Samuel I. Miller

Acute bacterial meningitis in adults. A review of 493 episodes.

BACKGROUND AND METHODS To characterize acute bacterial meningitis in adults, we reviewed the charts of all persons 16 years of age or older in whom acute bacterial meningitis was diagnosed at Massachusetts General Hospital from 1962 through 1988. We included patients who were admitted after initial treatment at other hospitals. RESULTS During the 27-year period, 445 adults were treated for 493 episodes of acute bacterial meningitis, of which 197 (40 percent) were nosocomial. Gram-negative bacilli (other than Haemophilus influenzae) caused 33 percent of the nosocomial episodes but only 3 percent of the community-acquired episodes. In the 296 episodes of community-acquired meningitis, the most common pathogens were Streptococcus pneumoniae (37 percent), Neisseria meningitidis (13 percent), and Listeria monocytogenes (10 percent); these organisms accounted for only 8 percent of the nosocomial episodes. Only 19 of the 493 episodes of meningitis (4 percent) were due to H. influenzae. Nine percent of all patients had recurrent meningitis; many had a cerebrospinal fluid leak. Seizures occurred in 23 percent of patients with community-acquired meningitis, and 28 percent had focal central nervous system findings. Risk factors for death among those with single episodes of community-acquired meningitis included older age (> or = 60 years), obtunded mental state on admission, and seizures within the first 24 hours. Among those with single episodes, the in-hospital mortality rate was 25 percent for community-acquired and 35 percent for nosocomial meningitis. The overall case fatality rate was 25 percent and did not vary significantly over the 27 years. CONCLUSIONS In our large urban hospital, a major proportion of cases of acute bacterial meningitis in adults were nosocomial. Recurrent episodes of meningitis were frequent. The overall mortality rate remained high.

Transcriptional activation of Salmonella typhimurium invasion genes by a member of the phosphorylated response‐regulator superfamily

The Salmonella typhimurium PhoP‐repressed locus prgHIJK encodes components of a sec‐independent type III secretion apparatus. This apparatus is composed of at least 17 proteins encoded on a 40kb pathogenicity island located at centisome 63 on the S. typhimurium chromosome. The secretion apparatus and some of its targets, SspB, SspC and SspD, are necessary for epithelial cell invasion. The transcription of many invasion genes, including prgHIJK, is co‐ordinately activated by HilA, a transcription factor encoded within the pathogenicity island. In this report we identify sirA, a gene located outside the pathogenicity island that is essential for induction of prgHIJK and hilA transcription. sirA encodes a 234‐amino‐acid protein that is essential for S. typhimurium Ssp (Salmonella secreted protein) secretion and invasion and is similar to response regulators of two‐component regulatory systems. sirA‐mutant phenotypes could be suppressed by two DNA clones from unlinked loci, designated sirB and sirC. These data suggest that SirA may be phosphorylated in response to S. typhimurium sensing a mammalian microenvironment. Furthermore, SirA phosphorylation is predicted to initiate a cascade of transcription‐factor synthesis which results in invasion‐gene transcription, Ssp secretion, and bacterial invasion of epithelia.

Salmonella typhimurium secreted invasion determinants are homologous to Shigella lpa proteins

Salmonella typhimurium secreted proteins (Ssp) were previously implicated in epithelial cell invasion. Here we describe four genes (sspB, sspC, sspD, and sspA), located between spaT and prgH, which encode proteins of 63, 42, 36, and 87 kDa, respectively. These Ssp are homologous to Shigella flexneri secreted proteins lpaB, lpaC, lpaD and lpaA. A non‐invasive mutant with a transposon insertion in sspC lacks Ssp of 87,42 and 36 kDa. Complementation analyses show that sspC and sspD encode the 42 and the 36 kDa Ssp, while the 87 kDa Ssp is encoded by sspA. sspC and sspD, but not sspA are required for invasion. Amino‐terminal sequencing shows that SspC and SspA are secreted without amino‐terminal processing. We further demonstrate that Ssp secretion requires proteins encoded by prgHIJK, homologous to the Shigella lpa secretion system, since SspA is abundantly secreted by wild‐type bacteria but is completely retained within the cellular fraction of a prgHIJK mutant. A precipitate containing abundant SspC and three other major Ssp of 63,59 and 22 kDa was isolated from culture supernatants of wild‐type bacteria. These data indicate that major secreted invasion determinants of S. typhimurium are structurally and functionally homolgous to S. flexneri lpa proteins.

