This review discusses the various types of bacterial genomic islands that can be transferable by conjugation, their intra- and intercellular mobility, and the m

CmeABC, a multidrug efflux pump, is involved in the resistance ofCampylobacter jejunito a broad spectrum of antimicrobial agents and is essential forCampylobactercolonization in animal intestine by mediating bile resistance. Previously, we have shown that expression of this efflux pump is under the control of a transcriptional repressor named CmeR. Inactivation of CmeR or mutation in thecmeABCpromoter (P_cmeABC) region derepressescmeABC, leading to overexpression of this efflux pump. However, it is unknown if the expression ofcmeABCcan be conditionally induced by the substrates it extrudes. In this study, we examined the expression ofcmeABCin the presence of various antimicrobial compounds. Although the majority of the antimicrobials tested did not affect the expression ofcmeABC, bile salts drastically elevated the expression of this efflux operon. The induction was observed with both conjugated and unconjugated bile salts and was in a dose- and time-dependent manner. Experiments using surface plasmon resonance demonstrated that bile salts inhibited the binding of CmeR to P_cmeABC, suggesting that bile compounds are inducing ligands of CmeR. The interaction between bile salts and CmeR likely triggers conformational changes in CmeR, resulting in reduced binding affinity of CmeR to P_cmeABC. Bile did not affect the transcription ofcmeR, indicating that altered expression ofcmeRis not a factor in bile-induced overexpression ofcmeABC. In addition to the CmeR-dependent induction, some bile salts (e.g., taurocholate) also activated the expression ofcmeABCby a CmeR-independent pathway. Consistent with the elevated production of CmeABC, the presence of bile salts in culture media resulted in increased resistance ofCampylobacterto multiple antimicrobials. These findings reveal a new mechanism that modulates the expression ofcmeABCand further support the notion that bile resistance is a natural function of CmeABC.

Conjugation is a key mechanism of bacterial evolution that involves mobile genetic elements. Recent findings indicated that the main actors of conjugative transfer are not the well-known conjugative or mobilizable plasmids but are the integrated elements. This paper reviews current knowledge on “integrative and mobilizable elements” (IMEs) that have recently been shown to be highly diverse and highly widespread but are still rarely described. IMEs encode their own excision and integration and use the conjugation machinery of unrelated co-resident conjugative element for their own transfer. Recent studies revealed a much more complex and much more diverse lifecycle than initially thought. Besides their main transmission as integrated elements, IMEs probably use plasmid-like strategies to ensure their maintenance after excision. Their interaction with conjugative elements reveals not only harmless hitchhikers but also hunters that use conjugative elements as target for their integration or harmful parasites that subvert the conjugative apparatus of incoming elements to invade cells that harbor them. IMEs carry genes conferring various functions, such as resistance to antibiotics, that can enhance the fitness of their hosts and that contribute to their maintenance in bacterial populations. Taken as a whole, IMEs are probably major contributors to bacterial evolution.

Macrolide-resistant mutants of Campylobacter jejuni and Campylobacter coli were selected in vitro using erythromycin and tylosin. These mutants exhibited modifications in the ribosomal proteins L4 (G74D) and L22 (insertions at position 86 or 98). A synergy between the CmeABC efflux pump and these modifications in conferring macrolide resistance was observed.

Bovine isolates of S treptococcus agalactiae ( n = 76), S treptococcus dysgalactiae subsp. dysgalactiae ( n = 32), and S treptococcus uberis ( n = 101) were analyzed for the presence of different integrative and conjugative elements (ICEs) and their association with macrolide, lincosamide, and tetracycline resistance. The diversity of the isolates included in this study was demonstrated by multilocus sequence typing for S. agalactiae and pulsed-field gel electrophoresis for S. dysgalactiae and S. uberis . Most of the erythromycin-resistant strains carry an ermB gene. Five strains of S. uberis that are resistant to lincomycin but susceptible to erythromycin carry the lin (B) gene, and one has both linB and lnuD genes. In contrast to S. uberis , most of the S. agalactiae and S. dysgalactiae tetracycline-resistant isolates carry a tet (M) gene. A tet (S) gene was also detected in the three species. A Tn 916 -related element was detected in 30 to 50% of the tetracycline-resistant strains in the three species. Tetracycline resistance was successfully transferred by conjugation to an S. agalactiae strain. Most of the isolates carry an ICE integrated in the rplL gene. In addition, half of the S. agalactiae isolates have an ICE integrated in a tRNA lysine (tRNA ^Lys ) gene. Such an element is also present in 20% of the isolates of S. dysgalactiae and S. uberis . A circular form of these ICEs was detected in all of the isolates tested, indicating that these genetic elements are mobile. These ICEs could thus also be a vehicle for horizontal gene transfer between streptococci of animal and/or human origin.