Antibodies to the pneumococcal surface protein A, PspA, can be produced in splenectomized and can protect splenectomized mice from infection with Streptococcus pneumoniae

Asplenic individuals have increased susceptibility to septicemia caused by encapsulated bacteria. Streptococcus pneumoniae, a pathogen carried in the nasal passages of many humans without complication, is responsible for a large proportion of infections seen in asplenic individuals. Our studies have evaluated the efficacy of antibodies to pneumococcal surface protein A (PspA) in protection of asplenic mice. In passive immunity studies, pneumococci were more completely cleared from the blood of splenectomized mice receiving passive antiserum to PspA than those receiving normal rabbit serum. From active mucosal (intranasal) and systemic (subcutaneous) immunizations with rPspA, we determined that the levels of PspA antibodies produced in splenectomized mice were not significantly different from levels seen in mock-splenectomized animals. This active immunity to PspA was able to protect splenectomized mice against death following infection with live pneumococci. Our results suggest that PspA immunization may also protect asplenic humans from pneumococcal infections.

Association between antecedent intravenous antimicrobial exposure and isolation of vancomycin-resistant enterococci

Vancomycin-resistant enterococci (VRE) have become important causes of nosocomial infections. This study evaluated the association between a variety of intravenous antimicrobial exposures and the isolation of VRE using two control groups: (1) a vancomycin-susceptible enterococci (VSE) group, to assess factors associated with development of VRE, and (2) a nonenterococci control group, to assess factors associated with positive cultures for enterococci without regard to vancomycin resistance. After adjusting for the effect of other antimicrobials, time at risk, and patient morbidity, compared to vancomycin-susceptible enterococci controls, exposures to imipenem (OR = 4.9, 95% CI = 1.6-14.1) and ceftazidime (OR = 2.6, 95% CI = 1.1-6.1) were significant predictors of VRE. When compared to nonenterococci controls, exposures to ampicillin (OR = 20.1, 95% CI = 1.5-263.1) and imipenem (OR = 5.1, 95% CI = 1.5-17.1) were significantly associated with VRE. Neither piperacillin nor vancomycin was associated with VRE compared to either control group. This study offers further evidence that the replacement of broad-spectrum cephalosporins by extended-spectrum penicillins, specifically piperacillin, may be effective in reducing VRE.

Vancomycin-resistant enterococci: 15 years and counting

We review the history of vancomycin-resistant enterococci (VRE) and propose a causal model illustrating the roles of exposure to VRE reservoirs, patient characteristics, antimicrobial exposure, and prevalence of VRE in the progression from potential VRE reservoirs to active disease in hospitalized patients. Differences in VRE colonization and VRE infection are discussed with respect to hospital surveillance methodology and implications for interventions. We further document clonal transmission of VRE in a large, urban, teaching hospital and demonstrate VRE susceptibility to a wide array of antimicrobial agents. This model can guide the identification of mutable factors that are focal points for intervention.

In vitro activity of ABT-773, telithromycin and eight other antimicrobials against erythromycin-resistant Streptococcus pneumoniae respiratory isolates of children

The activity of the ketolide ABT-773 against 180 erythromycin-resistant Streptococcus pneumoniae obtained from children was compared with telithromycin, azithromycin, clarithromyin, roxithromycin, clindamycin, penicillin, levofloxacin and gatifloxacin. Ketolide MICs were all < or =1 mg/l, with ABT-773 being the most potent of all drugs tested. MIC(90)s for macrolides and azithromycin in mefE+ isolates were 16-32 compared with >128 mg/l for ermB+ isolates. ABT-773 and telithromycin MIC(90)s for mefE+ isolates were 0.125 and 0.5, compared with 0.032 and 0.016 mg/l for ermB+ isolates and 0.5 and 1 mg/l, respectively, for isolates containing both genes. Clindamycin was active against mefE+ but not ermB+ isolates. 155 isolates were resistant to penicillin. All fluoroquinolone MICs were < 1 mg/l. Further studies of ketolides for treatment of paediatric S. pneumoniae infections are warranted.

Value of Mycobacterium tuberculosis fingerprinting as a tool in a rural state surveillance program

OBJECTIVE

This study demonstrates the value of Mycobacterium tuberculosis fingerprinting used in conjunction with traditional epidemiologic methods to identify smoldering outbreaks of tuberculosis in endemic areas where background rates of tuberculosis are high.

METHODS

IS6110 DNA fingerprinting was performed on isolates of M tuberculosis from verified cases of tuberculosis in Alabama from 1994 to 1998. A statewide database groups isolates into "clusters" and tracks them cumulatively over time. A large cluster was identified and was secondarily investigated using traditional epidemiologic methods.

RESULTS

Twenty-five isolates were found to be identical by fingerprinting analysis. Patients were living within 10 counties across the state, and 12 cases were localized to a single county. This represented an ongoing, statewide tuberculosis outbreak previously unrecognized by local and state health officials. Secondary investigation of the cases revealed the primary sites of transmission to be a correctional facility and two homeless shelters.

CONCLUSIONS

Population surveillance using M tuberculosis fingerprinting was successfully utilized to detect a significant and smoldering tuberculosis outbreak. Measures are currently in place to identify and prevent further transmission in the involved locations.

Epidemiologic usefulness of spoligotyping for secondary typing of Mycobacterium tuberculosis isolates with low copy numbers of IS6110

Restriction fragment length polymorphism (RFLP) analysis of IS6110 is commonly used to DNA fingerprint Mycobacterium tuberculosis. However, low-copy (< or =5) IS6110 M. tuberculosis strains are poorly differentiated, requiring secondary typing. When spoligotyping was used as the secondary method, only 13% of Maryland culture-positive tuberculosis (TB) patients with low-copy IS6110-spoligotyped clustered strains had epidemiologic linkages to another patient, compared to 48% of those with high-copy strains clustered by IS6110 alone (P < 0.01). Spoligotyping did not improve a population-based molecular epidemiologic study of recent TB transmission.

