Molecular surveillance of carbapenem-resistant Enterobacterales in two nearby tertiary hospitals to identify regional spread of high-risk clones in Germany, 2019-2020.

BACKGROUND: Understanding the transmission dynamics of carbapenem-resistant Enterobacterales (CRE) is critical to addressing the escalating global threat of antimicrobial resistance (AMR). Although hospital transmission of CRE has been extensively studied, information on community transmission is lacking. AIM: To identify genomic clusters of CRE from two nearby institutions that may be indicative of community or inter-facility transmission. METHODS: CRE isolates between January 1st, 2019 and December 31st, 2020 from two tertiary hospitals, detected in the respective routine microbiology laboratories, were collected and characterized by short-read whole-genome sequencing. FINDINGS: A total of 272 CRE were collected, with Enterobacter cloacae complex (71/192, 37%) predominant in Heidelberg and Escherichia coli (19/80, 24%) in Mannheim. The most common carbapenem resistance gene, blaOXA-48, was detected in 38% of CRE from both centres. Several putative transmission clusters were found, including six clusters of E. cloacae complex, five clusters of Klebsiella pneumoniae, four clusters of Citrobacter freundii, and two clusters each of Escherichia coli and K. aerogenes. No clusters involved isolates from both study centres, except for an ST22 C. freundii cluster. Globally circulating clones were identified between the two centres for ST131 E. coli, ST66 E. hormaechei, and ST22 C. freundii. CONCLUSION: This study found no widespread transmission clusters among isolates from both centres, suggesting a hospital-specific clonal structure. This suggests that CRE clusters involving both institutions may indicate emerging or circulating clones in the community, highlighting the need for intersectoral surveillance and data sharing.

[Results of preoperative SARS-CoV-2 testing in the coronavirus pandemic]. / Ergebnisse der präoperativen SARS-CoV-2-Testung ("severe acute respiratory syndrome coronavirus 2") in der Coronaviruspandemie.

BACKGROUND: Surgery is challenging during the coronavirus disease 2019 (COVID-19) pandemic. This study aimed to investigate the preoperative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing in elective and emergency surgery and to calculate the patient contacts during hospital stay. MATERIALS AND METHODS: All surgeries defined by the German procedural classification (starting with a 5) from 1 June until 29 November 2020 were retrospectively evaluated regarding the preoperative SARS-CoV­2 nasopharyngeal swab test. The results were then divided in emergency and elective surgeries. To show the personal contacts of the patients in a university hospital, we calculated the patient pathway within the department of urology and urosurgery for April 2020. Therefor we used the electronic patient records. RESULTS: Altogether 7745 surgical procedures in 5985 patients were performed, whereby 39 (0.5%) SARS-CoV­2 tests were positive. 2833 (37%) surgical procedures were emergency cases and 4912 (63%) were elective procedures. 25 (0.9%) of the emergency group and 14 (0.3%) of the elective surgeries had a positive SARS-CoV­2 test. The average number of contacts in the patient room was 12.83 (0-50) and 84.22 (0-249) at the ward level, not counting contacts with the clinic staff. CONCLUSIONS: Nearly 1% of the preoperative SARS-CoV­2 tests of either emergency or elective surgeries tested positive in the 6 months prior to November 2020. Although the risk of undetected SARS-CoV­2 infection appears to be low in terms of costs and personnel, preoperative screening is useful in high-risk areas to ensure further necessary surgeries, especially concerning cancer patients and to prevent virus spread in a hospital.

Course of colonization by multidrug-resistant organisms after allogeneic hematopoietic cell transplantation.

