A randomised phase II clinical trial of low-dose cyclophosphamide and transarterial chemoembolization (TACE) with or without vaccination with dendritic cells (DC) pulsed with HepG2 lysate ex vivo in patients with hepatocellular carcinoma (HCC): The ImmunoTACE trial

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Background: A previous study by our group using autologous monocyte-derived DC pulsed ex vivo with HepG2 cell lysate showed some clinical benefit with evidence of antigen-specific T-cell responses in patients with advanced HCC. The current trial reports the activity of this vaccine in combination with TACE in patients with HCC. All patients also received low-dose cyclophosphamide to deplete regulatory T cells and thereby enhance vaccination. Methods: Patients with intermediate stage HCC (performance status 0-2, Child Pugh A/B7) were randomised 1:1 to TACE plus low-dose cyclophosphamide (Group 1) or TACE plus low-dose cyclophosphamide plus dendritic cell vaccination (Group 2). Cyclophosphamide was administered on Day 1 and 29 followed by TACE on Day 31 (+/- DC infusion), with further cyclophosphamide on Days 60, 90 and 120 (+/- additional DC infusions on Days 62, 92 and 122). The primary endpoint was progression free survival (PFS) by RECIST v1.1. Secondary endpoints included radiological response by RECIST v1.1, PFS and radiological response according to modified (m) RECIST, overall survival (OS), immune response and toxicity. Target recruitment was 48 evaluable patients (24 patients in each arm) to detect a 20% increase in PFS rate at 1 year (30% vs 50%) with a relaxed one-sided statistical significance level of 20% and 80% power using a logrank test. Results: Between March 2016 and October 2019, 55 patients from 3 UK centres were randomised of whom 48 were evaluable (24 each arm). Median PFS by RECIST criteria was significantly longer in Group 2 compared to Group 1 (18.6 vs 10.4 months: hazard ratio (HR) 0.43, 80% CI -∞-0.59; one-sided p = 0.02). Median PFS using mRECIST criteria showed a similar magnitude of benefit (18.6 vs 10.8 months: HR 0.48, 95% CI 0.22-1.02). Median OS was 25.7 months in Group 2 vs 21.5 months in Group 1 (HR 0.61, 95% CI 0.27-1.38). Group 2 showed a higher overall response rate (complete and partial response) by RECIST (54% vs 29%) and mRECIST (75% vs 54%) and a higher disease control rate (complete and partial response and stable disease) by RECIST (92% vs 67%) and mRECIST (88% vs 67%). Treatment with DC infusions was well tolerated; the most common adverse events were chills (30%), fatigue (22%) and nausea (22%), all of which were low grade. Immune response analyses are currently ongoing. Conclusions: The addition of tumour lysate pulsed DC infusions to treatment with TACE plus low-dose cyclophosphamide significantly increased PFS in patients with HCC. To the best of our knowledge, this is the first randomised study to demonstrate efficacy using DC in HCC. Further investigation of the role of DC infusions in the treatment of HCC are warranted but will need to take into account the current evolving immunotherapy landscape. Clinical trial information: 11889464.

The potential of PIVKA-II as a treatment response biomarker in hepatocellular carcinoma: a prospective United Kingdom cohort study

Prothrombin induced by vitamin K absence II (PIVKA-II) has recently been validated internationally as a diagnostic biomarker for hepatocellular carcinoma (HCC), as part of the GALAD model. However, its role as a treatment response biomarker has been less well explored. We, therefore, undertook a prospective study at a tertiary centre in the UK to evaluate the role of PIVKA-II as a treatment response biomarker in patients with early, intermediate and advanced stage HCC. In a cohort of 141 patients, we found that PIVKA-II levels tracked concordantly with treatment response in the majority of patients, across a range of different treatment modalities. We also found that rises in PIVKA-II levels almost always predated radiological progression. Among AFP non-secretors, PIVKA-II was found to be informative in 60% of cases. In a small cohort of patients undergoing liver transplantation, pre-transplant PIVKA-II levels predicted for microvascular invasion and poorer differentiation. Our results demonstrate the potential utility of PIVKA-II as a treatment response biomarker and in predicting microvascular invasion, in a Western population. PIVKA-II demonstrated improved performance over AFP but, as a single biomarker, its performance was still limited. Further larger prospective studies are recommended to evaluate PIVKA-II as a treatment response biomarker, within the GALAD model.