Identification of a contaminating Mycobacterium tuberculosis strain with a transposition of an IS6110 insertion element resulting in an altered spoligotype

Molecular fingerprinting with the IS6110 insertion sequence is useful for tracking transmission of Mycobacterium tuberculosis within a population or confirming specimen contamination in the laboratory or through instrumentation. Secondary typing with other molecular methods yields additional information as to the relatedness of strains with similar IS6110 fingerprints. Isolated, relatively rare, random events within the M. tuberculosis genome alter molecular fingerprinting patterns with any of the methods; therefore, strains which are different by two or more typing methods are usually not considered to be closely related. In this report, we describe two strains of M. tuberculosis, obtained from the same bronchoscope 2 days apart, that demonstrated unique molecular fingerprinting patterns by two different typing methods. They were closely linked through the bronchoscope by a traditional epidemiologic investigation. Genetic analysis of the two strains revealed that a single event, the transposition of an IS6110 insertion sequence in one of the strains, accounted for both the differences in the IS6110 pattern and the apparent deletion of a spacer in the spoligotype. This finding shows that a single event can change the molecular fingerprint of a strain in two different molecular typing systems, and thus, molecular typing cannot be the only means used to track transmission of this organism through a population. Traditional epidemiologic techniques are a necessary complement to molecular fingerprinting so that radical changes within the fingerprint pattern can be identified.

Direct identification of Mycobacterium avium complex and Mycobacterium gordonae from MB/BacT bottles using AccuProbe

We evaluated the ability of the AccuProbe (Gen-Probe, San Diego, Calif.) to detect Mycobacterium gordonae and Mycobacterium avium complex directly in liquid medium flagged positive by the MB/BacT (Organon Teknika Corp., Durham, N.C.). Seventy-one bottles from clinical specimens containing M. gordonae and 34 containing M. avium, confirmed by culture, were tested by direct AccuProbe assay for both organisms after additional incubation for > or = 48 h and centrifugation at 4,500 x g for 15 min. Relative light unit (RLU) values were analyzed using the manufacturer's recommended cutoff of 30,000 RLU and a lower cutoff of 10,000 RLU. Using the 30,000 RLU cutoff, 55 of 71 (77.5%) specimens containing M. gordonae yielded positive results, whereas 28 of 34 (82.3%) M. avium complex specimens were correctly identified by direct probe. No specimens shown by culture to contain either M. gordonae or M. avium complex tested positive with the probe for the opposite organism (100% specificity). When the cutoff was lowered to 10,000 RLU, 67 of 71 M. gordonae (94.4%) and 32 of 34 M. avium complex (94.1%) specimens were correctly identified. This difference was significant for M. gordonae (P = 0.004) but not for M. avium complex (P = 0.26) compared to detection using the recommended RLU cutoff. Specificity was 100% for specimens containing M. gordonae that were tested with the M. avium complex probe using the 10,000 RLU cutoff, whereas specificity for specimens containing M. avium complex tested with the M. gordonae probe was 97%. Using a lower RLU cutoff for determining a positive result using the M. gordonae or M. avium complex probes when testing instrument-positive MB/BacT bottles directly will improve sensitivity without substantially compromising specificity.

Human C-reactive protein is protective against fatal Salmonella enterica serovar typhimurium infection in transgenic mice

C-reactive protein (CRP) is an acute-phase protein with a well-known association with infection and other inflammatory conditions. We have shown that expression of human CRP by CRP transgenic (CRPtg) mice is protective against lethal infection by Streptococcus pneumoniae, an effect likely mediated by CRP's ability to bind to this gram-positive pathogen. In the present study we tested whether CRPtg mice are resistant to infection with Salmonella enterica serovar Typhimurium, a gram-negative pathogen that causes the murine equivalent of typhoid fever. CRPtg mice experimentally infected with a virulent Typhimurium strain lived longer and had significantly lower mortality than their non-tg littermates. The greater resistance of CRPtg mice could be attributed to significantly increased early (0 to 4 h) blood clearance of salmonellae and significantly decreased numbers of bacteria in the liver and spleen on day 7 postinfection. In addition, 14 days after infection with an avirulent Salmonella strain, the serum titer of anti-Salmonella immunoglobulin G antibodies was higher in CRPtg than non-tg mice. This study provides unequivocal evidence that CRP plays an important role in vivo in host defense against salmonellae during the early stages of infection. In addition, as the beneficial effect of CRP includes enhancement of the host's humoral immune response, CRP may also contribute indirectly to host defense during later stages of infection.

Comparison of direct inoculation and Copan transport systems for isolation of Neisseria gonorrhoeae from endocervical specimens

Two commercial swab transport systems, Copan Amies gel agar with and without charcoal (Copan Diagnostics, Corona, Calif.), were compared to direct inoculation onto modified Thayer-Martin medium for detection of Neisseria gonorrhoeae in 1,490 endocervical specimens obtained from women attending a sexually transmitted disease clinic. Copan swabs were held in the transport system for 24 h at room temperature prior to inoculation onto modified Thayer-Martin medium. All cultures were incubated at 35 degrees C in 5% CO(2), and bacteria were identified on the basis of Gram stain, oxidase, and biochemical reactions. Copan Amies gel agar transport system without charcoal detected 77 of 81 (95%) direct inoculation culture-positive specimens, and Copan Amies gel agar transport system with charcoal detected 53 of 56 (95%) directly inoculated culture-positive specimens. Copan Amies gel agar without charcoal inoculated after 6 h supported growth of 56 (98%) positive cultures out of only 55 directly inoculated culture-positive specimens. This study demonstrates that Copan swabs represent a reasonable alternative, providing convenience, low cost, and ease of use while still maintaining a satisfactory recovery rate of N. gonorrhoeae from clinical specimens, if specimens can be inoculated onto selective media within a relatively short time period not involving overnight shipment.

Spot sputum screening: evaluation of an intervention in two homeless shelters

SETTING

Two homeless shelters in Birmingham, Alabama.

OBJECTIVE

To interrupt tuberculosis transmission and evaluate the utility of spot sputum screening.

DESIGN

Two shelters participated in the study between May 1996 and February 1997. A spot sputum specimen was collected on a given evening from each overnight client. Information was obtained regarding symptoms and tuberculin skin test (TST) status. There were four screenings during two rounds, with TST in round one only.

RESULTS

Of 127 persons involved in the study, 120 (95%) provided specimens, and four tuberculosis cases were identified (4/127, 3.1%). Symptoms were infrequently reported. RFLP analysis (IS6110) confirmed a two-band cluster in three of the four cases; another matching two-band strain was found in a drug rehabilitation client staying in one shelter. Secondary RFLP typing (pTBN12) confirmed the homeless cluster. Costs were $1311 per case identified. Among 92 clients with a prior TST, 40% reported a positive result (37/92). Of 21 PPD tests read, 11 were > or =10 mm (52%).

