In vitro activity of tigecycline against extended-spectrum β-lactamase-producing Enterobacteriaceae and MRSA clinical isolates from Mexico: a multicentric study

Phenotypic and molecular characterization of clinically isolated antibiotics-resistant S. aureus (MRSA), E. coli (ESBL) and Acinetobacter 1379 bacterial strains

Antibiotic-resistant bacteria causing nosocomial infections pose a significant global health concern. This study focused on examining the lipid profiles of both non-resistant and clinically resistant strains of Staphylococcus aureus (MRSA 1418), E. coli (ESBL 1384), and Acinetobacter 1379. The main aim was to investigate the relationship between lipid profiles, hydrophobicity, and antibiotic resistance so as to identify the pathogenic potential and resistance factors of strains isolated from patients with sepsis and urinary tract infections (UTIs). The research included various tests, such as antimicrobial susceptibility assays following CLSI guidelines, biochemical tests, biofilm assays, and hydrophobicity assays. Additionally, gas chromatography mass spectrometry (GC-MS) and GC-Flame Ionization Detector (GC-FID) analysis were used for lipid profiling and composition. The clinically isolated resistant strains (MRSA-1418, ESBL-1384, and Acinetobacter 1379) demonstrated resistance phenotypes of 81.80%, 27.6%, and 63.6%, respectively, with a multiple antibiotic resistance index of 0.81, 0.27, and 0.63. Notably, the MRSA-1418 strain, which exhibited resistance, showed significantly higher levels of hemolysin, cell surface hydrophobicity, biofilm index, and a self-aggregative phenotype compared to the non-resistant strains. Gene expression analysis using quantitative real-time PCR (qPCR). Indicated elevated expression levels of intercellular adhesion biofilm-related genes (icaA, icaC, and icaD) in MRSA-1418 (pgaA, pgaC, and pgaB) and Acinetobacter 1379 after 24 h compared to non-resistant strains. Scanning electron microscopy (SEM) was employed for structural investigation. These findings provide valuable insights into the role of biofilms in antibiotic resistance and suggest potential target pathways for combating antibiotic-resistant bacteria.

Antimicrobial susceptibility trends among gram-positive and -negative clinical isolates collected between 2005 and 2012 in Mexico: results from the Tigecycline Evaluation and Surveillance Trial

Background

The Tigecycline Evaluation and Surveillance Trial (T.E.S.T) is a global antimicrobial surveillance study of both gram-positive and gram-negative organisms. This report presents data on antimicrobial susceptibility among organisms collected in Mexico between 2005 and 2012 as part of T.E.S.T., and compares rates between 2005–2007 and 2008–2012.

Method

Each center in Mexico submitted at least 200 isolates per collection year; including 65 gram-positive isolates and 135 gram-negative isolates. Minimum inhibitory concentrations (MICs) were determined using Clinical Laboratory Standards Institute (CLSI) broth microdilution methodology and antimicrobial susceptibility was established using the 2013 CLSI-approved breakpoints. For tigecycline US Food and Drug Administration (FDA) breakpoints were applied. Isolates of E. coli and K. pneumoniae with a MIC for ceftriaxone of >1 mg/L were screened for ESBL production using the phenotypic confirmatory disk test according to CLSI guidelines.

Results

The rates of some key resistant phenotypes changed during this study: vancomycin resistance among Enterococcus faecium decreased from 28.6 % in 2005–2007 to 19.1 % in 2008–2012, while β-lactamase production among Haemophilus influenzae decreased from 37.6 to 18.9 %. Conversely, methicillin-resistant Staphylococcus aureus increased from 38.1 to 47.9 %, meropenem-resistant Acinetobacter spp. increased from 17.7 to 33.0 % and multidrug-resistant Acinetobacter spp. increased from 25.6 to 49.7 %. The prevalence of other resistant pathogens was stable over the study period, including extended-spectrum β-lactamase-positive Escherichia coli (39.0 %) and Klebsiella pneumoniae (25.0 %). The activity of tigecycline was maintained across the study years with MIC₉₀s of ≤2 mg/L against Enterococcus spp., S. aureus, Streptococcus agalactiae, Streptococcus pneumoniae, Enterobacter spp., E. coli, K. pneumoniae, Klebsiella oxytoca, Serratia marcescens, H. influenzae, and Acinetobacter spp. All gram-positive organisms were susceptible to tigecycline and susceptibility among gram-negatives ranged from 95.0 % for K. pneumoniae to 99.7 % for E. coli.