Evaluation of a phoP/phoQ-deleted, aroA-deleted live oral Salmonella typhi vaccine strain in human volunteers

Improved live oral typhoid fever vaccines may be engineered by deletion of Salmonella-specific virulence genes in Salmonella typhi. Ty445, an aroA-deleted S. typhi Ty2 strain also deleted for the phoP/phoQ Salmonella typhimurium virulence regulatory locus, was tested in human volunteers. Volunteers received escalating single doses of the vaccine; subsequently 14 individuals received two doses of 10(10) c.f.u. without significant side-effects. Control vaccinees received four doses of the live oral typhoid vaccine Ty21a. Of controls, 5/8 seroconverted as measured by increases in serum IgG directed against S. typhi O antigen or whole bacterial antigens in ELISAs. Only 2/14 volunteers receiving the experimental vaccine Ty445 seroconverted. Although a delta aroA delta phoP/phoQ S. typhi strain is overattenuated for use as a typhoid fever vaccine, our data demonstrate that the deletion of the phoP/phoQ locus in S. typhi significantly attenuates this human pathogen.

Hypoglycemia as a manifestation of sepsis

Hypoglycemia has rarely been described as a clinical sign of severe bacterial sepsis. We recently encountered nine patients in whom hypoglycemia (mean serum glucose of 22 mg/dl) was associated with overwhelming sepsis. Clinical disease in these patients included pneumonia and cellulitis; in three patients, no focus of infection was apparent. Altered mental status, metabolic acidosis, leukopenia, abnormal clotting studies and bacteremia were common features in these cases. In four patients, no cause for hypoglycemia other than sepsis was present. In five patients, another possible metabolic cause for hypoglycemia was present (alcoholism in four and chronic renal insufficiency in one) although none had been observed to be hypoglycemic on previous hospitalizations. Streptococcus pneumoniae (three cases) and Hemophilus influenzae, type b, (two cases) were the most common pathogens, and the over-all mortality was 67 per cent. The mechanism(s) for hypoglycemia with sepsis is not well defined. Depleted glycogen stores, impaired gluconeogenesis and increased peripheral glucose utilization may all be contributing factors. Incubation of bacteria in fresh blood at room temperature does not increase the normal rate of breakdown of glucose suggesting that the hypoglycemia occurs in vivo. Hypoglycemia is an important sign of overwhelming sepsis that may be more common than has previously been recognized.

Purification and primary structure of murine cryptdin-1, a Paneth cell defensin

We have purified and determined the amino acid sequence of cryptdin‐1, a murine Paneth cell defensin. The peptide corresponds to a previously characterized mRNA that accumulates to high abundance during postnatal ontogeny of the small bowel. Acid‐extracted intestinal protein was fractionated by cation‐exchange chromatography and fractions were assayed for antimicrobial activity. One peak of anti‐Salmonella activity contained a putative defensin, based on its predicted electrophoretic migration in acid‐urea PAGE. The peptide was purified to homogeneity by RP‐HPLC and sequenced. These studies demonstrate defensin expression in non‐myeloid tissue. The N‐terminal extension of cryptdin‐1 is a unique structural feature of this novel epithelial defensin.

