Mycobacterium xenopi multiplies within human macrophages and enhances HIV replication in vitro

Mycobacterium xenopi can cause opportunistic infections, particularly in persons infected with human immunodeficiency virus type 1 (HIV-1). The primary focus of this effort was to determine if M. xenopi isolates could survive and grow in human peripheral blood macrophage (MPhi), and if these isolates could promote the replication of HIV-1 in vitro. M. xenopi bacilli survived and replicated 10-fold within 48 h in human MPhi while avirulent Mycobacterium smegmatis, did not grow within the MPhi. M. xenopi bacilli when cultured with peripheral blood mononuclear cells enhanced HIV-1 replication 30- and 50-fold with the macrophage-tropic HIV-1(Ba-L) and 50- and 75-fold with T-cell-tropic strain HIV-1(LAI) by 6 days post-infection when compared to M. smegmatis. The enhanced HIV replication was associated with increased production of TNF-alpha. Partial inhibition of HIV-1 induction was observed using a neutralizing anti-TNF-alpha monoclonal antibody, pentoxifylline, and matrix metalloproteinase (MMP) inhibitor I. Similar mechanisms of pathogenesis among mycobacterial species may help elucidate better treatment approaches in HIV co-infected persons.

Changes in the virulence of Mycobacterium avium after passage through embryonated hens' eggs

Eight-day-old embryonated hen's eggs were used as a model to study Mycobacterium avium virulence. Strains isolated from human patients caused 20-90% mortality when eggs were infected by injection of bacterial suspensions into the amniotic sac. Virulence of examined strains subsequently decreased with passage through eggs to between 0 and 40% mortality in four passages. Virulence of the egg-attenuated strains could be restored by passage through human peripheral blood mononuclear cells. The site of infection in the egg was usually the mesodermal layer of the chorioallantoic membrane. A few small granulomas containing acid-fast bacteria were seen in the liver, but not in other organs. Death of chicken embryos may have resulted from destruction of the mesodermal layer of the chorioallantoic membrane with consequent respiratory failure. PBMCs infected with less virulent egg-passaged strains of M. avium produced higher levels of tumor necrosis factor-alpha than did peripheral blood mononuclear cells infected with more virulent nonpassaged strains.

Observed differences in virulence-associated phenotypes between a human clinical isolate and a veterinary isolate of Mycobacterium avium

Mycobacterium avium, the most common opportunistic pathogen in patients with AIDS, is frequently isolated from a variety of environmental sources, but rarely can these environmental isolates be epidemiologically linked with isolates known to cause human disease. Using a number of in vitro tissue culture assays, we found significant pathogenic differences between a serotype 4 human clinical M. avium isolate and a serotype 2 veterinary isolate. Cell association of the patient strain with a human intestinal cell line was 1.7 times that of the veterinary strain. Growth of this clinical strain in human peripheral blood mononuclear cell-derived macrophages increased from 12-fold higher than that of the veterinary isolate after 2 days to 200-fold higher after 4 days. By the conclusion of each experiment, lysis of all examined host cell types and accumulation of cell debris were observed in infections with the human isolate, but monolayers remained relatively intact in the presence of the animal isolate. The two strains also differed in the ability to stimulate human immunodeficiency virus replication in coinfected host cells, with p24 antigen levels after 6 days threefold higher in the cells coinfected with the clinical strain than in those infected with the veterinary strain. If the genetic differences responsible for the phenotypes observed in these assays can be identified and characterized, it may be possible to determine which M. avium strains in the environment are potential human pathogens.

An in vitro tissue culture bilayer model to examine early events in Mycobacterium tuberculosis infection

A tissue culture bilayer system that mimics some aspects of early alveolar infection by Mycobacterium tuberculosis was developed. This model incorporates human lung epithelial type II pneumocyte (A549) (upper chamber) and endothelial cell (lower chamber) layers separated by a microporous membrane. This construction makes it possible to observe and quantify the passage of bacteria through the two layers, to observe the interaction of the bacteria with the various cell types, and to examine the basic mechanisms of immune cell recruitment to the site of infection. After 10(7) organisms were added to the upper chamber we microscopically observed large numbers of bacteria attached to and within the pneumocytes and we determined by viable-cell counting that a small percentage of the inoculum (0.02 to 0.43%) passed through the bilayer into the lower chamber. When peripheral blood mononuclear cells were added to the lower chamber, microscopic examination indicated a migration of the mononuclear cells through the bilayer to the apical surface, where they were seen associated with the mycobacteria on the pneumocytes. The added complexity of the bilayer system offers an opportunity to define more precisely the roles of the various lung cell types in the pathogenesis of early tuberculosis.

