Resistotyping of campylobacters: fulfilling a need

A 9-month trial of a simple typing scheme for ¿thermophilic' enteric campylobacter isolates at a large Public Health Laboratory is described. Resistotyping was performed with six agents in a method modified by Bolton and colleagues from an earlier scheme, and biotyping was performed by a modified Lior scheme involving three tests. Reproducibility was excellent in both schemes, with test variation < 2%. Five household clusters and one larger presumptive milk-borne outbreak were identified in this scheme, and confirmed in pyrolysis mass spectrometry. The 328 isolates from new patients, excluding duplication from these clusters, were divided into 35 resistotypes with the largest group comprising 22% of isolates. In combined bio- and resistotyping, 86 types were found, with the largest group comprising 9.5% of isolates. The results are contrasted with salmonella sero- and phage-typing, where, on the same basis, the 176 isolates in the same period were divided into 40 groups, with the largest comprising 45% of isolates. Resistotyping, with or without additional biotyping, proved to be a convenient, simple, rapid, highly discriminatory, reproducible and inexpensive method well suited to use in local laboratories. It is a strong candidate for first-line national and local surveillance of campylobacter infections, fulfilling a need for monitoring of this important cause of enteric disease.

A 13C NMR characterization of lysine residues in apolipoprotein B and their role in binding to the low density lipoprotein receptor

NMR spectroscopy of 13C-labeled human low density lipoprotein (LDL) has been employed to characterize the lysine (Lys) residues in apo B-100. Reductive methylation with [13C]formaldehyde converts up to two-thirds of the Lys to the dimethylamino derivative; this pool of Lys is exposed at the surface of the LDL particle. The [13C]dimethyl-Lys which are visualized exhibit resonances at chemical shifts of 42.8 and 43.2 ppm (pH 7.6) indicating that they exist in two different microenvironments; this is a reflection of the native conformation of apo B associated with lipid, because the labeled, reduced, and alkylated protein gives a single resonance when dissolved in 7 M guanidine hydrochloride. The pH dependences of the Lys chemical shifts indicate that the two types of Lys titrate with different pK values; "active" Lys have a pK of 8.9, while "normal" Lys have a pK of 10.5. About 53 active Lys and 172 normal Lys are exposed on the surface of LDL with the remaining 132 Lys which are present in the human apo B-100 molecule being buried and unavailable for methylation. Addition of paramagnetic ions indicates that the active and normal Lys have different exposures to the aqueous phase; apparently this is a reflection of folding of the apo B molecule. The relative involvement of active and normal Lys in binding of apo B-100 to the LDL receptor on fibroblasts was explored by measuring the decrease in receptor binding as a function of the degree of methylation of the two types of Lys. Upper limits of 21 active and 31 normal Lys in the entire apo B-100 molecule are involved in the binding of LDL to the receptor. It is likely that these Lys are located in domains of apo B which contain clusters of basic amino acid residues and also bind heparin. If the sequence corresponding to apo B-48 (residues 1-2151) which does not bind to the receptor is excluded, then the above limits are halved; an upper limit of 10 active Lys may be particularly involved in receptor binding.

Interferon and cell division. I. Inhibition of the multiplication of mouse leukemia L 1210 cells in vitro by interferon preparations

Mouse interferon preparations inhibited the multiplication of mouse leukemia L 1210 cells in stationary suspension cultures. The degree of inhibition was found to correlate with the antiviral titer of the interferon preparations. The factor(s) responsible for inhibition of L 1210 cell multiplication could not be dissociated from interferon by standard physicochemical means.

Increased survival in mice inoculated with tumor cells and treated with interferon preparations

Repeated administration of potent mouse interferon preparations increased the survival of Balb/c and C 57/B1(6) mice inoculated with 2,000-3,000 RC(19) and EL(4) tumor cells. Only 7/188 (3.7%) untreated mice (or mice treated with control preparations) survived more than 22 days after intraperitoneal inoculation of RC(19) tumor cells. None survived more than 60 days. In contrast, 101/103 (98%) interferon-treated mice survived beyond 22 days, and sixteen (15%) survived more than 60 days. None of these 16 surviving mice show any sign of tumor at present. Three mice (of the 16) from an early experiment are alive ten months after inoculation of RC(19) tumor cells. Mouse interferon preparations derived from three different tissue sources- brain, serum, and monolayer cell cultures (with Newcastle disease virus and West Nile virus as interferon-inducing agents)-all proved effective. A purified preparation of mouse brain interferon was as effective as crude brain interferon. Human amniotic membrane interferon and control tissue preparations were without effect. These findings suggest that interferon itself (or a factor closely associated with interferon) is the active moiety in these preparations.