The influence of iron on Neisseria meningitidis infection in C-57 mice was examined. Iron sulfate, ferric ammonium citrate, and iron sorbitol citrate all proved to be too toxic for use as infection-enhancing agents. Iron dextran displayed an extremely low toxicity, enhanced infection in a dose-dependent manner, and resulted in infection enhancement factors approaching 10(9) for virulent strains of N. meningitidis. Fatal iron dextran-enhanced infection was shown to be reversible by in vivo chelation of iron. Virulent strains of N. meningitidis produced symptoms of infection and pathological lesions in mice both with and without iron pretreatment, but an avirulent strain failed to produce symptoms of infection or pathological lesions, regardless of iron administration. Iron dextran-enhanced infection in mice proved to be a useful model for the examination of virulence of various N. meningitidis strains. All of 9 isolates from clinical disease possessed virulence, whereas only 3 of 10 isolates from carriers possessed virulence, when examined by using this model.

An assessment was made of the association between tag (mud, bedding, and manure) attached to hides of beef cattle at slaughter and bacterial deposition on carcasses. A total of 624 carcasses from 52 lots of cattle in southern Alberta from January to June 1996 were studied at a high-line-speed abattoir (HLSP) which processed 285 carcasses per h and at a slow-line-speed abattoir (SLSP) which processed 135 carcasses per h. Tag was quantitatively assessed on the belly, legs, and sides of 12 carcasses per lot by the same project worker (lot tag score) and for each incoming lot of cattle by plant personnel (plant lot tag score). Swabs (approximately 10 by 10 cm) were taken from the medial rump and sacrum immediately after hide removal and from the brisket and top of shoulder after carcass splitting. These samples were pooled for each carcass and aerobic mesophilic bacteria, coliforms, and Escherichia coli were enumerated. The lot bacterial count was calculated by averaging the individual bacterial results of the 12 carcasses in a lot. At the HLSP, the lot side scores and the plant lot tag scores were negatively associated (P < 0.05) with the aerobic bacteria, coliforms, and E. coli. Counts were lower when tag was shaven off of the hides or when the line speed was slowed, but the reductions in counts were less than 0.5 log10/cm2. At the SLSP, the lot belly score was negatively associated (P < 0.003) with the aerobic bacterial counts. Neither the lot tag score nor the plant lot tag score were associated (P > 0.05) with the bacterial counts. Surface wetness of the hides was weakly (P < 0.05) associated with coli forms and E. coli counts. This study indicates that there is no consistent association between lot tag scores, plant lot tag scores, and bacterial contamination of carcasses. Changes in bacterial counts when associated with lot tag scores, plant lot tag scores, surface wetness of hides, line speed, or shaving off of tag were generally less than 0.5 log10/cm2. Thus, these variables are individually assessed as control points, but not critical control points of HACCP plans for the prevailing beef slaughter processes (including line speed adjustment at the HLSP) at the two plants studied.

No abstract

To enhance food safety and keeping quality, beef carcasses are cooled immediately after leaving the slaughter floor. Within hazard analysis and critical control point (HACCP) systems, this cooling process needs to be monitored by the industry and verified by regulatory agencies. This study assessed the usefulness of the temperature-function integration technique (TFIT) for the verification of the hygienic adequacy of two cooling processes for beef carcasses at one abattoir. The cooling process passes carcasses through a spray cooler for at least 17 h and a holding cooler for at least 7 h. The TFIT is faster and cheaper than culture methods. For spray cooler 1, the Escherichia coli generations predicted by TFIT for carcass surfaces (pelvic and shank sites) were compared to estimated E. coli counts from 120 surface excision samples (rump, brisket, and sacrum; 5 by 5 by 0.2 cm) before and after cooling. Counts of aerobic bacteria, coliforms, and E. coli were decreased after spray cooler 1 (P < or = 0.001). The number of E. coli generations (with lag) at the pelvic site calculated by TFIT averaged 0.85 +/- 0.19 and 0.15 +/- 0.04 after emerging from spray coolers 1 and 2, respectively. The TFIT (with lag) was considered convenient and appropriate for the inspection service to verify HACCP systems for carcass cooling processes.

A repeatable, automated method was developed for estimating aerobic bacterial populations on surfaces of groups of beef carcasses. Ten sample cluster sites (CS) were identified by localizing visual demerits (Canadian Streamlined Inspection System) on 200 carcasses at one plant. Most probable number growth units per cm2 (MPNGU/cm2) on hydrophobic grid membrane filters (HGMF) were assessed by an automated HGMF interpreter for excision samples from the centers of these CS. Between-sample variation of more than 90% of the total log10 MPNGU/cm2 variance indicated good repeatability between HGMF of the same sample and interpretations of the same HGMF. Variance component estimates indicated that there was considerable variation in MPNGU/cm2 between carcasses and between paired adjacent samples for a CS. A statistically significant but weak association was found between the demerit scores of a CS and MPNGU at its center. The variance component estimates will be used to estimate the sample size required for future group-carcass evaluations.