High prevalence of trimethoprim-resistance cassettes in class 1 and 2 integrons in Senegalese Shigella spp isolates.
BACKGROUND
Integrons have a well-established role in the dissemination of resistance among Gram-negative pathogens and are thus a useful marker of antibiotic resistance. Shigellae are noteworthy for their multiple drug resistance, having gradually acquired resistance to most widely use and inexpensive antimicrobial drugs.


METHODS
A total of 32 Shigella strains belonging to serotypes flexneri, dysenteriae, and boydii 20, a new Shigella serovar, resistant to at least four antibiotics were analyzed by molecular techniques.


RESULTS
Class 1 integrons were the most prevalent (92.8%); class 2 integrons were found in 16 strains (57.1%). Fifty percent of the strains harboured both class 1 and 2 integrons (intI1 and intI2 genes); this combination of integrase genes was most prevalent in S. boydii 20 and S. dysenteriae strains. The class 1 integrons detected contained dfr and aadA cassettes, alone or in combination (dfrA5/dfrA15, or dfrA15-aadA1, dfrA1-aadA2), and an atypical cassette array with an insertion sequence (oxa30-aadA1-IS1). For class 2 integrons, we detected either the same cassettes as those found in Tn7 (dfrA1-sat1-aadA1-orfX) or truncated class 2 integrons without aadA1 or orfX. The tns genes were absent from all class 2 integrons.The distribution of integrons among RAPD profiles and serotypes revealed a clonal spread of integrons into serotypes and a transfer of integrons between different serotypes.


CONCLUSIONS
The detection of integrons in a new Shigella serovar, in addition with a high integron prevalence among Shigella strains, confirms the propensity of shigellae to acquire and disseminate resistance determinants.
Gassama Sow
Amy
A
Unité de Bactériologie Expérimentale, Institut Pasteur, Dakar, Senegal. gassama@pasteur.sn
Aïdara-Kane
Awa
A
Barraud
Olivier
O
Gatet
Martine
M
Denis
François
F
Ploy
Marie Cécile
MC
D015373:Bacterial Typing Techniques; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D004405:Dysentery, Bacillary / Q000382:microbiology*; D005798:Genes, Bacterial; D006801:Humans; D032023:Integrons; D015995:Prevalence; D019105:Random Amplified Polymorphic DNA Technique; D012675:Senegal; D012760:Shigella / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D014296:Trimethoprim Resistance
D004269:DNA, Bacterial