John Merlino

Introduction: This study evaluated the performance of the Ceftazidime-avibactam-Aztreonam (CAZA/AZT) overlay, the Colistin Broth Disk Elution (CBDE), the VITEK 2, and an agar dilution method as reliable methods for screening for colistin resistance in a local collection of 30 carbapenemase-producing Enterobacterales (CPE) isolates collected between 2023 and 2025 with different sequence type (ST) lineages in Sydney, Australia. Methods: Susceptibility to aztreonam (AZT), ceftazidime-avibactam (CAZA), and CAZA/AZT overlay synergy was assessed using Etest methods. Colistin minimum inhibitory concentrations (MICs) were determined using the VITEK 2XL AST-XN24 card, CBDE as described by the Clinical Laboratory Standards Institute (CLSI, 2025), and an agar dilution method. Agreement between methods was assessed using percentage concordance, positive percentage agreement, negative percentage agreement, and overall categorical agreement. Results: A total of 14 isolates (47%) were resistant to AZT, 25 (83%) to CAZA, and 4 isolates (13%) were resistant to the CAZA/AZT overlay, with MIC values >4 mg/L. CBDE showed 93.3% concordance with VITEK 2XL and 90% concordance with agar dilution for colistin MIC categories. Using the CLSI colistin intermediate breakpoint category of ≤2 mg/L, CBDE demonstrated 100% positive percentage agreement, negative percentage agreement, and overall categorical agreement with VITEK 2XL. One Morganella morganii isolate showed high-level intrinsic resistance to colistin. Conclusion: The CBDE method showed strong categorical agreement with other established colistin MIC methods. Results from this study indicate that CBDE may provide smaller laboratories with a simple and practical option for routine screening of CPE isolates for colistin resistance in low-endemic settings where colistin MIC broth microdilution is not available or routinely performed. Continued research with a larger sample size, including more colistin-resistant isolates, is needed to further investigate the CBDE method and its routine use alongside other accepted methods currently in practice.

In this study, we compared and assessed the agreement of two commercial chromogenic agars, Brilliance Group B (BGB; Thermo Fisher, Australia) and ChromID STRB (bioMérieux, Australia), in the detection and presumptive identification of Group B streptococci (GBS; Streptococcus agalactiae ) by colour and later confirmed by MALDI-TOF MS (Bruker Australia). The sensitivity and specificity based on colour were 100 and 91% for BGB and 97 and 100% for ChromID STRB. The NPV (negative predictive value) for GBS on BGB was 100%, and the PPV (positive predictive value) was 73%. ChromID STRB had an NPV of 99% and a PPV of 100%. While both plates compared well in accuracy in the presumptive identification of GBS by colour, both plate media required the integration of MALDI-TOF MS for confirmatory identification. MALDI-TOF MS allowed accurate detection of GBS from both chromogenic plates with a score of >=2.0 after prior treatment with formic acid.

In this study we compared and assessed the agreement of two commercial chromogenic agars, Brilliance Group B (ThermoFisher, Australia) and ChromID STRB (bioMerieux, Australia) in the detection and presumptive identification of GBS (Streptococcus agalactiae) by colour and later confirmed by MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization, Mass Spectrometry, Bruker Australia). The sensitivity and specificity based on colour were 100% and 91% for Brilliance Group B (BGB) and 97% and 100% for ChromID STRB. The PNV (predictive negative value) for GBS on BGB was 100% and the PPV (positive predicted value) was 73%. Chrom IDSTRB had a NPV of 99% and a PPV of 100%. While both plates compared well in accuracy in the presumptive identification of GBS by colour, both plate media required the integration of MALDI-TOF MS for confirmatory identification. MALDI-TOF MS allowed accurate detection of GBS from both chromogenic plates with a score >= 2.0 after prior-treatment with formic acid.

In this study we compared and assessed the agreement of two commercial chromogenic agars, Brilliance Group B (ThermoFisher, Australia) and ChromID STRB (bioMerieux, Australia) in the detection and presumptive identification of GBS (Streptococcus agalactiae) by colour and later confirmed by MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization, Mass Spectrometry, Bruker Australia). The sensitivity and specificity based on colour were 100% and 91% for Brilliance Group B (BGB) and 97% and 100% for ChromID STRB. The PNV (predictive negative value) for GBS on BGB was 100% and the PPV (positive predicted value) was 73%. Chrom IDSTRB had a NPV of 99% and a PPV of 100%. While both plates compared well in accuracy in the presumptive identification of GBS by colour, both plate media required the integration of MALDI-TOF MS for confirmatory identification. MALDI-TOF MS allowed accurate detection of GBS from both chromogenic plates with a score >= 2.0 after prior-treatment with formic acid.

