Antimicrobial susceptibility among gram-positive and gram-negative blood-borne pathogens collected between 2012-2016 as part of the Tigecycline Evaluation and Surveillance Trial.

Background: Antimicrobial activity of tigecycline and comparator agents was assessed in vitro against 27857 isolates source from blood samples collected between 2012 and 2016 as part of the Tigecycline Evaluation and Surveillance Trial (TEST).

Methods: The broth microdilution methods was used to determine  minimum inhibitory concentrations (MIC) of blood-borne isolates according to guildlines of the Clinical and Laboratory Standards Institute (CLSI). Antimicrobial susceptibility breakpoints from CLSI guidelines were used as standards to determine susceptibility against comparator agents, whereas tigecycline breakpoints were provided by the US Food and Drug Administration (FDA).

Results: More than 91% Enterobacteriaceae isolates, belonging to Escherichia coli , Klebsiella pneumoniae , Enterobacter cloacae and Serratia marcescens , were susceptible to amikacin, meropenem, and tigecycline. Meropenem resistance was observed in 8% of K.pneumoniae isolates worldwide. Extended-spectrum β-lactamase (ESBL) was produced in 15.9 and 20.9% E.coli and  K.pneumoniae isolates, respectively. MIC90 of tigecycline against Acinetobacter baumannii was 2 μg/ml.  The highest proportion of susceptible A.baumannii isolates was 70.8% for minocycline. Among  P.aeruginose  isolates worldwide, 71.1-94.9% were susceptible to six antibiotics. Almost all Staphylococcus aureus isolates were susceptible to linezolid(100%), vancomycin(100%), and tigecycline (99.9%). The proportion of methicillin-resistant S.aureus (MRSA) was 33.0% among S.aureus isolates worldwide; it was highest in Asia with 46.6%, followed by North America and Latin America with 37.7 and 34.2%, respectively. Vancomycin-resistant (VR) isolates represented 1.4% of Enterococcus faecalis (VR. E.faecalis ) and 27.6% of  Enterococcus faecium (VR. E.faecium ). Highest percentages of VR. E.faecium were found in North America and Latin America, with 61.6 and 58.1% of the isolates, respectively. Production of penicillin-resistant  Streptococcus pneumoniae (PRSP) represented 9.0% of S. pneumoniae isolates worldwide; the PRSP proportion was 25.8% in Asia, 13.0% in Africa, and 11.8% in Latin America.

Conclusions: In our study, tigecycline was the only antibiotic that was active against over 90% of all major blood-borne pathogens. A global comparison revealed that antimicrobial resistance was higher in Africa, Asia and Latin America than in Europe and North America.