Macrolide and tetracycline resistance in clinical strains of Streptococcus agalactiae isolated in Tunisia

Between 2007 and 2009, 226 clinical strains of Streptococcus agalactiae, recovered from female genital specimens and from gastric fluid or ear specimens from infected newborns, were isolated at the Laboratory of Microbiology of Charles Nicolle Hospital of Tunis. They were investigated to determine the prevalence of antibiotic resistance and to characterize the mechanisms of resistance to macrolide and tetracycline. All strains were susceptible to penicillin, ampicillin and quinupristin-dalfopristin. They were resistant to chloramphenicol (3.1%), rifampicin (19.1%), erythromycin (40%) and tetracycline (97.3%); 3.1% were highly resistant to streptomycin and 1.3% to gentamicin. Among the erythromycin-resistant isolates, 78.7% showed a constitutive macrolide-lincosamide-streptogramin B (MLS(B)) phenotype with high-level resistance to macrolides and clindamycin (MIC(50) >256 µg ml(-1)), 10% showed an inducible MLS(B) phenotype with high MICs of macrolides (MIC(50) >256 µg ml(-1)) and low MICs of clindamycin (MIC(50)=8 µg ml(-1)) and 2.2% showed an M phenotype with a low erythromycin-resistance level (MIC range=12-32 µg ml(-1)) and low MICs of clindamycin (MIC range: 0.75-1 µg ml(-1)). All strains were susceptible to quinupristin-dalfopristin and linezolid (MIC(90): 0.75 µg ml(-1) for each). MLS(B) phenotypes were genotypically confirmed by the presence of the erm(B) gene and the M phenotype by the mef(A) gene. Resistance to tetracycline was mainly due to the tet(M) gene (93.1%) encoding a ribosome protection mechanism. This determinant is commonly associated with the conjugative transposon Tn916 (P≤0.0002). tet(O) and tet(T) existed in a minority (2.2% and 0.4%, respectively). The efflux mechanism presented by tet(L) was less frequently present (4.5%). No significant association was found between erm(B) and tet(M) genes.

Nosocomial outbreak of imipenem-resistant Pseudomonas aeruginosa producing VIM-2 metallo-β-lactamase in a kidney transplantation unit

Background

Twenty four non replicate imipenem resistant P. aeruginosa were isolated between January and November 2008, in the kidney transplantation unit of Charles Nicolle Hospital of Tunis (Tunisia). This study was conducted in order to establish epidemiological relationship among them and to identify the enzymatic mechanism involved in imipenem resistance.

Methods

Analysis included antimicrobial susceptibility profile, phenotypic (imipenem-EDTA synergy test) and genotypic detection of metallo-β-lactamase (MBL) (PCR), O-serotyping and pulsed-field gel electrophoresis.

Results

All strains showed a high level of resistance to all antimicrobials tested except to colistin. The presence of MBL showed concordance between phenotypic and genotypic methods. Sixteen isolates were identified as VIM-2 MBL-producers and 13 of them were serotype O4 and belonged to a single pulsotype (A).

Conclusions

This study describes an outbreak of VIM-2-producing P. aeruginosa in a kidney transplantation unit. Clinical spread of bla_VIM-2 gene is a matter of great concern for carbapenem resistance in Tunisia.

Virulence determinants, phylogenetic groups and fluoroquinolone resistance in Escherichia coli isolated from cystitis and pyelonephritis

AIM OF THE STUDY

The aim of this study is to assess the relation between virulence genotype, phylogenetic group and susceptibility to fluoroquinolones and the urinary tract infection type including pyelonephritis and cystitis due to Escherichia coli.

MATERIALS AND METHODS

Between 2006 and 2007, 129 non-duplicate E. coli isolates from pyelonephritis (n=56) and cystitis (n=73) were prospectively collected. The antibiotic susceptibility was done by disk diffusion method. The phylogenetic groups, A, B1, B2 and D and 18 virulence genes were determined by multiplex PCR. Statistical analysis was done with the Pearson χ2 test, Mann-Whitney U-test, Kruskal-Wallis test and stepwise multivariable logistic regression analysis, P values below 0.05 were considered statistically significant.

RESULTS

For the pyelonephritis group, sex ratio was 0.3, the median age for women was 30 years and for men it was 54 years. For the cystitis group, sex ratio was 0.4, the median age for women was 41.5 years and for men it was 67.8 years. Significant statistical correlations were found between pyelonephritis isolates and susceptibility to ciprofloxacin (P=4 10(-5)), papG allele II (P=2 10(-6)), hlyA (P=10(-03)), iroN (P=0.04), iha (P=0.03) and ompT (P=0.03) virulence genes, high virulence score (P=0.008) and B2 phylogenetic group (P=0.03). In multivariate logistic regression analysis, papG II as predictor of pyelonephritis, no correlation could be established for the cystitis group.

