Microbiological study of bacterial antibiotic resistance

In a subset of women from sites in London and South East England that were randomised to the rapid test strategy, we obtained individual consent to test additional vaginal-rectal maternal swabs and the faecal samples of their babies from 6 to 12 weeks of age for maternal antibiotic resistance profile of GBS, maternal colonisation by other antibiotic-resistant bacteria and the carriage of those specific bacteria or resistance elements by the infant. The swabs underwent selective enrichment culture for GBS, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and extended-spectrum β-lactamase producing (ESβL) Enterobacteriaceae. The presence of any bacteria of interest was profiled by a variety of techniques (including, but not necessarily limited to, antibiotic resistance, molecular/genetic characterisation and matrix-assisted laser desorption ionisation time of flight mass spectrometry). Antibiotic resistance was tested using the EUCAST methods and break points [19]. Enterobacterales were tested for sensitivity to ampicillin, piperacillin and tazobactam, amoxicillin and clavulanate, cefpodoxime, gentamicin, cefuroxime, amikacin, co-trimoxazole, temocillin, ceftazidime, ertapenem and ciprofloxacin on Muller Hinton agar. Molecular testing for Gram-negative antibiotic resistance genes was performed using the GSL EasyScreen™ Sample Processing Kit (SP006, Genetic Signatures Ltd., Newtown, Australia) designed to rapidly isolate nucleic acids (DNA and RNA) from clinical samples via an automated purification system. Fisher’s exact test was used to compare the proportions. We reported the relative risk of carriage of resistant E. coli or resistance genes in infants born to mothers with or without carriage of strains with specific characteristics using a binomial regression model with a log-link.