Multidrug-resistant organisms (MDRO) have been developing as an emerging problem in allogeneic hematopoietic cell transplantation (HCT). Since no data are available on the course of MDRO colonization after HCT, we investigated in this retrospective, single-center study, persistence and clearance of MDRO after HCT. From June 2010 to December 2015, 121 consecutive HCT patients were included. Patients received a MDRO screening before conditioning as well as surveillance cultures after HCT. In MDRO-colonized patients, surveillance specimens were taken until MDRO were no longer detectable. Thirty-three patients (27%) were found to be colonized by at least one MDRO at any time point until day 100 post HCT. Day 100 (2-year) non-relapse mortality (NRM) and overall survival (OS) of MDRO-colonized (MDRO+) versus non-colonized (MDRO-) patients were essentially the same. NRM is 15% (21%) versus 15% (24%). Two-year OS is 60 versus 55% for MDRO+ versus MDRO- patients. Out of the 33 MDRO+ patients, 21 cleared the MDRO. Median time to non-detectability of MDRO was 6 months. In 12 patients, the MDRO persisted. There was a significant (p < 0.0001) survival difference between patients who cleared the MDRO versus those with MDRO persistence (2-year OS 80 vs 40%). Except for the length of antibiotic therapy as a potential risk factor for MDRO persistence after HCT, no other conventional factors could be identified. (a) colonization by MDRO per se had no negative impact on the outcome, (b) MDRO can be cleared by the majority of patients after allogeneic HCT, and (c) to increase the probability to clear MDRO, the use of antibiotics in MDRO+ patients should be reviewed critically.

Rapid detection of cefotaxime-resistant Escherichia coli by LC-MS.

Antibiotic resistance is an unsolved healthcare problem with increasing impact on patient management in the last years. In particular, multidrug resistance among Gram-negative bacterial strains has become the most pressing challenge. In order to deliver the most efficacious antimicrobial therapy with minimum delay, rapid diagnostic tests are required in order to detect multidrug resistant pathogens early during infection. In line with these efforts, we have developed a mass spectrometry-based assay for the rapid determination of ampicillin and cefotaxime resistance. The assay quantifies beta-lactamase activities towards ampicillin and cefotaxime within a turnaround time of 150 min, which is substantially faster than classical susceptibility testing.

Rapid detection of ampicillin resistance in Escherichia coli by quantitative mass spectrometry.

Early targeted antimicrobial therapy helps decrease costs and prevents the spread of antimicrobial resistance, including in Escherichia coli, the most frequent Gram-negative bacterium that causes sepsis. Therefore, rapid susceptibility testing represents the major prerequisite for knowledge-based successful antimicrobial treatment. To accelerate testing for antibiotic susceptibility, we have developed a new mass spectrometry-based assay for antibiotic susceptibility testing (MAAST). For proof of principle, we present an ampicillin susceptibility test for E. coli with a turnaround time of 90 min upon growth detection.

[Increasing therapeutic challenges through multi-resistant bacteria in the hospital]. / Zunehmende therapeutische Herausforderungen durch multiresistente Keime in der Klinik.

BACKGROUND: Multi-resistant bacteria endanger with increasing frequency the successful outcome of antibiotic therapy, which represents the presumably most successful discovery of medicine. Due to a worldwide misuse of antibiotics and combined with a lacking awareness of hospital hygiene, multi-resistant bacteria spread with a worrisome pace within the clinic. These bacteria also spread globally via modern transportation systems. Today bacteria are present in hospitals, which are sensitive to a rather limited number of antibiotics or even -worse are pan-resistant. The growing threat of multi-resistant bacteria is further increased by the fact that the pipeline of the pharmaceutical industry for new antibiotics is more or less empty. Furthermore, economical pressure will increase the workload for hospital employees and by that support the spread of -multi-resistant bacteria. In addition, patients will be more susceptible to infections since on the one hand they are on average of older age and on the other hand treated with more aggressive surgical or immuno-suppressive regimens. CONCLUSION: This threatening but realistic future scenario can only be avoided by a combination of measures: absolute justified application of antibiotics, a consequent use of standard hygiene, -isolation of contaminated or infected patients and sufficient employees and their education in the prevention of infections.

Chemokine response induced by Chlamydia trachomatis in prostate derived CD45+ and CD45- cells.

The role of innate cells and their receptors within the male genital tract remains poorly understood. Much less is known about the relative contribution of different genital tract cells such as epithelial/stromal cells and resident leucocytes. In this study, we examined innate immune responses to Chlamydia trachomatis by prostate epithelial/stromal cells and prostate resident leucocytes. Murine prostate primary cultures were performed and leucocyte and epithelial/stromal cells were sorted based on surface protein expression of CD45 by magnetism-activated cell sorting or fluorescence-activated cell sorting. Prostate derived CD45- and CD45+ cells were infected with C. trachomatis and chemokine secretion assayed by ELISA. Similar experiments were performed using prostate CD45+ and CD45- cells from myeloid differentiation factor 88 (Myd88(-/-)) mice or toll-like receptor (Tlr2(-/-)) and Tlr4(mutant) double-deficient mice. Moreover, a TLR-signalling pathway array was used to screen changes in different genes involved in TLR-signalling pathways by real-time PCR. Prostate derived CD45- and CD45+ cells responded to chlamydial infection with the production of different chemokines. Both populations expressed genes involved in TLR signalling and required to respond to pathogen-associated molecular patterns and to C. trachomatis infection. Both populations required the adaptor molecule MYD88 to elicit chemokine response against C. trachomatis. TLR2-TLR4 was essential for chemokine production by CD45+ prostate derived cells, but in their absence, CD45- cells still produced significant levels of chemokines. We demonstrate that C. trachomatis is differentially recognised by prostate derived CD45+ and CD45- cells and suggest that diverse strategies are taking place in the local microenvironment of the host in response to the infection.