CONCLUSION

Our findings argue for a direct link between pyelonephritis, virulence factors, susceptibility to fluroquinolones and B2 phylogenetic group among uropthogenic E. coli.

Epidemiological markers of Streptococcus pyogenes strains in Tunisia

To further understand the epidemiology of Streptococcus pyogenes or group A streptococcus (GAS) infections in Tunisia, phenotypic and genomic markers of GAS isolates, including antibiotic susceptibility, biotypes, T and emm types and toxin gene profiles, have been characterized. A total of 103 isolates, collected between 2000 and 2006, were investigated; 47 were recovered from invasive infections, and 56 from non-invasive infections. Rates of resistance to tetracycline, erythromycin, clindamycin and rifampin were 70.8%, 4.8%, 4.8% and 0.9%, respectively. High levels of resistance to streptomycin and kanamycin were observed in 1.9% and 4.8% of isolates, respectively. Biotype 3 was most common. Twenty different T patterns were observed, with a predominance of T3/13/B3264, and 38 different emm types. In both invasive and non-invasive isolates, emm118 (9.7%), emm42 (8.7%), emm1 (7.8%), st432 (6.8%), emm28 (5.8%) and emm76 (5.8%) were the most prevalent types; emm1, emm76 and emm18 were mainly observed among invasive infections, whereas emm118 (12.5%), emm42 (10.7%) and emm28 (8.9%) were predominant among non-invasive infections. The speB gene was detected in all isolates, but there were variable frequencies of speA, speC and ssa (20.3%, 32% and 25.2% respectively). Significant associations of emm1, emm18 and emm3 with speA and of emm4 and st432 with ssa were found. This first report from Tunisia revealed a unique emm distribution of GAS that differs from those of other regions. This information on the distribution of such emm types will be useful for the development of an appropriate vaccine in a country where the incidence of rheumatic fever remains high.

High rates of macrolide resistance among clinical isolates of Streptococcus agalactiae in Tunisia

One hundred sixty non duplicate erythromycin resistant Streptococcus agalactiae isolates were collected in Tunisia from January 2005 to December 2007 They were investigated to determine their resistance level to different macrolides and the mechanisms involved. Most erythromycin resistant S. agalactiae isolates were isolated from urinary specimens (38.75%, 62/160). The constitutive MLSB phenotype (cMLS) showed in 84.3% (135/160) with high MICs of macrolides and lincosamides (MIC90>256 microg/mL) and 8.2% (13/160) inducible MLSB phenotype (iMLS) with high MICs of macrolides (MIC90>256 microg/mL) and moderately increased MICs of lincosamides (MIC90=8 microg/mL). The M phenotype showed in 7.5% (12/160) with moderately increased MICs of macrolides (MIC90=32 microg/mL) and low MICs of lincosamides (MIC90=0.75 microg/mL). All strains were susceptible to quinupristun-dalfopristin association and linezolid (MIC90: 05 and 0.38 microg/mL respectively). Strains with MLSB phenotype harboured erm(B) gene with 825% (n=132), erm(TR) gene with 8.12% (n=13) and erm(B) plus mef (A) with 1.88% (n=3). All strains categorized as M phenotype carried the mef(A) gene (75%, n=12). cMLSB phenotype conferring cross resistance to macrolides, lincosamides and streptogramins B with high level of resistance was the most prevalent.

Correlation between meticillin-resistant Staphylococcus aureus prevalence and infection control initiatives within southern and eastern Mediterranean hospitals

The Mediterranean region has been identified as an area of hyper-endemicity for multi-resistant hospital pathogens. To better understand potential drivers behind this situation, we attempted to correlate already published meticillin-resistant Staphylococcus aureus (MRSA) data from 27 hospitals, participants in the Antibiotic Resistance Surveillance & Control in the Mediterranean Region (ARMed) project, with responses received from the same institutions to questionnaires which dealt with various aspects of infection control and antibiotic stewardship. No difference could be ascertained between high and low prevalence hospitals in terms of scores from replies to structured questions regarding infection control set-up, hand hygiene facilities and antibiotic stewardship practices. However, we did identify differences in terms of bed occupancy and isolation facilities. Hospitals reporting frequent episodes of overcrowding, particularly involving several departments, and which found regular difficulties sourcing isolation beds, had significantly higher MRSA proportions. This suggests that infrastructural deficits related to insufficient bed availability and compounded by inadequate isolation facilities could potentiate MRSA hyper-endemicity in south-eastern Mediterranean hospitals.

