In Vitro Susceptibility of Typhoidal, Nontyphoidal, and Extended-Spectrum-ß-Lactamase-Producing Salmonella to Ceftolozane/Tazobactam.

Both typhoidal and nontyphoidal salmonellae are included in the top 15 drug-resistant threats described by the U.S. Centers for Disease Control and Prevention. There is an urgent need to look for alternative antibiotics for the treatment of Salmonella infections. We used the broth microdilution test to examine the in vitro susceptibilities of typhoidal and nontyphoidal salmonellae, including isolates positive for extended-spectrum ß-lactamase (ESBL), to ceftolozane/tazobactam and six other antibiotics. Of the 313 (52 typhoidal and 261 nontyphoidal) Salmonella isolates tested, 98.7% were susceptible to ceftolozane/tazobactam. Based on the overall MIC50/90 values, Salmonella isolates were more susceptible to ceftolozane/tazobactam (0.25/0.5 mg/L) than all the comparator agents: ampicillin (≥64/≥64 mg/L), levofloxacin (0.25/1 mg/L), azithromycin (4/16 mg/L), ceftriaxone (≤0.25/4 mg/L), chloramphenicol (8/≥64 mg/L), and trimethoprim/sulfamethoxazole (1/≥8 mg/L). Comparison of the activities of the antimicrobial agents against nontyphoidal Salmonella isolates according to their serogroups showed that ceftolozane/tazobactam had the highest activity (100%) against Salmonella serogroup D, G, I, and Q isolates, whereas the lowest activity (85.7%) was observed against serogroup E isolates. All 10 ESBL-producing Salmonella isolates (all nontyphoidal), of which 8 were CTX-M-55 producers and 2 were CTX-M-65 producers, were sensitive to ceftolozane/tazobactam, albeit with MIC50/90 values higher (1/2 mg/L) than those for non-ESBL producers (0.25/0.5 mg/L). In summary, our data indicate that ceftolozane/tazobactam is active against most strains of both typhoidal and nontyphoidal salmonellae and also against ESBL-producing salmonellae.

Streptococcus oriscaviae sp. nov. Infection Associated with Guinea Pigs.

Pet bite-related infections are commonly caused by the pet's oral flora transmitted to the animal handlers through the bite wounds. In this study, we isolated a streptococcus, HKU75T, in pure culture from the purulent discharge collected from a guinea pig bite wound in a previously healthy young patient. HKU75T was alpha-hemolytic on sheep blood agar and agglutinated with Lancefield group D and group G antisera. API 20 STREP showed that the most likely identity for HKU75T was S. suis I with 85.4% confidence while Vitek 2 showed that HKU75T was unidentifiable. MALDI-TOF MS identified HKU75T as Streptococcus suis (score of 1.86 only). 16S rRNA gene sequencing showed that HKU75T was most closely related to S. parasuis (98.3% nucleotide identity), whereas partial groEL and rpoB gene sequencing showed that it was most closely related to S. suis (81.8% and 89.8% nucleotide identity respectively). Whole genome sequencing and intergenomic distance determined by ANI revealed that there was <85% identity between the genome of HKU75T and those of all other known Streptococcus species. Genome classification using concatenated sequences of 92 bacterial core genes showed that HKU75T belonged to the Suis group. groEL gene sequences identical to that of HKU75T could be directly amplified from the oral cavities of the two guinea pigs owned by the patient. HKU75T is a novel Streptococcus species, which we propose to be named S. oriscaviae. The oral cavity of guinea pigs is presumably a reservoir of S. oriscaviae. Some of the reported S. suis strains isolated from clinical specimens may be S. oriscaviae. IMPORTANCE We reported the discovery of a novel Streptococcus species, propose to be named Streptococcus oriscaviae, from the pus collected from a guinea pig bite wound in a healthy young patient. The bacterium was initially misidentified as S. suis/S. parasuis by biochemical tests, mass spectrometry. and housekeeping genes sequencing. Its novelty was confirmed by whole genome sequencing. Comparative genomic studies showed that S. oriscaviae belongs to the Suis group. S. oriscaviae sequences were detected in the oral cavities of the two guinea pigs owned by the patient, suggesting that the oral cavity of guinea pigs could be a reservoir of S. oriscaviae. Some of the reported S. suis strains may be S. oriscaviae. Further studies are warranted to refine our knowledge on this novel Streptococcus species.