Conjugation-Mediated Transfer of Antibiotic-Resistance Plasmids Between Enterobacteriaceae in the Digestive Tract of Blaberus craniifer (Blattodea: Blaberidae).

Cockroaches, insects of the order Blattodea, seem to play a crucial role in the possible conjugation-mediated genetic exchanges that occur among bacteria that harbor in the cockroach intestinal tract. The gut of these insects can be thought of as an effective in vivo model for the natural transfer of antimicrobial resistance plasmids among bacteria. In our study, we evaluated the conjugation-mediated horizontal transfer of resistance genes between Escherichia coli and other microorganisms of the same Enterobacteriaceae family within the intestinal tract of Blaberus craniifer Burmeister, 1838 (Blattodea: Blaberidae). Different in vivo mating experiments were performed using E. coli RP4 harboring the RP4 plasmid carrying ampicillin, kanamycin, and tetracycline resistance genes as the donor and E. coli K12 resistant to nalidixic acid or Salmonella enterica serovar Enteritidis IMM39 resistant to streptomycin as the recipients. The RP4 plasmid was successfully transferred to both recipients, producing E. coli K12-RP4 and S. Enteritidis IMM39-RP4 transconjugants. Conjugation frequencies in vivo were similar to those previously observed in vitro. The transfer of the RP4 plasmid in all transconjugants was confirmed by small-scale plasmid isolation and agar gel electrophoresis, suggesting that the intestinal tract of cockroaches is an effective in vivo model for natural gene transfer. Our results confirm that cockroaches allow for the exchange of antimicrobial resistance plasmids among bacteria and may represent a potential reservoir for the dissemination of antibiotic-resistant bacteria in different environments. These findings are particularly significant to human health in the context of health care settings such as hospitals.

Ecological behaviour of three serogroups of Legionella pneumophila within a model plumbing system.

Three Legionella pneumophila strains isolated from water samples and belonging to serogroups (sgs) 1, 6 and 9 were analysed for their capacity to colonise an experimental model simulating a domestic hot water distribution system. Ecological factors that could influence the persistence of the sgs such as intracellular life within protozoan hosts and bacterial interference by the production of antagonistic compounds were also studied. Viable counts of L. pneumophila increased both in the planktonic and in the sessile phases. Sg 6 showed a marked prevalence during the whole experiment and exhibited the highest host infection efficiency. Sg 1 was significantly less represented, but showed the highest capacity to reproduce in the protozoan hosts. Sg 9 was poorly represented and less adapted to intracellular life. Among the 14 bacteria constantly isolated in the system, five (35.7%) produced antagonistic substances against Legionella, with differences according to the bacterial strain and L. pneumophila sgs.

Influence of Legionella pneumophila and other water bacteria on the survival and growth of Acanthamoeba polyphaga.

We investigated in solid medium, in water microcosm co-cultures and by light and transmission electron microscopy the influence of Legionella pneumophila Lp-1, Pseudomonas aeruginosa ATCC 27853, Burkholderia cepacia ATCC 25416 and Pseudomonas fluorescens SSD35 on the growth and survival of Acanthamoeba polyphaga. The infection with L. pneumophila was microscopically characterized by the presence of few bacteria inside protozoa at 4th h, and by the beginning of disruptive effects in late phase of trial. In water microcosm studies, performed at different temperature, the more significant interactions were observed at 30°C. In these conditions, L. pneumophila caused a marked reduction in trophozoite and cyst counts from the 4th day until the end of incubation (11 days). B. cepacia showed, by microscopic observation, few and generally single rods within protozoan phagosomes and caused a light reduction of trophozoite viability and cyst formation in co-cultures. A more invasive type of endocytosis, characterized by an early invasion with the presence of a high bacteria number inside amoebae, was observed for Pseudomonas strains. P. fluorescens produced a violent lysis of the host, whereas P. aeruginosa did not cause lysis or suffering. These results underline that water bacteria other than legionella are capable of intracellular survival in Acanthamoeba, influencing the protozoa viable cycle.

Detection of bacteriocin production and virulence traits in vancomycin-resistant enterococci of different sources.

AIM: Three hundred and two enterococci were isolated from food, animal and clinical samples in order to evaluate the incidence of vancomycin-resistant enterococci (VRE) and bacteriocin, cytolysin, haemolysin, gelatinase production. METHODS AND RESULTS: Among the isolates, 27 (8.9%) were VRE, and 17 (63%) of these showed, by the deferred antagonism method, bacteriocin production against gram-positive and some gram-negative indicators. Eight bacteriocin producers displayed by polymerase chain reaction an enterocin structural gene: six Enterococcus faecium the Enterocin A, two Enterococcus faecalis the Enterocin P genes. The enterocins AS-48, 31, L50 and 1071A/B genes were not found. Regarding the virulence factors, two VRE produced gelatinase and seven were haemolytic. Gelatinase gelE gene was found in 19 strains and cytolysin cylL(L) gene in eight. Among the strains showing the cylL(L) gene, only two E. faecalis expressed a beta-haemolysis. CONCLUSIONS: Our results showed the persistence of VRE in food, animal and clinical samples. Many of these strains displayed antibacterial activity and sometimes different components of virulence, which could emphasize their pathogenicity. SIGNIFICANCE AND IMPACT OF THE STUDY: This work indicates the need of a constant monitoring of enterococci in order to assess their possible pathogenic properties. The strains of interest in the food industry or used as probiotics should be tested for antibiotic resistance and virulence traits.