Phenotypic and genotypic characterization of macrolide resistant Streptococcus pneumoniae in Tunisia

One hundred of non duplicate Streptococcus pneumoniae resistant to erythromycin collected from three teaching hospitals in Tunisia from January 1998 to December 2004 were investigated to evaluate determine their resistance level to different macrolides and the mechanisms involved. Most erythromycin resistant S. pneumoniae were isolated from respiratory tract (34%). Eighty-three percent showed constitutive MLS(B) phenotype with high MICs of macrolides and lincosamides (MIC90 >256 microg/ml), 12% M phenotype with moderately increased MICs of macrolides (MIC90: 12 microg/ml) and low MICs of lincosamides (MIC90=0.75 microg/ml) and 5% inducible MLS(B) with high MICs of macrolides (MIC90 >256 microg/ml) and moderately increased MICs of lincosamides (MIC90=8 microg/ml). All strains were susceptible to quinupristun-dafopristin association and linezolid (MIC90=1 microg/ml). Strains belonging to MLS(B) phenotype were PCR positive for the erm B gene (88%). Twelve percent categorized as M phenotype carried the mef A gene. The rates of associated resistance were 68% to penicillin G, 53% to tetracyclines, 61% to cotrimoxazole, 21% to chloramphenicol and 13% to ciprofloxacin. MLS(B) constitutive phenotype conferring cross resistance to macrolides, lincosamides and streptogramins B with high level of resistance was the most prevalent. Thus, quinupristin-dalfopristin association and linezolid remain the most active molecules.

Accessory gene regulator (agr) typing of Staphylococcus aureus isolated from human infections

Staphylococcus aureus is a major hospital and community acquired pathogen. A total of one hundred strains were investigated. They were collected from January 2004 to July 2006 in the laboratory of microbiology at Charles Nicolle University hospital of Tunis. The isolates were identified by conventional methods. Methicillin resistance was confirmed by amplification of mecA gene by PCR. The agr groups were identified by multiplex PCR. The agr groups were distributed as follows: 19 strains belonged to group I, 16 to group II and 65 to group III. Among methicillin resistant S. aureus (MRSA), 9 (16.4%) belonged to group 1, 8 (14.5%) to group II and 38 (69.1%) to group IlI. For methicillin susceptible S. aureus (MSSA), only 10 strains (22.2%) belonged to group I, 8 (17.8%) to group II and 27 (60%) to group III. A preferential link was observed between agr group I and invasive infections (P=0.003) especially bacteremia (P=10(-4). Besides, agr groups II and III were closely related with non invasive infections (P=0.003). No association was found between other types of infections and agr groups. Likewise, no correlation was observed between agr groups, age or sex of patients and type of infections.

Prevalence of agr specificity groups among methicilin resistant Staphylococcus aureus circulating at Charles Nicolle hospital of Tunis

Methicillin resistant Staphylococcus aureus (MRSA) is a major human pathogen with many clinical aspects. In S. aureus, the accessory gene regulator (agr) globally controls the production of virulence factors. There are four agr groups. Our study was done to define the agr specificity of MRSA circulating at Charles Nicolle hospital and to investigate a possible relationship between agr groups and human disease types. From January 2004 to June 2005, a total of 57 MRSA isolated from individual hospitalized patients were collected, representing 12% of the total S. aureus isolates. The isolates were identified by conventional methods. Methicillin resistance was detected by oxacillin and cefoxitin disks and confirmed by the amplification of mecA gene by PCR. The agr groups were identified by multiplex PCR. All the strains were recovered from different wards: medicine (57.8%) especially from dermatology (56.2%), surgery (28%) and pediatrics (7%). Cutaneous pus (36.84%) and blood culture (35.08%) represented the main specimens. The agr groups were distributed as follow nine (15.7%) belonged to group I, two (3.5%) belonged to group II and 23 (40.3%) belonged to group III. For 23 strains, the agr group was not identified. A relationship between agr group and type of disease was observed: agr group III strains were associated with non invasive infections (P=0.02) and agr group I strains with invasive infections especially bacteremia (P=0.002).

Identification of staphylococcal cassette chromosome mec encoding methicillin resistance in Staphylococcus aureus isolates at Charles Nicolle Hospital of Tunis

Staphylococcal cassette chromosome is a mobile element that carries the gene mecA mediating the methicillin resistance in staphylococci. In Staphylococcus aureus five types of SCCmec have been described, which differs in size and genetic composition among strains. SCCmec typing of 34 non redundant methicillin-resistant S. aureus (MRSA) recovered in 2004 at Charles Nicolle Hospital of Tunis was carried out. The isolates were identified by conventional methods. Methicillin resistance was detected by oxacillin and cefoxitin disks and confirmed by mecA PCR. The SCCmec complex types were determined by using PCR which amplify a sequence overlapping the right SCCmec chromosome junction. Strains were recovered mainly from cutaneous pus (61.7%) and blood cultures (17.64%). They were isolated from different wards: medicine (53.1%) especially from dermatology (41.2%); surgery (40.6%) and pediatrics (3.1%). Only two strains were community-acquired MRSA. Two strains (5.9%) were harboring SCCmec type I; five (14.7%) SCCmec type II and 27 (79.4%) SCCmec type III. The two community-acquired MRSA were harboring type II and III SCCmec, usually found in hospital acquired MRSA. Our findings indicate that there are only three SCCmec types at Charles Nicolle Hospital. However, the existence of SCCmec types II and III in community incite us to investigate more community-acquired MRSA.