The PhoP virulence regulon and live oral Salmonella vaccines

The PhoP virulence regulon is essential to Salmonella typhimurium mouse typhoid fever pathogenesis and survival within macrophages. This virulence regulon is composed of the PhoP (transcriptional regulator) and PhoQ (environmental sensor) proteins and the genetic loci they positively (pags for PhoP activated genes) and negatively (prgs for PhoP repressed genes) regulate. Three regulated loci pagC, pagD, and prgH, when singly mutated, affect the virulence of S. typhimurium for mice. Strains with phoP locus mutations are effective as live vaccines in mice, and strains with a constitutive regulatory mutation, a point mutation in PhoQ, can protect mice against typhoid fever when only very few organisms are administered. The addition of various PhoP regulon mutations further attenuates aroA mutants of S. typhimurium, suggesting that these mutations would be useful in further attenuating vaccine strains with metabolic pathway mutations. The phoP, phoQ, pagC, and pagD genes are highly conserved between S. typhimurium and S. typhi and may be valuable as mutations in live vaccines for human typhoid fever. A plasmid suicide vector that allows deletion of the pagC gene and stable insertion of heterologous antigen genes within the deleted pagC locus has been constructed and used successfully in S. typhimurium and S. typhi.

Malignant hypertension and hypertensive encephalopathy.

Abstract Twenty-seven patients with severe hypertension, most of whom exhibited various degrees fof encephalopathy, were treated with continuous infusions of intravenous veriloid. The blood pressure decreased significantly in all patients. Seventeen patients were maintained on continuous infusions for prolonged periods of time with improvement of the encephalopathic manifestations in thirteen. However, the drug was discontinued within twenty-four hours in four patients because of vomiting in three and severe hiccoughing in the fourth. One patient died (unrelated to veriloid therapy) eighteen hours after admission. Most of the patients exhibited minor side reactions at some time during the veriloid administration. The cerebral blood flow studies showed a marked reduction in cerebrovascular resistance which paralleled the reduction in systemic blood pressure, indicating that cerebrovascular dilatation is physiologically possible. Cerebral blood flow was thus maintained. Cerebral oxygen uptake was not altered significantly. These observations are another indication that the regulation of cerebral blood flow is probably not under the control of the autonomie nervous system. Hypertensive encephalopathy of relatively short duration is not associated with depressed cerebral blood flow. The changes in cerebral function appear to be related to the high arterial pressure which is probably transmitted to the post-arteriolar capillaries resulting in increased cerebral tissue pressure and altered cellular function.

CEREBRAL HEMODYNAMICS IN PATIENTS WITH HEART FAILURE ASSOCIATED WITH HYPERTENSION AND THE RESPONSE TO TREATMENT 1

Cerebral blood flow and cerebral oxygen consumption are not altered in patients with uncomplicated hypertension (1). Scheinberg observed that in a mixed group of patients who had congestive heart failure, the cerebral blood flow was depressed (2). This suggests altered cerebral hemodynamics either as a primary abnormality or as a result of disturbances in the cerebral circulatory dynamics secondary to the cardiac failure. Novack, Goluboff, Bortin, Soffe, and Shenkin (3) studying the same problem concluded that the cerebral blood flow is not depressed to any greater extent in patients with heart failure than it would be in a similar group of patients of the same age group who were not in heart failure. Since cerebral blood flow and cerebral oxygen consumption are relatively normal (1, 4) in patients with essential hypertension which is uncomplicated by the co-existence of heart failure, it seemed worth making observations on cerebral hemodynamics in a group of patients with hypertension who had developed heart failure. Since all but three of these patients were under the age of sixty years, if a significant reduction in cerebral blood flow were found, it could then be considered to be a result of the heart failure rather than secondary to cerebral arteriosclerosis. In addition, observations were made on the cerebral hemodynamic response when twelve patients were given maximum therapy for heart failure. If cerebral blood flow and oxygen consumption were depressed because of heart failure, one might well have expected these functions to improve following treatment.

Strategies for the Development of Vaccines for Typhoid Fever, Shigellosis, and Cholera

Enteric fevers and diarrheal diseases are major causes of morbidity and mortality throughout the developing world.1 Traditional approaches to the development of vaccines for bacterial diseases include the parenteral injection of purified components or killed organisms.2 These methods require technologically advanced preparation and are relatively expensive despite their proven benefits. Live oral vaccine strains have several advantages over parenteral vaccines: low cost, ease of administration, and simple preparation.