[Antibiotic prophylaxis in primary and revision hip arthroplasty: what is the evidence?]. / Antibiotische Infektionsprophylaxe in der Primär- und Revisionsendoprothetik der Hüfte: Was ist erwiesen?

Advances in the perioperative and postoperative management of total joint replacement have led to a steady decrease in the infection rate, which in the case of total hip replacement presently lies between 0.25 and 1%. Unfortunately there is disparity in current practice nationally and internationally, regarding duration, time of application and choice of antibiotics. Currently there are only Level 1a recommendations for primary hip arthroplasty, whereas, due to the heterogeneity and complexity of most revision cases as well as a lack of randomized controlled trials, antibiotic prophylaxis for hip revision arthroplasty is mostly based on the surgeon's preference. In this article the current literature is reviewed and scientifically sound data and recommendations are summarized.

Effectiveness of ozone against endodontopathogenic microorganisms in a root canal biofilm model.

AIM: To assess the antimicrobial efficacy of aqueous (1.25-20 microg mL(-1)) and gaseous ozone (1-53 g m(-3)) as an alternative antiseptic against endodontic pathogens in suspension and a biofilm model. METHODOLOGY: Enterococcus faecalis, Candida albicans, Peptostreptococcus micros and Pseudomonas aeruginosa were grown in planctonic culture or in mono-species biofilms in root canals for 3 weeks. Cultures were exposed to ozone, sodium hypochlorite (NaOCl; 5.25%, 2.25%), chlorhexidine digluconate (CHX; 2%), hydrogen peroxide (H(2)O(2); 3%) and phosphate buffered saline (control) for 1 min and the remaining colony forming units counted. Ozone gas was applied to the biofilms in two experimental settings, resembling canal areas either difficult (setting 1) or easy (setting 2) to reach. Time-course experiments up to 10 min were included. To compare the tested samples, data were analysed by one-way anova. RESULTS: Concentrations of gaseous ozone down to 1 g m(-3) almost and aqueous ozone down to 5 microg mL(-1) completely eliminated the suspended microorganisms as did NaOCl and CHX. Hydrogen peroxide and lower aqueous ozone concentrations were less effective. Aqueous and gaseous ozone were dose- and strain-dependently effective against the biofilm microorganisms. Total elimination was achieved by high-concentrated ozone gas (setting 2) and by NaOCl after 1 min or a lower gas concentration (4 g m(-3)) after at least 2.5 min. High-concentrated aqueous ozone (20 microg mL(-1)) and CHX almost completely eliminated the biofilm cells, whilst H(2)O(2) was less effective. CONCLUSION: High-concentrated gaseous and aqueous ozone was dose-, strain- and time-dependently effective against the tested microorganisms in suspension and the biofilm test model.

Management of facial necrotizing fasciitis.

Necrotizing fasciitis is a progressive, life-threatening, bacterial infection of the skin, the subcutaneous tissue and the underlying fascia, in most cases caused by ss-hemolytic group A streptococcus. Only early diagnosis and aggressive therapy including broad spectrum antibiotics and surgical intervention can avoid systemic toxicity with a high mortality rate. This uncommon disease generally occurs in the lower extremities and trunk, and only rarely affects the head and neck region. When located in the face necrotizing fasciitis is associated with severe cosmetic and functional restrictions due to the invasive infection and often to the necessary surgical treatment. Generally surgical intervention cannot be performed in the face as aggressively as in the extremities and trunk, since a lot of vital structures are found in a relatively small area. In the following article, we present the successful diagnostic and therapeutic management of an isolated facial necrotizing fasciitis as a consequence of a nasal bone fracture with a minor dermal cut.

