection: Do We See the Same Level of Agreement as with the CLSI Observations.

INTRODUCTION: Rapid identification of carbapenemase producing organisms is of great importance for timely detection, treatment and implementation of control measures to prevent the spread. The Modified Hodge Test (MHT) and Carba NP test is recommended by CLSI for the detection of carbapenemases in Enterobacteriaceae. However, MHT may give false positive results or fail to detect metallo ß-lactamases (MBLs). In the US, MHT is the most widely used test for detection of carbapenemases and has been found to have a sensitivity and specificity of >90% for bla KPC producers. However, in India, the prevalence of bla NDM is higher than bla KPC producers. AIM: To evaluate the usefulness of CarbaNP in an Indian setting. MATERIALS AND METHODS: A total of 260 isolates of carbapenem resistant E.coli (n=57), Klebsiella spp. (n=85), Pseudomonas aeruginosa (n=60), and Acinetobacter baumannii (58) isolated from clinical specimens between 2012-2014 at the Christian Medical College, Vellore were included in the study. All the carbapenem resistant isolates were subjected to CarbaNP, MHT and multiplex PCR for detection of carbapenemase genes. RESULTS: CarbaNP was found to be positive in 88% (n=50/57), 81% (n=69/51), 38% (n=23/60) and 81% (n=47/58) for E.coli, Klebsiella spp., P. aeruginosa, and A. baumannii respectively. While in MHT it showed, 89% (n=51/57) and 81 % (n=69/85) for E.coli and Klebsiella spp. respectively. In P.aeruginosa, synergy testing of imipenem plus cloxacillin showed that, 65% of CarbaNP negatives were ampC producers. Overall, the sensitivity and specificity of CarbaNP was found to be 94% and 100 for bla NDM; 77% and 100 % for bla OXA-48 like producers and 81% and 100% for CarbAcinetoNP respectively. CONCLUSION: This observation was more than what was reported in CLSI guidelines. Therefore, it is advisable to evaluate an assay for better laboratory diagnosis at respective regions.