Nontyphoidal Salmonella invasive bloodstream infections resistant to quinolone and/or an extended spectrum cephalosporin in a country with extensive use of these antimicrobials in food animals

Abstract number: p557

Kulwichit  W., Chatsuwan  T., Unhasuta  C., Pulsrikarn  C., Bangtrakulnonth  A., Chongthaleong  A.


Nalidixic acid and extended spectrum cephalosporin resistant nontyphoidal Salmonella infection has been a growing global problem and more worrisome in certain countries. In our country, enrofloxacin, a veterinary fluoroquinolone, is extensively used in virtually all food animals. In addition, ceftiofur, a veterinary third-generation cephalosporin, is also widely used here in swine, not only for treatment but also for disease prevention. With complex plasmids capable of carrying both antimicrobial-resistance and virulence genes in a package, a general principle of microbes sacrificing virulence for resistance may not always apply. We have embarked on exploring clinical and molecular aspects of this growing problem, and wish to report our pilot survey here to alert the medical community.


Archival nontyphoidal Salmonella isolated from bacteremic patients in our university hospital from January 2003 to October 2005 and from bacteremic patients nationwide sent to The WHO National Salmonella and Shigella Center during the first half of 2005 entered the study. These collections are non-overlapping. E-test was used to evaluate MICs of nalidixic acid, ciprofloxacin, and ceftriaxone and susceptibility was defined using Clinical Laboratory Standards Institute (CLSI/NCCLS) 2005 criteria for Salmonella.


The bacteria were resistant to the antimicrobials tested at very high rates (Table). All Choleraesuis isolates with ceftriaxone resistance also expressed high levels of nalidixic acid resistance (MIC > 256 mg/ml) and thus reduced susceptibility to ciprofloxacin (MIC = 0.125 mg/ml or more). Of 73 nalidixic acid resistant isolates, 55 (75%) had ciprofloxacin MIC at 0.125 or more, 14 (19%) at 0.094, and 4 (6%) at 0.064 mg/ml. A case of aortitis from a ceftriaxone resistant organism resulted in a fatal ruptured mycotic aneurysm.


Compared to susceptibility patterns in the past, current nontyphoidal Salmonella infections in humans in our country are obviously more resistant to quinolone and cephalosporin without sacrificing its virulence. Nalidixic acid susceptibility correlates well with reduced susceptibility to ciprofloxacin. Alarming ceftriaxone resistance in Salmonella choleraesuis may be associated with inappropriate ceftiofur usage in pig farming. A reconsideration and probable major revision in policy on antimicrobial use in food animals for various purposes in our country is warranted.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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