[Molecular diagnosis of mycobacterial infections]. / Molekulare Mykobakterien-Diagnostik.

Tuberculosis remains a leading cause of morbidity and mortality worldwide. A rapid and reliable diagnosis and discrimination from infections with nontuberculous mycobacteria (NTM) is critical. Frequently, formalin-fixed, paraffin-embedded (FFPE) tissues remain the only source for detection of micro-organisms in suspected cases of mycobacterial infection. Recently, numerous methods, including PCR assays, in situ hybridization and immunohistochemistry have been developed for detection of mycobacteria in FFPE samples. PCR-based assays are directed either against M.tbc.-specific sequences, such as IS6110, or amplify regions common to many mycobacterial species, e.g. the 65 kDa antigen, and then require sequencing or restriction fragment length polymorphism for species identification. Whereas the detection of DNA of M.tbc. in the correct setting is always of clinical relevance, the presence of various NTM species has to be interpreted with great caution due to their ubiquitous nature. However, the routine application of molecular tests has demonstrated that NTM infections are more common than previously thought, even in non-immunosuppressed hosts. The introduction of real-time PCR technology allows precise quantification of mycobacterial DNA and can be used for species identification through melting point analysis or appropriate DNA probes. Application of these assays originally developed for clinical microbiology offer a great opportunity for diagnostic improvement in molecular pathology as compared to qualitative PCR, mainly due to an increased specificity and a lower risk of contamination. Given the clinical impact of a positive molecular result for M. tbc., future efforts have to be aimed at standardization and quality control.

Previous cytomegalovirus infection and restenosis after coronary stent placement.

BACKGROUND: Reactivated cytomegalovirus may promote neointima formation after percutaneous coronary interventions by facilitating cell cycle progression through inhibition of the eukariotic tumor suppressor protein p53. This prospective study sought to investigate the effect of previous cytomegalovirus infection on restenosis after coronary stenting. METHODS AND RESULTS: In 551 consecutive patients with successful stent placement, we determined cytomegalovirus IgG titers. Primary and secondary end points were the rate of angiographic restenosis at 6 months and the rate of target vessel reintervention at 1 year, respectively. Three hundred forty patients (62%) had a positive cytomegalovirus IgG titer. We obtained angiographic follow-up in 82% of all patients. Angiographic restenosis rate was 28.7% in patients with positive cytomegalovirus titers and 34.6% in patients with negative titers (P=0.18). Between the groups with and without positive cytomegalovirus titers, there were no significant differences in late lumen loss (1.16+/-0.90 mm and 1.23+/-0.86 mm, respectively, P=0.44). Target vessel reintervention was performed in 16.8% of the patients with positive cytomegalovirus titers and in 17.5% of those without (P=0.82). Even after correction for potential confounding variables by multivariate analysis, positive cytomegalovirus titers did not manifest as a predictor of angiographic restenosis (adjusted odds ratio [95% confidence interval], 0.78 [0.52 to 1.19]). CONCLUSIONS: Previous cytomegalovirus infection does not carry an increased risk of restenosis after stenting.

Predominant role of toll-like receptor 2 versus 4 in Chlamydia pneumoniae-induced activation of dendritic cells.

Chlamydia pneumoniae is an obligate intracellular human pathogen causing diseases such as pneumonia, bronchitis, and pharyngitis. Because of its intracellular replication, cell-mediated immune responses are needed to mediate successful defenses of the host. Because dendritic cells play a central role in linking innate immunity and Ag-specific cell-mediated immune responses we asked whether dendritic cells are activated upon contact with C. pneumoniae and whether known Toll like receptors (TLR) are involved in this process. Here we show that C. pneumoniae was taken up by bone marrow-derived murine dendritic cells. Ingested C. pneumoniae appeared to be unable to develop mature inclusion inside dendritic cells. Furthermore, upon contact with C. pneumoniae dendritic cells were potently stimulated because NF-kappaB was activated and translocated to the nucleus, cytokines like IL-12p40 and TNF-alpha were secreted, and expression of MHC class II molecules, CD40, CD80, and CD86 was up-regulated. Importantly, secretion of cytokines as well as translocation of NF-kappaB were dependent on the presence of TLR2 and independent from TLR4 with the exception of IL-12p40 secretion, which was attenuated in the absence of either a functional TLR2 or 4. In conclusion, we show here that recognition of the Gram-negative bacterium C. pneumoniae depends largely on TLR2 and only to a minor extent on TLR4.

