A large-scale surveillance is an important measure to monitor the regional spread of antimicrobial resistance. We prospectively studied the prevalence and molecular characteristics of clinically important Gram-negative bacilli, including Escherichia coli (EC), Klebsiella pneumoniae (KP), Acinetobacter baumannii complex (ABC), and Pseudomonas aeruginosa (PA) from blood, respiratory tract, urine, and sterile sites at 47 hospitals across Thailand. Among 187,619 isolates, 93,810 isolates (50.0%) were critically drug-resistant. Of which, 12,915 isolates (13.8%) were randomly selected for molecular characterization. EC was most commonly isolated from all specimens, except the respiratory tract in which ABC was predominant. Prevalence of extended-spectrum cephalosporin resistance (ESCR) was higher in EC (42.5%) than KP (32.0%), but carbapenem-resistant (CR)-KP (17.2%) was 4.5-fold higher than CR-EC (3.8%). A majority of ESCR-/CR-EC and KP carried bla CTX-M (64.6%-82.1%). bla NDM and bla OXA-48-like were the most prevalent carbapenemase genes in CR-EC/CR-KP (74.9%/52.9% and 22.4%/54.1%, respectively). Besides, 12.9%/23.0% of CR-EC/CR-KP co-carried bla NDM and bla OXA-48-like. Among ABC, 41.9% were extensively drug-resistant (XDR), and 35.7% were multidrug-resistant (MDR), while PA showed XDR/MDR at 6.3%/16.5%. A. baumannii (AB) was the most common species among ABC isolates. The major carbapenemase gene in MDR-AB/XDR-AB was bla OXA-23-like (85.8%/93.0%), which had much higher rates than other ABC species. bla IMP , bla VIM , bla OXA-40-like, and bla OXA-58-like were also detected in ABC at lower rates. The most common carbapenemase gene in MDR-/XDR-PA was bla IMP (29.0%/30.6%), followed by bla VIM (9.5%/25.3%). The findings reiterate an alarming situation of drug resistance that requires serious control measures.

Candidemia, a bloodstream infection caused by genus Candida, has a high mortality rate. Candida albicans was previously reported to be the most common causative species among candidemia patients. However, during the past 10 years in Thailand, Candida tropicalis has been recovered from blood more frequently than C. albicans. The cause of this shift in the prevalence of Candida spp. remains unexplored. We conducted in vitro virulence studies and antifungal susceptibility profiles of 48 C. tropicalis blood isolates collected during 2015-2017. To compare to global isolates of C. tropicalis, multilocus sequence typing (MLST), a minimum spanning tree, and an eBURST analysis were also conducted. C. tropicalis and C. albicans were the most (47-48.7%) and second-most (21.5-33.9%) common species to be isolated from candidemia patients, respectively. Of the C. tropicalis blood isolates, 29.2, 0, 100, and 93.8% exhibited proteinase activity, phospholipase activity, hemolytic activity, and biofilm formation, respectively. Moreover, 20.8% (10/48) of the isolates were resistant to voriconazole and fluconazole, and also showed high minimum inhibitory concentrations (MICs) to posaconazole and itraconazole. In contrast, most of the isolates were susceptible to anidulafungin (97.9%), micafungin (97.9%), and caspofungin (97.9%), and showed low MICs to amphotericin B (100%) and 5-flucytosine (100%). The MLST identified 22 diploid sequence types. Based on the eBURST analysis and minimum spanning tree, 9 out of 13 members (69.2%) of an eBURST group 3 were resistant to voriconazole and fluconazole, and also showed high MICs to posaconazole and itraconazole. Association analysis revealed the eBURST group 3 was significantly associated with the four triazole resistance (p < 0.001). In conclusion, the eBURST group 3 was associated with the triazole resistance and resistance to many antifungal drugs might be collectively responsible for the prevalence shift.

Candida albicans, an opportunistic pathogen, has the ability to form biofilms in the host or within medical devices in the body. Biofilms have been associated with disseminated/invasive disease with increased severity of infection by disrupting the host immune response and prolonging antifungal treatment. In this study, the in vivo virulence of three strains with different biofilm formation strengths, that is, non-, weak-, and strong biofilm formers, was evaluated using the zebrafish model. The survival assay and fungal tissue burden were measured. Biofilm-related gene expressions were also investigated. The survival of zebrafish, inoculated with strong biofilms forming C. albicans,, was significantly shorter than strains without biofilms forming C. albicans. However, there were no statistical differences in the burden of viable colonogenic cell number between the groups of the three strains tested. We observed that the stronger the biofilm formation, the higher up-regulation of biofilm-associated genes. The biofilm-forming strain (140 and 57), injected into zebrafish larvae, possessed a higher level of expression of genes associated with adhesion, attachment, filamentation, and cell proliferation, including eap1, als3, hwp1, bcr1, and mkc1 at 8 h. The results suggested that, despite the difference in genetic background, biofilm formation is an important virulence factor for the pathogenesis of C. albicans. However, the association between biofilm formation strength and in vivo virulence is controversial and needs to be further studied.