In vivo Fitness of Acinetobacter baumannii Strains in Murine Infection Is Associated with International Lineage II-rep-2 and International Lineage III Clones Showing High Case Fatality Rates in Human Infections.

We previously reported that the 14-day case fatality rate (CFR) in patients with carbapenem-resistant Acinetobacter baumannii (CRAB) bacteremia varied between infecting clones. Here, we evaluated the in vitro and in vivo fitness of CRAB blood isolates belonging to clones with low CFR (< 32% 14-day mortality) and high CFR (65% 14-day mortality). Fitness was measured in vitro using a growth curve assay and in vivo using murine thigh muscle and septicemia models of infection. Our sample included 38 CRAB isolates belonging to two clones with low CFR (international lineage (IL)-II-rep-1, n = 13 and IL-79, n = 6) and two clones with high CFR (IL-III, n = 9 and IL-II-rep-2, n = 10). In in vitro growth curves, mean lag time, generation time and maximal growth varied between clones but could not discriminate between the high and low CFR clones. In the in vivo models, bacterial burdens were higher in mice infected with high CFR clones than in those infected with low CFR clones: in thigh muscle, 8.78 ± 0.25 vs. 7.53 ± 0.25 log10CFU/g, p < 0.001; in infected spleen, 5.53 ± 0.38 vs. 3.71 ± 0.35 log10CFU/g, p < 0.001. The thigh muscle and septicemia model results were closely correlated (r = 0.93, p < 0.01). These results suggest that in vivo but not in vitro fitness is associated with high CFR clones.

Does Acinetobacter baumannii Serve as a Source for blaNDM Dissemination into Enterobacteriaceae in Hospitalized Patients?

The goal was to study the possibility that Acinetobacter baumannii serve as an epidemiologically significant source for transmission of the blaNDM gene to Enterobacteriaceae by horizontal gene transfer (HGT) in hospitalized patients. The study was done at the Tel-Aviv Sourasky Medical Center from December 2014 until August 2015. Clinical and surveillance rectal cultures were collected as per hospital policies and were analyzed for the presence of New Delhi metallo-beta-lactamase-producing Enterobacteriaceae (NDME) and A. baumannii (NDMAb). Isolates were typed by pulsed-field gel electrophoresis (PFGE). The location of the blaNDM gene within the Tn125 transposon was studied by sequencing. A transmission event (TE) was determined if patients shared the same PFGE type of either NDME or NDMAb and were simultaneous in the same ward. HGT-related TE was considered if the two isolates shared identical blaNDM gene allele and transposon. There were 16 NDMAb- (clinical, 10; surveillance, 4; both, 2) and 13 NDME- (clinical, 3; surveillance, 8; both, 2) infected/colonized patients. All NDMAb isolates except two harbored the blaNDM-1 allele that was located within a Tn125 transposon and was plasmid borne. The majority of patients (n = 10/16) were infected by one PFGE type of NDMAb, and five clonal TEs were identified. NDME were either Escherichia coli (n = 4) or Klebsiella pneumoniae (n = 9) of different PFGE types with only one NDME TE. The blaNDM gene was within a Tn125 in three K. pneumoniae isolates. Although one HGT-related TE between NDMAb and K. pneumoniae was epidemiologically suspected, the low similarity between the Tn125 transposons (75.7%) excluded that possibility. In conclusion, whereas NDMAb appears to disseminate by clonal spread, we did not find evidence for HGT-mediated transmission in NDME in hospitalized patients.

Novel rat model of methicillin-resistant Staphylococcus aureus-infected silicone breast implants: a study of biofilm pathogenesis.

BACKGROUND: Clinical infection of breast implants occurs in 7 to 24 percent of breast reconstructions. It may persist over time in the form of biofilm without overt manifestation and is extremely difficult to eradicate. The authors' aim was to establish a novel model for biofilm infection of silicone breast implants in rats. METHODS: Fifty-six rats underwent implantation of miniature silicone breast implants and/or methicillin-resistant Staphylococcus aureus (MRSA) bacteria. Group A received implants covered with MRSA biofilm. Group B received implants and free planktonic MRSA. Group C received free planktonic MRSA without implants. A control group received sterile implants without MRSA. Each group was divided to receive either saline or vancomycin injections between days 4 and 11. Clinical evaluation, bacterial counts, and scanning electron microscopy were performed. RESULTS: The mortality rate in group B (implants infected with free planktonic MRSA) was significantly higher than that in all other groups [37 percent versus groups A and D (0 percent) and group C (7 percent)]. Treatment with vancomycin lowered temperature in groups B and C (p < 0.05) and improved wound healing in group B (p < 0.01). Vancomycin treatment reduced wound bacterial counts in free planktonic MRSA groups B and C but had no significant effect on biofilm MRSA-infected group A. CONCLUSIONS: The model successfully induced persistent breast implant infection. Free planktonic MRSA produced in situ biofilm on silicone implants. Biofilm infection has milder manifestations than free planktonic MRSA infection, which has higher rates of systemic infections and death when compared with either isolated biofilm infection or free planktonic MRSA infection without implant. Vancomycin has limited effect against mature biofilm.

High prevalence of methicillin-resistant Staphylococcus aureus among residents and staff of long-term care facilities, involving joint and parallel evolution.

Six long-term care facilities were surveyed for methicillin-resistant Staphylcoccus aureus (MRSA). Among 191 residents, 14% were carriers; 1 strain predominated (ST5-SCCmec II). Among 132 staff members, 11% were positive; 2 strains predominated (ST5-SCCmec II, ST8-SCCmec IV). All strains were Panton-Valentine leukocidin-negative. The epidemiology of MRSA among residents and staff involved joint and parallel evolution.

Increase in rhamnolipid synthesis under iron-limiting conditions influences surface motility and biofilm formation in Pseudomonas aeruginosa.

Iron is an essential element for life but also serves as an environmental signal for biofilm development in the opportunistic human pathogen Pseudomonas aeruginosa. Under iron-limiting conditions, P. aeruginosa displays enhanced twitching motility and forms flat unstructured biofilms. In this study, we present evidence suggesting that iron-regulated production of the biosurfactant rhamnolipid is important to facilitate the formation of flat unstructured biofilms. We show that under iron limitation the timing of rhamnolipid expression is shifted to the initial stages of biofilm formation (versus later in biofilm development under iron-replete conditions) and results in increased bacterial surface motility. In support of this observation, an rhlAB mutant defective in biosurfactant production showed less surface motility under iron-restricted conditions and developed structured biofilms similar to those developed by the wild type under iron-replete conditions. These results highlight the importance of biosurfactant production in determining the mature structure of P. aeruginosa biofilms under iron-limiting conditions.