Phenotypic detection of plasmid-acquired AmpC in Escherichia coli--evaluation of screening criteria and performance of two commercial methods for the phenotypic confirmation of AmpC production.

The phenotypic detection of plasmid-acquired AmpC (pAmpC) in Escherichia coli is challenging, and molecular methods are required for confirmation. In addition to cefoxitin resistance, multiresistance and high-level resistance to cephalosporins have both been suggested as criteria for targeting isolates with pAmpC, but data to support these proposed criteria are lacking. A Swedish collection of 378 isolates with either putative chromosomal hyperproduction of AmpC (cAmpC) or pAmpC were subjected to disk diffusion and minimum inhibitory concentration (MIC) determination with the Etest. The frequency of resistance to gentamicin, ciprofloxacin, and trimethoprim among cAmpC and pAmpC was compared to elucidate the issue of multidrug resistance. Lastly, methods for the phenotypic confirmation of pAmpC were compared. One in-house disk diffusion method, one method employing NeoSensitabs (Rosco), and one Etest method (bioMérieux) were compared. The analysis of histograms based on both disk diffusion and the Etest showed that resistance [according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST)] to cefotaxime and/or ceftazidime occurred in almost all isolates. By coining resistance instead of non-susceptibility, the number of isolates required to subject to phenotypic testing/genotypic confirmation dropped by more than 40 %, without compromising the sensitivity substantially. Further, almost 70 % of isolates with pAmpC were non-multidrug resistant, clearly indicating that this is an inappropriate criterion for further investigation. The phenotypic tests all had more than 90 % sensitivity, and the best sensitivities were obtained with the in-house method and with the ceftazidime ± cloxacillin NeoSensitab. In conclusion, clinical resistance to cefotaxime and/or ceftazidime seems to be an appropriate criterion for pAmpC screening, and several phenotypic methods perform well for the phenotypic confirmation of AmpC production prior to genotypic confirmation.

Calibrated serological techniques demonstrate significant different serum response rates to an oral killed cholera vaccine between Swedish and Nicaraguan children.

Serum responses to oral cholera vaccines were assessed in three paediatric vaccine trials, two in León, Nicaragua and one in Stockholm, Sweden. A calibrated anti-cholera toxin B subunit (CTB) IgA ELISA was used together with an assay for vibriocidal antibodies. Swedish children had lower pre-vaccination levels of antibody, but serum responses were more pronounced in Swedish children than in Nicaraguan children. Post-vaccination levels of anti-toxin antibody were generally above those found after natural infections with enterotoxigenic Escherichia coli, that cross-reacts serologically with Vibrio cholerae. Adverse events seen after vaccination were generally mild and of little clinical significance.

Analysis of incidence of infection with enterotoxigenic Escherichia coli in a prospective cohort study of infant diarrhea in Nicaragua.

Diarrheal episodes with enterotoxigenic Escherichia coli (ETEC) were prospectively monitored during the first 2 years of life in a cohort of 235 infants from Leon, Nicaragua. ETEC was an etiological finding in 38% (310 of 808) of diarrheal episodes and in 19% (277 of 1,472) of samples taken as asymptomatic controls at defined age intervals (P = <0.0001). The majority of diarrheal episodes (80%) occurred before 12 months of age. The major ETEC type was characterized by colonization factor CFA I and elaboration of both heat-labile enterotoxin and heat-stable enterotoxin (ST). The proportion of E. coli strains with CFA I was significantly higher in cases with diarrhea (P = 0.002). The second most prevalent type showed putative colonization factor PCFO166 and production of ST. The prevalence of PCFO166 was approximately 20%, higher than reported before. Children with a first CFA I episode contracted a second ETEC CFA I infection 24% of the time, compared with 46% for ETEC strains of any subtype. Most of the ETEC episodes were of moderate severity, and only 5% (15 of 310) were characterized as severe. In conclusion, our results give valuable information for the planning of intervention studies using ETEC vaccines.