A current major healthcare problem is represented by antibiotic resistance, mainly due to multidrug resistant (MDR) Gram negative bacilli (GNB), because of their extended spread both in hospital facilities and in the community’s environment. The aim of this study was to investigate the virulence traits of Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa MDR, XDR, and PDR strains isolated from various hospitalized patients. These GNB strains were investigated for the presence of soluble virulence factors (VF), such as hemolysins, lecithinase, amylase, lipase, caseinase, gelatinase, and esculin hydrolysis, as well as for the presence of virulence genes encoding for VF involved in adherence (TC, fimH, and fimA), biofilm formation (algD, ecpRAB, mrkA, mrkD, ompA, and epsA), tissue destruction (plcH and plcN), and in toxin production (cnfI, hlyA, hlyD, and exo complex). All P. aeruginosa strains produced hemolysins; 90% produced lecithinase; and 80% harbored algD, plcH, and plcN genes. The esculin hydrolysis was detected in 96.1% of the K. pneumoniae strains, whereas 86% of them were positive for the mrkA gene. All of the A. baumannii strains produced lecithinase and 80% presented the ompA gene. A significant association was found between the number of VF and the XDR strains, regardless of the isolation sources. This study opens new research perspectives related to bacterial fitness and pathogenicity, and it provides new insights regarding the connection between biofilm formation, other virulence factors, and antibiotic resistance.
Introduction: The increased dissemination of multidrug-resistant Gram-negative bacilli along with a lag in the development of novel, broad-spectrum antimicrobials determined the reintroduction of colistin into clinical practice. In this context, antibiotic susceptibility testing for colistin using high-performance methods has become a requirement. Objective: We compared the performances of the Becton Dickinson (BD) Phoenix 50 automated system and the Micronaut MIC-Strip, a commercial broth microdilution (BMD) method, for the detection of colistin resistance in clinical multidrug-resistant Gram-negative bacilli, isolated from patients admitted in a tertiary hospital in southern Romania. Methods: 54 clinical isolates with different multidrug-resistant phenotypes (Enterobacterales and Pseudomonas aeruginosa) were tested for colistin susceptibility with the BD Phoenix 50 automated system and the Micronaut MIC-Strip, following the Clinical Laboratory Standard Institute recommendations (CLSI, 2021) and were further classified according to the interpretative categories (resistant and intermediate, respectively). The statistical data was calculated using Microsoft Excel 2007 and OpenEPI software. Results: BD Phoenix system failed to detect 11 colistin resistant isolates (false susceptibility). By contrast, all 38 clinical isolates defined as intermediate by the BMD method were also classified as intermediate by the Phoenix system. Conclusion: BD Phoenix system is a reliable technology for detecting colistin resistance. However, high rates of false susceptibility were observed for the BD Phoenix system, indicating that the intermediate / susceptible results should be confirmed with the standard BMD method. Keywords: colistin susceptibility testing, Gram-negative bacilli, multidrug resistance.
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