Emergence of plasmid-mediated colistin resistance (mcr-1) among Enterobacteriaceae strains: Laboratory detection of resistance and measures to control its dissemination.

The increasing use of colistin has contributed to the emergence of resistant bacteria and to an increase in the frequency of infections caused by naturally resistant Enterobacteriaceae strains such as Proteus, Providencia, Morganella, and Serratia. In August 2016, the French High Council for Public Health (French acronym HCSP) received a request from the Ministry of Health on the advice of the French National Public Health agency (Santé publique France) with regard to measures that should be taken to tackle the emergence of plasmid-mediated colistin resistance among Enterobacteriaceae strains. French healthcare facilities were asked to take the necessary measures as soon as possible, such as updating the definition of emerging highly resistant bacteria and defining the identification methods so as to take account of the evolving epidemiology of this type of resistance. This article describes the epidemiological context of the discovery of this emergence in France and worldwide, the resistance mechanisms, the microbiological methods of routine laboratory detection and the level of hygiene measures to implement in French facilities.

Genetic, biochemical characterization and mutagenesis of the chromosomal class A ß-lactamase of Raoultella (formerly Klebsiella) terrigena.

BACKGROUND: Chromosomal class A ß-lactamases have been characterized in Raoultella ornithinolytica and Raoultella planticola. The purpose of this study was to characterize that of Raoultella terrigena. MATERIALS AND METHODS: The blaTER-1 gene of R. terrigena strain ATCC33257(T) was cloned (pACter-1) and sequenced. It was then used to detect the bla gene of strains BM 85 01 095 and SB2796. The hypermutable Escherichia coli strain AB1157 mutS::Tn10 was transformed with pACter-1 and mutants growing on plates containing>2mg/L ceftazidime were studied. Notably, the impact of mutations only observed in the promoter region on ß-lactam resistance was assessed by site-directed mutagenesis experiments. RESULTS: R. terrigena strains ATCC33257(T) and BM 85 01 095 had the same bla gene and deduced protein (TER-1) whereas there were 3 substitutions in those of strain SB2796 (TER-2). Class A ß-lactamases TER showed 78%, 69.9% and 38.7% identity with PLA or ORN, TEM-1 and KOXY, respectively. Compared with TEM-1, TER-1 and TER-2 showed 2 particular substitutions, Leu75Pro and Glu240Asn demonstrated to be involved in the inherent ß-lactam resistance profile of R. terrigena. TER-1 (pI of 7.6) had a high activity against penicillin G and a significantly low one against amoxicillin. Substitution G/T observed in the -35 region of the blaTER gene harbored by strains growing in the presence of≥2mg/L ceftazidime was shown to be responsible for this growth. CONCLUSION: TER is a new class A ß-lactamase belonging to functional group 2b.

Faecal carriage of extended-spectrum ß-lactamase (ESBL)-producing enterobacteria in liver disease patients from two hospitals in Egypt and France: a comparative epidemiological study.

This study aimed to assess and compare the epidemiology of faecal carriage of extended spectrum ß-lactamase-producing enterobacteria (ESBL-E) in Hepatology departments of two hospitals specializing in liver diseases, Theodor Bilharz Research Institute (TBRI) in Cairo (Egypt) and Beaujon Hospital (Bj) in Clichy (France). CTX-M groups were identified by PCR, and TEM and SHV derivatives with the check-point system. Phylogenetic groups of E. coli were determined by multiplex PCR, and clone ST131 by PCR of gene pabB. Prevalence of ESBL-E was 77·6% (45/58) in TBRI and 6·5% (13/199) in Bj (P < 10-7). Previous hospitalization was more common (P = 0·003) in Bj patients (93%) than in TBRI patients (45%) suggesting high prevalence of ESBL-E in the Egyptian community. The presence of E. coli B2 ST131 among ESBL-E faecal E. coli in Egypt confirms its pervasiveness in the community and raises concern regarding this highly virulent and resistant clone.

Molecular epidemiology of OXA-48-producing Klebsiella pneumoniae in France.

We characterized 53 OXA-48-producing Klebsiella pneumoniae (OXA-48-Kp) isolated between 2011 and 2013 in 21 French hospitals. All the isolates were genotyped using MLST and PFGE and the population structure of the species was determined by a nucleotide-based analysis of the entire K. pneumoniae MLST database. Most of the OXA-48-Kp isolates also produced CTX-M-15 and remained susceptible to imipenem and meropenem. The isolates were distributed into 20 STs, of which five were dominant (ST15, ST101, ST147, ST395 and ST405). All the OXA-48-Kp clustered in the major clade of K. pneumoniae KpI.

