SUMMARYThe chemical composition of whole organisms and cell membranes of eight saprophytic and parasitic Mycoplasma strains was studied.

SUMRlARYThe susceptibility to lysis of several Mycoplasma organisms, bacterial protoplasts, spheroplasts, L-forms and intact bacteria was compared. The Mycoplasma and L-forms were much more resistant to lysis by osmotic shock and to alternate freezing and thawing than were the bacterial protoplasts and spheroplasts. Like bacterial protoplasts, the mycoplasmas were very sensitive to lysis by surface-active substances, primary alcohols and alkali; bacterial spheroplasts and L-forms were less sensitive to lysis by these agents. All the organisms tested, except intact bacteria, showed various degrees of sensitivity to lysis by pancreatic lipase. The mycoplasmas and the L-forms were completely resistant to the lytic action of lysozyme. The mycoplasmas differed from all other microorganisms tested in being sensitive to lysis by digitonin and saponin. This sensitivity to digitonin was considerably smaller when the organism was grown in a cholesterol-free defined medium. The structure and properties of the Mycoplasma cell envelope are discussed on the basis of the present findings.

SUMMARYFree and esterified cholesterol were determined in the lipid extract of nine parasitic and saprophytic Mycoplasma strains. The saprophytic strains were usually free from esterified cholesterol. Esterified cholesterol was found in the parasitic strains at a ratio of 1 : 8 to 1 : 3 to free cholesterol; in the growth medium the ratio was about 4 : 1. [4-14C]-cholesterol added to the growth medium was incorporated by all Mycoplasma strains without esterification or any other chemical change. [4-14C]-cholesteryl oleate was incorporated into the lipid of the parasitic strains and was not hydrolysed to yield free cholesterol. The small amounts of radioactive oleic acid incorporated by several Mycoplasma strains during growth was not detected in the cholesteryl ester fraction. Our results show that under the growth conditions examined, the Mycoplasma organisms tested were unable to esterify cholesterol or hydrolyse cholesteryl esters.

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Enteric bacteria of 1,335 individual strains were studied for serological cross-reactions with Neisseria meningitidis groups A and C and Diplococcus pneumoniae types I and III. Enterobacterial antigens cross-reactive with the capsular polysaccharides of these four bacteria were found. Bacteria cross-reactive with noncapsular antigens of meningococci and pneumococci were also observed. Since some enteric bacteria possess antigens with serological specificities similar to those of meningococci, the possibility that enteric bacteria cross-reactive with meningococcal antigens provide an antigenic stimulus for the observed age-related "natural" immunity to this pathogen is discussed.

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Cross-reacting Escherichia coli strains Easter and 89 and Bacillus pumilis fed to newborn rabbits and E. coli fed to adult rhesus monkeys did not exert untoward reactions. The E. coli regularly colonized the newborns' intestinal tract from 1 to 7 weeks. High doses of E. coli were necessary to colonize adult primates. Colonization occurred in fewer newborn rabbits and lasted only 1 to 3 weeks with B. pumilis. Colonized newborn rabbits and adult rhesus had an active Haemophilus influenzae type b (HITB) immune response. In the rabbit, colonization resulted in accelerated induction of immunoglobulin (Ig) M-, IgA-, and IgG-producing cells in the spleen, mesenteric lymph nodes, and Peyer's patches after HITB challenge. E. coli-fed and control newborn primates were naturally colonized with nasopharyngeal and enteric cross-reacting bacteria and both groups rapidly developed HITB antibodies in the absence of the homologous organisms. Human newborn stool cultures, taken at the time of discharge from the nursery, showed a 0.9% carriage rate for cross-reacting E. coli. These "carrier" infants acquired HITB antibodies more rapidly than their age-matched "noncarrier" controls.