Activités in vitro de l'amoxicilline et de l'association amoxicilline-acide clavulanique vis-à-vis d'Escherichia coli en médecine de ville

Increasing prevalence of antimicrobial resistance among Enterobacteriaceae uropathogens in Dakar, Senegal: a multicenter study

To assess antibiotic susceptibility among Enterobacteriaceae isolated in urine from outpatients in Dakar, Senegal, a prospective multicenter study involving 3 laboratories had been conducted between June and October 2001. During this period, 300 strains were isolated and susceptibility testing was performed against antibiotics commonly used in treatment of community-acquired urinary tract infections (UTI). E. coli and K. pneumoniae represented 89% of isolates. The overall resistance rates of ampicillin, amoxicillin-clavulanic acid, nalidixic acid, fluoroquinolones and cotrimoxazole were respectively 77.3%, 34.7%, 14.7%, 13.3%, and 55%. In the light of these results, a re-evaluation of first line therapies and prudent use of fluoroquinolones is advised. At the same time a continued surveillance of antimicrobial resistance should be developed in Senegal in order to control the emergence of multidrug resistant strains and to establish a national therapeutic guideline for treatment of UTI.

Evidence for a true post-beta-lactamase-inhibitor effect of clavulanic acid against Klebsiella pneumoniae and Haemophilus influenzae

OBJECTIVE

The purpose of this study was to investigate and characterize in vitro the post-beta-lactamase inhibitor effect (PLIE) of clavulanic acid against two beta-lactamase-producing species of bacteria.

METHODS

The PLIE was investigated against one strain of Klebsiella pneumoniae and one strain of Haemophilus influenzae. A stationary-phase inoculum of about 107 colony-forming units per mL of each bacterium was pre-exposed for 2 h to clavulanic acid, either alone or in combination with amoxicillin at various concentrations. After pre-exposure, the dilution required to remove the beta-lactamase inhibitor was 1:100 or 1:1000 according to the bacterial species and their susceptibilities to clavulanic acid. Bacteria were counted hourly after drug removal, on solid agar medium.

RESULTS

Control cultures exposed to amoxicillin alone after dilution, showed a delay in growth, which may be inherent to the time required to synthesize sufficient beta-lactamase after the dilution steps. Control experiments clearly distinguished the post-antibiotic effect and the growth delay from the PLIE.

CONCLUSION

The PLIE could be one of several factors explaining why beta-lactam/beta-lactamase inhibitor combinations remain effective throughout the dosing interval, even if a few hours after in vivo administration, serum concentrations of beta-lactamase inhibitor fall below levels that are active in vitro.

[Antibiotic sensitivity to isolated bacteria in pediatric urinary tract infections]

Of the childhood urinary tract infections, more than 50% are caused by Escherichia coli (E Coli), followed by Proteus mirabilis (P mirabilis), Klebsiella sp, other enterobacteria, enterococci, Pseudomonas aeruginosa, and staphylococci. Of E coli isolates, 50 to 60% are resistant to ampicillin (ampi-R), 10% being susceptible to amoxicillin + clavulanic acid (AMC). For P mirabilis, ampi-R isolates are less frequent and more often susceptible to AMC. Klebsiella sp is resistant to ampicillin, 75% of isolates being susceptible to AMC. In these three species, the susceptibility of isolates to third generation cephalosporins, aminogly-cosides, and ciprofloxacin is still high (> 90%), but 15 to 35% are resistant to cotrimoxazole. In the other enterobacteria (Enterobacter cloacae, Morganella morganii, P vulgaris, Citrobacter freundii and Serratia marcescens) the resistance to cefalotin (hence to ampicillin and AMC) is permanent, with an exception: the susceptibility of P vulgaris to AMC. Enterococci are mostly susceptible to ampicillin, and P aeruginosa to ceftazidime, but in both species, the percentage of resistant strains in hospitalised patients is greater than in outpatients. For Staphylococcus aureus, the community-acquired isolates are susceptible to oxacillin and other anti-staphylococcal agents. All the coagulase negative staphylococci isolates are susceptible to vancomycin, but 70% of those from hospitalised patients are resistant to oxacillin, aminoglycosides and cotrimoxazole.

Antibiotic prophylaxis in children with relapsing urinary tract infections: review

Recurrent urinary tract infections (UTIs) are observed in 30-50% of children after the first UTI. Of these, approximately 90% occur within 3 months of the initial episode. The basic aim of antibiotic prophylaxis in children with malformative uropathy and/or recurrent UTIs, is to reduce the frequency of UTIs. The bacteria most frequently responsible for UTI are gram-negative organisms, with Escherichia coli accounting for 80% of urinary tract pathogens. In children with recurrent UTIs and in those treated with antibiotic prophylaxis there is a greater incidence of UTI due to Proteus spp., Klebsiella spp. and Enterobacter spp., whereas Pseudomonas spp., Serratia spp. and Candida spp. are more frequent in children with urogenital abnormalities and/or undergoing invasive instrumental investigations. Several factors are involved in the pathogenesis of UTI, the main ones being circumcision, periurethral flora, micturition disorders, bowel disorders, local factors and hygienic measures. Several factors facilitate UTI relapse: malformative uropathies, particularly of the obstructive type; vesico-ureteric reflux (VUR); previous repeated episodes of cystitis and/or pyelonephritis (3 or more episodes a year), even in the absence of urinary tract abnormalities; a frequently catheterized neurogenic bladder; kidney transplant. The precise mechanism of action of low-dose antibiotics is not yet fully known. The characteristics of the ideal prophylactic agent are presented in this review, as well as indications, dosages, side effects, clinical data of all molecules. While inappropriate use of antibiotic prophylaxis encourages the emergence of microbial resistance, its proper use may be of great value in clinical practice, by reducing the frequency and clinical expression of UTIs and, in some cases such as VUR, significantly helping to resolve the underlying pathology.

Antimicrobial survey of urinary tract isolates from a pediatric department

The epidemiology of urinary tract colonization/infection in children admitted during 1996 to the Pediatric Department of the University of Verona has been studied; 501/1959 urine cultures were positive (25.57%). 584 microorganisms (64.89% Gram-negative, 24.82% Gram-positive, 10.27% fungi) were isolated. The highest rate of Gram-negative isolation (80.0%) was observed in infants, while the highest rate of Gram-positive isolation (29.6%) was found in newborns admitted to the neonatal intensive care unit. Escherichia coli was the most frequently isolated microorganism in infants and children, but not in newborns. A 3-fold increase in resistant E. coli strains to cotrimoxazole/sulfamethoxazole and amoxicillin/clavulanic acid was documented during the last 3 years in this pediatric population. Our observations underline the importance of the survey of microbial maps in pediatric departments in order to optimize therapeutic and preventive choices.