Clonal dissemination of a CTX-M-15 beta-lactamase-producing Escherichia coli strain in the Paris area, Tunis, and Bangui

One hundred twenty CTX-M-15-producing Escherichia coli strains isolated in 10 different hospitals from Paris (France), in the Hospital Charles Nicolle in Tunis (Tunisia), and in the Pasteur Institute in Bangui, Central African Republic (CAR), between 2000 and 2004 were studied. Eighty isolates, recovered from the three countries, were clonally related by repetitive extragenic palindromic PCR and pulsed-field gel electrophoresis. Various resistance profiles were identified among these clonal strains. After conjugation or electroporation of plasmids from E. coli strains representative of each profile and each geographic region, we observed seven resistance profiles in the recipient strains. Incompatibility typing showed that all the plasmids transferred from the clonal strains studied, except one, belonged to the incompatibility group FII. They all shared a multidrug resistance region (MDR) resembling the MDR region located in pC15-1a, a plasmid associated with an outbreak of a CTX-M-15-producing E. coli strain in Canada. They also shared the common backbone of an apparent mosaic plasmid, including several features present in pC15-1a and in pRSB107, a plasmid isolated from a sewage treatment plant. This study suggests that although the plasmid-borne blaCTX-M-15 gene could be transferred horizontally, its dissemination between France, Tunisia, and CAR was due primarily to its residence in an E. coli clone with a strong propensity for dissemination.

Antibiotic resistance in the southeastern Mediterranean - preliminary results from the ARMed project

Sporadic reports from centres in the south and east of the Mediterranean have suggested that the prevalence of antibiotic resistance in this region appears to be considerable, yet pan-regional studies using comparable methodology have been lacking in the past. Susceptibility test results from invasive isolates of Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Enterococcus faecium and faecalis routinely recovered from clinical samples of blood and cerebrospinal fluid within participating laboratories situated in Algeria, Cyprus, Egypt, Jordan, Lebanon, Malta, Morocco, Tunisia and Turkey were collected as part of the ARMed project. Preliminary data from the first two years of the project showed the prevalence of penicillin non-susceptibility in S. pneumoniae to range from 0% (Malta) to 36% (Algeria) [median: 29%] whilst methicillin resistance in Staphylococcus aureus varied from 10% in Lebanon to 65% in Jordan [median: 43%]. Significant country specific resistance in E. coli was also seen, with 72% of isolates from Egyptian hospitals reported to be resistant to third generation cephalosporins and 40% non-susceptible to fluoroquinolones in Turkey. Vancomycin non-susceptibility was only reported in 0.9% of E. faecalis isolates from Turkey and in 3.8% of E. faecium isolates from Cyprus. The preliminary results from the ARMed project appear to support previous sporadic reports suggesting high antibiotic resistance in the Mediterranean region. They suggest that this is particularly the case in the eastern Mediterranean region where resistance in S. aureus and E. coli seems to be higher than that reported in the other countries of the Mediterranean.

Antibiotic resistance in the southeastern Mediterranean--preliminary results from the ARMed project

Sporadic reports from centres in the south and east of the Mediterranean have suggested that the prevalence of antibiotic resistance in this region appears to be considerable, yet pan-regional studies using comparable methodology have been lacking in the past. Susceptibility test results from invasive isolates of Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, Enterococcus faecium and faecalis routinely recovered from clinical samples of blood and cerebrospinal fluid within participating laboratories situated in Algeria, Cyprus, Egypt, Jordan, Lebanon, Malta, Morocco, Tunisia and Turkey were collected as part of the ARMed project. Preliminary data from the first two years of the project showed the prevalence of penicillin non-susceptibility in S. pneumoniae to range from 0% (Malta) to 36% (Algeria) [median: 29%] whilst methicillin resistance in Staphylococcus aureus varied from 10% in Lebanon to 65% in Jordan [median: 43%]. Significant country specific resistance in E. coli was also seen, with 72% of isolates from Egyptian hospitals reported to be resistant to third generation cephalosporins and 40% non-susceptible to fluoroquinolones in Turkey. Vancomycin non-susceptibility was only reported in 0.9% of E. faecalis isolates from Turkey and in 3.8% of E. faecium isolates from Cyprus. The preliminary results from the ARMed project appear to support previous sporadic reports suggesting high antibiotic resistance in the Mediterranean region. They suggest that this is particularly the case in the eastern Mediterranean region where resistance in S. aureus and E. coli seems to be higher than that reported in the other countries of the Mediterranean.

