Rickettsia typhi cultivated in the yolk sac of chicken embryos or in L cells irradiated 7 days previously was separated from host cell components by two cycles of Renografin density gradient centrifugation. Preliminary steps involved differential centrifugation and centrifugation over a layer of 10% bovine plasma albumin of infected yolk sac suspensions, or trypsinization and passage through filters of wide porosity of infected L cell suspensions. Rickettsial preparations obtained by these methods appeared to be free from host cell components while retaining high levels of hemolytic activity, egg infectivity, and capacity to catabolize glutamate. Average yields were 3.3 mg of rickettsial protein per yolk sac or 0.44 mg per 16-oz (ca. 475-ml) L cell culture. Extracts from these two preparations displayed malate dehydrogenase activity of electrophoretic mobility identical to each other but quite different in migration patterns from the corresponding host cell enzymes. This method of separation of rickettsiae from host cell constituents appears to be particularly well suited for the study of rickettsial enzymatic activity.

Fifteen Aeromonas isolates from various human infections and nine isolates from polluted water were identified as either Aeromonas hydrophila or Aeromonas sobria and examined for cytotoxigenicity, enterotoxigenicity, adherence to epithelial cells, and other virulence-associated factors, including proteases, lipases, elastases, and hemolysins. Two groups cf organisms (I and II) were distinguishable based on differences in median lethal doses in mice and cytotoxicity for Y-1 adrenal cells. Group I clinical and environmental strains had median lethal doses of <107 colony-forming units, were cytotoxic, frequently possessed several virulence-associated factors, and had lysine decarboxylase-positive or Voges-Proskauer-positive phenotypes or both. Piliation of Aeromonas was associated strongly with ability to adhere to human buccal cells, and these characteristics were associated with group I strains. Group Il clinical and environmental strains had median lethal doses of '107 colony-forming units, were not cytotoxic, and usually were lysine decarboxylase negative or Voges-Proskauer negative or both. Clinical strains in group II exhibited enterotoxigenicity, which was not detected in group Il environmental strains. A. sobria was more frequently associated with human infections; 13 of the 15 clinical strains were A. sobria, and 2 were A. hydrophila. On the other hand, the majority of the environmental strains (seven of nine) were A. hydrophila.Aeromonas species are ubiquitous, waterborne microorganisms that have been implicated repeatedly as the causative agents of clinical illnesses, often serious, ranging from gastrointestinal and wound infections to septicemia (4,8,9,12,18,25,26). In compromised patients these illnesses may be fatal. Whereas a small proportion of humans, approximately 1%, are carriers of Aeromonas (26), infections frequently are acquired as a direct result of exposure to water harboring this microorganism (8,9,12,27).

No abstract

The incidence of persistent group A beta-haemolytic streptococci in tonsils, despite penicillin therapy, has increased in recent years. beta-Lactamase-producing organisms have previously been recovered from 74% of patients with persisting group A streptococci. We investigated the possibility that beta-lactamase-producing strains of Bacteroides spp. can protect streptococci from penicillin. A mixed infection was induced in mice in the form of a subcutaneous abscess involving a penicillin-susceptible group A streptococcus, and a beta-lactamase-producing strain of either Bact. melaninogenicus or Bact. fragilis. The infected animals were treated for seven days with parenteral penicillin, penicillin and clavulanic acid or clindamycin. Penicillin treatment prevented the formation of abscesses in animals inoculated with group A streptococci alone, but not in those inoculated with group A streptococci and Bacteroides spp. We attributed this resistance to penicillin therapy, and the subsequent formation of abscesses in mice, to protection of the streptococci from penicillin by beta-lactamase-producing strains of Bacteroides spp. Effective therapy for mixed infections was achieved when clavulanic acid, a beta-lactamase inhibitor, was administered with penicillin. A similar effect was noted with clindamycin, which is active against both group A streptococci and Bacteroides spp.