Intention to treat outcomes among patients with pancreatic cancer treated using International Study Group on Pancreatic Surgery recommended pathways for resectable and borderline resectable disease

BACKGROUND

The International Study Group on Pancreatic Surgery recommends upfront surgery for resectable pancreatic cancer or borderline resectable-venous (BR-V) disease and neoadjuvant therapy (NAT) among those with arterial involvement (BR-A or locally advanced, LA). Though neoadjuvant therapy (NAT) is a promising strategy, outcomes are rarely reported on intention-to-treat (ITT) basis. This study presents ITT outcomes where pathways to surgery were in line with International Study Group on Pancreatic Surgery guidelines.

METHODS

Patients recommended for potentially curative treatment with PDAC between 2012 and 2017 (n = 345) were classified as resectable, BR-A/BR-V or LA, according to NCCN criteria. The primary outcome was overall survival. Secondary outcomes were resection rates, positive margins and toxicity among patients receiving NAT.

RESULTS

At surgery, the resection rates were 78% (172/221), 65% (35/54) and 54% (21/39) for those with resectable, BR-V and BR-A/LA disease, respectively (P < 0.0001). The median survival of those resected in the BR-A/LA cohort was 31 months. However, on an ITT basis, there was no significant difference in survival between resectable, BR-V and BR-A/LA disease (median: 19 versus 15 versus 19 months; P = 0.585). On review, some 31 (44%) patients of the BR-A/LA cohort either did not receive or did not complete NAT.

CONCLUSION

To realize benefits of NAT, more patients need to complete NAT and to undergo resection. Upfront resection for BR-V disease is associated with equivalent outcomes to upfront surgery for resectable disease or NAT for BR-A/LA disease. Strategies to increase the proportion of patients who complete NAT and undergo resection are needed.

Development and validation of a risk score to predict the overall survival following surgical resection of hepatocellular carcinoma in non-cirrhotic liver

BACKGROUND

The aim of this study was to develop and validate a risk score to predict overall survival (OS) in patients undergoing surgical resection for hepatocellular carcinoma in non-cirrhotic liver (NC-HCC).

METHODS

Patients who underwent resection for NC-HCC between 2004 and 2013 were identified from the SEER database. A derivation set of 75% of this cohort was used to develop a risk score. This was then internally validated on the remaining patients, and externally validated using a cohort of patients from The HPB Unit, Birmingham, UK.

RESULTS

A total of 3897 patients were included from the SEER database, with a median post-diagnosis survival of 59 months. In the derivation set, multivariable analyses identified male sex, increasing tumour size, the presence of multiple tumours, bilobar tumours and major vascular invasion as adverse prognostic factors. A risk score generated from these factors was significantly predictive of OS, and was used to classify patients into low, medium and high-risk groups. These groups had a five-year OS of 69%, 51% and 19% in the internal, and 73%, 50% and 45% in the external validation sets.

CONCLUSION

The proposed risk score is useful in the selection, pre-operative consenting and counselling of patients for surgery and to allow patients to make an informed decision regarding treatment.

The role of down staging treatment in the management of locally advanced intrahepatic cholangiocarcinoma: Review of literature and pooled analysis

Backgrounds/Aims

Approximately 60–80% of patients with intrahepatic cholangiocarcinoma (iCCA) are not suitable for surgical resection due to advanced disease at presentation. This review assesses the role of surgical resection followed by down staging treatment in the management of patients with locally advanced iCCA.

Methods

A systematic review and pooled analysis were performed of the relevant published studies published between January 2000-December 2018. The primary outcome measure was overall survival. Secondary outcome measures were rates of clinical benefit, margin-negative (R0) resections, overall and surgery-specific complications, and post-operative mortality.

Results

Eighteen cohort studies with 1880 patients were included in the review. The median overall survival in all patients was 14 months (range, 7–18 months). Patients undergoing resection following down staging had significantly longer survival than those who did not (median: 29 vs. 12 months, p<0.001). The Clinical Benefit Rate with this strategy (complete response+partial response+stable disease) was 64% (244/383), ranging from 33-90%. Thirty-eight percent of the patients underwent resections with a 60% R0 resection rate and 6% postoperative mortality.

Conclusions

Although the evidence to support the benefits of NAT for iCCA is limited, the review supports the use of down staging treatment and also surgical resection in the cohort with response to NAT in order to improve long-term survival in patients with locally advanced iCCA.

