C. Phillip Miller

Effect of Streptomycin on Susceptibility of Intestinal Tract to Experimental Salmonella Infection.

Summary 1. Preliminary treatment by mouth with a large dose (50 mg) of streptomycin increased the susceptibility of mice to infection following oral inoculation with a streptomycin-resistant strain of Salmonella enteritidis. In mice treated with streptomycin 24 hours before inoculation, <3 Salmonella sufficed to initiate infection in 50% as compared with approximately 105 in untreated controls. 2. This effect of streptomycin decreased as the interval between treatment and inoculation was lengthened but was still detectable on the 5 th day. Smaller doses of streptomycin (5-10 mg) resulted in smaller increases in susceptibility. 1 mg was ineffective. 3. Representative numbers of mice killed for culture showed the spleen to be infected in 90% and hearts blood in 72% of those with positive fecal cultures at the time of autopsy. 4. It is believed that this increase in susceptibility following streptomycin treatment resulted from a disturbance of the normal intestinal microflora caused by the antibacterial action of the drug. 5. It is suggested that this method may be applicable to the experimental study of other enteric infections.

THE EFFECT OF IRRADIATION ON NATURAL RESISTANCE TO INFECTION

Of the various rays and particles that the physicists have developed, the only ones with which we need be concerned are X or gamma rays and fast neutrons. I shall discuss fast neutrons very briefly toward the end of this paper. For our purposes, the effects of X and gamma rays may be considered identical provided they are delivered at approximately the same rate. In most experimental work, X rays have been used for purely practical reasons. In all of the experiments that I shall describe, the radiation was delivered uniformly to the whole body of the animal and, unless otherwise noted, in a single exposure lasting about a quarter of an hour. The dosage of radiation falls within the range commonly described as moderate, that is, a dose that causes death of 50 to 100 per cent of the animals within 30 days, with the maximum mortality occurring about the 11th or 12th day. If the dose of radiation is progressively increased, more and more of the animals die earlier, with evidence of injury to the intestinal tract. Bond, Silverman, and Cronkitel have called this effect of very high doses the “intestinal syndrome” to differentiate it from the effects of moderate doses designated the “bone-marrow syndrome.” The early, or intestinal, syndrome results from exposure to high doses of radiation, above the LDloo. The mean survival-time is short, and, of the pathological findings, damage to the gut is the most prominent. In fact, this syndrome can be produced by irradiation of the gut alone, or of even a portion of it. The intestinal syndrome is a most interesting phenomenon, but one that does not concern us here because death occurs quickly and inevitably. It is mentioned solely for the benefit of those who may not be familiar with the various effects of irradiation. The bone-marrow syndrome is produced by lower doses of radiation, provided all of the bone marrow is exposed. The mean survival-time is approximately 11 days, and the pathological findings include anemia, hemorrhage, and evidence of generalized infection. This comparison of the effects of high and moderate doses of radiation explains why the latter are used in the study of host resistance to bacterial infection. This paper is limited to discussing bacterial infection because resistance to virus infections is not much altered by irradiation, a t least not in the adult mammalian host. The effect of irradiation as measured by the 30-day LDso varies considerably among the various species of laboratory animals. Rather than belabor you with the values reported by various workers, I shall merely list the following animals in the order of their decreasing susceptibility: the guinea pig (most susceptible), the dog, mice of various strains, rats of various strains, the hamster, and the rabbit (most resistant). Of these laboratory animals, the mouse

The effect of streptomycin therapy on mice irradiated with fast neutrons.

In a recent communication (1) it was shown that the mortality of mice after acute fast neutron irradiation was closely correlated in time with the development of generalized infection as demonstrated by the recovery of enteric bacteria from hearts blood and/or spleen. Such positive cultures were first obtained on the fourth day post-irradiation, coinciding with the onset of mortality. Between the fourth and the eighth days after exposure, the period of maximum mortality, approximately 40 % of the sacrificed mice showed positive cultures. It seemed to be established, therefore, that generalized infection, including invasion of the blood stream, occurred in mice after a single acute irradiation with fast neutrons. The present series of experiments was designed to determine the effect of streptomycin therapy on the mortality of neutron-irradiated mice in order to evaluate the importance of infection as a cause of death. Streptomycin was chosen because it had been found to be the most effective of the antibiotics used in the treatment of mice exposed to X-rays (2).