[Use of molecular subtyping methods to investigate two nosocomial outbreaks due to Salmonella Livingstone in Sfax hospital, Tunisia]

OBJECTIVE

The aim of the study was to investigate two nosocomial outbreaks due to Salmonella Livingstone in a pediatric ward in Sfax hospital using molecular typing techniques.

MATERIALS AND METHODS

We included 84 strains of S. Livingstone isolated from patients hospitalized in a pediatric ward between November 1999 through August 2002 in addition to one environmental sample. Three epidemiological unrelated strains of S. Livingstone were also tested. The molecular typing techniques were: plasmid analysis, enterobacterial repetitive intergenic consensus (ERIC-PCR), random amplification of polymorphic DNA (RAPD-PCR) and pulsed field gel electrophoresis (PFGE).

RESULTS

The plasmid analysis and the ERIC-PCR generated a similar profile for outbreak isolates including the environmental sample while the epidemiologically unrelated strains demonstrated distinct patterns. The RAPD-PCR applied on 20 strains showed three patterns but one profile was predominating. All the strains isolate of S. Livingstone, except the veterinary strain, could not be typed by PFGE.

CONCLUSION

Using the molecular typing techniques, we showed that these two outbreaks in the pediatric ward were due to the clonal spread of a single strain of S. Livingstone. The identification of the source of contamination and the improvement of hygiene conditions are required.

[Use of combined detection of hepatitis C virus core antigen and antibodies to reduce the serological window-phase]

OBJECTIVES

In this study, we aimed at evaluating the performances of a combined assay for the detection of hepatitis C virus core antigen and antibodies and comparing this test with conventional third generation Elisa.

MATERIAL AND METHODS

Two hundred forty-one samples were included in this study and tested by Monolisa HCV Ag-Ab ULTRA, Biorad and compared to Monolisa Anti-HCV Plus. A comparative study was performed on a HCV seroconversion panel (Monolisa anti-HCV Plus, Biorad; Innotest HCV Ab IV, Innogenetics and Murex anti-HCV, Abbott). False positive samples were detected with western blot assay (INNO-LIA HCV Ab III, Innogenetics). Two anti-HCV negative haemodialysis patients with rise in ALT have been tested for RNA detection (Amplicor v2.0, Roche).

RESULTS

Results obtained with Biorad Ag-Ab were in agreement with third generation ELISA on HCV seroconversion panel. From anti-HCV negative patients, four samples were found low positive with HCV Ag-Ab. Two anti-HCV negative haemodialysis patients/HCV RNA positive were also negative with HCV Ag-Ab and 13 low positive samples with Biorad Ab were found negative with Ag-Ab.

CONCLUSION

The HCV Ag-Ab assay has a high specificity and sensitivity comparatively to conventional ELISA; but in our study we don't prove the reduction of the "serologic window" for detection of anti-HCV antibodies.

[Bacteriologic profile of bacteremia due to multi-drug resistant bacteria at Charles-Nicolle Hospital of Tunis]

OBJECTIVE

The authors had for aim to evaluate the place of multi-drug resistant bacteria (MDR) in nosocomial bacteremia.

MATERIALS AND METHODS

A retrospective study was carried out at the Microbiology laboratory of Charles Nicolle hospital of Tunis (2001-2003). One hundred and ninety-five isolated MDR [third generation cephalosporin resistant enterobacteria, methicillin-resistant Staphylococcus aureus (MRSA), Acinetobacter baumannii and Pseudomonas aeruginosa resistant to ceftazidime and imipenem]. An automated system was used to detect bloodstream infections. Microorganism identification was performed by conventional methods and antibiotic susceptibilities were determined by the disk diffusion method.

RESULTS

MDR bacteria were resistant to third generation cephalosporins (29%), A. baumannii (24%), P. aeruginosa (24%), and MRSA (10%). ERC3G were resistant to aminosides and fluorquinolones. A. baumannii and P. aeruginosa had high resistance rates. Associated resistance rates in MRSA were moderate.

CONCLUSION

MDR bacteria are of great concern in our hospital. This situation emphasizes the importance to maintain rigorous measures of hygiene as well as adapted antibiotic prescriptions.

