Abstract
Cefoperazone/sulbactam (CSL) and piperacillin/tazobactam (TZP) are commonly used in clinical practice in China because of their excellent antimicrobial activity. CSL and TZP-nonsusceptible Enterobacteriaceae are typically resistant to extended-spectrum cephalosporins such as ceftriaxone (CRO). However, 11 nonrepetitive Enterobacteriaceae strains, which were resistant to CSL and TZP yet susceptible to CRO, were collected from January to December 2020. Antibiotic susceptibility tests and whole-genome sequencing were conducted to elucidate the mechanism for this rare phenotype. Antibiotic susceptibility tests showed that all isolates were amoxicillin/clavulanic-acid resistant and sensitive to ceftazidime, cefepime, cefepime/tazobactam, cefepime/zidebactam, ceftazidime/avibactam, and ceftolozane/tazobactam. Whole-genome sequencing revealed three of seven Klebsiella pneumoniae strains harbored blaSHV-1 only, and four harbored blaSHV-1 and blaTEM-1B. Two Escherichia coli strains carried blaTEM-1B only, while two Klebsiella oxytoca isolates harbored blaOXY-1-3 and blaOXY-1-1, respectively. No mutation in the β-lactamase gene and promoter sequence was found. Outer membrane protein (Omp) gene detection revealed that numerous missense mutations of OmpK36 and OmpK37 were found in all strains of K. pneumoniae. Numerous missense mutations of OmpK36 and OmpK35 and OmpK37 deficiency were found in one K. oxytoca strain, and no OmpK gene was found in the other. No Omp mutations were found in E. coli isolates. These results indicated that narrow spectrum β-lactamases, TEM-1, SHV-1, and OXY-1, alone or in combination with Omp mutation, contributed to the resistance to CSL and TZP in CRO-susceptible Enterobacteriaceae.
Antibiotic susceptibility tests
| Antibiotics | Breakpoint, (μg/ml) | Klebsiella pneumoniae | Escherichia cou | Klebriehd axyoca | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| E1 | E3 | E4 | E7 | E9 | E10 | E11 | E6 | E8 | E2 | E5 | ||
| CRO | ≤1≥4 | ≤0.5 | ≤0.5 | ≤0.5 | ≤0.5 1 | ≤0.5 | 1 | ≤0.5 | ≤0.5 | 1 | 1 | |
| CAZ | 4 ≥16 | 1 | 2 | 1 | 4 | 4 | 4 | 4 | 2 | 4 | 1 1 | |
| FEP | ≤2 216 1 | 1 | 0.25 | 1 | 2 | 2 | 2 | 0.5 | 2 | 1 1 | ||
| AMC | ≤8 ≥32 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 | ≥128 |
| CSL | ≤16 ≥64 | 64 | 64 | 64 | 64 | ≥128 | 128 | ≥128 | 64 | 128 | 128 | ≥128 |
| TZP | ≤16 ≥128 | ≥256 | ≥256 | ≥256 | ≥256 | 2256 | 2256 | ≥256 | ≥256 | ≥256 | ≥256 | ≥256 |
| FPT | ≤2 ≥16 | 1 | 0.5 | 0.06 | 0.125 | 2 | 1 | 2 | 0.25 | 1 | 0.125 | 0.25 |
| FPZ | ≤2 216 | 0.25 | 0.25 | 0.06 | 0.125 | 0.25 | 0.25 1 | 0.125 | 0.25 | 0.125 | 0.125 | |
| CZA | ≤8 216 1 | 0.5 | 0.25 | 0.25 | 1 | 0.25 | 1 | 0.5 | 0.5 | 0.5 | 0.25 | |
| CZT | ≤2 28 | 2 | 1 | 0.5 1 | 2 | 2 | 2 1 | 1 | 2 | 2 | ||
CROceftriaxone, CAZceftazidime, FEPcefepime, AMC:amoxicillin clavulanic-acid, CSLcefoperazone/sulbactam, TZP:piperadllin/tazobactam, FPT:cefepime tazobactam, FPZ:cefepime/zidebactam, CZA:ceftazidime/avibactam, CZTceftolozane/tazobactam
Gene sequencing results
| Number | Strain | ST | p-Lactamase gene | Promoter sequence mutation | Omp mutation |
|---|---|---|---|---|---|
| El | Kpn | 45 | blaSHV-1, blaTEM-lB | none | OmpK36, OmpK3 7 |
| E3 | Kpn | 45 | blaSHV-1, blaTEM-lB | none | OmpK36. OmpK3 7 |
| E4 | Kpn | 2854 | blaSHV-1 | none | OmpK36, OmpK3 7 |
| E7 | Kpn | 2358 | blaSHV-1 - blaTEM-lB | none | OmpK36, OmpK3 7 |
| E9 | Kpn | 2358 | blaSHV-1. blaTEM-lB | none | OmpK36. OmpK3 7 |
| E10 | Kpn 18 | 9 | blaSHV-1 | none | OmpK36. OmpK3 7 |
| Ell | Kpn | 45 | blaSHV-1 | none | OmpK36, OmpK3 7 |
| E6 | Eco | 88 | blaTEM-lB | none | none |
| ES | Eco | 409 | blaTEM-1B | none | none |
| E2 | Kox | 194 | blaOXY-1-3 | none | OmpK36 mutations. OmpK35 and OmpK 37 deficiency |
| E5 | Kox 11 | blaOXY-1-1 | none | no OmpK (OmpK3 5, OmpK36 and OmpK37) gene found |