CONCLUSION

Spot sputum screening is effective in identifying unsuspected tuberculosis cases in shelters. It has acceptable costs, is logistically simple and efficient. Symptom screening was not useful in this general homeless population. RFLP analysis showed cloning of the two-band strain. Given the evidence for ongoing transmission, sputum screening should be considered in shelter settings.

In vitro evidence of two-component system phosphorylation between the Mycobacterium tuberculosis TrcR/TrcS proteins

Two-component regulatory proteins, histidine kinases and response regulators, function in bacteria as sensing and adaptive factors in response to a wide range of environmental stimuli. Conserved histidine and glycine regions of histidine kinase sensor proteins were used to design degenerate oligonucleotide primers for amplification of DNA fragments from Mycobacterium tuberculosis. Two adjacent genes, trcR and trcS, which encode a response regulator and a histidine kinase, respectively, have been identified. Full-length and truncated TrcR and TrcS proteins have been expressed in Escherichia coli. Difficulties in expressing recombinant full-length TrcS and a truncated N -terminal form of TrcS reveal that the transmembrane domains are toxic to E. coli. Overexpressed truncated C-terminal transmitter domains of TrcS have been autophosphorylated in vitro and have transphosphorylated both the full-length recombinant TrcR protein and the N -terminal receiver/regulator domain of TrcR. In vitro autophosphorylation of TrcS requires the presence of Mn2+or Ca2+as a divalent cation cofactor and subsequent transphosphorylation of TrcR is evident in the presence of TrcS-phosphate and Ca2+. Transphosphorylation between these two proteins provides evidence that these M. tuberculosis genes encode functional two-component system regulatory proteins that are members of a signal transduction circuit.

Comparison of the MB/BacT system with a revised antibiotic supplement kit to the BACTEC 460 system for detection of mycobacteria in clinical specimens

The MB/BacT system (MB/BacT) with a revised antibiotic supplement kit was compared with the BACTEC 460 system (BACTEC 460) in a test of 488 specimens submitted for mycobacterial culture from 302 patients. Twenty-four Mycobacterium tuberculosis isolates were detected by the BACTEC 460 versus 23 isolates by the MB/BacT. Mean time until detection of M. tuberculosis isolates identified by both systems was 11.9 days for the BACTEC 460 versus 13.7 days for the MB/BacT (P = 0.046). M. avium complex was detected in 12 specimens by the MB/BacT versus 10 specimens by the BACTEC 460. Only 8 of 14 (57%) M. avium isolates were detected by both systems, with a mean time until detection of 10.1 days for the BACTEC 460 and 14.2 days for the MB/BacT (P = 0.009). The BACTEC 460 and the MB/BacT detected M. gordonae in four specimens, but only a single specimen was positive by both systems. One M. fortuitum isolate and one of five M. kansasii isolates were recovered only by the BACTEC 460. The bacterial overgrowth rate was 7.0% for the MB/BacT versus 4.1% for the BACTEC 460. We found the MB/BacT to be comparable to the BACTEC 460 for mycobacterial detection. Even though time until detection with the MB/BacT was slightly longer (1.8 days longer for M. tuberculosis and 4.1 days for M. avium [mean values]) and the bacterial overgrowth rate was somewhat higher, the decreased labor, the availability of a computerized data management system, and the noninvasive, nonradiometric aspects of the MB/BacT offset these relative disadvantages and make it an acceptable alternative for use in the diagnostic laboratory.

Restriction fragment length polymorphism screening of Mycobacterium tuberculosis isolates: population surveillance for targeting disease transmission in a community

SETTING

Alabama State Tuberculosis Control Program, USA.

OBJECTIVE

To combine molecular screening data with routine information to assess transmission of Mycobacterium tuberculosis and improve control efforts.

DESIGN

Since January 1994, samples from tuberculosis cases statewide have been systematically analyzed by IS6110 restriction fragment length polymorphism (RFLP). All cases during 1994-1995 with a predominate RFLP pattern were evaluated and risk factors assessed. pTBN12 was used to evaluate a large cluster in the Birmingham-Jefferson County (BJC) area.

RESULTS

Statewide, a common two-band pattern was found, named JH2 (99/566, 17.5%). The most important risk associated with this pattern was homelessness (odds ratio, 8.9; P < 0.001). In the BJC area, the homeless accounted for 29% (51/175) of new cases diagnosed during the study period. For the BJC homeless, there were 13 unique RFLP patterns, and JH2 was predominant (29/33, 88%) among three clusters. Secondary analysis of the homeless JH2 cluster revealed a large group that included 19 of 24 (79%) isolates analyzed. Compared with the BJC non homeless (n = 124), the homeless were younger (P < 0.001), of male gender (P < 0.001), black race (P = 0.002), and were heavy alcohol (P < 0.001) and non-injection drug (P = 0.001) users.

CONCLUSIONS

By screening tuberculosis cases statewide, a common two-band RFLP pattern was identified. Its predominance is explained by an ongoing tuberculosis epidemic among Birmingham's homeless population, highlighting RFLP as a tool for population surveillance. The pattern differences observed by pTBN12 typing clearly demonstrate that the isolates might be related but are not clonal.

Bacterial phenotypes mediated by mviA and their relationship to the mouse virulence of Salmonella typhimurium

The focus of this study was the phenotypic characterization of Salmonella typhimurium mutants lacking the function of the response regulator mviA. The inactivation of mviA+ (mviA::kan) is shown to induce a significant change in the growth of most virulent strains, as reflected in the size of the colonies formed on agar plates. The colony phenotype observed in these strains has been designated as the small colony morphology (Scm+) phenotype. Mutants exhibiting the Scm+ phenotype are shown to be significantly attenuated for virulence in susceptible (ItyB) mice. The Scm+ phenotype therefore provides an in vitro phenotypic marker for mviA+ activity. Further examination of Scm+ mutants has revealed that they lack expression of a 55 kDa periplasmic protein which is detected in isogenic mviA+ strains. This protein has been designated mviA+ related protein A (MrpA) and was expressed in direct correlation with virulence in all S. typhimurium strains examined.

Avirulence of LT2 strains of Salmonella typhimurium results from a defective rpoS gene

In order to identify the genetic basis for the attenuation of Salmonella typhimurium LT2 strains, experiments were performed to identify a gene(s) which restores virulence to an avirulent LT2 strain. These and further experiments confirmed that an rpoS mutation is the sole determinant of the attenuation of S. typhimurium LT2.

