Applicability of an immunoblot technique combined with a semiautomated electrophoresis system for detection of staphylococcal enterotoxins in food extracts

Enterotoxigenic potential of coagulase-negative staphylococci

Staphylococci are a worldwide cause of human and animal infections including life-threatening cases of bacteraemia, wound infections, pyogenic lesions, and mastitis. Enterotoxins produced by some staphylococcal species were recognized as causative agents of staphylococcal food poisoning (SFP), being also able to interrupt human and animal immune responses. Only enterotoxins produced by Staphylococcus aureus were as yet well characterized. Much less is known about enterotoxigenic potential of coagulase-negative species of genus Staphylococcus (CNS). The pathogenic role of CNS and their enterotoxigenicity in developing SFP has not been well established. Although it has been reported that enterotoxigenic CNS strains have been associated with human and animal infections and food poisoning, most of research lacked a deeper insight into structure of elements encoding CNS enterotoxins. Recent studies provided us with strong evidence for the presence and localization of enterotoxin-coding elements in CNS genomes and production of enterotoxins. Thus, the importance of pathogenic potential of CNS as a source of staphylococcal enterotoxins has been highlighted in human and animal infections as well as in food poisoning.

Characterization of Staphylococcus aureus Isolated from Chronically Infected Dairy Goats

A herd of 88 Alpine goats in Northern Italy was monitored for a complete lactation. Milk samples were taken from each udder half during 8 monthly visits. Goats (n = 28) with > or =2 consecutive positive tests for Staphylococcus aureus in the same udder half were identified as chronically infected, and all of those had > or =4 positive tests of the 8 samples. Goats with no infections in either udder half during any visit were considered healthy (n = 26). Linear mixed models were used to examine the relationship between chronic infection by S. aureus and SCC and production traits. The bacteria isolated from one sample from each infected goat were genotyped on the basis of polymorphism in several genes and evaluated for the presence of genes encoding for enterotoxins. The bacteria isolated from each animal were also subject to a test for beta-lactamase production and to minimum inhibitory concentration tests for 11 antimicrobial agents. As expected, SCC (log2) was significantly higher in infected goats than in healthy goats (7.55 vs. 5.50). Also, mean log SCC from infected udder halves (8.02) was greater than that in uninfected udder halves from the same goats (6.44). No significant differences were observed in milk yield or for fat and protein percentages between infected and healthy goats. No genetic variability was observed among the bacteria isolated, suggesting that all were from the same strain, although isolates did vary in susceptibility to various antimicrobial agents. All S. aureus isolates were negative for the beta-lactamase production test. The most effective drugs when tested in vitro were benzylpenicillin, amoxicillin plus clavulanic acid, cloxacillin, and cephalosporins.

A comparative analysis of antibody repertoire against Staphylococcus aureus antigens in patients with deep-seated versus superficial staphylococcal infections

Immunoblot and an enzyme-linked immunosorbent assays were used to evaluate and compare IgG antibodies against S. aureus whole cell lysate, cell wall peptidoglycan and lipoteichoic acid to discriminate between deep-seated and superficial S. aureus infection. Serum samples were examined from patients with deep-seated (n = 25) and superficial (n = 25) S. aureus infections and 15 healthy controls. Patients with deep-seated infections exhibited a large number of immuno-reactive bands in their IgG immunoblot profile as compared to those with superficial infections and healthy controls. Anti-staphylococcal IgG antibodies that reacted with two antigens of apparent molecular weight 110 and 98 kDa were specifically present in 96% (24/25) of patients with deep-seated infections, and were absent in, superficial and control sera. Moreover other Gram-positive and Gram-negative bacteria did not share these two unique antigens. The ELISA assays revealed significantly elevated levels of IgG antibodies to peptidoglycan (PG) in 18 of 25 (72%) patients with deep infection and 15 of 25 (60%) patients with superficial staphylococcal infection. The elevated levels of IgG antibodies to teichoic acid (TA) antigen were detected in all (100%) deep-seated group patients and among 40% (10/25) patients with superficial infection. An increase in levels of antibodies to PG showed a positive correlation trend with levels of IgG antibodies to TA only in deep infection group. Thus immunoblot detection of these two unique antigens as well as detection of elevated antibodies against PG and TA may be useful for the discrimination of staphylococcal deep-seated and superficial infection in humans.