A large community outbreak of salmonellosis caused by intentional contamination of restaurant salad bars

CONTEXT

This large outbreak of foodborne disease highlights the challenge of investigating outbreaks caused by intentional contamination and demonstrates the vulnerability of self-service foods to intentional contamination.

OBJECTIVE

To investigate a large community outbreak of Salmonella Typhimurium infections.

DESIGN

Epidemiologic investigation of patients with Salmonella gastroenteritis and possible exposures in The Dalles, Oregon. Cohort and case-control investigations were conducted among groups of restaurant patrons and employees to identify exposures associated with illness.

SETTING

A community in Oregon. Outbreak period was September and October 1984.

PATIENTS

A total of 751 persons with Salmonella gastroenteritis associated with eating or working at area restaurants. Most patients were identified through passive surveillance; active surveillance was conducted for selected groups. A case was defined either by clinical criteria or by a stool culture yielding S Typhimurium.

RESULTS

The outbreak occurred in 2 waves, September 9 through 18 and September 19 through October 10. Most cases were associated with 10 restaurants, and epidemiologic studies of customers at 4 restaurants and of employees at all 10 restaurants implicated eating from salad bars as the major risk factor for infection. Eight (80%) of 10 affected restaurants compared with only 3 (11%) of the 28 other restaurants in The Dalles operated salad bars (relative risk, 7.5; 95% confidence interval, 2.4-22.7; P<.001). The implicated food items on the salad bars differed from one restaurant to another. The investigation did not identify any water supply, food item, supplier, or distributor common to all affected restaurants, nor were employees exposed to any single common source. In some instances, infected employees may have contributed to the spread of illness by inadvertently contaminating foods. However, no evidence was found linking ill employees to initiation of the outbreak. Errors in food rotation and inadequate refrigeration on ice-chilled salad bars may have facilitated growth of the S Typhimurium but could not have caused the outbreak. A subsequent criminal investigation revealed that members of a religious commune had deliberately contaminated the salad bars. An S Typhimurium strain found in a laboratory at the commune was indistinguishable from the outbreak strain.

CONCLUSIONS

This outbreak of salmonellosis was caused by intentional contamination of restaurant salad bars by members of a religious commune.

Evaluation of the chick embryo for the determination of relative virulence of Neisseria meningitidis

The chick embryo model was evaluated as a method to compare virulence between selected strains of Neisseria meningitidis. Inoculation of 13-day-chick embryos via the egg yolk distinguished strains having an LD50 of 10(3) colony forming units (CFU) or greater (low virulence) from those having an LD50 of approximately 10(1) or less (high virulence). A strain of serogroup B and a spontaneous nonpiliated strain of group C were found to be of relatively high virulence while a strain of N. lactamica, a serogroup A carrier strain, and certain nongroupable strains were found to be of low virulence. Strains having an LD50 of 10(2) were not differentiated from either of these. Alternatively, inoculation of the chorioallantoic membrane (CAM) of 9-day-old chick embryos statistically differentiated most strains of N. meningitidis although inoculation via this route was less sensitive.

A tissue culture bilayer model to study the passage of Neisseria meningitidis

A tissue culture bilayer system has been developed as a model to study the mechanisms of attachment and invasion involved in the pathogenesis of Neisseria meningitidis. The model incorporates epithelial and endothelial cell layers separated by a microporous membrane and makes it possible to observe and quantify the passage of bacteria through the multiple layers and to study the mechanisms by which they make this passage. This model is adaptable to a wide variety of microbial pathogens and can be modified by substituting any physiologically relevant eucaryotic cells for the component layers. The system's makeup of cells of human origin and its reproducibility give it advantages over animal and primary organ culture models, while the added complexity of multiple layers allowing cell-to-cell communication makes it a more realistic human tissue model than standard cell monolayers.