Observational Study to Assess Quality of Life in Patients with Pancreatic Neuroendocrine Tumors Receiving Treatment with Everolimus: The OBLIQUE Study (UK Phase IV Trial)

BACKGROUND/AIMS

To assess health-related quality of life (HRQoL), treatment patterns, and clinical outcomes of adult (≥18 years) patients with advanced (unresectable or metastatic) pancreatic neuroendocrine neoplasms (PanNENs) treated with everolimus in routine clinical practice.

METHODS

In a prospective, non-interventional, multi-center study patients administered at least one 10 mg dose of everolimus were evaluated for change in HRQoL (EORTC QLQ-C30 Global Health Status scale) from baseline after 6 months treatment (primary endpoint). Secondary endpoints included disease-specific HRQoL measures (EORTC QLQ-G.I.NET21), clinical outcomes, everolimus treatment patterns, and safety.

RESULTS

Forty-eight patients were recruited (between August 2013 and March 2015); the median treatment duration was 27.8 months. EORTC QLQ-C30 Global Health score was not significantly different from baseline after 6 months of treatment (mean difference -1.9 points, p = 0.660, n = 30). In pairwise analyses, the only significant changes in HRQoL from baseline were for EORTC QLQ-C30 physical functioning score at month 3 (adjusted mean difference -8.8 points, p = 0.002, n = 36) and the EORTC QLQ-G.I.NET21 disease-related worries scores at months 1 and 2 (adjusted mean differences: -11.5 points [p = 0.001, n = 44] and -8.8 points [p = 0.017, n = 43], respectively). Disease progression or death was recorded in 44.4% (n = 20/45) patients during follow-up; median progression-free survival was 25.1 months and the cumulative survival rate at 3 years was 71%. No new safety signals were detected.

CONCLUSIONS

The OBLIQUE study demonstrates that HRQoL is maintained in patients with PanNENs during treatment with everolimus in a UK real-world setting. This study adds to the limited HRQoL data available in this patient group.

Gemcitabine-Induced Cardiotoxicity in Patients Receiving Adjuvant Chemotherapy for Pancreatic Cancer: A Case Series

Gemcitabine is not considered a cardiotoxic agent generally; so far only very few case reports have been reported in the literature on different aspects of cardiac side effects. Here we report a case series of 3 patients who developed congestive cardiac failure, when treated with gemcitabine monotherapy in the adjuvant setting for pancreatic cancers. Adjuvant chemotherapy with gemcitabine has been the standard of care for pancreatic cancer patients after successful surgery since the results of the CONKO-001 and ESPAC3 study were published. Gemcitabine was administered on days 1, 8, and 15 of a 28-day cycle at 1,000 mg/m². All 3 patients developed symptoms suggestive of cardiac failure with a drop in ejection fraction on echocardiography, and responded to conservative treatment for heart failure after withdrawal of gemcitabine therapy. Early withdrawal of gemcitabine chemotherapy is recommended in addition to a need for studies required to evaluate the mechanism of cardiotoxicity. As per available literature, patients with diabetes and having received a total dose greater than 15,000 mg/m² are generally at a higher risk and require close surveillance.

Non-secretion of AFP and neutrophil lymphocyte ratio as predictors for survival in hepatocellular carcinoma patients treated with sorafenib: a large UK cohort

Background

Sorafenib is the current standard of care for patients with advanced or metastatic hepatocellular carcinoma. Currently no universally agreed model exists correlating the Neutrophil Lymphocyte ratio (NLR) and non-secretion of AFP with the survival of HCC patients treated with sorafenib.

Patients and Methods

We retrospectively analysed patient records with a confirmed diagnosis of HCC treated with sorafenib between April 2009 and March 2014. Survival analysis was performed using the Kaplan–Meier method and Cox regression.

Results

Patients separated into groups based on NLR (≤3 or >3), or AFP secretion profile (<7 ng/ml or ≥7 ng/ml) derived diverging Kaplan–Meier curves for overall survival (OS). The median OS in those with NLR ≤3.0 was 9.0 months (95% CI: 7.7–11.1 months) and in those with NLR >3.0 it was 6.0 months (95% CI: 4.9–8.2 months) [HR 1.32 (95% CI: 0.96–1.80)]. The median overall survival post sorafenib was higher in the “non-secretor” AFP group. OS for AFP <7 ng/ml was 10.0 months (95% CI: 7.7–19.3 months) compared to AFP ≥7ng/ml: 6.6 months (95% CI: 5.3–8.4 months) [HR 1.64 (95% CI: 1.15–2.33)].

Conclusion

NLR and AFP non - secretion at diagnosis are potential significant prognosticators for overall survival from initiation of sorafenib.