Immunoprotection by monoclonal antibodies to the porins and lipopolysaccharide of Salmonella typhimurium

Monoclonal antibodies (MAbs) were raised against the outer membrane (OM) antigens of Salmonella typhimurium. Enzyme-linked immunosorbent assays and Western immunoblots indicated that 10 MAbs in the panel were specific for surface epitopes, and 10 recognized buried epitopes of OmpC or OmpD porins; three MAbs reacted with smooth lipo-polysaccharide (LPS), two bound rough LPS, and the remaining three MAbs apparently reacted with a porin-LPS complex. We screened these MAbs and immune polyclonal sera in CAF1 (Ity) mice for their relative immunoprotective potential against a challenge with 10 to 500 LD50 of the virulent S. typhimurium LT-2 strain WB600, or against two LD50 of purified OM from this organism. Polyclonal sera that contained high titers of antibodies to porin monomers and trimers, and LPS, provided significant protection (33 to 100% survivors). Antiporin MAbs, when administered individually, did not protect or prolong the survival of mice. A mixture of MAbs with specificity for the surface, but not buried epitopes of porins, prolonged the survival of mice against endotoxemia, but none provided significant protection against mouse typhoid. MAbs specific for smooth (but not rough) LPS on the other hand, conferred significant protection against endotoxemia and mouse typhoid. Finally, MAbs that presumably recognized epitopes present in porin-LPS complexes, were also protective against endotoxemia and mouse typhoid. These results support the role of antibodies to LPS O-chains, porin-LPS complexes, and to a lesser degree, native porins in acquired resistance to infection by S. typhimurium.

The predicted amino acid sequence of the Salmonella typhimurium virulence gene mviAA(+) strongly indicates that MviA is a regulator protein of a previously unknown S. typhimurium response regulator family

The Salmonella typhimurium virulence gene mviA+ has a predicted amino acid sequence with homology to the N-terminal 112-amino-acid sequence of response regulator proteins. A previously described mutant allele (mviA), which restores virulence to avirulent LT2 strains, was shown to contain a point mutation which would be predicted to cause a single amino acid change, V-102-->G (W. H. Benjamin, Jr., J. Yother, P. Hall, and D. E. Briles, J. Exp. Med. 1,74:1073-1083, 1991). A comparison of the nucleotide sequence of mviA+ with that of the Escherichia coli and Salmonella typhi genes revealed a high degree of conservation.

Acid shock induction of RpoS is mediated by the mouse virulence gene mviA of Salmonella typhimurium

Salmonella typhimurium encounters a variety of acid stress situations during growth in host and nonhost environments. The organism can survive potentially lethal acid conditions (pH <4) if it is first able to adapt to mild or more moderate acid levels. The molecular events that occur during this adaptive process are collectively referred to as the acid tolerance response and vary depending on whether the cells are in log- or stationary-phase growth. The acid tolerance response of logarithmically growing cells includes the participation of an alternate sigma factor, sigmaS (RpoS), commonly associated with stationary-phase physiology. Of 51 acid shock proteins (ASPs) induced during shifts to pH 4.4, 8 are clearly dependent on sigmaS for production (I. S. Lee, J. Lin, H. K. Hall, B. Bearson, and J. W. Foster, Mol. Microbiol. 17:155-167, 1995). The acid shock induction of these proteins appears to be the result of an acid shock-induced increase in the level of sigmaS itself. We have discovered that one component of a potential signal transduction system responsible for inducing rpoS expression is the product of the mouse virulence gene mviA+. MviA exhibits extensive homology to the regulatory components of certain two-component signal transduction systems (W. H. Benjamin, Jr., and P. D. Hall, abstr. B-67, p. 38, in Abstracts of the 93rd General Meeting of the American Society for Microbiology 1993, 1993). Mutations in mviA (mviA::Km) caused the overproduction of sigmaS and sigmaS-dependent ASPs in logarithmically growing cells, as well as increases in tolerances to acid, heat, osmolarity and oxidative stresses and significant decreases in growth rate and colony size. Mutations in rpoS suppressed the mviA::Km-associated defects in growth rate, colony size, ASP production, and stress tolerance, suggesting that the effects of MviA on cell physiology occur via its control of sigmaS levels. Western blot (immunoblot) analyses of sigmaS produced from natural or arabinose-regulated promoters revealed that acid shock and MviA posttranscriptionally regulate sigmaS levels. Turnover experiments suggest that MviA regulates the stability of sigmaS protein rather than the translation of rpoS message. We propose a model in which MviA or its unknown signal transduction partner senses some consequence of acid shock, and probably other stresses, and signals the release of sigmaS from proteolysis. The increased concentration of sigmaS drives the elevated expression of the sigmaS-dependent ASPs, resulting in an increase in stress tolerance. The avirulent nature of mviA insertion mutants, therefore, appears to result from inappropriate sigmaS-dependent gene expression during pathogenesis.

Transmission of Mycobacterium tuberculosis to recipients of single lung transplants from the same donor

Recipients of organ transplants are at increased risk for infection both because of immunosuppression and because of the transfer of microbes through the donor organs. We report two cases of M. tuberculosis disease in recipients of single lung transplants who shared a common donor. Both recipients developed pulmonary tuberculosis, one having fever and pulmonary infiltrates and the other having subclinical disease with M. tuberculosis organisms being recovered from bronchoalveolar lavage. Restriction fragment length polymorphism analysis on both isolates of M. tuberculosis revealed a common source. The donor of both lungs had a normal chest radiograph and no known prior history of M. tuberculosis infection of disease. These cases are the first report of two single lung recipients developing pulmonary tuberculosis from a common donor.

Laboratory contamination of Mycobacterium tuberculosis cultures

The purpose of this study was to investigate possible laboratory contamination of Mycobacterium tuberculosis cultures which resulted in the misdiagnosis of tuberculosis. We have investigated three cases in which a patient's culture was positive for M. tuberculosis but there was not a high clinical suspicion for disease. In each instance, another patient with clinically obvious pulmonary tuberculosis had specimens cultured concurrently within the same clinical laboratory. The isolates from both the obvious cases of tuberculosis and the suspect cases were obtained through the State of Alabama TB Laboratory, but these isolates originated at a commercial laboratory, a community hospital laboratory, and at a university hospital. MTB isolates were fingerprinted by probing for the insertion sequence IS6110. With each of the three pairs of isolates (case and suspicious case), identical IS6110 banding patterns were found suggesting identical MTB strains. Because the patients were geographically separated, it is strongly suspected that laboratory contamination of M. tuberculosis cultures resulted in the three suspect cases being diagnosed with tuberculosis. These findings indicate that positive M. tuberculosis cultures resulting from laboratory contamination can occur.

