Case Report of Treatment of Polymicrobial Bacteremia Caused by Carbapenem-Resistant Klebsiella pneumoniae, and Bacillus Species in an Immunocompetent Patient With Meropenem-Vaborbactam.

Klebsiella pneumoniae carbapenemases (KPCs) are the most common carbapenemases in the United States. The Infectious Disease Society of America (IDSA) recommends meropenem-vaborbactam, ceftazidime-avibactam, or imipenem-cilastatin-relebactam as preferred options with cefiderocol as an alternative, all of which are also alternative options for CTX-M Enterobacterales. Bacillus species, comprising 22 different species, are not commonly pathogenic, but can cause invasive nosocomial infections typically in immunocompromised hosts commonly treated with vancomycin or carbapenems. This case report illustrates the treatment course of CTX-M and KPC-producing Klebsiella pneumoniae, and Bacillus species bacteremia that included cefiderocol, followed by vancomycin and meropenem-vaborbactam, and then meropenem-vaborbactam monotherapy. The patient was a 74-year-old female who had a prolonged hospital course and several courses of intravenous antimicrobials prior to the multidrug resistant (MDR) Klebsiella pneumoniae, and Bacillus species bloodstream infection. The IDSA does not have treatment recommendations for Bacillus species, though the Clinical & Laboratory Standards Institute (CLSI) reports breakpoints for vancomycin and meropenem. In our case, the patient's Bacillus isolate was susceptible meropenem-vaborbactam (0.023 mcg/mL) based on a meropenem breakpoint of 4 mcg/mL. In our report, an immunocompetent patient developed a polymicrobial bloodstream infection caused by an MDR Klebsiella pneumoniae, and Bacillus species, which was successfully treated with meropenem-vaborbactam. This unusual infection and treatment course also serves to promote awareness of another treatment option for invasive Bacillus species infection and furthermore encourages providers to request testing & sensitivities to consolidate therapy, particularly in cases of polymicrobial infection.