Frequency and epidemiology of extended-spectrum ß-lactamase-producing Enterobacteriaceae isolates susceptible to third-generation cephalosporins or to aztreonam.

OBJECTIVE: We evaluated among 400 strains of extended-spectrum ß-lactamase-producing Enterobacteriaceae (ESBLE) the rate of strains categorized as intermediate or resistant to 3rd generation cephalosporins or aztreonam according to the 2011 guidelines of the French Society of Microbiology Antibiogram Committee. MATERIAL AND METHODS: MICs of cefotaxime, ceftazidime, cefepime or aztreonam were determined by the E-test method for isolates with susceptible zones to these antibiotics. RESULTS: Overall, 109/400 (27.3%) isolates were susceptible to at least one of these 4 agents. Notably, 21.8% of Escherichia coli isolates were susceptible to ceftazidime, and 21.1% of Klebsiella pneumoniae isolates were susceptible to cefepime. Discrepancies between categorization by disk diffusion and MIC determination were observed for aztreonam and cefepime. CONCLUSION: These results indicate alternatives to carbapenems for treating infections caused by ESBLE.

Risk factors associated with preoperative fecal carriage of extended-spectrum ß-lactamase-producing Enterobacteriaceae in liver transplant recipients.

OBJECTIVE: The aim of the study was to identify risk factors associated with pre-transplant fecal carriage of extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae in liver transplant recipients. PATIENTS AND METHODS: Over a 3-year period (January 2009-December 2011), 317 patients who underwent liver transplantation were screened preoperatively for fecal carriage of ESBL-producing Enterobacteriaceae. Risk factors for fecal carriage were investigated by univariate analysis and stepwise logistic regression. RESULTS: Of the 317 patients screened, 50 (15.7%) harbored an ESBL-producing isolate. Previous infection with an ESBL-producing organism had developed during the last 6 months in 20% of fecal carriers versus in none of the non-carriers. Other variables associated with fecal carriage were a model for end-stage liver disease score ≥25, pre-transplant stay in the intensive care unit ≥48 h, hospital stay ≥10 days in the last 6 months, a history of spontaneous bacterial peritonitis (SBP), exposure to a ß-lactam agent in the last month, and prophylaxis with norfloxacin. Independent predictors of fecal carriage in the multivariate logistic regression model were exposure to a ß-lactam agent in the month preceding transplantation (odds ratio [OR] = 7.8, confidence interval [CI] = 4-15.5, P < 0.001), and a history of SBP (OR = 2.4, CI = 1.1-4.9, P = 0.02). CONCLUSIONS: Previous infection with an ESBL-producing isolate, recent exposure to a ß-lactam agent, and a history of SBP are risk factors for preoperative fecal carriage of ESBL-producing Enterobacteriaceae in liver transplant recipients. Patients at risk of fecal carriage should receive intraoperative prophylaxis and, when necessary, empiric postoperative antimicrobial treatment that includes coverage for these organisms.

The emergence of multidrug-resistant Klebsiella pneumoniae of international clones ST13, ST16, ST35, ST48 and ST101 in a teaching hospital in the Paris region.

Despite infection control measures, an important increase in the extended-spectrum ß-lactamase (ESBL)-producing Klebsiella pneumoniae incidence density occurred in our hospital from 2006 onwards. This study, focusing on the 2005-2007 period, was performed in an attempt to explain this increase. ESBLs were characterized, isolates were typed by ERIC2-PCR, and sequence type (ST) of clustered isolates was determined. Temporal-spatial relationships of patients were analysed to assess possible cross-contamination. Of the 74 ESBL-producing isolates, 30 (40%) were detected at admission, 53 (71∙5%) produced CTX-M enzymes, 40 displayed unique ERIC2-PCR profiles and 34 were assigned into six clusters: ST16 (n=21), ST101, ST48, ST35, ST13, and ST436. Relationships were identified in 22 of the 34 patients harbouring clustered isolates. This study highlights the complex epidemiology of ESBL-producing K. pneumoniae in the mid-2000s with potential cross-contamination for only 30% of the 74 patients in our hospital, and the emergence of clones that are currently spreading worldwide.

