The intracellular multiplication factor (IcmF) protein is a component of the recently described type VI secretion system (T6SS). IcmF has been shown to be required for intra-macrophage replication and inhibition of phagosome–lysosome fusion inLegionella pneumophila. InVibrio choleraeit is involved in motility, adherence and conjugation. Given that we previously reported that two T6SS genes (hcpandclpV) contribute to the pathogenesis of a septicaemic strain (SEPT362) of avian pathogenicEscherichia coli(APEC), we investigated the function of IcmF in this strain. Further elucidation of the virulence mechanisms of APEC is important because this pathogen is responsible for financial losses in the poultry industry, and is closely related to human extraintestinal pathogenicE. coli(ExPEC) strains, representing a potential zoonotic risk, as well as serving as a reservoir of virulence genes. Here we show that an APECicmFmutant has decreased adherence to and invasion of epithelial cells, as well as decreased intra-macrophage survival. TheicmFmutant is also defective for biofilm formation on abiotic surfaces. Additionally, expression of the flagella operon is decreased in theicmFmutant, leading to decreased motility. The combination of these phenotypes culminates in this mutant being altered for infection in chicks. These results suggest that IcmF in APEC may play a role in disease, and potentially also in the epidemiological spread of this pathogen through enhancement of biofilm formation.

Pseudomonas aeruginosa is an opportunistic pathogen with high resistance to a wide variety of antimicrobials. The multidrug resistance pump MexAB-OprM promotes the efflux of various antibiotics, mostly when mutations accumulate in the transcriptional regulators MexR, NalC and NalD, thereby causing MexAB-OprM overexpression. In this work, it was done a characterization of 50 P. aeruginosa isolates obtained from Brazilian agricultural soils to determine the reasons of their resistance to aztreonam. The majority of the isolates showed higher aztreonam resistance than wild-type strain by MIC method. DNA sequence analysis of mexR , nalC and nalD genes from 13 of these isolates showed the amino acid substitution in NalC for all tested isolates, just one mutation was detected in MexR and none in NalD. Furthermore, it was found an increase in the level of mexA expression by Real-time RT-PCR analysis in eight isolates harboring mutations in NalC. Although there was not a relationship between MIC of aztreonam and the level of mexA expression, on the other hand, the results presented here suggest that novel mutations in NalC, including Arg97-Gly and Ala186-Thr, are related to MexAB-OprM overexpression causing aztreonam resistance in P. aeruginosa environmental isolates.