1829. Antimicrobial Susceptibility of Carbapenem-Susceptible and -Resistant Acinetobacter baumannii (Ab): PRIMERS-III, part 1
Session: Poster Abstract Session: Treatment of HAIs/Antimicrobial Resistant Infections
Saturday, October 10, 2015
Room: Poster Hall

Background: In this study, the susceptibility (S) of a collection of carbapenem-susceptible and -resistant Ab (CSAB and CRAB) was determined to evaluate the activity of agents of “last resort” (tetracyclines and polymyxins) to help inform empiric selection when CRAB are identified. We asked the questions: if CRAB are detected, i) how likely are they to be S to “last resort” agents, and ii) can one use this information to inform treatment decisions?

 

Methods: 103 CSAB and 97 CRAB obtained from a worldwide collection were tested. MICs were determined by CLSI broth microdilution and interpreted according to CLSI/FDA breakpoints (Table). Breakpoints for Enterobacteriaceae or Pseudomonas aeruginosa were used if not available for Ab.

Results:  >90% of isolates of CSAB were S to amikacin, tobramycin, ampicillin-sulbactam, ceftazidime, minocycline, tigecycline, colistin, and polymyxin B, while 80–89% were S to piperacillin-tazobactam, ciprofloxacin, levofloxacin, tetracycline, and trimethoprim-sulfamethoxazole (Table). In contrast, the only agents with activity against CRAB were colistin (89% S), polymyxin B (90% S), and tigecycline (84% S). Amikacin (20% S), tobramycin (14% S), ampicillin-sulbactam (19% S), and minocycline (37% S) had activity against some CRAB isolates.

Conclusion:  After CRAB are identified, tigecycline and polymyxins (colistin) are possibilities for empiric therapy in ~90% of cases. Minocycline is the only orally available oral agent to be considered, but resistance rates are surprisingly high (63% R). CRAB presents a major clinical challenge as isolates are frequently resistant to all conventional agents used to treat CSAB. Detection of CRAB should prompt empiric treatment by colistin and/or tigecycline.

 

Table. Susceptibility of CSAB and CRAB to antimicrobial agents (%)

Antimicrobial agent (susceptible breakpoint in mg/L)

CRAB (N=97)

% shown

CRAS (N=103)

% shown

Amikacin (16)

20

95

Gentamicin (4)

2

66

Ampicillin-sulbactam (8/4)

19

96

Piperacillin-tazobactam (16/4)

1

87

Cefepime (8)

5

89

Ceftazidime (8)

6

90

Ciprofloxacin (1)

0

83

Imipenem (2)

3

100

Tetracycline (4)

10

84

Minocycline (4)

37

98

Tigecycline (2)

84

100

Colistin (2)

89

97

Polymyxin B (2)

90

98

 

Michael R. Jacobs, MD, PhD1, Andrea Hujer, BS2, Kristine M. Hujer, BS3, Barry N. Kreiswirth, PhD4, Claudia Manca, PhD5, Liang Chen, PhD5 and Robert A. Bonomo, MD6, (1)Case Western Reserve University/University Hospitals of Cleveland, Cleveland, OH, (2)Case Western Reserve University, Cleveland, OH, (3)Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, (4)Phri TB Center, Rutgers University, Newark, NJ, (5)Public Health Research Institute - Rutgers University, Newark, NJ, (6)Pharmacology, Molecular Biology, and Microbiology, Case Western Reserve University, Cleveland, OH

Disclosures:

M. R. Jacobs, None

A. Hujer, None

K. M. Hujer, None

B. N. Kreiswirth, None

C. Manca, None

L. Chen, None

R. A. Bonomo, AstraZeneca: Grant Investigator , Research grant
Merck: Grant Investigator , Research grant
Melinta: Grant Investigator , Research grant
VA Merit Review Board: Grant Investigator , Research grant
NIH: Grant Investigator , Research grant

Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 7th with the exception of research findings presented at the IDWeek press conferences.