Conclusion

Antimicrobial resistance continues to be high in Mexico. Tigecycline was active against gram-positive and gram-negative organisms, including resistant phenotypes, collected during the study.

An in vitro combined antibiotic-antibody treatment eliminates toxicity from Shiga toxin-producing Escherichia coli

Treating Shiga toxin-producing Escherichia coli (STEC) gastrointestinal infections is difficult. The utility of antibiotics for STEC treatment is controversial, since antibiotic resistance among STEC isolates is widespread and certain antibiotics dramatically increase the expression of Shiga toxins (Stxs), which are some of the most important virulence factors in STEC. Stxs contribute to life-threatening hemolytic uremic syndrome (HUS), which develops in considerable proportions of patients with STEC infections. Understanding the antibiotic resistance profiles of STEC isolates and the Stx induction potential of promising antibiotics is essential for evaluating any antibiotic treatment of STEC. In this study, 42 O157:H7 or non-O157 STEC isolates (including the "big six" serotypes) were evaluated for their resistance against 22 antibiotics by using an antibiotic array. Tigecycline inhibited the growth of all of the tested STEC isolates and also inhibited the production of Stxs (Stx2 in particular). In combination with neutralizing antibodies to Stx1 and Stx2, the tigecycline-antibody treatment fully protected Vero cells from Stx toxicity, even when the STEC bacteria and the Vero cells were cultured together. The combination of an antibiotic such as tigecycline with neutralizing antibodies presents a promising strategy for future STEC treatments.

Evaluation of the Antimicrobial Activity of a Super Oxidized Solution in Clinical Isolates

This study evaluated the antimicrobial activity of Estericide(®) QX (super oxidized solution) in 524 bacterial clinical isolates causing nosocomial infections. The minimum inhibitory concentration (MIC) was determined by the serial broth microdilution method. The bacterial viability of the isolates and control strains was tested. The bactericidal effect of the disinfectant was determined according to the European Standards (EN) Test Methods-1040 guidelines. Assay of stability in Estericide QX after 1 year of storage was performed. The microdilution assays showed that the isolates were inhibited at concentrations of 10-40 parts per million (ppm). For gram-positive bacteria, the MIC values 20 and 40 ppm were more predominant (95%), whereas for gram-negative bacteria, the MIC values 10 and 20 ppm had the highest percentage (91.7%). The difference between the two groups was statistically significant (p<0.001). The results of the assay of bactericidal activity showed that all tested bacteria (99.999%) were killed within 30 sec of contact time. The stability test showed that Estericide QX maintained its disinfectant action over time. In conclusion, the results of the present study showed that the super oxidized solution of Estericide QX provides a high antibacterial activity on both gram-positive and gram-negative bacteria. Based on these results and under the conditions of the present study, we believe that Estericide QX can be used efficiently against multiresistant nosocomial bacteria, providing an opportunity for new disinfection alternatives.

Membrane interactions and biological activity of antimicrobial peptides from Australian scorpion