Membrane permeability, a pivotal function involved in antibiotic resistance and virulence in Enterobacter aerogenes clinical isolates.

Imipenem-susceptible E. aerogenes isolates exhibiting extended spectrum ß-lactamases, target mutations and a basal efflux expression, were identified in five patients. After imipenem treatment, imipenem-intermediate susceptible (IMI-I) or resistant (IMI-R) isolates emerged in these patients. Alteration in porin synthesis and increase in efflux expression were observed in the IMI-I isolates whereas complete loss of the porins, LPS alteration and efflux overexpression were observed in the IMI-R isolates. Bacterial virulence of the strains was investigated by the Caenorhabditis elegans model. The IMI-R isolates were shown to be significantly less virulent than the IMI-susceptible or IMI-I isolates. The pleiotropic membrane alteration and its associated fitness burden exhibited by E. aerogenes isolates influence their antibiotic resistance and their virulence behaviour. These findings highlight the balance between the low permeability-related resistance and virulence and their relationships with the treatment of resistant pathogens.

Molecular epidemiology of Escherichia coli bacteremia in liver transplant recipients.

The characteristics of Escherichia coli strains causing bacteremia in profoundly immunosuppressed patients such as transplant recipients are undefined. The phylogenetic group and the virulence genotype of 57 distinct E. coli strains that caused bacteremia in 53 liver transplant recipients were investigated, and the association of these characteristics with host factors and in-hospital mortality was examined. Phylogenetic groups A, B1, B2, and D accounted for 39%, 10%, 25%, and 26% of the isolates, respectively. The most prevalent virulence genes were fyuA (yersiniabactin system: 70%) and iutA (aerobactin system: 63%), whereas hlyA (alpha-hemolysin) and cnf1 (cytotoxic necrotizing factor 1) occurred in only 14% and 12% of isolates, respectively. Most virulence genes were significantly more prevalent among group B2 and D isolates, vs. group A and B1 isolates. The overall rate of in-hospital mortality after E. coli bacteremia was 20%. Predictors of mortality included onset of bacteremia within 30 days of transplantation or during the intensive care unit stay, and non-urinary source and cutaneous source, but not E. coli phylogenetic group or virulence profile. Compared with historical E. coli bloodstream isolates from non-transplant patients, those from liver transplant recipients are characterized by a higher prevalence of groups A and B1 isolates and reduced virulence gene content. This finding can be explained by the severely immunocompromised status of the patients and the predominance of abdominal-source bacteremic episodes. Time of onset and source of bacteremia, not bacterial characteristics, predict mortality.

Microbiological findings of culture-positive preservation fluid in liver transplantation.

Bacterial and fungal infections are the leading cause of mortality in liver transplant (LT) recipients. Few studies have examined the incidence of culture-positive preservation fluid (PF) and the outcome of related recipients. The aim of this study was to determine the incidence and the microbiologic findings of PF positive cultures, and to evaluate the impact on morbidity and mortality of LT recipients. A retrospective analysis of PF cultures performed after 477 LTs from cadaveric grafts between January 2001 and February 2008 was conducted. Forty-five (9.5%) PFs were found to be positive with 1 or 2 pathogens. The demographic profiles of recipients of PF with positive or negative cultures were similar. Enterobacteriaceae species were the most frequent organisms (n = 30), followed by Staphylococcus aureus (n = 5), coagulase-negative staphylococci (n = 5), enterococci (n = 4), and yeasts (n = 3). Mortality rate at 1 month was not significantly different in recipients with positive or sterile PF cultures (88.1% vs. 87.7%, respectively). The rate of bacteremia among LT recipients with positive or negative PF cultures was not statistically different. Systemic infections caused by the pathogen cultured from the PF occurred in 8 (18%) of the 45 recipients, including bacteremia (4/8) or intra-abdominal sepsis (5/8). Causative organisms were Enterobacteriaceae species (n = 5), Candida species (n = 2), and Enterococcus faecium (n = 1). Among the 8 patients who developed infection with the PF organism, 4 (50%) died in the intensive care unit (ICU) vs. an ICU mortality rate of 8% (3/37) in those who did not develop infection with the PF organism (P < 0.05). Infection occurred less frequently in recipients who received antimicrobial therapy with activity against the PF isolate than in those without appropriate treatment (41% vs. 3.8%, P < 0.005). Those who develop infection with organisms recovered from PF cultures appear to have high early mortality rates; therefore, appropriate antimicrobial therapy against organisms cultured from PF should be given.