Intracellular growth of Afipia felis, a putative etiologic agent of cat scratch disease

The organism Afipia felis, which is though to be an etiologic agent of cat scratch disease, is a gram-negative rod that is clearly seen in infected tissue but is very difficult to isolate from clinical specimens; there has been only one report to date of the successful isolation and maintenance of the bacterium on artificial medium. We have found that A. felis will attach, invade via phagocytosis, and multiply intracellularly within the phagosomes of primary human monocytes and HeLa cells. Once in the cell, the bacterium appears to change morphologically, becoming longer and more pleomorphic, and loses its ability to grow on an artificial medium. Unique proteins have been identified in both the intra- and extracellular variants of A. felis. Convalescent-phase sera from patients with cat scratch disease react poorly with intracellular and extracellular bacteria, suggesting a poor humoral response. The tissue culture protocol presented has been used to isolate 14 new strains of A. felis and has for the first time permitted study of the pathogenesis of this unique organism.

Isoprenoid quinones of "Afipia" spp

The isoprenoid quinone contents of seven strains of "Afipia felis," the type strains of "A. clevelandensis" and "A. broomeae," and reference strains of three unnamed "Afipia" genospecies were determined by reverse-phase high-performance liquid chromatography. The quinone profiles of all "Afipia" strains were essentially identical, with ubiquinone 10 as the major component. The identity of ubiquinone 10 was confirmed by mass spectrometry.

Proposal of Afipia gen. nov., with Afipia felis sp. nov. (formerly the cat scratch disease bacillus), Afipia clevelandensis sp. nov. (formerly the Cleveland Clinic Foundation strain), Afipia broomeae sp. nov., and three unnamed genospecies

On the basis of phenotypic characterization and DNA relatedness determinations, the genus Afipia gen. nov., which contains six species, is described. The type species is Afipia felis sp. nov. (the cat scratch disease bacillus). Afipia clevelandensis sp. nov., Afipia broomeae sp. nov., and three unnamed not associated with cat-borne disease. All but one strain (Afipia genospecies 3) were isolated from human wound and respiratory sources. All Afipia species are gram-negative, oxidase-positive, nonfermentative rods in the alpha-2 subgroup of the class Proteobacteria. They are motile by means of a single flagellum. They grow on buffered charcoal-yeast extract agar and nutrient broth, but rarely on MacConkey agar, at 25 and 30 degrees C. They are urease positive; but they are negative in reactions for hemolysis, indole production, H2S production (triple sugar iron agar), gelatin hydrolysis, esculin hydrolysis, and peptonization of litmus milk. They do not produce acid oxidatively from D-glucose, lactose, maltose, or sucrose. The major cell wall fatty acids are 11-methyloctadec-12-enoic (CBr19:1), cis-octadec-11-enoic (C18:1omega7c), and generally, 9,10-methylenehexadecanote and 11,12-methyleneoctadecanoate; and there are only trace amounts of hydroxy acids. The guanineplus-cytosine content is 61.5 to 69 mol%. A. felis is positive for nitrate reduction and is delayed positive for acid production from D-xylose, but it is catalase negative. A. clevelandensis is negative in all of these tests. A. broomeae is weakly positive for catalase production and acid production from D-xylose, but it is negative for nitrate reduction.

Laboratory observations on Plesiomonas shigelloides strains isolated from children with diarrhea in Peru

Eleven strains of Plesiomonas shigelloides isolated from 10 Peruvian children with diarrhea were examined. All the strains were resistant to two or more antibiotics, most commonly ampicillin, gentamicin, erythromycin, kanamycin, and streptomycin. The strains were all negative in the Sereny and cell culture assays used to test for enteroinvasiveness. One strain showed cytotoxic activity on Vero cells. The strains showed no antigenic relationship with Shigella organisms. Both bioassays and enzyme-linked immunosorbent assays used for detection of Escherichia coli enterotoxins were negative. Nucleic acid probes for such toxins likewise gave negative results. The strains all possessed a large (approximately 200-megadalton) plasmid in addition to one or more other plasmids. Several different plasmid profiles were observed among these 11 P. shigelloides strains, indicating that the isolates were not acquired from a common source or from a single bacterial clone.