In vivo administration of the anticancer agent bryostatin 1 activates platelets and neutrophils and modulates protein kinase C activity

Bryostatin 1 is a naturally occurring macrocyclic lactone which when applied to cells in culture activates protein kinase C (PKC). In vivo bryostatin 1 functions as an anticancer agent with activity against murine lymphomas, leukemias, and melanoma. Because all organs and tissues contain PKC, normal cells would also be a likely target for this agent. Here we demonstrate that in vivo administration of bryostatin 1 activates platelets over a dose range of 0.4 to 40 micrograms/kg with half-maximal activation occurring at 3 micrograms/kg and stimulation of neutrophils over a similar dose range. This in vivo activation of neutrophils is associated with a rapid decrease in measurable cytosolic PKC, a finding consistent with translocation of the enzyme to the membrane. In contrast, no statistically significant change in PKC location was found in liver, spleen, brain, or L10A B-cell lymphoma. However, in culture the L10A lymphoma did respond to bryostatin 1 with translocation of PKC. To evaluate whether the lack of effect of bryostatin 1 on PKC in organs was secondary to rapid degradation, we developed a bioassay to measure the levels of bryostatin 1 in the blood. To measure the presence of bryostatin 1, human neutrophils were incubated with plasma from mice given injections of different concentrations of bryostatin 1. Using this assay, bryostatin 1 at levels as low as 60 nM could be measured in the plasma. A time course with this bioassay demonstrated that less than 10% of the bryostatin 1 injected was detectable after 2.5 min. These results demonstrate that bryostatin 1 is capable of activating platelets and neutrophils and modulating PKC in vivo. The lack of effect of bryostatin 1 on specific organs may be secondary to the rapid clearance/degradation of this compound from the blood.

A 'safe-site' for Salmonella typhimurium is within splenic polymorphonuclear cells

Following oral or systemic infection with Salmonella typhimurium, the focus of infection is in the liver and spleen. The majority of Salmonella surviving in the liver and spleen by 4 h post infection are already in an environment where they are largely protected from subsequent killing. Previous studies have shown that the majority of surviving Salmonella are intracellular. In the present study we sought to determine the cell type containing most of the cell-associated Salmonella liberated from the spleen. We enriched for Salmonella-containing cells by Ficoll-Hypaque separation followed by fluorescence-activated cell sorting. Approximately 85% of the total intracellular Salmonella were found in Mac-1+/J-11d+ cell fractions of the Ficoll-Hypaque band and pellet. By microscopic examination of stained cells from the sorted cell populations, it was evident that virtually all of the Salmonella were in polymorphonuclear cells (PMN). The numbers of Salmonella observed microscopically were similar in numbers to Salmonella colony forming units detected by plating. Salmonella containing PMN in the Ficoll band generally contained a single bacterium, while those from the probably less healthy cells in the Ficoll pellet generally contained several Salmonella.

In vivo administration of bryostatin 1, a protein kinase C activator, decreases murine resistance to Salmonella typhimurium

Bryostatin 1, a potent activator of protein kinase C, has antitumor activity against murine lymphoma, leukemia, and melanoma. In vitro, this compound stimulates the release of gamma-interferon, interleukins, and hematopoietic growth factors from accessory cells and activates both T- and B-cells. Bryostatin 1 is also able to stimulate neutrophils to undergo oxidative burst and degranulation. Because of the ability of this compound to stimulate the immune system, cause release of immune mediators, and activate neutrophils, we have examined its effect on bacterial infection by using the gram-negative bacterium Salmonella typhimurium in mice. We find that animals given injections i.v. of S. typhimurium have a shortened life span if they are also given injections i.p. of nonlethal doses of bryostatin 1. There is a dose-response relationship with 100 micrograms/kg bryostatin 1 having a greater effect on survival than 40 micrograms/kg. Below 40 micrograms/kg there are no effects on survival. Analysis of the first 4 h of Salmonella infection demonstrates that bryostatin 1 does not affect the blood clearance of the bacterium. However, by day 2 of infection greater numbers of bacteria are found in the livers and spleens of mice given injections of bryostatin 1. By day 5, 10-fold more S. typhimurium bacteria are found in the livers and spleens of mice receiving 40 micrograms/kg of bryostatin 1. To determine whether bryostatin 1 was affecting growth or causing the death of bacteria, we used a Salmonella carrying a plasmid which has a temperature-sensitive origin of replication and is unable to replicate when the bacteria are in mice. This experiment demonstrates that bryostatin 1 represses bacterial killing but does not affect bacterial growth. Bryostatin 1 given i.p. stimulates a transient syndrome of weight loss and diarrhea from which the mice recover and regain weight, suggesting that bryostatin 1 may release a number of important humoral mediators in vivo. The weight loss is exacerbated by Salmonella infection with mice receiving bryostatin 1 and S. typhimurium, in that they lose approximately 33% of body weight prior to death. Thus, at doses used to treat murine tumors, bryostatin 1 treatment does not affect the clearance of S. typhimurium from the blood but does decrease the killing of bacteria in the liver and spleen, leading to early animal death. Such potential effects of bryostatin 1 on the outcome of bacterial infections should be evaluated in ongoing human trials of this agent.

The Salmonella typhimurium locus mviA regulates virulence in Itys but not Ityr mice: functional mviA results in avirulence; mutant (nonfunctional) mviA results in virulence

The virulent Salmonella typhimurium strain WB600 carries the mviA allele of the gene mouse virulence A. As shown here, the virulent phenotype of WB600 is the result of a nonfunctional mviA gene. As compared to the functional allele mviA+, mviA increases virulence in Itys mice, but not in Ityr mice. A specific BglII site, mviA4185, between osmZ and galU, located at approximately 35 min on the salmonella chromosome, was within mviA. Insertion of an antibiotic cassette in the mviA4185 site of mviA+ or the homologous mviA4093 site of mviA DNA resulted in virulence when either cassette was recombined into the chromosome. When mviA and mviA+ were both expressed in the same strain with one carried in the chromosome and the other on a plasmid, avirulence was dominant. Replacement of the mviA allele of strain WB600 using P22 transductions of linked antibiotic cassettes cloned into the chromosome of virulent S. typhimurium strains (SR-11, TML, SL1344, C5, ATCC14028, W118-2, and WB600) showed that all but WB600 contained the avirulent mviA+ allele. Southern hybridizations provided no evidence for a second mviA allele anywhere in the genome of the six non-WB600 strains.