Exceptional serological and radiological response to sorafenib in 2 patients with advanced hepatocellular carcinoma and chronic hepatitis C viral infection: case report and review of the literature

Background

In patients with advanced hepatocellular carcinoma (HCC), the multikinase inhibitor sorafenib is the only systemic treatment that has been shown to increase overall survival. However, similar to other tyrosine kinase inhibitors, most patients achieve disease stabilisation radiologically, and only 2–3% of patients achieve a partial response. Recent exploratory subgroup analyses of the large phase 3 trials have demonstrated that patients with chronic hepatitis C virus (HCV) infection associated HCC survive longer than those who are negative for HCV. The mechanism underlying this currently remains unknown. A small number of cases of complete response to sorafenib treatment have now been reported worldwide, however a prolonged response has only been reported in 2 cases, both of whom had HCV-related HCC.

Case presentation

A 55 year old gentleman was diagnosed with hepatocellular carcinoma and concomitant chronic hepatitis C viral infection. He progressed following transarterial chemoemoblisation treatment and was commenced on sorafenib treatment. His serum alphafetoprotein level normalised within 2 months of treatment and he achieved an almost complete radiological response. This response was maintained for 20 months before the patient progressed. A 75 year old lady was diagnosed with advanced hepatocellular carcinoma and concomitant chronic hepatitis C viral infection. She was commenced on sorafenib treatment but required early dose reductions due to palmar plantar erythrodysesthesia, and liver decompensation. Despite this she achieved an excellent serological and radiological response that was maintained for 24 months.

Conclusions

Our two cases show that patients with HCV-associated HCC can attain excellent responses to sorafenib treatment that is durable. Furthermore, such exceptional responses can be achieved even with dose reductions and treatment breaks.

FOLFIRINOX for the treatment of advanced pancreatic cancer: U.K. West Midlands experience

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Background: The PRODIGE 4/ACCORD 11 trial demonstrated that FOLFIRINOX significantly improved response rates and survival in patients with metastatic pancreatic cancer, compared to gemcitabine. However this regimen is associated with significant toxicity. We have thus analysed the safety, tolerability and efficacy of FOLFIRINOX given outside a clinical trial setting. Methods: A retrospective analysis was conducted on all patients treated with FOLFIRINOX for advanced pancreatic cancer between July 2012 and July 2014, within the West Midlands region in the UK. Data was collected on baseline demographics, disease stage, toxicity and response to chemotherapy. Results: A total of 60 patients were identified (28 locally advanced, 32 metastatic). The median age was 59 (range 34-74) and 12% of patients were aged 70 or over. The primary tumour was located in the head of the pancreas in 68% of patients and 38% of patients had a biliary stent. All patients had an ECOG performance status of 0 or 1 (45% and 55% respectively), and had received no prior chemotherapy for advanced pancreatic cancer. FOLFIRINOX was commenced at reduced doses in 79% of patients, and subsequent dose reductions were required in 81% of patients. The median number of FOLFIRINOX cycles administered was 6 (range 1-14) but 33% of patients currently remain on treatment. Hospital admissions were required in 58% of patients but only 22% of hospital admissions were for neutropenic sepsis. FOLFIRINOX was discontinued in 30% of patients due to toxicity. There were no treatment related deaths. Of 40 patients who were eligible for assessment of response, 38% achieved a partial response and a further 45% achieved stable disease. Four patients with LA pancreatic cancer became suitable for curative surgical resection following chemotherapy; 2 of these also received chemoradiotherapy. The median overall survival for patients with metastatic disease was 12 months and the median overall survival for patients with locally advanced disease has not been reached. Conclusions: Our data shows that FOLFIRINOX can be safely delivered in a real world setting. Even with reduced doses, the response rates and survival outcomes are comparable with the results from the PRODIGE 4/ACCORD 11 trial.

Biliary stenting in advanced malignancy: an analysis of predictive factors for survival

Purpose

Stenting of the biliary tree is a common palliative procedure to relieve obstructive jaundice in advanced malignancy. Although effective in relief of biliary obstruction and palliation of symptoms, little information is available on predictive factors for survival post-procedure. This retrospective study sought to assess factors influencing post-procedure survival in cancer patients after biliary stenting.

Methods

Case notes of all patients from a regional academic cancer center, who underwent biliary stenting for obstructive jaundice related to malignancy during 2008 and 2009 were reviewed. We collected epidemiological, biochemical, treatment and survival data on all patients. We used Kaplan–Meyer analysis to assess survival from day of first biliary stenting (adjusted for cancer types), and the Cox proportional hazards model for univariate and multivariate analysis.

