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Antimicrobial susceptibility testing is essential for guiding the treatment of many types of bacterial infections, especially in the current context of rising rates of antibiotic resistance. The most commonly employed methods rely on the detection of phenotypic resistance by measuring bacterial growth in the presence of the antibiotic being tested. Although these methods are highly sensitive for the detection of resistance, they require that the bacterial pathogen is isolated from the clinical sample before testing and must employ incubation times that are sufficient for differentiating resistant from susceptible isolates. Knowledge regarding the molecular determinants of antibiotic resistance has facilitated the development of novel approaches for the rapid detection of resistance in bacterial pathogens. PCR-based techniques, mass spectrometry, microarrays, microfluidics, cell lysis-based approaches and whole-genome sequencing have all demonstrated the ability to detect resistance in various bacterial species. However, it remains to be determined whether these methods can achieve sufficient sensitivity and specificity compared with standard phenotypic resistance testing to justify their use in routine clinical practice. In the present review, we discuss recent progress in the development of methods for rapid antimicrobial susceptibility testing and highlight the limitations of each approach that still remain be addressed. [ABSTRACT FROM PUBLISHER]

Objectives The rapid detection of antibiotic resistance in clinical isolates of Acinetobacter baumannii would shorten the period during which patients receive empirical therapy and facilitate the early initiation of directed antibiotic therapy. The objective of this study was to evaluate the ability of a real-time PCR assay to detect antibiotic resistance to four clinically relevant antibiotics from different antibiotic classes in clinical isolates of A. baumannii. Methods The growth of 48 clinical isolates of A. baumannii with a broad range of MICs of imipenem, ciprofloxacin, colistin and amikacin was evaluated using a real-time PCR assay targeting a highly conserved region of the ompA gene. Fold changes in the number of copies of genomic DNA after 6 h of growth were used to determine resistance and the results were compared with those obtained using broth microdilution. Results The results obtained using the real-time PCR assay were concordant with broth microdilution for 184 of 192 determinations (95.8%). The global values for specificity (97.5%), sensitivity (92.9%), positive predictive value (95.6%) and negative predictive value (96.0%) indicated that the real-time PCR assay was able to reliably differentiate between resistant and non-resistant strains. Conclusions The use of real-time PCR to monitor bacterial growth in the presence of antibiotics is effective for rapidly identifying antibiotic resistance in A. baumannii. [ABSTRACT FROM PUBLISHER]

Treatment options for multidrug-resistant (MDR) strains of Acinetobacter baumannii that acquire resistance to colistin are limited. Acinetobacter baumannii can become highly resistant to colistin through complete loss of lipopolysaccharide (LPS) owing to mutations in the genes encoding the first three enzymes involved in lipid A biosynthesis ( lpxA , lpxC and lpxD ). The objective of this study was to characterise the susceptibility to 15 clinically relevant antibiotics and 6 antimicrobial peptides (AMPs) of MDR A. baumannii clinical isolates that acquired colistin resistance due to mutations in lpxA , lpxC and lpxD as well as their colistin-susceptible counterparts. A dramatic increase in antibiotic susceptibility (≥16-fold increase) was observed upon LPS loss for azithromycin, rifampicin and vancomycin, whereas a moderate increase in susceptibility was seen for amikacin, ceftazidime, imipenem, cefepime and meropenem. Importantly, concentrations ranging from 8 mg/L to 32 mg/L of the six AMPs were able to reduce bacterial viability by ≥3 log 10 in growth curve assays. We also demonstrate that colistin resistance results in partial colistin dependence for growth in LPS-deficient strains containing mutations in lpxA , lpxC and lpxD , but not when colistin resistance occurs via LPS modification due to mutations in the PmrA/B two-component system. The results of this study indicate that loss of LPS expression results in collateral sensitivity to azithromycin, rifampicin and vancomycin, and that the six AMPs tested retain activity against LPS-deficient strains, indicating that these antibiotics may be viable treatment options for infections caused by these strains. [ABSTRACT FROM AUTHOR]