UyCT peptides are antimicrobial peptides isolated from the venom of the Australian scorpion. The activity of the UyCT peptides against Gram positive and Gram negative bacteria and red blood cells was determined. The membrane interactions of these peptides were evaluated by dye release (DR) of the fluorophore calcein from liposomes and isothermal titration calorimetry (ITC); and their secondary structure was determined by circular dichroism (CD). Three different lipid systems were used to mimic red blood cells, Escherichia coli and Staphylococcus aureus membranes. UyCT peptides exhibited broad spectrum antimicrobial activity with low MIC for S. aureus and multi-drug resistant Gram negative strains. Peptide combinations showed some synergy enhancing their potency but not hemolytic activity. The UyCT peptides adopted a helical structure in lipid environments and DR results confirmed that the mechanism of action is by disrupting the membrane. ITC data indicated that UyCT peptides preferred prokaryotic rather than eukaryotic membranes. The overall results suggest that UyCT peptides could be pharmaceutical leads for the treatment of Gram negative multiresistant bacterial infections, especially against Acinetobacter baumanni, and candidates for peptidomimetics to enhance their potency and minimize hemolysis. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Changes in Staphylococcus aureus susceptibility across Latin America between 2004 and 2010

The Tigecycline Evaluation and Surveillance Trial is a global surveillance study monitoring the efficacy of tigecycline and comparators against clinically important pathogens. Between 2004 and 2010, 3126 isolates of Staphylococcus aureus were collected from 66 centers in 13 countries in Latin America; of these, 1467 (46.9%) were resistant to methicillin. The main contributors of S. aureus isolates were Mexico (n = 846), Argentina (n = 740), and Colombia (n = 445). The methicillin-resistant S. aureus rate was greater than 50% in five countries, the highest reported in Puerto Rico (73.9%). Methicillin-resistant S. aureus rates across Latin America ranged from 40.1% to 50.6% over the study period. All S. aureus isolates were susceptible to linezolid and vancomycin, while 100% of methicillin-susceptible S. aureus isolates and 99.8% of methicillin-resistant S. aureus isolates were susceptible to tigecycline. Both methicillin-susceptible S. aureus and methicillin-resistant S. aureus were highly susceptible to minocycline (99.2% and 97.0%, respectively). Latin American methicillin-susceptible S. aureus were highly susceptible to levofloxacin (94.6%) while only 16.2% of methicillin-resistant S. aureus were levofloxacin-susceptible. This study shows that linezolid, vancomycin, and tigecycline are all highly active against S. aureus from Latin America, regardless of methicillin resistance.

Trends in the susceptibility of clinically important resistant bacteria to tigecycline: results from the Tigecycline In Vitro Surveillance in Taiwan study, 2006 to 2010

The Tigecycline In Vitro Surveillance in Taiwan (TIST) study, a nationwide, prospective surveillance during 2006 to 2010, collected a total of 7,793 clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA) (n = 1,834), penicillin-resistant Streptococcus pneumoniae (PRSP) (n = 423), vancomycin-resistant enterococci (VRE) (n = 219), extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (n = 1,141), ESBL-producing Klebsiella pneumoniae (n = 1,330), Acinetobacter baumannii (n = 1,645), and Stenotrophomonas maltophilia (n = 903), from different specimens from 20 different hospitals in Taiwan. MICs of tigecycline were determined following the criteria of the U.S. Food and Drug Administration (FDA) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST-2011). Among drug-resistant Gram-positive pathogens, all of the PRSP isolates were susceptible to tigecycline (MIC(90), 0.03 μg/ml), and only one MRSA isolate (MIC(90), 0.5 μg/ml) and three VRE isolates (MIC(90), 0.125 μg/ml) were nonsusceptible to tigecycline. Among the Gram-negative bacteria, the tigecycline susceptibility rates were 99.65% for ESBL-producing E. coli (MIC(90), 0.5 μg/ml) and 96.32% for ESBL-producing K. pneumoniae (MIC(90), 2 μg/ml) when interpreted by FDA criteria but were 98.7% and 85.8%, respectively, when interpreted by EUCAST-2011 criteria. The susceptibility rate for A. baumannii (MIC(90), 4 μg/ml) decreased from 80.9% in 2006 to 55.3% in 2009 but increased to 73.4% in 2010. A bimodal MIC distribution was found among carbapenem-susceptible A. baumannii isolates, and a unimodal MIC distribution was found among carbapenem-nonsusceptible A. baumannii isolates. In Taiwan, tigecycline continues to have excellent in vitro activity against several major clinically important drug-resistant bacteria, with the exception of A. baumannii.