A hemA mutation renders Salmonella typhimurium avirulent in mice, yet capable of eliciting protection against intravenous infection with S. typhimurium

The hemA mutation reduces the virulence of Salmonella typhimurium for mice by at least 10(7)-fold, as measured by change in LD50. The hemA mutation does not appear to affect killing of salmonella in mice. The salmonella with the hemA mutation persist in the spleen and liver for 2 to 3 weeks following intravenous injection. The most likely effect of the hemA mutation is to block, or retard, growth of S. typhimurium in an aerobic in vivo environment. Intravenous vaccination of susceptible ltys mice with hemA salmonella was able to elicit about 4 logs of protection against invasive infection with wild-type S. typhimurium 78 days after vaccination, at a time when the vaccine strain was no longer detectable in the spleen and liver.

A 'safe-site' for Salmonella typhimurium is within splenic cells during the early phase of infection in mice

Salmonella typhimurium infection in mice is focused on the spleen and liver, and prolonged infection can lead to sepsis and death. After intravenous infection with a moderate dose of S. typhimurium, the few bacteria that survive in the spleen and liver grow in a 'safe-site' where they are protected from immune destruction. In this study, we demonstrated that the lack of killing of resident salmonella in the spleen and liver was not because the salmonella were transformed within the host and became resistant to killing, or because the infected mice lost the ability to kill salmonella. We showed that the salmonella were within an intracellular 'safe-site' that protected them from killing. Brief treatment of salmonella-infected mice with gentamicin reduced the numbers of salmonella in the blood but had no effect on the numbers in the liver and spleen, suggesting an intracellular location of the salmonella. After dissociation of spleen cells from recently infected mice, 60% of the salmonella remained cell associated. These cell-associated salmonella, unlike cell-free salmonella, were resistant to killing by gentamicin. The cell-associated salmonella were rendered susceptible to gentamicin after sonication, providing confirmation of their previous intracellular location.

Mouse hepatitis virus strain UAB infection enhances resistance to Salmonella typhimurium in mice by inducing suppression of bacterial growth

We have previously shown that intranasal infection of mice with mouse hepatitis virus (MHV) strain UAB (MHV-UAB) increases their resistance to Salmonella typhimurium injected intravenously 6 days later. To study how salmonella resistance was induced, BALB/cAnNCr mice were infected with salmonella strains carrying specific genetic alterations. One set of studies compared the effect of MHV infection on subsequent salmonella infections with AroA- (avirulent) and Aro+ (virulent) salmonellae. Unlike its effect on Aro+ salmonellae, MHV failed to reduce the number of AroA- salmonellae recovered from mice. Because AroA- S. typhimurium shows almost no growth in vivo, this failure indicated that the effect of MHV on salmonella resistance required growth of the infecting salmonellae. In other studies, the effect of MHV infection on both growth and killing were monitored simultaneously in mice with growing salmonellae carrying a single copy of the temperature-sensitive pHSG422 plasmid, which is unable to replicate in vivo. MHV infection reduced salmonella growth but caused no increase in salmonella killing. MHV infection of mice given wild-type salmonellae also resulted in no increase in salmonella killing 4 h after salmonella challenge. These studies demonstrate that MHV-UAB infection increases host resistance to salmonellae by enhancing suppression of bacterial growth instead of by increasing the amount of salmonella killing.

The primary effect of the Ity locus is on the rate of growth of Salmonella typhimurium that are relatively protected from killing

The Ity locus affects the net increase in numbers of Salmonella typhimurium in the liver and spleen of infected mice. There has been controversy, however, about whether the effects of this locus are due to differential killing of S. typhimurium or differential growth rates of S. typhimurium in mice. Our studies using S. typhimurium aroA mutants, which do not grow in vivo, demonstrate that growth of the infecting salmonella is necessary for the observation of the Ity phenotype. To examine the effects of the Ity locus on the growth and killing of fully virulent salmonella, we infected Ity-congenic mice i.v. with stationary phase S. typhimurium containing a single copy of the plasmid pHSG422. This plasmid exhibits defective replication at body temperature and is diluted out during salmonella growth in vivo. Thus, the frequency of plasmid-containing salmonella recovered from mice provides a measure of salmonella cell divisions in vivo. Inasmuch as the numbers of plasmid-containing salmonella are only slightly affected by bacterial division, any decline in the numbers of plasmid-containing salmonella is an unbiased measure of killing. By infecting mice with these plasmid-containing salmonella we observed that: 1) during the first four h post infection (during blood clearance of injected salmonella) there is about 3-fold more killing of salmonella in Ityr mice than in Itys mice; 2) from 4 to 44 h postinfection (after blood clearance is completed) there is little if any additional killing in either Itys or Ityr mice; and 3) during the first 48 h postinfection there is about 18-fold more growth of salmonella in Itys mice than in Ityr mice. Thus, the major effect of the Ity locus on resistance to salmonella, is the regulation of growth within a "safe" (relatively nonbactericidal) site in the liver and spleen.

The primary effect of the Ity locus is on the rate of growth of Salmonella typhimurium that are relatively protected from killing

The Ity locus affects the net increase in numbers of Salmonella typhimurium in the liver and spleen of infected mice. There has been controversy, however, about whether the effects of this locus are due to differential killing of S. typhimurium or differential growth rates of S. typhimurium in mice. Our studies using S. typhimurium aroA mutants, which do not grow in vivo, demonstrate that growth of the infecting salmonella is necessary for the observation of the Ity phenotype. To examine the effects of the Ity locus on the growth and killing of fully virulent salmonella, we infected Ity-congenic mice i.v. with stationary phase S. typhimurium containing a single copy of the plasmid pHSG422. This plasmid exhibits defective replication at body temperature and is diluted out during salmonella growth in vivo. Thus, the frequency of plasmid-containing salmonella recovered from mice provides a measure of salmonella cell divisions in vivo. Inasmuch as the numbers of plasmid-containing salmonella are only slightly affected by bacterial division, any decline in the numbers of plasmid-containing salmonella is an unbiased measure of killing. By infecting mice with these plasmid-containing salmonella we observed that: 1) during the first four h post infection (during blood clearance of injected salmonella) there is about 3-fold more killing of salmonella in Ityr mice than in Itys mice; 2) from 4 to 44 h postinfection (after blood clearance is completed) there is little if any additional killing in either Itys or Ityr mice; and 3) during the first 48 h postinfection there is about 18-fold more growth of salmonella in Itys mice than in Ityr mice. Thus, the major effect of the Ity locus on resistance to salmonella, is the regulation of growth within a "safe" (relatively nonbactericidal) site in the liver and spleen.

