The effect of glucose, starch, and pH on growth, enterotoxin and haemolysin production by strains of Bacillus cereus associated with food poisoning and non-gastrointestinal infection.

Brain-Heart Infusion medium, modified by (a) 1.0% w/v glucose supplement, (b) 1.0% w/v soluble starch supplement, (c) pH adjustment to 8.8 or (d) pH adjustment to 5.0, was used to investigate the influence of glucose, starch and pH on growth, enterotoxin and haemolysin production by Bacillus cereus. The four test strains selected for comparison originated from episodes of emetic-syndrome food poisoning, diarrhoeal-syndrome food poisoning, traumatic wound infection and bovine mastitis, respectively. In the presence of either glucose or starch, growth of all strains was found to be near-optimum and accompanied by enhanced enterotoxin production. However, under the moderately acid and alkaline test conditions B. cereus strains exhibited varying degrees of growth inhibition and partial repression of enterotoxin and haemolysin production. In this respect the food-poisoning isolates proved to have greater resistance to adverse pH environments than did the non-gastrointestinal infection isolates.

Numerical taxonomy of Bacillus isolated from orally administered drugs.

Numerical taxonomy procedures were used to study 118 strains of Bacillus isolated from non-sterile drugs prepared for oral administration. Similarities between pairs of strains were calculated by the simple matching coefficient of Sokal and Michener (SSM). Each strain was tested for 60 unit characters and three clusters were defined. The strains in each cluster presented a similarity level of at least 60%. Cluster A comprised the strains identified as Bacillus cereus (SSM = 93.13%), cluster B contained three subgroups corresponding to the species B. pumilus, B. subtilis and B. licheniformis (SSM = 84.35%) and cluster C also included three subgroups that belonged to the species B. firmus, B. lentus and B. badius (SSM = 80.14%). The most discriminating tests were selected to differentiate the clusters from the subgroups. The feature with the highest discriminating power between clusters A and B was the lack of acid production from arabinose and mannitol. The Voges-Proskauer, methyl red tests and sensitivity to polymyxin B clearly distinguished cluster A from C. The Voges-Proskauer test and acid production from arabinose were the best to differentiate between B and C. Bacillus pumilus and B. subtilis differed in starch hydrolysis and B. licheniformis in growing anaerobically. To discriminate B. firmus from B. lentus the most important tests were the acid production from glucose and sucrose; intermediate strains were found. Bacillus badius was differentiated from B. firmus by 10 tests, and from B. lentus by the production of urease.

Characterization of Bacillus cereus strains isolated from drugs and evaluation of their toxins.

The microbial contamination of 68 samples of topical and 324 samples of oral medicaments has been studied. The most common group of contaminants was members of the genus Bacillus (34.4%). Because of the pathogenic significance of B. cereus, 39 strains were characterized by morphology and biochemical properties. All except three showed most of the characteristics of the type strain. They were highly resistant to lincomycin, polymyxin B and penicillin G-cephalosporin and were susceptible to streptomycin, erythromycin and chloramphenicol. Enterotoxin, phospholipase C and haemolysin production were also studied: 33 strains gave a positive vascular permeability reaction, four of them causing necrosis, and 24 showed positive mouse lethal tests. All the strains had phospholipase activity. The majority also exhibited differing degrees of haemolysis. Permeability factor was related to mouse lethality and haemolytic activity. Phospholipase C was not related to any of the above activities.