Results

One hundred and ninety-four patients were included in the final analysis. Most cases were related to pancreatic cancer or cholangiocarcinoma (89 and 46 cases respectively). Median survival for all patients was 143 days. In multivariate analysis serum albumin ≥34 g/L at the time of procedure (hazard ratio 0.573; 95% confidence interval 0.424–0.773, P<0.001) and chemotherapy post-stent (hazard ratio 0.636; 95% confidence interval 0.455–0.889, P=0.008) were two independent prognostic factors predicting a better survival post-stenting. The 30 day mortality post-procedure in the 194 patients was 12%.

Conclusion

This study suggests that stenting of the biliary tree in cases of malignant obstruction allows durable palliation of symptoms even in cases where further active chemotherapy treatment is not possible. However, the better outcome observed in patients with albumin ≥34 g/L and those receiving chemotherapy post-stent requires further validation.

Beta-hemolytic streptococcal infections in trauma patients

PURPOSE

β-hemolytic streptococci (βHS) causes a diverse array of human infections. The molecular epidemiology of β-hemolytic streptococcal infections in trauma patients has not been studied. This study reports the molecular and clinical epidemiology of β-hemolytic streptococcal infections at a level 1 trauma centre of India.

METHODS

A total of 117 isolates of βHS were recovered from clinical samples of trauma patients. The isolates were identified to species level and subjected to antimicrobial susceptibility testing. Polymerase chain reaction (PCR) assay was done to detect exotoxin virulence genes. The M protein gene (emm gene) types of GAS strains were ascertained by sequencing.

RESULTS

Group A Streptococcus (GAS) was the most common isolate (64 %), followed by group G Streptococcus (23 %). A large proportion of GAS produced speB (99 %), smeZ (91 %), speF (95 %) and speG (87 %). smeZ was produced by 22 % of GGS. A total of 25 different emm types/subtypes were seen in GAS, with emm 11 being the most common. Resistance to tetracycline (69 %) and erythromycin (33 %) was commonly seen in GAS.

CONCLUSIONS

β-hemolytic streptococcal infections in Indian trauma patients are caused by GAS and non-GAS strains alike. A high diversity of emm types was seen in GAS isolates, with high macrolide and tetracycline resistance. SpeA was less commonly seen in Indian GAS isolates. There was no association between disease severity and exotoxin gene production.

Predictive factors for outcome after biliary stenting in malignant obstructive jaundice

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Background: Stenting of the biliary treeis a common palliative procedure to relieve obstructive jaundice in advanced malignancy. Although effective in relief of biliary obstruction and subsequent palliation of symptoms, little information is available on predictive factors for survival post-procedure to better guide selection of patients. This retrospective study sought to assess factors influencing post-procedure survival in cancer patients after biliary stenting. Methods: Case notes of all patients from a regional academic cancer centre, who underwent biliary stenting for obstructive jaundice related to malignancy during 2008 and 2009, were reviewed. We collected epidemiological, biochemical, treatment (post-stenting) and survival data on all patients. Kaplan-Meyer analysis was used to assess median survival of patients from the day of first biliary stenting (adjusted for cancer types) and Cox proportional hazard model was used for univariate and multivariate analysis. Results: 194 patients were included in the final analysis. Most cases were related to pancreatic cancer or cholangiocarcinoma (89 and 46 cases each). Median survival (MS) for all the patients was 143 days. Median survival was similar, whether obstruction was secondary to the primary tumor (141cases) or metastatic disease (53 cases). In multivariate analysis serum albumin < 3.4 g/dL ( HR 1.770; 95% confidence interval 1.312 – 2.389, P < 0.001) and age > 75 years (HR 1.490; 95% confidence interval 1.086 – 2.043, p = 0.013) at the time of procedure were two independent prognostic factors predicting for a worse survival post-stenting. The 30 day mortality post-procedure in the 194 patients was 12%. Conclusions: This study suggests that stenting of the biliary tree in cases of malignant obstruction allows durable palliation of symptoms even in cases where further active chemotherapy treatment is not possible. However, the worse outcome observed in those > 75 yrs old or with low albumin at the time of procedure, identify groups with less certain benefit from this invasive procedure and requires confirming in future studies.