Antipneumococcal effects of C-reactive protein and monoclonal antibodies to pneumococcal cell wall and capsular antigens

Antibodies to pneumococcal capsular polysaccharides are well known for their ability to protect against pneumococcal infection. Recent studies indicate that antibodies to cell wall antigens, including pneumococcal surface protein A and the phosphocholine (PC) determinant of teichoic acids as well as human C-reactive protein (which also binds to PC), can protect mice against pneumococcal infection. In the present study we compared the protective effects of these agents as measured by mouse protection, the blood bactericidal assay, and clearance of pneumococci from the blood and peritoneal cavity. Our findings extend previous results indicating that human C-reactive protein and antibodies to noncapsular antigens are generally less protective than anticapsular antibodies. The new results obtained indicate the following: (i) mouse protection studies with intraperitoneal and intravenous infections provide very similar results; (ii) monoclonal immunoglobulin G2a (IgG2a) antibodies to PC, like IgG1, IgG2b, and IgG3 antibodies to PC, are highly protective against pneumococcal infection in mice; (iii) human antibody to PC is able to protect against pneumococcal infection in mice; (iv) antibodies to PspA are effective at mediating blood and peritoneal clearance of pneumococci; (v) complement is required for the in vivo protective effects of both IgG and IgM antibodies to PC; (vi) IgG1, IgG2b, and IgG3 anti-PC antibodies all mediate complement-dependent lysis of PC-conjugated erythrocytes; and (vii) antibodies and human C-reactive proteins that are reactive with capsular antigens but not cell wall antigens are able to mediate significant antibacterial activity in the blood bactericidal assay.

Modulation of resistance to Salmonella typhimurium infection in mice by mouse hepatitis virus (MHV)

Prior infection of mice with a field strain of mouse hepatitis virus (MHV) increased the early resistance of euthymic mice to virulent Salmonella typhimurium strain SR-11 infections (as defined by significantly fewer salmonella colony-forming units (cfu) present in spleens and livers 4 days after salmonella infection). This increase in salmonella resistance was observed when the interval between MHV and salmonella infections was 6 days, but not at 3, 10, or 14 day intervals. The mouse Ity locus, which controls the number of intracellular salmonella, had a significant effect on the ability of MHV to induce resistance to salmonella. MHV caused an increase in resistance to salmonella in Itys (salmonella susceptible) mice at all doses of salmonella tested (100 to 10,000 cfu). In the Ityr (salmonella resistant) mice tested the beneficial effect of MHV on salmonella resistance was small and when observed, was only present at salmonella doses of 10,000 cfu or greater. Neither the Lpsd nor Xid mutations affected the ability of MHV to increase resistance to salmonella infection. In contrast to euthymic mice, MHV infection greatly decreased the resistance of athymic (nude) mice to salmonella infection. Since the Nu locus does not affect the resistance of mice to salmonella (at 4 days post salmonella infection), these results indicate that MHV infection and the nude phenotype interact to increase susceptibility to salmonella. These findings re-emphasize the importance of keeping laboratory mice used in research free of MHV and other immunomodulatory pathogens.

Effects of in vitro growth phase on the pathogenesis of Salmonella typhimurium in mice

The growth phase of a bacterial (Salmonella typhimurium) culture was shown to have pronounced effects on the pathogenic properties of the harvested bacteria. Salmonellae obtained from a culture in primary (exponential) growth phase (PP) were more readily cleared from the blood and more readily killed by phagocytes than were salmonellae obtained from a more slowly growing secondary growth phase (SP) culture. PP salmonellae were observed to cause death of mice sooner than SP salmonellae. This appeared to be because the more rapid growth of PP, as compared to SP, salmonellae continued in the liver and spleen for several hours following intravenous injection, and more than compensated for their high in vivo death rate. As a result, within 4 h there were approximately 10-fold more live salmonellae in the spleens and livers of mice that had received PP, as compared to SP, salmonellae. This 10-fold difference was maintained until the death of the mice, indicating that after the first 4 h post-inoculation, the net in vivo growth of the salmonellae was the same regardless of their growth phase in the inoculating culture. This transition between PP and SP salmonellae occurred long before a dense stationary phase culture was obtained. Salmonellae grown in minimal media exhibited the biological properties of SP salmonellae and never entered as rapid a growth phase as did salmonellae in complete media.

Genetic mapping of novel virulence determinants of Salmonella typhimurium to the region between trpD and supD

Salmonella typhimurium strains are known to vary greatly in their virulence for mice. A few of the genes affecting their virulence have been described. In this report we have localized at least two genes that affect the ability of S. typhimurium to grow in BALB/cByJ to a 6 unit section of the salmonella chromosome which does not contain any previously described virulence determinants. The genetic mapping was done by interrupted matings using Hfr strains made in a virulent LT2 strain. The Hfr strains were constructed by inserted the plasmid F'(TS)114 lac+ Tn::10 into the LT2 chromosome at specific sites through homologous recombination with chromosomal Tn10s. Short interrupted matings to an avirulent LT2 strain in either direction through the portion of the chromosome from trpD at 34 units to supD at 40 units resulted in transconjugants which were fully virulent. Since we also found several transconjugants with intermediate virulence it appears that more than one virulence gene may exist in this area of the chromosome. The mechanisms of action of these genes are not known.

Salmonella typhimurium virulence genes necessary to exploit the Itys/s genotype of the mouse

The studies described in this paper provide evidence that the pathogenesis of Salmonella typhimurium in mice is dependent on interactions between particular genotypes of the infected mice and the infecting Salmonella strain. This conclusion was based on data obtained by infecting a panel of BXD recombinant inbred mice with each of three S. typhimurium strains. One of the S. typhimurium strains was a transconjugant (WB500) produced in an interrupted mating between the two other strains, one (SR-11) of high and the other (LT2-Z) of low virulence for BALB/c mice. We found that strain WB500 appeared to have inherited from SR-11 a gene (or genes) which was required to exploit the Itys/s genotype in mice. However, WB500 apparently lacked other SR-11 virulence gene(s), whose effect on the in vivo growth of SR-11 was independent of the Ity genotype of the mouse.

