Epistasis influences the gene-environment interactions that shape bacterial fitness through antibiotic exposure which can ultimately affect the availability of certain resistance phenotypes to bacteria. The substitutions present within blaTEM-50 confer both cephalosporin and β-lactamase inhibitor resistance. We wanted to compare the evolution of blaTEM-50 with another variant, blaTEM-85, which differs in that blaTEM-85 contains only substitutions that contribute to cephalosporin resistance. Differences between the landscapes and epistatic interactions of these TEM variants are important for understanding their separate evolutionary responses to antibiotics. We hypothesized the substitutions within blaTEM-50 would result in more epistatic interactions than blaTEM-85. As expected, we found more epistatic interactions between the substitutions present in blaTEM-50 than in blaTEM-85. Our results suggest that selection from many cephalosporins is required to achieve the full potential resistance to cephalosporins, but that a single β-lactam and inhibitor combination will drive evolution of the full potential resistance phenotype. Surprisingly, we also found significantly positive increases in growth rates as antibiotic concentration increased for some of the strains expressing blaTEM-85 precursor genotypes but not the blaTEM-50 variants. This result further suggests additive interactions more effectively optimize phenotypes than epistatic interactions which means that exposure to numerous cephalosporins actually increases the ability of a TEM enzyme to confer resistance to any single cephalosporin.

The COVID-19 shutdown forced many institutions of higher education to shift in-person teaching to emergency remote teaching. This was particularly challenging for laboratory courses, where students are expected to learn hands-on skills needed for their career goals.

The evolution and dissemination of antibiotic resistance genes throughout the world are clearly affected by the selection and migration of resistant bacteria. However, the relative contributions of selection and migration at a local scale have not been fully explored. We sought to identify which of these factors has the strongest effect through comparisons of antibiotic resistance gene abundance between a distinct location and its surroundings over an extended period of six years. In this work, we used two repositories of extended spectrum β-lactamase (ESBL)-producing isolates collected since 2013 from patients at Dignity Health Mercy Medical Center (DHMMC) in Merced, California, USA, and a nationwide database compiled from clinical isolate genomes reported by the National Center for Biotechnology Information (NCBI) since 2013. We analyzed the stability of average resistance gene frequencies over the years since collection of these clinical isolates began for each repository. We then compared the frequencies of resistance genes in the DHMMC collection with the averages of the nationwide frequencies. We found DHMMC gene frequencies are stable over time and differ significantly from nationwide frequencies throughout the period of time we examined. Our results suggest that local selective pressures are a more important influence on the population structure of resistance genes in bacterial populations than migration. This, in turn, indicates the potential for antibiotic resistance to be controlled at a regional level, making it easier to limit the spread through local stewardship.

Ceftolozane/tazobactam (c/t) is a potent β-lactam antibiotic which combines the fifth generation cephalosporin ceftolozane and tazobactam, a β-lactamase inhibitor. The c/t combination therapy was approved in 2014 for the treatment of multidrug resistant (MDR) Enterobacteriaceae, especially intra-abdominal and urinary tract infections. The aim of this study is to assess c/t activity and to examine the association of c/t resistance with four common β-lactamase resistance genes found in clinical Enterobacteriaceae isolates collected from mainly urinary tract infections in an agricultural region in California (USA) between 2013-2020. We tested 993 Extended Spectrum β-lactamases (ESBL) producing Enterobacteriaceae isolates (885 E. coli, 94 K. pneumoniae, 14 other) for c/t susceptibility by Kirby-Bauer disk diffusion and screened using PCR for four common resistance genes with β-lactamase activity(blaTEM, blaOXA, blaSHV, and blaCTX-M) for 855 of the isolates. We also investigated co-resistance of c/t and nine other β-lactam antibiotics. We found that most isolates were susceptible to c/t (58.3%), while 38.5% showed intermediate resistance, and 3.2% were resistant. We also found that K. pneumoniae isolates were more resistant to c/t than E. coli isolates, and that c/t may be a good alternative to carbapenems, in that that some carbapenem resistant isolates were susceptible to c/t. Genotypic analysis showed blaSHV and blaCTX-M are independently associated with elevated c/t resistance. Although c/t demonstrated strong activity against Enterobacteriaceae, the high percentage of isolates with intermediate susceptibility emphasizes the need for close monitoring and continued surveillance for c/t resistance among ESBLs