Outermost-cell-surface changes in an encapsulated strain of Staphylococcus aureus after preservation by freeze-drying

LENTICULE discs provide a homogenous format for external quality assessment samples: a comparison with freeze-dried samples for shellfish microbiology

AIMS

The aim was to compare the variability in Escherichia coli enumeration data and detection of Salmonella spp. between four samples of LENTICULE discs and freeze-dried samples for the Health Protection Agency's External Quality Assessment (EQA) scheme for shellfish microbiology.

METHODS AND RESULTS

Four samples of known but undisclosed microbiological content were dispatched in both freeze-dried and LENTICULE disc formats to 57 participating laboratories in 20 countries. Participants examined samples using their routine methods for the most probable number (MPN) of E. coli per 100 g and the presence/absence of Salmonella spp. There was no significant difference between the Food and Environmental Proficiency Testing Unit and participating laboratories for E. coli and Salmonella spp. results. There were significantly less outlying results using the LENTICULE discs than freeze-dried sample format and equivalent or less variance for the former for E. coli MPN. There was no significant difference between LENTICULE discs and freeze-dried samples for the presence/absence of Salmonella spp.

CONCLUSIONS

Overall the results indicated that there was equivalent or less variance in results for the LENTICULE discs than for freeze-dried samples, therefore LENTICULE discs are a homogenous and stable matrix for EQA samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides validation data for the replacement of freeze-dried samples by LENTICULE discs for the Health Protection Agency Shellfish EQA Scheme.

Role of capsule in serotypic differences and complement fixation by Lactococcus garvieae

Seventeen geographically distinct isolates of Lactococcus garvieae, isolated from diseased fish, were compared serologically using antiserum raised against the various isolates in rainbow trout. Sera raised against a capsule deficient isolate did not agglutinate capsulated isolates, regardless of origin. In contrast, all antisera raised against capsulated isolates cross reacted strongly with non-capsulated isolates. Antisera raised against capsulated Japanese isolates cross reacted with other capsulated Japanese isolates including isolates from geographically distinct prefectures within Japan (Ehime and Oita). However, antisera against these virulent capsulated isolates did not cross react with European capsulated isolates. Antisera raised against European capsulated isolates cross reacted with other European isolates, regardless of origin within Europe (UK, Italy, Spain), but did not cross-react with Japanese capsulated isolates. Agglutination assays performed with a range of fifteen lectins revealed differences in surface carbohydrate structure: capsule deficient isolates agglutinated with concanavalin A, Ricinis communis agglutinin, Pisum sativum agglutinin, Lens culinaris agglutinin, wheat germ agglutinin and succinylated wheat germ agglutinin. European capsulated isolates agglutinated with concanavalin A only. The Japanese capsulated isolates were not agglutinated by any of the lectins used in this study. Representative isolates from each group (Japanese capsulated and non-capsulated, European capsulated and non-capsulated) were investigated for their ability to fix complement. Non-capsulated isolates fixed complement regardless of origin, and antibody did not markedly enhance complement fixation. In contrast, the capsulated isolates were less efficient at fixing complement, but complement fixation was markedly increased by homologous antibody.

Characterization of strains of Neisseria meningitidis recovered from complement-sufficient and complement-deficient patients in the Western Cape Province, South Africa

Complement deficiency has been associated with increased susceptibility to meningococcal disease. In order to determine whether special meningococcal strains caused disease in complement-deficient (CD) patients, 17 Neisseria meningitidis strains recovered from patients in the Western Cape Province, South Africa, known to be CD were compared with 124 routine isolates obtained from patients living in the same area. Serogrouping of the strains from the CD subjects revealed that the common serogroups, particularly serogroup B, predominated. However, the prevalence of rare serogroups among isolates from CD subjects was significantly higher than that found among isolates from the control group. Sero- and subtyping of the class 1 and class 2 or 3 outer membrane proteins showed no significant difference between isolates from CD subjects and the routine clinical isolates. Multilocus enzyme electrophoresis of the 141 isolates revealed six clusters of electrophoretic types (ETs) and two unrelated ETs. The same degree of genetic diversity existed in ETs of isolates from CD subjects and the control group. However, the ET-5 complex, which is known to be associated with epidemic disease, was found in 22 (18%) of the routine clinical isolates but in none of the isolates from the CD subjects. This difference was marginally significant. What was highly significant was the finding that 8 of the 17 isolates from CD subjects were in one ET cluster, cluster F, which comprised a total of 20 isolates. Thus, our results show a difference in the clonal compositions of the strains that infect CD subjects in comparison with the clonal compositions of those that cause clinical infections in the population at large.

The effects of medium and rate of freezing on the survival of chlamydias after lyophilization

The effects of suspension media and rate of freezing on the survival of Chlamydia trachomatis LGV2 and Chlamydia pneumoniae after lyophilization were assessed. The highest loss in infectious elementary bodies (EBs) occurred during lyophilization. The survival was higher after freezing at a rate of 1 degree C min-1 and lyophilization than that after rapid freezing at -70 degrees C or -196 degrees C. The recovery (+/- 5%) was higher when fetal calf serum (FCS) containing glucose, saccharose or lactose were used as lyophilization media than that (0.5-3%) when yolk-sac, skimmed milk or phosphate buffer containing sucrose, glutamine and 10% FCS (SPG) were used. After lyophilization, the survival was not affected in the tested range from 10(4) to 5 x 10(6) inclusion-forming units (ifu) ml-1 prior to freezing. After storage for 4 months at 4 degrees C, the numbers of ifu of both Chlamydia serovars that were recovered were identical to the numbers of ifu immediately after lyophilization. It was concluded that chlamydias can be stored and transported in lyophilized form. However, a loss of 95% in infectious EBs should be taken into account.