Insulin resistance and geographical origin: major predictors of liver fibrosis and response to peginterferon and ribavirin in HCV-4.

BACKGROUND AND AIMS: Hepatitis C virus (HCV) genotype 4 (HCV-4) is increasing in prevalence in Western countries. However, little is known about the severity of the disease and response to treatment. The aim of this study was to assess the predictors (logistic regression) of severe fibrosis (METAVIR score F3-F4), and sustained virological response (SVR) to peginterferon and ribavirin in 226 consecutive HCV-4 patients (Egyptians 40%, Europeans 35% and Africans 24%). PATIENTS AND METHODS: Insulin resistance was assessed using the homeostasis model (HOMA-IR). Serum HCV-RNA level (bDNA) and subtypes of HCV (LiPA) were determined for all patients. RESULTS: Insulin resistance (HOMA-IR >3) was present in 105 patients (46%), and was associated with: age >45 years (OR, 2.614; 95% CI, 1.316 to 5.194), body mass index (BMI) >25 kg/m(2) (OR, 2.105; 95% CI, 1.048 to 4.229), serum HCV-RNA >800 000 IU/ml (OR, 3.143; 95% CI, 1.503 to 6.574), severe fibrosis (OR, 2.657; 95% CI, 1.214 to 5.818), and steatosis >30% (OR, 2.488; 95% CI, 1.105 to 5.602). Severe fibrosis was present in 67 patients (29%) and was associated with Egyptian origin (OR, 5.872; 95% CI, 2.747 to 12.553), excessive alcohol intake (OR, 5.311; 95% CI, 1.287 to 21.924), and HOMA-IR >3 (OR, 3.864; 95% CI, 1.859 to 8.034). 108 patients received a 48 week course of peginterferon plus ribavirin. SVR (undetectable serum HCV-RNA (TMA) 24 weeks after treatment stopping) was achieved in 59 patients (55%) and was associated with Egyptian origin (OR, 13.119; 95% CI, 3.089 to 55.706), HOMA-IR <2 (OR, 5.314; 95% CI, 1.953 to 14.459), and non-severe fibrosis (OR, 8.059; 95% CI, 2.512 to 25.855). CONCLUSION: Insulin resistance and geographical origin are major predictors of liver fibrosis and response to peginterferon and ribavirin in HCV-4 patients. Insulin resistance is frequently encountered in these patients, and correlated independently with serum HCV-RNA.

[Emergence of vancomycin-dependent enterococci following glycopeptide therapy: case report and review]. / Emergence d'entérocoque dépendant de la vancomycine à la suite d'un traitement par glycopeptide: cas clinique et revue.

INTRODUCTION: Outbreaks of vancomycin-resistant enterococci have been increasingly reported in France over the last three years. We report here, the emergence of a vancomycin-dependent enterococci isolate following glycopeptide therapy. PATIENTS AND METHODS: An Enterococcus faecium isolate that required vancomycin for growth was cultured from the stools of a liver transplant recipient who was colonised with vancomycin-resistant enterococci and who received vancomycin treatment for methicillin-resistant Staphylococcus aureus infection. The resistant isolate and the dependent isolate were typed by pulsed-field gel electrophoresis. The sequence of the ddl gene coding for the D-Ala: D-Ala ligase was analysed. RESULTS: The dependent isolate was primary cultured onto a vancomycin-containing screening medium and could not be subcultured in the absence of vancomycin. Both the resistant and dependent isolates harboured the vanA gene and they had the same DNA restriction pattern after pulsed-field gel electrophoresis. Dependence on vancomycin was associated with a 1-bp deletion in the D-Ala: D-Ala ligase gene leading to an early stop odon. CONCLUSION: Cultures onto vancomycin-containing media are warranted for clinical specimens from patients, who are known to carry vancomycin-resistant enterococci and receive vancomycin therapy.

Genetic background of Escherichia coli isolates from patients with spontaneous bacterial peritonitis: relationship with host factors and prognosis.