Evaluation of a cefoxitin disk diffusion test for the routine detection of methicillin-resistant Staphylococcus aureus

Two oxacillin disk methods were compared with a cefoxitin disk diffusion test for detection of methicillin-resistant Staphylococcus aureus (MRSA), with PCR for mecA as the reference method. When tested with 115 MRSA and 350 methicillin-susceptible S. aureus isolates, the cefoxitin disk test (specificity 100%, sensitivity 96.5%) was superior to the oxacillin disk methods (specificity 99.1%, sensitivity 90.4%). Testing with both oxacillin and cefoxitin disks would give better sensitivity (100%) than the cefoxitin test alone, but at the expense of specificity (99.1%). The cefoxitin disk test required no special test conditions and would improve the reliability of routine tests for detection of MRSA.

Evolution of acquired resistance to third-generation cephalosporins in Enterobacteriaceae in a Tunisian hospital 1993-2001

Between January 1993 and December 2001, the overall frequency of resistance to third-generation cephalosporins in isolates of Enterobacteriaceae from Charles Nicolle Hospital, Tunis, rose from 2.4% to 7.4%. Klebsiella pneumoniae was the most prevalent species (56%), followed by Escherichia coli (15%) and Proteus mirabilis (9%). A rate of 49% was observed among isolates from paediatric patients in 1999, caused mostly by outbreaks in the neonatal intensive care unit of K. pneumoniae and P. mirabilis isolates that produced extended-spectrum beta-lactamases.

[Outbreak of nosocomial urinary tract infections due to a multidrug resistant Pseudomonas aeruginosa]

An outbreak of a multidrug resistant Pseudomonas aeruginosa including imipenem resistance occurred in the urology intensive care unit at Charles Nicolle Hospital (Tunis). All isolates presented the same antibiotic resistance pattern and were only susceptible to colistin. The epidemic strain was detected in different sites of this unit. Pulsed-field gel electrophoresis after enzymatic restriction using XbaI was performed in order to establish an epidemiologic link between these infections. Genotypic analysis showed two different patterns and the environmental source was identified in both cases. Although the same antibiotype was harbored by all the isolates, two outbreaks occurring in the same period were identified. The strengthening of hygiene measures allowed to stop the outbreak spreading. Since the hospital environment is the major source of Pseudomonas aeruginosa contamination, a continuous surveillance of the patients and the environmental sources is required for the implementation efficient control measures.

Prevalence of methicillin-resistant Staphylococcus aureus in eight African hospitals and Malta

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious therapeutic problem worldwide, and its frequency in most African countries has not been reported. This study was aimed at determining the prevalence and antibiotic susceptibility patterns of MRSA in eight large hospitals (>500 beds) in Africa and Malta, from 1996 to 1997. Susceptibility to methicillin (oxacillin) and to other drugs was determined by E test (AB Biodisk, Solna, Sweden) on a total of 1440 clinical isolates of S. aureus. Methicillin resistance was detected in 213 (15%) of the 1440 isolates tested. The rate of MRSA was relatively high in Nigeria, Kenya, and Cameroon (21-30%), and below 10% in Tunisia, Malta, and Algeria. All MRSA isolates were sensitive to vancomycin, with MICs <or= 4 mg/L. The isolates were also highly sensitive to ciprofloxacin, except in Kenya, Morocco, and Tunisia, where relative resistance to this drug was noted. Susceptibility to rifampin and fusidic acid seems to be correlated with the clinical use of these compounds. Only 46% of 59 MRSA strains analyzed were susceptible to rifampin, fusidic acid, and ciprofloxacin. The majority (> 60%) of MRSA strains were multiresistant. There is a need to maintain surveillance and control of MRSA infections in Africa.

[Bacillus anthracis: causative agent of anthrax]

Anthrax, an acute infectious disease of historical importance, is once again regaining interest with its use as a biological weapon. It is caused by B. anthracis, a Gram positive spore forming rod usually surrounded by a capsule and producing toxin. It occurs most frequently as an epizootic or enzootic disease of herbivores that acquire spores form direct contact with contaminated soil. Spores can survive for many years in soil. Animal vaccination programs have reduced drastically the disease in developed countries. In humans, the disease is acquired following contact with anthrax infected animals or their products. 3 types of anthrax infection can occur: cutaneous, inhalational and gastro intestinal. Cutaneous anthrax is the most common observed form. When germination occurs, replicating bacteria release toxin leading to hemorrhage, edema, necrosis and death. Full virulence of B. anthracis requires the presence of both antiphagocytic capsule and 3 toxin components (protective antigen, lethal factor and edema factor). Most naturally occurring anthrax strains are sensitive to penicillin but resistant to third generation cephalosporins. Post exposure prophylaxis is indicated to prevent inhalational anthrax.