Purification and characterization of a pilin specific for Brazilian purpuric fever-associated Haemophilus influenzae biogroup aegyptius (H. aegyptius) strains

Brazilian purpuric fever (BPF) is a recently described fatal pediatric disease caused by systemic infection with Haemophilus influenzae biogroup aegyptius. Previous studies have shown that all H. influenzae biogroup aegyptius strains isolated from BPF cases and case contacts share several unique phenotypic and genotypic characteristics that differentiate them from other H. influenzae biogroup aegyptius strains isolated from conjunctivitis cases in Brazil. One key characteristic of this BPF clone is reactivity in a BPF-specific monoclonal antibody enzyme-linked immunosorbent assay. We have purified and partially characterized a pilin, referred to as the 25-kilodalton (kDa) protein. Aggregates of this protein contain a heat-labile epitope which is recognized by a monoclonal antibody used in the BPF-specific enzyme-linked immunosorbent assay. The protein has a molecular weight of approximately 25,000, is insoluble in most detergents, and fractionates with outer membrane vesicles after LiCl extraction. Biochemical analysis of the 25-kDa protein shows it to have an amino acid composition similar but not identical to that of the H. influenzae type b pilin. The sequence of 20 N-terminal amino acids of the 25-kDa protein shows almost complete homology with the N terminus of the H. influenzae type b pilin and the types 1 and P pilins of Escherichia coli. Transmission electron microscopic analysis of the purified protein shows the presence of filamentous structures similar in morphology to those of H. influenzae pili. Reactivity between the 25-kDa protein and the BPF-specific monoclonal antibody is demonstrated by Western blotting (immunoblotting) and colloidal gold-enhanced immunoelectron microscopy. Hemadsorption analysis shows that expression of this protein is associated with increases in piliated cells and enhanced binding of these cells to human erythrocytes. These studies indicate that expression of the 25-kDa protein is a characteristic unique to the BPF clone and suggest that this protein plays a role in the pathogenesis of BPF.

In vitro antimicrobial susceptibility, plasmid analysis, and serotyping of epidemic-associated Campylobacter jejuni

Campylobacter jejuni strains from 11 outbreaks were characterized by antimicrobial susceptibility, plasmid profile, and serotyping by the methods of Lior et al. and Penner and Hennessy. All 31 strains were susceptible to erythromycin, clindamycin, chloramphenicol, kanamycin, tobramycin, streptomycin, and gentamicin. A total of 21 strains from nine outbreaks were resistant to one or more of the following antimicrobial agents: tetracycline, metronidazole, ampicillin, or carbenicillin. Of the 31 strains, 19 possessed plasmid DNA; 4 of the strains containing plasmids were sensitive to all antimicrobial agents tested. All of the strains that were resistant to tetracycline contained a 38-megadalton plasmid, and these plasmids shared common nucleic acid sequences. No other antimicrobial resistance was associated with the presence of plasmid DNA. Eight outbreaks appeared to have been caused by a single serotype, whereas in three outbreaks multiple serotypes were found. In two of the three outbreaks with multiple serotypes, plasmid profiles were also indicative of multiple strains of C. jejuni. Antimicrobial susceptibility and plasmid profile are potentially useful epidemiological markers for C. jejuni and may be used to supplement serotyping.

Persistence of plasmids, cholera toxin genes, and prophage DNA in classical Vibrio cholerae O1

Plasmid profiles, the location of cholera toxin subunit A genes, and the presence of the defective VcA1 prophage genome in classical Vibrio cholerae isolated from patients in Bangladesh in 1982 were compared with those in older classical strains isolated during the sixth pandemic and with those in selected eltor and nontoxigenic O1 isolates. Classical strains typically had two plasmids (21 and 3 megadaltons), eltor strains typically had no plasmids, and nontoxigenic O1 strains had zero to three plasmids. The old and new isolates of classical V. cholerae had two HindIII chromosomal digest fragments containing cholera toxin subunit A genes, whereas the eltor strains from Eastern countries had one fragment. The eltor strains from areas surrounding the Gulf of Mexico also had two subunit A gene fragments, which were smaller and easily distinguished from the classical pattern. All classical strains had 8 to 10 HindIII fragments containing the defective VcA1 prophage genome; none of the Eastern eltor strains had these genes, and the Gulf Coast eltor strains contained a different array of weakly hybridizing genes. These data suggest that the recent isolates of classical cholera in Bangladesh are closely related to the bacterial strain(s) which caused classical cholera during the sixth pandemic. These data do not support hypotheses that either the eltor or the nontoxigenic O1 strains are precursors of the new classical strains.

