Shiga Toxin (Stx) Phage-Encoded Lytic Genes Are Not Required for the Mouse Virulence of O157:H7 Escherichia coli Stx2-Producing Clinical Isolates.

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a major cause of foodborne diarrheal illness in the United States and globally, and serotype O157:H7 is frequently associated with STEC outbreaks and sporadic cases in the United States. Severe systemic diseases associated with STEC are mediated by Stx types, particularly subtype Stx2a, encoded on inducible bacteriophages. We previously identified two STEC O157:H7 clinical isolates, JH2010 and JH2012, that exhibit a large difference in virulence in a streptomycin (Str)-treated mouse model. In this study, we aimed to identify a genetic basis for the difference in virulence between those strains. Comparison of the stx2a phage sequences showed that JH2012 lacks the lytic genes S and R on the phage genome. We also demonstrated that compared to JH2012 cultures, cultures of JH2010 released more Stx2 into the supernatant and were more sensitive to bacterial lysis during growth with ciprofloxacin (Cip), an inducer of stx phages. We therefore generated an stx2a phage SR deletion mutant strain of JH2010 to determine if those genes were responsible for the high virulence of that strain. We found that deletion of the SR genes from the stx2a phage in JH2010, and another O157:H7 strain, JH2016, resulted in increased cellular retention of Stx2, but there was no difference in virulence compared to the wild-type strains. Our results indicate that the stx2a phage SR genes are involved in Stx2 localization and phage-mediated cell lysis in vitro but that they are not required in wild-type STEC strains for virulence in a mouse model. IMPORTANCE The release of Stx from STEC has been thought to be tied to phage-mediated lysis of the host bacterial cell. In this study, we found that the stx2a phage lytic genes are not required for the virulence of pathogenic O157:H7 clinical isolates in a murine model of STEC infection or for release of Stx2a into the supernatant of bacterial cultures. These results point to an alternate mechanism for Stx2a release from STEC strains.

Inflight application of three pilot workload measurement techniques.

Three measures of workload were tested during 11 routine missions conducted by the NASA Kuiper Airborne Observatory: communications performance, subjective ratings, and heart rate. The activities that contributed to crewmember workload varied; the commander was responsible for aircraft control and navigation whereas the copilot handled communications with ATC and the astronomers. Ratings of workload, stress, and effort given by the two crewmembers were highly correlated and varied across flight segments, peaking during takeoff and landing. Since the pilots performed different tasks during each segment, their ratings appeared to reflect overall crew workload, rather than experiences specific to each pilot. Subjective fatigue increased significantly from takeoff to landing for all flights, although the increase was significantly greater as landing times shifted from 10:00 p.m. to 9:00 a.m. The type, source, number, and frequency of communications varied significantly across flight segments, providing an objective indicator of pilot workload. Heart rate was significantly higher for the aircraft commander than for the copilot. Although heart rate peaked for both positions during takeoff and landing, the amount of change was significantly greater for the aircraft commander. Subjective ratings of stress, workload, and mental effort were significantly correlated with heart rate and communications frequency but were unrelated to mission duration, rated fatigue, or pilot evaluation of performance.

Ion implanted photodiode detectors in epitaxial (Ga(x) In(1-x))As.

Ion implanted p-n junction photodiodes in epitaxially grown (Ga(x) In(1-x))As material are reported on here. Photoresponse in these diodes was investigated for approximately the entire composition range of 0 < x < 1. High values for quantum efficiency were obtained for the devices with a high value of x. Peak D(*)(lambda,f) of greater than 10(11) [cm(Hz)(1/2)/W] at room temperature was obtained at 0.8-microm wavelength, while a peak D(*)(lambda,f) of 5 x 10(10) [cm(Hz)(1/2)/W] was obtained at 165 K at 1.4-microm wavelength.