Treatment of Chlamydia pneumoniae infection with roxithromycin and effect on neointima proliferation after coronary stent placement (ISAR-3): a randomised, double-blind, placebo-controlled trial.

BACKGROUND: Vascular infection with Chlamydia pneumoniae might boost inflammatory responses that play a pivotal part in neointima formation, which is the main cause of restenosis after stenting. Our aim was to investigate whether or not treatment of C pneumoniae infection with antibiotics prevents restenosis after coronary stent placement. METHODS: We enrolled 1010 consecutive patients with successful coronary stenting into a randomised, double-blind trial. Patients received the macrolide antibiotic roxithromycin 300 mg once daily for 28 days (506), or placebo (504). Primary endpoint was frequency of restenosis (diameter stenosis >50%) at follow-up angiography, and secondary endpoint was rate of target vessel revascularisation during the year after stenting. A prespecified secondary analysis addressed treatment effect with respect to titre of C pneumoniae in serum. Analysis was by intention to treat. FINDINGS: Rate of angiographic restenosis was 31% (157 lesions) in the roxithromycin group and 29% (148) in the placebo group (relative risk 1.08 [95% CI 0.92-1.26]; p50.43), corresponding to a rate of target vessel revascularisation of 19% (120) and 17% (105), respectively (1.13 [0.95-1.36]; p50.30). The combined 1-year rates of death and myocardial infarction were 7% (36) in the roxithromycin group and 6% (30) in the placebo group (p50.45). We showed a significant interaction between treatment and C pneumoniae antibody titre (p50.038 for restenosis, p50.006 for revascularisation), favouring roxithromycin at high titres (adjusted odds ratios at a titre of 1/512 were 0.44 [0.19-1.06] and 0.32 [0.13-0.81], respectively). INTERPRETATION: Non-selective use of roxithromycin is inadequate for prevention of restenosis after coronary stenting. There is, however, a differential effect dependent on C pneumoniae titres. In patients with high titres, roxithromycin reduced the rate of restenosis.

Endocytosed HSP60s use toll-like receptor 2 (TLR2) and TLR4 to activate the toll/interleukin-1 receptor signaling pathway in innate immune cells.

Heat shock proteins (HSPs) require no adjuvant to confer immunogenicity to bound peptides, as if they possessed an intrinsic "danger" signature. To understand the proinflammatory nature of HSP, we analyzed signaling induced by human and chlamydial HSP60. We show that both HSP60s activate the stress-activated protein kinases p38 and JNK1/2, the mitogen-activated protein kinases ERK1/2, and the I-kappaB kinase (IKK). Activation of JNK and IKK proceeds via the Toll/IL-1 receptor signaling pathway involving MyD88 and TRAF6. Human fibroblasts transfected with TLR2 or TLR4 plus MD-2 gain responsiveness to HSP60, while TLR2- or TLR4-defective cells display impaired responses. Initiation of signaling requires endocytosis of HSP60 that is effectively inhibited by serum component(s). The results revealed that adjuvanticity of HSP60 operates similar to that of classical pathogen-derived ligands.

Functional evaluation of HIV/SIV Nef as superantigen.

It is speculated that a virus-encoded superantigen is involved in the pathogenesis of human and simian immunodeficiency virus infections and that the accessory protein Nef might be that superantigen. We are able to show, using a murine superantigen screening system, that Nef does not display features characteristic of a superantigen. Upon transfection into MHC class II expressing antigen-presenting cells, it is expressed, but fails to induce Vbeta-specific expansion of peripheral T lymphocytes, which is a characteristic feature of superantigens in mixed lymphocyte culture. Therefore, we cannot support the hypothesis that Nef is a superantigen. The observations in favor of that hypothesis must be explained by other mechanisms.

Functional analysis of the env open reading frame in human endogenous retrovirus IDDMK(1,2)22 encoding superantigen activity.

