Carbapenem inactivation method using bacterial lysate and MOPS (LCIM): a very sensitive method for detecting carbapenemase-producing Acinetobacter species.

OBJECTIVES: Detection of carbapenem-hydrolysing class D ß-lactamase (CHDL)-producing Acinetobacter spp. is critical for understanding antibiotic resistance. In this study, we compared the available detection techniques derived from the carbapenem inactivation method (CIM), using CHDL-producing Acinetobacter spp., and developed a modified method that uses bacterial lysate (lysate CIM; LCIM). METHODS: A total of 159 Acinetobacter spp. (102 carbapenemase producers and 57 non-producers) and 14 Pseudomonas spp. (7 carbapenemase producers and 7 non-producers) were tested. Modified CIM, simplified CIM, CIMTris, Triton-CIM and LCIM were compared using these strains. Distinct from the CIM, LCIM includes a longer incubation period (4 h) with 2.0% Triton X-100 (v/v) in 20 mM MOPS buffer instead of water. RESULTS: The sensitivity/specificity of the modified CIM, simplified CIM, CIMTris, Triton-CIM and LCIM were 71.6%/100%, 66.1%/89.1%, 88.1%/95.3%, 80.7%/100% and 97.2%/100%, respectively. LCIM was the most sensitive and specific. CONCLUSIONS: Use of bacterial lysate and MOPS increased the sensitivity of the CIM in detecting CHDL-producing Acinetobacter spp.

Bacterial keratoconjunctivitis caused by Staphylococcus argenteus belonging to sequence type 1223 isolated in Japan.

Staphylococcus argenteus, characterized by the formation of non-pigmented (white) colonies, was recently identified as a new lineage separated from Staphylococcus aureus. However, correct identification of this lineage is difficult because of the similar characteristics to S. aureus. Here, we describe the first known case of keratoconjunctivitis due to S. argenteus in a 64-year-old man with diabetes. The symptoms of the patient were not improved by antibiotic therapy using levofloxacin eye drops (15 mg/mL). The conjunctival scraping was cultured, and coagulase-positive staphylococci forming white colonies were detected. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry confirmed the species as S. argenteus with a spectral score of 1.97. After the antibiotic was changed to vancomycin eye drops (10 mg/mL), the patient's symptom clearly improved. Multi-locus sequence typing showed that this isolate belonged to sequence type 1223, which has been predominantly isolated worldwide. Furthermore, this isolate harbored various virulence genes associated with S. aureus, such as staphylococcal enterotoxins and leukocidin. Since only limited information is available for this organism, further studies are needed to establish the epidemiology of S. argenteus.

Evaluation of inhibitor-combination mCIM for detecting MBL-producing Enterobacterales using three MBL inhibitors.

The increase in carbapenemase-producing Enterobacterales (CPE), including metallo-ß-lactamase (MBL) producers, is a severe global health concern. Thus, highly sensitive and specific methods for detecting MBL producers are needed. In this study, we tested the detectability of MBL-producing Enterobacterales against three types of MBL inhibitors (sodium mercaptoacetate, SMA; ethylenediaminetetraacetic acid, EDTA; and dipicolinic acid, DPA) used in combination with a modified carbapenem inactivation method (mCIM). These inhibitor-combination mCIMs were tested against 129 CPE (IMP, 93; NDM, 11; KPC, 13; NMC, 1; OXA-48, 11) and 75 non-CPE. For evaluation of MBL inhibitors, we used two concentrations for each of the three inhibitors: DPA (200 and 300 mg l- 1), EDTA (5 and 10 mM), and SMA (1500 and 3000 mg l- 1). The overall sensitivities of SMA, EDTA and DPA were 97.1-99.0 %, 81.7-99.0 % and 88.5-96.2 %, respectively. Moreover, each method showed high specificity (99.0-100 %). Although inhibitor-combination mCIMs were highly sensitive and specific for the detection of MBL producers, we found that sensitivity was dependent on the concentration of inhibitors.