Effect of Somatotropic Hormone and Streptomycin on Mice Exposed to Total Body X-Irradiation.∗

Summary 1. Treatment with somatotropic hormone failed to reduce the mortality of mice exposed to 550 r total body x-radiation, even when it was combined with streptomycin to control the development of post-irradiation infection. 2. The mice which received both drugs maintained body weight, but those which received either drug alone lost weight.

Studies on the Action of Penicillin. III. Bactericidal Action of Penicillin on Meningococcus in vitro.

Summary and Conclusions Meningococci are readily killed by penicillin in nutrient broth at 37°. This meningococcidal action is markedly increased by fresh serum of man, rabbit, guinea pig and mouse, due to a heat-labile component, presumably complement. The meningococcus therefore is an unsuitable microorganism on which to test human sera for their content of penicillin by the bacteriostatic method commonly employed. The presence of inactivated serum, however, frequently reduces the activity of penicillin on meningococci in broth. Penicillin fails to kill meningococci in a non-nutrient medium (gelatin-Lockes solution) at 37° and in nutrient broth at ice box temperature, two conditions unfavorable for their growth. These findings lend support to the notion, already expressed by others, that penicillin acts on bacteria only in an environment which promotes their multiplication. Penicillin causes a certain degree of lysis of meningococci actively growing in broth. Meningococci in broth containing concentrations of penicillin just below the level of bacteriostasis develop enlarged forms which suggest an inability to complete the normal process of fission.

EFFECT OF CONTINUOUS GAMMA IRRADIATION OF MICE ON THEIR LEUKOCYTE COUNTS AND SUSCEPTIBILITY TO BACTERIAL INFECTION

CF-1 female mice 10 weeks old were exposed continuously to gamma - radiation at three dose levels: approximately 34, 72 to 67, and 130 to 127 r/day. Leukocyte counts and red cell volumes were followed, and at intervals susceptibility to bacterial infection was determined by intraperitoneal challenge with graded inocula of Pseudomonas aerugiosa. Increased susceptibility to this infection was related to the rate of irradiation rather than the total amount accumulated. At the lowest dose rate the accumulation of 2140 r during 9 weeks caused practically no increase in susceptibility to this experimental infection. At the next higher dose rate susceptibility began to increase after the third week. It was manifested principally by deaths among mice receiving smaller and smaller inocula of the test microorganism. At the highest dose rate used susceptibility increased more rapidly. The development of leukopenia and anemia was also related to the rate of irradiation rather than the total amount accumulated. (auth)

Effect of streptomycin therapy on the bacterial flora of the throat

Abstract Specimens from the throats of patients receiving streptomycin were cultured onto streptomycin media in order to detect the presence of streptomycin-resistant and streptomycin-dependent bacteria. Streptomycin-resistant bacteria in large numbers were cultured from the throats of 98.4 per cent of sixty-one patients who were receiving 1 to 4 Gm. of streptomycin per day. They began to appear during the first thirteen days of treatment in the twenty-four patients who were followed from the beginning of streptomycin therapy. Results of a single survey of another series of patients receiving small doses of streptomycin (0.5 to 0.75 Gm. per day) suggested that resistant flora appeared more slowly. These streptomycin-resistant bacteria all belonged to species normally inhabiting the human throat. Yeast-like forms (Monilia) were found in unusually high incidence. Streptomycin-dependent bacteria were found in two-fifths of the patients receiving large doses of streptomycin, i.e., 1 Gm. or more per day. Streptomycin-resistant bacteria in small numbers were recovered from only 4 per cent of 157 members of the hospital staff, student body and clerical personnel and from 10 per cent of untreated patients. The highest incidence of positive cultures in the control series, 21 per cent, occurred in the nursing and ward personnel. Strongly positive cultures were found in four nurses who were caring for patients receiving streptomycin. Streptomycin-dependent micro-organisms were recovered from the pharynx and large bowel of mice and rabbits after one week of treatment with large doses of streptomycin.

Protection of mice against lethal action of gonococcal endotoxin by penicillin.

Summary and Conclusions Large doses of penicillin repeatedly administered by subcutaneous injection protected a significant proportion of mice against the lethal action of a crude preparation of gonococcal endotoxin.