Microbiological methods for Group B Streptococci (GBS) screen have been greatly improved by the use of selective chromogenic substrates in chromogenic culture media. In this study we to compared and assessed the performance of two commercial chromogenic agars, Brilliance Group B (ThermoFisher, Australia) and ChromID STRB (bioMerieux, Australia) in the detection and identification of GBS (Streptococcus agalactiae). 163 antenatal low vaginal swabs were sent to the laboratory from pregnant women. The sensitivity and specificity were 100% and 91% for Brilliance Group B (BGB) and 97% and 100% for ChromID STRB. The predictive negative value for the detection of GBS on BGB was 100% and the positive predicted value was 73%. Chrom IDSTRB had a negative predicted value of 99% and a positive predicted value 100%. While both plates performed well in the screening detection of GBS, both plate media required the integration of MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization, Mass Spectrometry, Bruker Australia) in the identification after isolation of positive-coloured colonies as indicated by the manufacturers. MALDI-TOF MS allowed accurate detection of GBS from both chromogenic plates, after prior-treatment with formic acid.

Kosakonia cowanii is a Gram-negative bacillus belonging to the order Enterobacterales. K. cowanii is a plant pathogen; we report the isolation of this organism from a gardening puncture injury from a plant. Pus examined from the site of infection showed the infecting organism as K. cowanii by MALDI-TOF MS Biotyper Sirius One and 16S rRNA analysis. The organism failed to be identified biochemically by the Vitek 2 XL identification system as Kosakonia spp. The Gram-negative bacilli on the system were biochemically identified as Pantoea spp. Difficulties in species identification biochemically suggest that K. cowanii might potentially represent an underestimated opportunistic human pathogen in skin infections associated with plant injuries. The MALDI-TOF MS Biotyper Sirius One software was found to be a fast and reliable identification of the organism. The isolate was found to be susceptible to first-generation cephalosporins, both cefalexin and cefazolin, by disc diffusion and Vitek 2 XL, even though antibiotic breakpoints currently do not exist using European Committee on Antimicrobial Susceptibility Testing or Clinical and Laboratory Standards Institute (CLSI) guidelines for this organism.

Kosakonia cowanii is a Gram-negative bacillus belonging to the order Enterobacterales. Kosakonia cowanii is a plant pathogen, we report the isolation of this organism from a gardening puncture injury from a plant. Pus examined from the site of infection showed the infecting organism as Kosakonia cowanii by MALDI-TOF MS Biotyper Sirius one and 16s rRNA analysis. The organism failed to be identified biochemically by the Vitek 2 XL identification system as Kosakonia spp.. The Gram-negative bacilli on the system was biochemically identified as Pantoea spp.. Difficulties in species identification biochemically suggests that potentially, Kosakonia cowanii might represent an underestimated opportunistic human pathogen in skin infections associated with plant injuries. The MALDI-TOF MS Biotyper Sirius one software was found to be a fast and reliable identification of the organism. The isolate was found to be susceptible to first generation cephalosporins, both to cefalexin and cefazolin by disc diffusion and Vitek 2 XL even though antibiotic breakpoints currently do not exist using EUCAST or CLSI guidelines for this organism.

Kosakonia cowanii is a Gram-negative bacillus belonging to the order Enterobacterales. Kosakonia cowanii is a plant pathogen, we report the isolation of this organism from a gardening puncture injury from a plant. Pus examined from the site of infection showed the infecting organism as Kosakonia cowanii by MALDI-TOF MS Biotyper Sirius one and 16s rRNA analysis. The organism failed to be identified biochemically by the Vitek 2 XL identification system as Kosakonia spp.. The Gram-negative bacilli on the system was biochemically identified as Pantoea spp.. Difficulties in species identification biochemically suggests that potentially, Kosakonia cowanii might represent an underestimated opportunistic human pathogen in skin infections associated with plant injuries. The MALDI-TOF MS Biotyper Sirius one software was found to be a fast and reliable identification of the organism. The isolate was found to be susceptible to first generation cephalosporins, both to cefalexin and cefazolin by disc diffusion and Vitek 2 XL even though antibiotic breakpoints currently do not exist using EUCAST or CLSI guidelines for this organism.