Induction of germ-line anti-alpha 1-3 dextran antibody responses in mice by members of the Enterobacteriaceae family

A large panel of enteric organisms was screened for agglutination with a panel of lambda monoclonal antibodies of different heavy chain isotypes specific for alpha 1-3 dextran (DEX). Two strains were initially isolated that were bound by most of the anti-DEX antibodies. One organism, Enterobacter cloacae strain MK7, which was characterized in detail, induced a typical lambda anti-DEX response in Igh-Ca mice that had a fine idiotope profile comparable with that induced by purified B1355S dextran containing alpha 1-3 glucosidic linkages (alpha 1-3-DEX). The determinant on the bacterial surface was shown by binding inhibition with nigerotriose to contain alpha 1-3 linkages. Hyperimmunization with these organisms of normal, athymic (nu/nu), or germ-free mice induced large amounts of IgM antibodies but very little IgG. This is the first description of an organism isolated from the normal gut flora of mice that can be shown directly to be bound by alpha 1-3-DEX antibodies and to induce the typical germ-line response of the DEX family of antibodies.

Induction of germ-line anti-alpha 1-3 dextran antibody responses in mice by members of the Enterobacteriaceae family

A large panel of enteric organisms was screened for agglutination with a panel of lambda monoclonal antibodies of different heavy chain isotypes specific for alpha 1-3 dextran (DEX). Two strains were initially isolated that were bound by most of the anti-DEX antibodies. One organism, Enterobacter cloacae strain MK7, which was characterized in detail, induced a typical lambda anti-DEX response in Igh-Ca mice that had a fine idiotope profile comparable with that induced by purified B1355S dextran containing alpha 1-3 glucosidic linkages (alpha 1-3-DEX). The determinant on the bacterial surface was shown by binding inhibition with nigerotriose to contain alpha 1-3 linkages. Hyperimmunization with these organisms of normal, athymic (nu/nu), or germ-free mice induced large amounts of IgM antibodies but very little IgG. This is the first description of an organism isolated from the normal gut flora of mice that can be shown directly to be bound by alpha 1-3-DEX antibodies and to induce the typical germ-line response of the DEX family of antibodies.

The ability of Salmonella typhimurium to produce the siderophore enterobactin is not a virulence factor in mouse typhoid

One of the nonspecific defense mechanisms of higher animals is their ability to limit iron availability to infecting bacteria. Thus it has been argued that all pathogenic bacteria must have special mechanisms to obtain iron in the host environment. Salmonella typhimurium is known to produce a siderophore, enterobactin, with which it can obtain iron from host transferrin. Previous studies have indicated that the production of this molecule is necessary for the ability of intraperitoneally injected. S. typhimurium cells to cause mouse typhoid, a largely intracellular infection. We have reexamined this finding with wild-type S. typhimurium and isogenic strains carrying the nonenterobactin-producing mutation ent-1 or ent-7. Our findings demonstrate that, although enterobactin production is necessary for growth in normal mouse serum, it does not affect the ability of S. typhimurium to cause mouse typhoid. Based on these findings and published results of other investigators on the role of siderophores in intracellular pathogens, a more comprehensive investigation of the importance of siderophores in intracellular infections may be warranted.

Blood clearance by anti-phosphocholine antibodies as a mechanism of protection in experimental pneumococcal bacteremia

Previous studies have demonstrated that monoclonal IgG and IgM antibodies to phosphocholine (PC), a determinant in the cell wall of Streptococcus pneumoniae, can protect mice from fatal infection with S. pneumoniae. In this study we demonstrate that both passive and naturally occurring anti-PC antibodies promote the clearance of S. pneumoniae from the blood. The bulk of the cleared pneumococci are apparently killed, because they fail to accumulate in reticuloendothelial tissues. These findings suggest that their protective effect is probably dependent on their ability to promote phagocytosis. We have found that on a weight basis IgG antibody is more effective at promoting blood clearance than IgM antibody. This observation fits with our earlier findings that IgG anti-PC antibody is more protective against i.v. infection than IgM anti-PC antibody. We have also demonstrated that anti-PC antibodies are protective against S. pneumoniae infection when given as late as 24 hr postinfection. This finding makes it unlikely that the ability to protect against pneumococcal infection with anti-PC antibody is dependent on an artifact associated with either their in vitro growth or the harvesting procedure.

Blood clearance by anti-phosphocholine antibodies as a mechanism of protection in experimental pneumococcal bacteremia

Previous studies have demonstrated that monoclonal IgG and IgM antibodies to phosphocholine (PC), a determinant in the cell wall of Streptococcus pneumoniae, can protect mice from fatal infection with S. pneumoniae. In this study we demonstrate that both passive and naturally occurring anti-PC antibodies promote the clearance of S. pneumoniae from the blood. The bulk of the cleared pneumococci are apparently killed, because they fail to accumulate in reticuloendothelial tissues. These findings suggest that their protective effect is probably dependent on their ability to promote phagocytosis. We have found that on a weight basis IgG antibody is more effective at promoting blood clearance than IgM antibody. This observation fits with our earlier findings that IgG anti-PC antibody is more protective against i.v. infection than IgM anti-PC antibody. We have also demonstrated that anti-PC antibodies are protective against S. pneumoniae infection when given as late as 24 hr postinfection. This finding makes it unlikely that the ability to protect against pneumococcal infection with anti-PC antibody is dependent on an artifact associated with either their in vitro growth or the harvesting procedure.

A genetic locus responsible for salmonella susceptibility in BSVS mice is not responsible for the limited T-dependent immune responsiveness of BSVS mice

BSVS mice are known to be highly susceptible to salmonella infection. We have shown that the bulk of the difference in susceptibility between BSVS and salmonella-resistant A/J mice is the result of a genetic difference at a single locus not closely linked to H-2, Igh-C, or Hbb, and not X-linked. We have backcrossed the A/J allele at this locus into BSVS mice for 8 successive generations and have demonstrated that the salmonella resistance afforded by this allele is not the result of a restoration of the generalized poor T-dependent responsiveness of BSVS mice. The salmonella resistance locus we have examined with these 2 strains is probably the same as the Ity locus described by others.

A genetic locus responsible for salmonella susceptibility in BSVS mice is not responsible for the limited T-dependent immune responsiveness of BSVS mice

BSVS mice are known to be highly susceptible to salmonella infection. We have shown that the bulk of the difference in susceptibility between BSVS and salmonella-resistant A/J mice is the result of a genetic difference at a single locus not closely linked to H-2, Igh-C, or Hbb, and not X-linked. We have backcrossed the A/J allele at this locus into BSVS mice for 8 successive generations and have demonstrated that the salmonella resistance afforded by this allele is not the result of a restoration of the generalized poor T-dependent responsiveness of BSVS mice. The salmonella resistance locus we have examined with these 2 strains is probably the same as the Ity locus described by others.