First molecular characterization of HIV-1 Tunisian strains

In order to identify HIV-1 subtypes circulating in Tunisia, blood specimens from 25 HIV-1 infected Tunisian patients were collected. Proviral HIV-1 DNA was genotyped by sequence analysis of the C2-V3 env region. HIV-1 subtypes were determined in 21 DNA sequences: 20 were of subtype B and one was a circulating recombinant form (CRF02 AG). Subtype B largely dominates the epidemiology of HIV-1 infection in Tunisia, suggesting the probable imported origin of HIV-1 infection, but further studies are needed to investigate the potential diversification of HIV-1 isolates in Tunisia.

[Infectious endocarditis caused by a glycopeptide-resistant enterococus]

Enterococci are an important cause of infective endocarditis. Their resistance to most of the antibiotics involve real therapeutic problems. We report the first clinical isolate of glycopeptide resistant enterococcus from blood culture of patient with a prosthetic valve endocarditis. The strain is an E. faecium with a high level of resistance to vancomycin and teicoplanin (MIC > 256 mg/l), a low level of resistance to gentamycin (MIC = 6 mg/l) and susceptible to ampicillin (MIC = 1.5 mg/l). Therapeutic failure was observed leading to a surgical treatment. Therapy of such infection caused by multiresistant Enterococcus must be based on the study of bactericidal activity of antibiotic associations. In order to control the spread of this emerging resistance, the implementation of control measures is necessary.

[Study of the incidence and cost of nosocomial infections in general surgery]

Nosocomial infection incidence and its cost were study. We have identified 61 infected patients and 75 infectious episodes, is an incidence of 9.4% infected for 100 hospitalized by trimester. Operative site infections are the most frequent (60%), operative site infection (9.1%), inferior respiratory ways infections (2.2%). Incriminated germs are represented essentially by negative gram Bacillus (77.3%) with predominance of enterobacterias (59%). Invasive technique usage, surgery types and contamination classes have been identified as risk factors of nosocomial infection occurrence. The supplementary stay duration estimated by simple comparison between infected group and no-infected one is 9.3% days, responsible of an over cost of 336 TD by infected patient and 273 TD by infectious episode. The curative antibiotic costs have been estimated at 70 TD by infected patient being equivalent to two hospitalization days and to 57 TD by infectious episode.

Characterisation of CMY-4, an AmpC-type plasmid-mediated beta-lactamase in a Tunisian clinical isolate of Proteus mirabilis

A strain of Proteus mirabilis resistant to beta-lactams, including cefoxitin, was isolated from the urine of a woman from Tunisia. Its antibiotic susceptibility pattern and that of the Escherichia coli transconjugant suggested the presence of an AmpC-type beta-lactamase. Two bands of beta-lactamase activity (pI 5.4 and 9.2) were detected by isoelectric focusing. The nucleotide sequence of the gene encoding the AmpC-type enzyme was determined. The deduced amino acid sequence was 98-99% identical to CMY-3 and to those of the plasmid-mediated AmpC-type beta-lactamases originated from Citrobacter freundii and 97% identical to the chromosome-encoded beta-lactamase of a Tunisian clinical isolate of C. freundii. This enzyme differs from CMY-2 by one substitution (Arg for Trp at position 221) and from CMY-3 by two substitutions (Glu for Gly at position 42 and Ser for Asn at position 363) and we propose the denomination CMY-4.

[Conjugative and non-conjugative plasmids in Salmonella serovar Wien coded for broad-spectrum beta-lactamase]

The plasmid profile of 28 multiresistant Salmonella serovar Wien strains isolated between 1985 and 1990 is described. Four types of plasmids were individualised. Among these plasmids, two were responsable for beta-lactam resistance, type I plasmid of 110 kb and type II of 30 kb.

[Methicillin resistant Staphylococcus aureus. Decrease of incidence in a medical resuscitation unit at CHU Charles-Nicolle in Tunis]

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen in hospitals. Between 1985 to 1988, there has been an increase in the number of MRSA (92 %) caused by an epidemic emergency in medical care unit of our hospital. Infections control measures allowed to stop these outbreaks (20 % MRSA in 1990). But incidence of MRSA persist to decrease without supplement control measures and in 1994, only 7 % of Staphylococcus aureus strains are MRSA.

