1246. Tetracycline Resistance in Staphylococcus aureus Isolates from US Military Members Injured in Iraq or Afghanistan Who Had Received Doxycycline for Malaria Prophylaxis
Session: Poster Abstract Session: Staphylococcal Resistance and Epidemiology
Saturday, October 22, 2011
Room: Poster Hall B1
Background: Whether clinical doxycycline exposure impacts subsequent Staphylococcus aureus susceptibility to tetracyclines is not clear. We evaluated tetracycline resistance in S. aureus isolates recovered from US military members injured in Iraq or Afghanistan, many of whom had received doxycycline for malaria prophylaxis.

Methods: All S. aureus isolates from June 2009 to January 2011 collected at Brooke Army Medical Center from participants in the Trauma Infectious Disease Outcomes Study were included. Isolates were defined as doxycycline exposed if isolated from a patient that had received doxycycline malaria prophylaxis. Susceptibility to tetracycline (TCN), doxycycline (DCN), and minocycline (MCN) was determined using the BD Phoenix automated system. The presence of genes conferring resistance to tetracycline (tetK, tetM, tetL, and tetO) was assessed by PCR. Pulsed field gel electrophoresis (PFGE) was performed following CDC protocols to determine genetic relatedness of the isolates. Proportions were compared with chi-squared tests.

Results: Fifty-one colonizing and infecting isolates from 27 patients were characterized. Thirty-five (69%) were identified from patients who had previously received DCN, 32 (63%) were MRSA, and 24 (47%) were USA300. The percentages of isolates susceptible to TCN, DCN, and MCN were 75%, 76%, and 78%, respectively. The presence of tetM was found in 11 isolates with nonsusceptibility to all three drugs and one isolate with nonsusceptibility to TCN and DCN. One isolate resistant only to TCN contained tetK.  Eight (23%) DCN exposed isolates were nonsusceptible to any tetracycline drug compared with 5 (31%) DCN unexposed isolates (p=0.53). DCN exposed isolates were marginally more likely to be USA300 than unexposed isolates (54% vs 25%, respectively; p=0.05), whereas the proportion which were MRSA was similar (66% exposed vs 56% unexposed; p=0.52).

Conclusion: Prior exposure to doxycycline as malaria prophylaxis was not associated with phenotypic tetracycline resistance or the presence of tetracycline resistance genes. As tetK accounted for only 8% of tetracycline resistant isolates, inducible resistance to tetracyclines, appears unlikely in this patient population.

Subject Category: A. Antimicrobial agents and Resistance

Michael Landrum, MD1,2, Katrin Mende, PhD1,2, Miriam Beckius, MPH1, Wendy Zera, BS1,2, Xin Yu3, Kristelle Cheatle, BA1, David Tribble, MD, DrPH2 and Clinton K. Murray, MD4, (1)Brooke Army Medical Center, Fort Sam Houston, TX, (2)Infectious Disease Clinical Research Program, Uniformed Services University, Bethesda, MD, (3)Clinical Investigation, Brooke Army Medical Center, Fort Sam Houston, TX, (4)Brooke Army Medical Center, Ft. Sam Houston, TX


M. Landrum, None

K. Mende, None

M. Beckius, None

W. Zera, None

X. Yu, None

K. Cheatle, None

D. Tribble, None

C. K. Murray, None

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