Pulsed-field electrophoretic fingerprinting of Salmonella indiana and its epidemiological applicability

Eight Xba I-generated pulsed-field profile (PFP) types and four subtypes within one of the most common PFP types have been identified in Salmonella indiana from patients, poultry and human food in England and Wales in the three-year period from January 1994 to December 1996. Two PFP types have predominated, PFP X1 and PFP X2. Although the PFP X1 type was identified throughout the study period, the PFP X2 type was not identified until late 1995, subsequently becoming the most common PFP type in humans in the first six months of 1996 with a significant distribution in elderly patients. It is concluded that PFGE can be used in support of epidemiological investigations for the subdivision of Salm. indiana. Furthermore, as both conditions and interpretation criteria can be easily standardized, it is suggested that for many salmonella serotypes, PFGE can provide the basis for a definitive scheme of genotypic subtyping suitable for epidemiological investigations at both a national and international level.

The heteroduplex mobility assay (HMA) as a pre-sequencing screen for Norwalk-like viruses

Molecular epidemiological studies of Norwalk-like viruses (NLVs), previously known as small round structured viruses (SRSVs), are dependant currently on DNA sequencing of PCR amplicons, which is expensive and time consuming. The Heteroduplex Mobility assay (HMA) was evaluated as a method for identification of PCR amplicons from the commonly circulating NLV strains without DNA sequencing. The procedure was developed for use with two reference strains, a Mexico virus-like strain (MXV-like; Hu¿NLV¿RBH¿1993¿UK) and the Grimsby virus strain (Hu¿NLV¿Gimsby¿1995¿UK), and was optimised with regards to the annealing and electrophoresis conditions and the electrophoresis gel matrix. Using the optimised conditions, amplicons of less than 90% sequence identity formed visible heteroduplexes, allowing the strains to be placed into three categories; Mexico-like, Grimsby-like and non-Mexico virus/non-Grimsby virus strains. Outbreak strains 'genotyped' previously by DNA sequencing as Mexico virus or Grimsby virus were identified correctly by the heteroduplex mobility assay. The procedure was applied prospectively to strains from 130 outbreaks occurring in the UK between 1997 and 1998. Heteroduplex mobility assay was successful on 120 (92%) strains of which 68 (57%) were GRV-like strains, three (2.5%) were Mexico virus-like strains and 49 (41%) were categorised as non- Mexico/non-Grimsby virus strains. Amplicons from 50 of the 120 strains were sequenced and there was perfect correlation between the heteroduplex mobility assay categorisation and phylogenetic analysis. HMA offers a rapid, robust and far cheaper alternative to sequencing for the identification of prevalent Norwalk-like virus genotypes for molecular epidemiological studies.

National outbreak of Salmonella senftenberg associated with infant food

Eight cases of Salmonella senftenberg infection in infants were identified in the first half of 1995 in England, five were indistinguishable S. senftenberg strains. A case-control study showed an association between illness and consumption of one brand of baby cereal (P = 0.03). The cereal manufacturer reported isolating S. senftenberg in June 1994 from an undistributed cereal batch. Outbreak strains and the cereal strain were all plasmid-free in contrast to other human isolates of S. senftenberg in the same period. Changes in the production process were implemented to prevent further contamination. Surveillance centres should strengthen the detection and investigation of outbreaks of gastrointestinal infection in susceptible groups, especially young children. In this outbreak, the study of only five cases led to identification of the vehicle of infection. Even when few cases are reported, epidemiological investigation in conjunction with molecular typing may lead to public health action which prevents continuing or future outbreaks.

Plasmid characterization and pulsed-field electrophoretic analysis demonstrate that ampicillin-resistant strains of Salmonella enteritidis phage type 6a are derived from Salm. enteritidis phage type 4

Plasmid incompatibility studies have demonstrated that strains of Salmonella enteritidis phage type (PT) 6a resistant to ampicillin possess a 36 megadalton incompatibility group (Inc) X plasmid coding for resistance to ampicillin which is capable of converting strains of Salm. enteritidis belonging to PTs 1 and 4 to PT 6a, and PT 8 to PT 13. However, pulsed-field gel electrophoresis (PFGE) has demonstrated that all clinical isolates of PT 6a have a characteristic XbaI pulsed-field profile which is distinct from that of PT 1 and which can only be differentiated from that of PT 4 by the presence of plasmid-associated fragments of less than 45 kb. It is concluded that ampicillin-resistant strains of Salm. enteritidis PT 6a are derived from strains of Salm. enteritidis PT 4 by acquisition of an Inc X ampicillin resistance plasmid.