Haemolysins in coagulase-negative staphylococci

Delta toxin activity in coagulase-negative staphylococci from the bowels of neonates

Coagulase-negative staphylococci are prominent in stools of neonates in some intensive care units and have been associated with necrotizing enterocolitis. A plausible mediator of bowel damage is delta-like toxin, which is produced in vitro by most coagulase-negative staphylococci, but factors influencing the expression of toxin in the bowel are unknown. We examined 105 coagulase-negative staphylococcus isolates from stools of neonates by using an enzyme-linked immunosorbent assay and detected delta toxin production by 92 isolates (88%). The amount present in 18-h broth cultures varied over 100-fold, from 933 to 125,000 ng/ml. All broths positive by enzyme-linked immunosorbent assay except one caused hemolysis of human erythrocytes. The threshold concentration for consistent cytotoxicity to fibroblasts was greater than or equal to 24,000 ng/ml. Only 56% of Staphylococcus epidermidis isolates were capable of producing this much toxin, and these were more often obtained from premature infants in intensive care than from healthy full-term infants (P = 0.003) and were more often resistant to multiple antibiotics (P less than 0.001). Cultures grown anaerobically seldom caused hemolysis (4 positive of 29 tested; P less than 0.001) because potency of the toxin was decreased (at least ninefold for S. epidermidis isolates). We conclude that only a portion of the fecal coagulase-negative staphylococci tested produced enough delta toxin in vitro to be cytotoxic, that such isolates have accumulated in our intensive care nursery, and that development of toxin-mediated bowel injury may also require a favorable redox potential within the host bowel.

Synergistic hemolysis exhibited by species of staphylococci

The synergistic hemolysis reactions of 61 reference strains and 189 clinical isolates representing 17 species of staphylococci were examined on plates of Trypticase soy blood agar (BBL Microbiology Systems, Cockeysville, Md.). Some or all of the strains of Staphylococcus aureus, S. epidermidis, S. capitis, S. cohnii, S. haemolyticus, S. hyicus, S. simulans, S. warneri, and S. xylosus produced a delta-hemolysin that gave synergistic, complete hemolysis of washed human, sheep, and ox blood cells in an area of beta-lysin activity from strains of S. aureus and S. intermedius. Strains of the same nine species were positive with a commercial beta-lysin paper disk designed for presumptive identification of group B streptococci; most of these strains also gave synergistic, complete hemolysis with exotoxin from a strain of Corynebacterium pseudotuberculosis. None of the strains of S. auricularis, S. carnosus, S. caseolyticus, S. hominis, S. intermedius, S. saprophyticus, S. sciuri, or S. lentus were positive by any of these tests for synergistic hemolysis. These results indicate that a synergistic hemolysis test could prove very useful for differentiating these species; they also suggest that one role of some of these organisms in human infections could be that of a synergist. Further studies of synergism may clarify the clinical significance of these results.

The identification of staphylococci in clinical and food microbiology laboratories

A comprehensive review of the methods which have been utilized for the identification of staphylococci is presented. Biochemical characteristics which have assisted in the primary isolation of staphylococci, such as pigmentation, hemolytic activity, the egg yolk phenomenon, and deoxyribonuclease and coagulase production, are also analyzed. The potential applicability of advanced techniques to identify staphylococci, such as the detection of enterotoxin production, base ratio analysis, cell wall analysis, phage typing, and serology, is discussed. The following procedures are recommended for routine use: Idnetification of Staphylococcus sp. (clinical laboratories): microscopic observation, catalase activity, coagulase production, lysostaphin sensitivity, and (optional) facultative growth in thioglycolate medium. Identification of Staphylococcus aureus (food laboratories): microscopic observation, catalase activity, coagulase production, thermonuclease production, and (optional) lysostaphin sensitivity.