Mice harbor a family of endogenous retroviruses, the mouse mammary tumor viruses (MMTV), which encode superantigens. These superantigens are responsible for the deletion of T cells expressing certain Vbeta chains of the T-cell receptor in the thymus. Human T cells are able to recognize MMTV-encoded superantigens presented by human major histocompatibility complex class II-positive cells. Owing to this and to the similarity of the human and murine immune systems, it was speculated that human endogenous retroviruses might also code for superantigens. Recently, it was reported that a proviral clone (IDDMK(1,2)22) of the human endogenous retrovirus family HTDV/HERV-K encodes a superantigen. The putative superantigen gene was located within the env region of the virus. Stimulated by these findings, we amplified by PCR and cloned into eucaryotic expression vectors open reading frames (ORFs) which were identical or very similar to IDDMK(1,2)22. When we transfected these vectors into A20 cells, a murine B-cell lymphoma, we were able to demonstrate mRNA expression and protein production. However, we did not find any evidence that the ORF stimulated human or murine T cells in a Vbeta-specific fashion, the most prominent feature of superantigens.

Synthetic endotoxin-binding peptides block endotoxin-triggered TNF-alpha production by macrophages in vitro and in vivo and prevent endotoxin-mediated toxic shock.

Lipid A, the conserved portion of endotoxin, is the major mediator of septic shock; therefore, endotoxin-neutralizing molecules could have important clinical applications. Here we show that peptides derived from Limulus anti-LPS factor (LALF), bactericidal/permeability increasing protein (BPI) and endotoxin-binding protein, bind to lipid A and block the recombinant LALF/lipid A interaction in vitro. Because their neutralizing capacity in vitro as well as in vivo has been limited, we created hybrid peptides comprising two endotoxin-binding domains. The hybrid molecule LL-10-H-14, containing endotoxin-binding domains from LALF and endotoxin-binding protein, turned out to be the most active peptide within the series of peptides tested here to inhibit the CD14/lipid A interaction and is able in vitro to block the endotoxin-induced TNF-alpha release of murine macrophages up to 90%. Furthermore, LL-10-H-14 not only reduced peak serum levels of TNF-alpha of mice when preinjected but also reduced TNF-alpha levels when given 15 min after the endotoxin challenge. As compared with other peptides, only LL-10-H-14 is able to strongly decrease endotoxin-stimulated TNF-alpha release by human macrophage cell lines as well as by PBMC. Furthermore, the hybrid peptide is protective against endotoxin-provoked lethal shock. As such, LL-10-H-14 could have prophylactic and/or therapeutic properties in humans for the management of septic shock.

Failure of an automated blood culture system to detect nonfermentative gram-negative bacteria.

During a 1-year study we observed that both aerobic and anaerobic blood culture bottles from patients were negative by the BacT/Alert system during a 7-day incubation period. However, upon subcultivation of negative bottles, growth of Pseudomonas aeruginosa was detectable. In an attempt to explain this observation, aerobic BacT/Alert Fan bottles were seeded with a defined inoculum (0.5 McFarland standard; 1 ml) of Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, P. aeruginosa, Stenotrophomonas maltophilia, or Acinetobacter baumannii. Half of the inoculated bottles were loaded into the BacT/Alert system immediately, and the remainder were preincubated for 4, 8, 16, and 24 h at 36 degrees C. With preincubation all bottles seeded with the Enterobacteriaceae signaled positive during the next 1.5 h. Organisms in bottles seeded with the nonfermentative species P. aeruginosa and A. baumannii remained undetected by the BacT/Alert system for 7 days. S. maltophilia was detected if the preincubation time was equal or less than 8 h. Without preincubation all bottles seeded with the Enterobacteriaceae or nonfermentative species signaled positive. Since nonfermentative species seem to enter a state of bacteriostasis within the preincubation period, we reasoned that an unknown factor is consumed. Accordingly, a smaller inoculum should allow the detection of nonfermentative species, even after preincubation, and serial dilutions of P. aeruginosa were detected in preincubated bottles. In this case preincubated bottles signaled positive faster than bottles without preincubation. We conclude that all bottles from clinical settings should be subcultured prior to loading to avoid false negatives. An alternative may be preincubation at room temperature.

Superantigen expression is driven by both mouse mammary tumor virus long terminal repeat-associated promoters in transgenic mice.

In addition to the usual retroviral promoter, the mouse mammary tumor virus (MMTV) long terminal repeat carries a second promoter located in the U3 region. Here we show that both of these promoters are independently able to give rise to superantigen activity in transgenic mice. The ability of multiple MMTV promoters to drive superantigen expression underscores its importance in the virus life cycle.