Spontaneous bacterial peritonitis (SBP) is a severe complication in patients with cirrhosis and ascites. It is predominantly caused by Escherichia coli. The phylogenetic group and virulence genotype of E. coli isolates causing SBP were investigated, and the association of these characteristics with host factors and prognosis was examined. Seventy-six episodes of E. coli SBP that occurred over a 9-year period were studied. The phylogenetic group of the isolates and the presence of 36 virulence factor genes were investigated. The influence of bacterial and host factors on in-hospital mortality was assessed by multiple logistic regression. Phylogenetic groups A, B1, B2 and D were found in 26%, 4%, 46% and 24% of the isolates, respectively. Virulence factor genes were more frequent in B2 isolates than in non-B2 isolates (mean virulence score 15.4 vs. 7.3, p <10(-4)). Ciprofloxacin resistance was significantly associated with non-B2 groups and a low virulence score. Host factors independently associated with a shift from B2 to non-B2 isolates were norfloxacin prophylaxis (OR 13.01, p 0.0213) and prothrombin ratio (OR 1.04 for a 10% decrease, p 0.0211). The model for end-stage liver disease (MELD) score (OR 1.83, p 0.0007) and hospital-acquired SBP (OR 4.13, p 0.0247) were independent predictors of in-hospital mortality. In contrast, outcome was not influenced by the phylogenetic group or the virulence profile. These findings indicate that the characteristics of E. coli isolates causing SBP vary with the severity of liver disease and with fluoroquinolone prophylaxis. Host factors are more important than bacterial factors in predicting in-hospital mortality.

[Interest of the disk diffusion method for screening Clostridium difficile isolates with decreased susceptibility to antibiotics]. / Evaluation de l'antibiogramme par diffusion en milieu gélosé pour le dépistage de souches de Clostridium difficile de sensibilité diminuée aux antibiotiques.

AIM: In vitro determination of Clostridium difficile susceptibility to antibiotics is not routinely performed. The aim of this study was to evaluate the performance of antibiotic susceptibility determination with the disk diffusion method for screening C. difficile isolates with decreased susceptibility to antibiotics. METHODS: Thirty-six C. difficile isolates (toxigenic or not) isolated in 2005 and 2006 from three hospitals Assistance publique-Hôpitaux de Paris (Jean-Verdier, René-Muret, Beaujon) were studied by disk diffusion method with 14 antibiotics. Mueller-Hinton agar supplemented with sheep blood (Bio-Rad*) were swabbed with a C. difficile suspension at 1 McFarland. To check the results obtained with the disk diffusion method, Minimal Inhibitory Concentration (MIC) were performed respectively with E-test for glycopeptides and metronidazole and with the agar dilution reference method and E-test for new molecules with a potential activity against anaerobes: imipenem, ertapenem, linezolid and moxifloxacin. RESULTS: The decreased susceptibility (resistant and intermediate) observed was 40% for amoxicillin-clavulanate, 60% for piperacillin-tazobactam, 100% for ceftriaxone, 81% for imipenem, 61% for ertapenem, 2% for chloramphenicol, 34% for erythromycin, 90% for lincomycin, 2% for linezolid, 98% for levofloxacin, 17% for moxifloxacin and 0% for vancomycin, teicoplanin and metronidazole. The results obtained with the disk diffusion method were compared to MICs obtained with E-test and reference method. CONCLUSION: The disk diffusion method seems to be a good method to detect isolates suspected to have a decreased susceptibility and consequently to reduce MIC determinations.

[Obtention of bacterial antibiotic susceptibility following standard conditions directly from infected biological fluids and positive blood cultures]. / Mesure de la sensibilité aux antibiotiques selon les conditions standards directement à partir de liquides biologiques infectés et d'hémocultures positives.

OBJECTIVE: Determining the conditions, which would allow us to apply bacterial antibiotic susceptibility tests directly to infected biological fluids and positive blood cultures and in accordance with the standard conditions of these tests. METHODS: For infected fluids (N=23), a correlation was determined between the bacterial count observed by microscopic field on a cystopin centrifugation pellet and the dilution required to obtain bacterial inocula corresponding to those used in the standard antibiogram and E-test methods. For blood cultures detected positive with the BactALERT system (26 Enterobacteriaceae, 29 Staphylococcus and 11 Pneumococcus), the broth dilution required to obtain such inocula was determined for each bacterial type. RESULTS: For infected fluids, the dilution required for the antibiogram of enterobacterial and staphylococcal isolates was respectively of 10(-1) and 10(0) when there were 50 to 100 bacteria/field, 10(-2) and 10(-1) for 100 to 500, 10(-3) and 10(-2) for 500 to 1000, and 10(-4) and 10(-3) for>1000. A minimum of 50 to 100 bacteria/field was required to determine beta-lactam MICs towards a pneumococcal isolate present in cerebrospinal fluid. For blood cultures, a broth dilution of 10(-4) for Enterobacteriaceae and of 10(-2) for Staphylococcus and Pneumococcus allowed to reproduce the standard antibiogram. To reproduce the standard conditions of the E-test method for beta-lactam MICs towards a pneumococcal isolate, the broth dilution was 10(-1). CONCLUSION: Following the procedure described, antibiotic susceptibility can be available 24 h earlier.