[Epidemiological pattern of the resistance of 153 Salmonella strains (S. typhi excluded) isolated in a Tunisian pediatric unit from 1985 to 1990]

Since 1985 to 1990, 153 isolates of non typhoidic Salmonella were recovered from pediatric unit of the Charles Nicolle Hospital in Tunis. The epidemiological profile of these isolates was established according to the biochemical and serological characterizations, the antibiotic susceptibility patterns (disk diffusion method) to betalactams and aminoglycosides. 127 isolates of Salmonella spp were from stools and 22 from blood cultures. The main serotypes were S. ser. Wien (108 isolates) and S. ser. Typhimurium (21). A sample of 50 isolates was selected among the different resistance phenotypes for determination of MICs and betalactamase identification by isolelectro-focusing (36 isolates). All of them were resistant to ampicillin and carbenicillin but variable for cephaloridine. Since 1986 appeared the resistance to cefotaxime and in 1990 all the S. ser. Wien isolates were resistant to the 4 betalactams tested including cefotaxime associated to streptomycin, kanamycin, gentamicin, tobramycin and amikacin. All of them had a high level of resistance to amoxicillin and gentamicin (mean MICs > 2048 and > 512 mg/l). The mean MIC of cefotaxime was 43.2 mg/l for S. ser. Wien, 64mg/l for S. ser. Typhimurium and decreased to 1.9 and 0.12 mg/l in combination with 1 mg/l of clavulanic acid. The beta-lactam resistance was mediated to enzymatic mechanism, at first the betalactamase of TEM-1 type alone, then associated to extended-spectrum betalactamase, mainly type SHV-2 since 1986, and other new types in 1990. They were under the control of plasmids with different sizes.

[Septicemia caused by A, B, C and G groups of beta-hemolytic streptococci]

During a five and a half years' period, 805 strains of beta-haemolytic groups A, B, C and G streptococci were isolated. Among these, 28 were responsible for bacteremia; 57 percent group B and 32 percent group A. All strains were susceptible to beta-lactam antibiotics; 4 strains were resistant to macrolides. The majority of patients had underlying diseases. Mortality was high in this group.

[Non-typhoid Salmonella in pediatric patients in Tunis (Hospital Charles-Nicolle) from 1980 to 1991]

252 nontyphoidic salmonellae strains isolated from pediatrics were identified by using standard laboratory procedures and were serotyped with commercial antisera. Antibiotic susceptibility tests were performed by the agar diffusion method. Mostly isolates obtained from feces (182) and blood (67) and 89% of them from newborns and nursings. S. sér. Wien represented 75% of the isolates. The other serovars were essentially S. sér Typhimurium, S. sér Infantis and S. sér Enteritidis. All the isolates of S. sér Wien and S. sér Typhimurium were resistant to amoxicillin, carbenicillin, cephalothin, streptomycin, chloramphenicol and tetracycline from 1980. From 1987 S. sér Wien isolates developed resistance to cefotaxime and amikacin. Distribution nontyphoidic salmonellae strains according to the year was variable. Maximal isolates were in September and October. Two major epidemics were observed in this study, in 1982 and 1989. 94% of the strains determined nosocomial infections. The source of infection was established during the epidemic of 1989. The application of hygiene measures led to decline the number of isolates in 1990 and their disappearance in 1991, any strains of S. sér Wien was isolated.

[Study of antibiotic sensitivity of Streptococcus pyogenes isolated in the hospital milieu (Charles Nicolle hospital of Tunis)]

The purpose of the present work was to investigate the susceptibility of S. pyogenes to antimicrobial agents. The strains have been taken from the bacteriological Service of Charles Nicolle's hospital at Tunis, and that during the period from January 1988- to December 1990. The antibiogram results as well as the minimal inhibitrice concentration determined by the agar diffusion technique, reveal that S. pyogenes continues to be very susceptible to the beta-lactamins (M.I.C. of penicillin G is "0.15 for 50% of strains tested. Resistance are noted for chloramphenicol; tetracycline and novobiocine (13%, 93%, 80%) not considered as good antibiotics anti-streptococcies. The macrolids are effective against S. pyogenes (100% of susceptibility) that's they are considered as the best alternating antimicrobiologents to the beta-lactamins (M.I.C. of erythromycin is 0.015.

[Pseudomonas aeruginosa and beta-lactam resistance phenotypes (Tunisia 1989-1990)]

366 strains of P. aeruginosa were studied. More than half of samples were issued from urology (40%) and general surgery (21%) and samples are mostly urine specimens (46%). The phenotypes of resistance to 3 beta-lactams (respectively ticarcillin, cefotaxime and ceftazidime) showed that 73% of the strains were wild phenotype (SSS-SIS-SRS). The MIC of ticarcillin +/- clavulanic acid, azlocillin, cefoperazone, cefsulodin, cefotaxime and ceftazidime against 93 strains chosen among different phenotypes of resistance showed that ceftazidime is the most active beta-lactam, 93% of strains being inhibited by 16 micrograms/ml. These MIC and iodometric test performed on 33 strains with ticarcillin MIC > 128 mg/l showed that acquired resistance was non enzymatic in 21% of cases and was related to beta-lactamase production in 79% of cases.