The Incidence of Endogenous Bacteremia in X-Irradiated Rabbits

In the mouse (1-5) and the rat (6-9) the development of generalized infection has been shown by a number of studies to play an important role as a cause of death during the second week after total-body exposure to moderate doses of ionizing radiation. Such infections, which are caused by microorganisms normally present in the gut, develop into overwhelming bacteremias, demonstrable by the recovery of large numbers of bacteria from the circulating blood. Although the guinea pig (7, 10) and the hamster (7) have not been as systematically studied, the available evidence suggests that in these species also bacteremia is a common finding in animals which die after irradiation. In the case of the dog, opinion is divided on the question of the importance of infection as a cause of death. Warren and Whipple (11), in an early study on irradiated dogs, regarded bacteremia as an agonal phenomenon. Howland (12) has concluded from a recent compilation of data on blood cultures that the occurrence of bacteremia bears no relationship to the survival or death of dogs exposed to 450 r. Among 30 dogs irradiated with 450 r, cultured for Dr. J. Garrott Allen (13), we found only 15 % of 88 blood cultures to be positive. Half of the dogs had been treated with aureomycin, but the incidence of positive cultures was the same as in the controls. On the other hand, Brecher and Cronkite (14) have observed such definite microscopic evidence of infection in the mouth, throat, and intestinal canal of irradiated dogs that they consider infection to play a definite role in the death of these animals. For a recent evaluation of the evidence regarding the importance of infection in the radiation syndrome, see Bond et al. (15). The apparent difference in occurrence of post-irradiation bacteremia in the mongrel dog and in the four species of rodents suggests a significant disparity in their ability to prevent the development of overwhelming sepsis. The dog not only belongs to another order taxonomically, but it is not customarily raised for laboratory use as are the rodents mentioned.In the mouse (1-5) and the rat (6-9) the development of generalized infection has been shown by a number of studies to play an important role as a cause of death during the second week after total-body exposure to moderate doses of ionizing radiation. Such infections, which are caused by microorganisms normally present in the gut, develop into overwhelming bacteremias, demonstrable by the recovery of large numbers of bacteria from the circulating blood. Although the guinea pig (7, 10) and the hamster (7) have not been as systematically studied, the available evidence suggests that in these species also bacteremia is a common finding in animals which die after irradiation. In the case of the dog, opinion is divided on the question of the importance of infection as a cause of death. Warren and Whipple (11), in an early study on irradiated dogs, regarded bacteremia as an agonal phenomenon. Howland (12) has concluded from a recent compilation of data on blood cultures that the occurrence of bacteremia bears no relationship to the survival or death of dogs exposed to 450 r. Among 30 dogs irradiated with 450 r, cultured for Dr. J. Garrott Allen (13), we found only 15 % of 88 blood cultures to be positive. Half of the dogs had been treated with aureomycin, but the incidence of positive cultures was the same as in the controls. On the other hand, Brecher and Cronkite (14) have observed such definite microscopic evidence of infection in the mouth, throat, and intestinal canal of irradiated dogs that they consider infection to play a definite role in the death of these animals. For a recent evaluation of the evidence regarding the importance of infection in the radiation syndrome, see Bond et al. (15). The apparent difference in occurrence of post-irradiation bacteremia in the mongrel dog and in the four species of rodents suggests a significant disparity in their ability to prevent the development of overwhelming sepsis. The dog not only belongs to another order taxonomically, but it is not customarily raised for laboratory use as are the rodents mentioned.

Studies on the Action of Penicillin. II. Therapeutic Action of Penicillin on Experimental Meningococcal Infection in Mice

Discussion and Summary It should be remembered that the method of producing experimental meningococcal infection in the mouse involves the use of mucin, without which meningococci, even the most virulent strains, will not initiate a genuine infection. The method, nevertheless, lends itself to investigation of the action of penicillin in vivo. These studies have so far brought out the following points: Penicillin was equally effective if injected intravenously, subcutaneously, or intramuscularly. When given intramuscularly, it was detectable in the hearts blood within 5 minutes and persisted there for about 2 hours. Its diffusion into the peritoneal cavity occurred simultaneously and its concentration there rose to a relatively higher level than in the blood. (Cf. the clinical observations of Rammelkamp and Keefer 7 on its diffusion out of serous cavities). The penetration of penicillin into the peritoneal cavity may or may not have been affected by the presence of mucin. The effect of penicillin on the bacterial population in the peritoneal fluid was an immediate decrease in numbers which was more striking if the infection had progressed for 3 hours than if the inoculum had been introduced only one hour before. Infection with a stock strain of meningococcus, although fully virulent by ordinary standards, was more easily brought under control than infection with strains recently isolated from human cases of meningococcal infection. The latter required repeated doses of penicillin.