Pasteurella multocida infection of a total knee arthroplasty after a "dog lick".

The patient we report here underwent a total knee arthroplasty (TKA) which got infected with P. multocida after her dog had licked a small wound at the third toe of the same foot. Despite a correct treatment comprising synovectomy and cleansing, and an active antibiotic treatment for 3 months, the patient was readmitted for persistent infection of the same knee 2 weeks after the end of the antibiotic treatment. Sampling during surgery allowed for the growth of a P. multocida isolate proven by a molecular method to be identical to the previously isolated strain. This recurrent P. multocida infection was treated by a two-step change of the TKA comprising a 2-month period of antibiotic treatment between the two surgical interventions.

Bacteriological investigation of infected pressure ulcers in spinal cord-injured patients and impact on antibiotic therapy.

STUDY DESIGN: Retrospective. OBJECTIVES: To improve the use of bacteriological results for treating spinal cord-injured patients with infected pressure ulcers. SETTING: Microbiology and Orthopaedics Department, Ambroise Paré University Hospital, Boulogne-Billancourt, France. METHODS: Tissue specimens, sampled at the end of the surgical intervention from unbridled and cleaned ulcers were analysed. Drainage liquids were cultured at day 1 (D1) and day 5 (D5) postsurgery. For part of the patients, a presurgery superficial sample was analysed and compared with the surgical and postsurgical samples. RESULTS: In all, 168 surgical samples from 101 patients, 183 D1 and 104 D5 wound drainage liquids were included in this study. Out of the 168 surgical samples 17 (10%) had a negative culture, whereas 151 (90%) had a positive culture. For drainage liquids, the culture was negative in 48% and 56% of the samples at D1 and D5, respectively. The most frequently isolated species were enterobacteria, followed by staphylococci and streptococci. CONCLUSION: Culturing deep tissue specimens sampled from the surgically cleaned and unbridled ulcers allows for the isolation of the bacterial species that are really involved in the ulcer infection. As the identification of these bacteria and their antibiotic susceptibility are available, when the culture results of the D1 postsurgical drainage liquid is also available, it is easier to choose targeted antibiotic treatment.

Clinical significance of tolerant strains of streptococci in adults with infective endocarditis.

OBJECTIVES: To compare the characteristics of patients with endocarditis due to tolerant and non-tolerant Streptococcus strains. PATIENTS AND METHODS: A retrospective nine-year study was conducted in a single tertiary-care hospital. The study included 24 cases of streptococcal endocarditis with known beta-lactam minimal inhibitory and bactericidal concentrations. RESULTS: Ten of the 24 patients concerned were infected with tolerant streptococcal strains, and 14 with non-tolerant strains. Bacterial tolerance was not associated with higher mortality or increased frequency of surgery. Fewer patients infected with tolerant than non-tolerant strains had serum bactericidal titers reaching success-predictive levels, and more of these experienced failure of initial antibiotic treatment and needed longer treatment. CONCLUSIONS: The results of this study strongly suggest that penicillin tolerance of the streptococci responsible for endocarditis has a clinical impact. Consequently, pending a larger prospective study addressing the problem of tolerance, it is clinically relevant to determine the minimal inhibitory and bactericidal penicillin concentrations for all streptococcal isolates causing endocarditis.

Imipenem resistance in Salmonella enterica serovar Wien related to porin loss and CMY-4 beta-lactamase production.

Two multidrug-resistant Salmonella enterica serovar Wien strains (SW468 and SW1107) were isolated in 2001 in Tunis. Both strains produced the beta-lactamases TEM-1, SHV-2a, and CMY-4, whereas strain SW1107 also produced the beta-lactamase CTX-M-3. The imipenem-resistant strain (SW468) was totally devoid of the OmpF-immunorelated porin. Imipenem resistance was shown as being related to porin loss and CMY-4 beta-lactamase production.