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Objectives: Combination therapy has been recommended when using ceftazidime-avibactam (CAZ-AVI) for the treatment of KPC-producing Klebsiella pneumoniae (KPC-Kp), but the optimal combination is unknown. Six common antimicrobial agents (ertapenem, imipenem, meropenem, gentamicin, tigecycline, and ciprofloxacin) were evaluated for synergy with the recently approved cephalosporin-β-lactamase inhibitor combination CAZ-AVI in this study., Methods: Different antimicrobial combinations were tested against 13 KPC-Kp, including CAZ-AVI-susceptible (n=11) and resistant (n=2) clinical isolates. In vitro interactions of CAZ-AVI with different antimicrobials were tested using the gradient synergy test. Changes in the minimum inhibitory concentration (MIC) value were interpreted using the fractional inhibitory concentration (FIC) index and susceptible breakpoint index (SBPI)., Results: The combination of CAZ-AVI with gentamicin or ciprofloxacin displayed no synergism against any of the KPC-Kp isolates, whereas synergistic activity was observed with imipenem and meropenem against all KPC-Kp isolates. Notably, CAZ-AVI reduced MICs for meropenem and imipenem below the resistance breakpoints against all strains. The SBPI analysis showed that CAZ-AVI in combination with imipenem achieved higher SBPI values than other CAZ-AVI-based combinations., Conclusions: These data suggest that combinations of CAZ-AVI with imipenem may be considered a useful therapeutic option for the treatment of KPC-Kp infections., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

In intensive care units (ICUs), the most important causes of nosocomial bacterial infections are mainly multidrug-resistant (MDR) and extensively drug-resistant (XDR) Acinetobacter baumannii and Klebsiella pneumoniae strains. Mortality related to these infections is very high due to lack of effective therapy and the severity of patient conditions. This study aimed to assess the prevalence of carbapenem resistance genes in 77 carbapenem-resistant Gram-negative bacteria isolated from severe infections (bloodstream, pulmonary and urinary tract) during the period 1 January to 31 July 2013 in a general ICU in Catania, Italy, and to examine their susceptibility to tigecycline and colistin using two different methods. In total, 52 A. baumannii belonging to the same sequence type (ST) 2 clone and carrying the bla(OXA-23) gene as well as 25 K. pneumoniae carrying bla(KPC-3) were isolated. Four distinct pulsotypes were identified in K. pneumoniae, which correlated with four distinct STs: ST258 and ST512, spread worldwide, and ST147 and ST395 detected for the first time in Italy. A. baumannii isolates showed an XDR profile and were fully susceptible only to colistin; all KPC-producing K. pneumoniae isolates were MDR, whilst colistin was active against 19 of 25 strains. These results show that broth microdilution (BMD) is a reliable in vitro susceptibility test for colistin, above all K. pneumoniae, whilst both the gradient test and BMD are suitable for tigecycline susceptibility testing of A. baumannii., (Published by Elsevier B.V.)

Antibiotic resistance in Klebsiella pneumoniae strains is an increasing problem in a lot of hospitals. It is a public health emergency because it relates with high mortality rate among patients in Intensive Care Unit (ICU). From 1/1/2009 to 31/08/2010, in ICU of SS Annunziata Hospital of Taranto, 140 isolated Klebsiella pneumoniae strains were detected. The strain identification and antimicrobial susceptibility testing were performed using a Vitek2 automated system. These isolate showed a low level of susceptibility to levofloxacin (3.4%), ciprofloxacin (6.2%), ceftazidime (2.8%) and piperacillin/tazobactam (8%). We reported also that the 10% and 13.9% of them were susceptible to meropenem and imipenem. An anti-Klebsiella pneumoniae activity in vitro to tigecycline was present in 64.6% of isolates while almost all strains (56/58) tested to colistin were susceptible. In order to our data of worryng high multiclass drug resistance including tygecicline, it needs to apply appropriate measures of surveillance and antibiotic prescription to avoid rapid spread of these mutiresistant strains in other areas.

The aim of this study was to investigate the presence of tetracycline and oxytetracycline resistance determinants in Bacillus cereus strains isolated from honey samples. Of a total of 77 isolates analyzed, 30 (39%) exhibited resistance to tetracyclines according to the results of a disk diffusion method. Resistant strains (n=30) were screened by PCR for the presence of the resistant determinants tetK, tetL, tetM, tetO, tetW, otrA and otrB and their MIC values for tetracycline, oxytetracycline and minocycline were assessed. According to the PCR results, 23 isolates (77%) presented at least one tetracycline or oxytetracycline resistance determinant. The tetK genotype was present in 10 isolates while the tetL, tetM, and otrA genotypes were present in 3, 2, and 5 isolates, respectively. In addition, 2 isolates of the tetK plus tetM genotype, 1 of the tetK plus tetL genotype, and 1 of the tetK plus otrA genotype were found. All isolates were tetW, tetO and otrB negatives. On the other hand, 7 isolates (23%) showed a tetracycline-resistant and/or minocycline-resistant phenotype (MIC) but did not carry any of the tet or otr determinants investigated in this study. This research has shown that B. cereus isolates from honey samples contain a variety of tetracycline and oxytetracycline resistance genes, including the tetK and tetL determinants which encode for efflux proteins, and tetM and otrA, which encode for ribosomal protection proteins. These findings indicate that strains isolated from honeys could represent a reservoir for tetracycline resistance genes. To our knowledge, this is the first report of tetracycline-resistant and oxytetracycline-resistant B. cereus strains carrying the tetK determinant, and also the first report of oxytetracycline-resistant and tetracycline-resistant Bacillus species carrying the otrA determinant.

Background: In a recent multi-centre Italian survey (2003-2004), conducted in 45 laboratories throughout Italy with the aim of monitoring microorganisms responsible for severe infections and their antibiotic resistance, Acinetobacter baumannii was isolated from various wards of 9 hospitals as one of the most frequent pathogens. One hundred and seven clinically significant strains of A. baumannii isolates were included in this study to determine the in vitro activity of tigecycline and comparator agents., Methods: Tests for the susceptibility to antibiotics were performed by the broth microdilution method as recommended by CLSI guidelines. The following antibiotics were tested: aztreonam, piperacillin/tazobactam, ampicillin/sulbactam, ceftazidime, cefepime, imipenem, meropenem tetracycline, doxycycline, tigecycline, gentamicin, amikacin, ciprofloxacin, colistin, and trimethoprim/sulphametoxazole. The PCR assay was used to determine the presence of OXA, VIM, or IMP genes in the carbapenem resistant strains., Results: A. baumannii showed widespread resistance to ceftazidime, ciprofloxacin and aztreonam in more than 90% of the strains; resistance to imipenem and meropenem was 50 and 59% respectively, amikacin and gentamicin were both active against about 30% of the strains and colistin about 99%, with only one strain resistant. By comparison with tetracyclines, tigecycline and doxycycline showed a higher activity. In particular, tigecycline showed a MIC90 value of 2 mg/L and our strains displayed a unimodal distribution of susceptibility being indistinctly active against carbapenem-susceptible and resistant strains, these latter possessed OXA-type variant enzymes., Conclusion: In conclusion, tigecycline had a good activity against the MDR A. baumannii strains while maintaining the same MIC(90) of 2 mg/L against the carbapenem-resistant strains.