Diagnostic value of plasmid analyses and assays for virulence in Yersinia enterocolitica

The possession of a 42- to 48-megadalton plasmid alone does not appear to be predictive of virulence in Yersinia species. Twelve of 100 Yersinia enterocolitica strains contained a 42 to 48-megadalton plasmid, and 4 of 30 Y. enterocolitica-like strains contained a 42- to 48-megadalton plasmid. Seven strains of Y. enterocolitica contained the 42- to 48-megadalton plasmid plus an 82-megadalton plasmid, and these were the only study strains lethal for mice. Based on restriction endonuclease digestion, the 42- to 48-megadalton plasmid DNA from these seven strains were similar and were not similar to the 42- to 48-megadalton plasmids present in the other nine strains. The ability to invade guinea pig eye tissues, calcium dependency, autoagglutination, and colonial morphology at 37 degrees C were also associated with plasmid DNA, but the relationships were either variable or not reciprocal. Neither tissue culture invasiveness nor heat-stable toxin production was associated with plasmid DNA. It was concluded that biochemical speciation and a total plasmid profile in combination with enzyme digests are predictive of virulence in Y. enterocolitica as it is measured by mouse lethality.

Importance of host factors in human salmonellosis caused by multiresistant strains of Salmonella

Antimicrobial resistance patterns of Salmonella isolates from persons in randomly selected urban and rural counties in the United States were examined along with clinical and epidemiological characteristics of the host. Multiresistant strains, isolated from 66 (12.2%) of 542 persons evaluated, were associated with five of 20 variables in univariate analyses: serotype heidelberg, host of Hispanic origin, host exposure to penicillins within four weeks before stool culture, age greater than or equal to 60 years, and regular antacid use. By multiple linear regression, the first three variables were each significantly associated with infections due to multiresistant Salmonella. One or more of the last three variables, thought to be host factors that may promote disease, were present for persons yielding 38% of multiresistant strains but only 12% of sensitive strains (P less than .001). The relatively large proportion of multiresistant Salmonella among isolates from persons with these risk factors suggests that to cause disease, resistant organisms are more dependent than are sensitive organisms on host characteristics.

Genetic probes for enterotoxigenic Escherichia coli isolated from childhood diarrhea in the Central African Republic

Escherichia coli strains were isolated from 778 children with diarrhea and 151 well children in the Central African Republic over a period of 1 year. These 929 strains were assayed for heat-labile and heat-stable enterotoxin production and were hybridized (probed) with structural genes for these enterotoxins. Twenty-four isolates from diarrheal patients and one isolate from a well child were found to be toxigenic by assay and probe. Minor discrepancies were encountered with both assays and probes during initial screening procedures, but the two methodologies were ultimately comparable.

Salmonellosis at rural and urban clinics in Bangladesh: epidemiologic and clinical characteristics

The authors studied the frequency of diarrheal illness associated with non-typhi Salmonella at two clinics in Bangladesh for the years 1977-1979. Non-typhi salmonellae were isolated from 0.29% of fecal specimens or rectal swabs in an urban area and 0.26% of similar specimens in a rural area; the frequency of isolations peaked in the summer months. Isolations of Shigella and Vibrio cholerae were much more common than Salmonella. Only two of 50 Salmonella isolates were resistant to more than one antibiotic. None of 13 isolates tested produced an enterotoxin. S. java and S. virchow accounted for 64% of all the isolates. Patients with diarrheal illness associated with isolation of Salmonella frequency had vomiting (88%), watery diarrhea (78%), abdominal pain (61%), and fever (39%), but the clinical features of the illnesses and the socioeconomic backgrounds of the patients could not be distinguished from those of matched controls who were attending the same clinic. The infrequency of Salmonella infection in an area where several other bacterial and viral enteric diseases are hyperendemic requires further investigation.