Co-existence of VIM-2-producing Pseudomonas aeruginosa and KPC-2 and OXA-232-co-producing Klebsiella pneumoniae in the United States

Dear Editor,

Infections due to carbapenem-resistant gram-negative bacteria are a major health problem worldwide. Carbapenem resistance in gram-negative bacteria can result from a diversity of mechanisms: carbapenemase production, porin mutations, increased efflux pump activity, or the presence of enzymes other than carbapenemases. Most carbapenem-resistant isolates produce carbapenemase enzymes, which are found on plasmids that can be easily shared with other gram-negative bacteria [1]. The most common carbapenemase types in gram-negative bacteria are Klebsiella pneumoniae carbapenemase (KPC), New Delhi metallo-β-lactamase (NDM), Verona integron-encoded metallo-β-lactamase (VIM), oxacillinase-48-type carbapenemases (OXA-48), and imipenemase (IMP). A bla_KPC-producing K. pneumoniae isolate was first recovered from a patient in North Carolina (NC), USA, in 1996 [2]. Since then, many reports of carbapenem-resistant Enterobacteriaceae (CRE) in hospitalized patients, particularly in the northeastern USA have been published. Carbapenem resistance is also an emerging problem among Pseudomonas aeruginosa isolates in many countries worldwide [3].

We report the co-existence of VIM-2-producing P. aeruginosa and KPC-2 and OXA-232 co-producing K. pneumoniae isolates in a patient. To the best of our knowledge, this is the first report of two different species of carbapenemase-producing organisms isolated from the same patient sample in the USA. In addition, while some cases of OXA-232 and NDM co-production have been identified in the USA and subsequently around the world [4], to the best of our knowledge, KPC and OXA-232 (a variant of OXA-48) co-production in a single K. pneumoniae isolate has not been reported worldwide to date.

A pediatric patient less than five years old who had received care in India was transferred to a pediatric outpatient clinic at Wake Forest Baptist Health, Winston Salem, NC, in May 2019 with a two-year history of bilateral mucopurulent and malodorous ear discharge. The Institutional Review Board of Wake Forest School of Medicine approved the study for saving the isolate and performing additional testing (IRB approval no. IRB00008691). No informed consent was obtained since CRE is a reportable disease in NC.

The patient was diagnosed as having chronic otorrhea through perforated tympanic membranes, and the ear discharge fluid was sent to the clinical microbiology laboratory for bacterial culture. Both K. pneumoniae and P. aeruginosa were recovered from the ear sample, and the organisms were identified to the species level using a matrix-assisted laser desorption/ionization-time of flight system (Bruker Daltonics, Billerica, MA, USA). Antibiotic susceptibility testing was performed with the MicroScan WalkAway system (Beckman Coulter, West Sacramento, CA, USA) using Neg MIC Panel Type 45, and the E-test system (BioMérieux, Durham, NC, USA) was used for ceftazidime/avibactam and ceftolozane/tazobactam testing. The antibiotic susceptibility results are shown in Table 1.

Table 1. Antibiotic susceptibility testing results for the K. pneumoniae and P. aeruginosa isolates.

Antibiotic(s)	MIC (µg/mL)*
	K. pneumoniae	P. aeruginosa
Ampicillin/sulbactam	> 16/8, R	NA
Amikacin	> 32, R	> 32, R
Amoxicillin/clavulanate	> 16/8, R	NA
Aztreonam	> 16, R	8, S
Ceftriaxone	> 32, R	NA
Ceftazidime	> 16, R	16, I
Cefoxitin	> 16, R	NA
Cefazolin	> 16, R	NA
Ciprofloxacin	> 2, R	> 2, R
Cefepime	> 16, R	16, I
Ertapenem	> 1, R	NA
Gentamicin	> 8, R	> 8, R
Imipenem	4, R	> 8, R
Meropenem	8, R	> 8, R
Piperacillin/tazobactam	> 64, R	16, S
Trimethoprim-sulfamethoxazole	≤ 2/38, S	NA
Tetracycline	≤ 4, S	NA
Tigecycline	≤ 2, S	NA
Ticarcillin/clavulanate	> 64, R	> 64, R
Tobramycin	> 8, R	> 8, R
Ceftolozane/tazobactam	32/4, R	128/4, R
Ceftazidime/avibactam	1/4, S	16/4, R

^*MICs were determined using the MicroScan WalkAway system (Beckman Coulter West Sacramento, CA, USA) with the Neg MIC Panel Type 45, except for ceftolozane/tazobactam and ceftazidime/avibactam, which were determined using the E-test.

Abbreviations: MIC, minimum inhibitory concentration; NA, not applicable; R, resistant; I, intermediate; S, susceptible (based on the CLSI guidelines [10]).

Owing to carbapenem resistance, the isolates were evaluated for carbapenemase production using the modified carbapenem inactivation method; both isolates yielded a positive result indicating the presence of a carbapenemase. The presence of specific carbapenemase genes was determined using the Xpert Carba-R test (Cepheid, Sunnyvale, CA, USA). The bla_KPC and bla_OXA-48 genes were detected in the K. pneumoniae isolate, and the bla_VIM gene was detected in the P. aeruginosa isolate. The Xpert Carba-R test does not provide differentiation of the variants, and therefore further characterization was performed. Both isolates were sent to the North Carolina State Laboratory of Public Health (NCSLPH), where the original findings were confirmed. Next generation sequencing and subsequent genomic analysis were performed as previously described [5]. Sequencing data demonstrated that the K. pneumoniae isolate had the bla_KPC-2, bla_OXA-232, and bla_CTX-M-15 genes, and the P. aeruginosa isolate had the bla_VIM-2 gene.

The patient was treated with topical ciprofloxacin/dexamethasone and oral trimethoprim-sulfamethoxazole for 10 days; subsequently, the patient returned to the pediatric outpatient clinic 19 days later for follow-up. His ear discharge had partially improved. A new ear sample collected during the second visit yielded VIM-2 producing P. aeruginosa, but not K. pneumoniae. He was seen by a pediatric otolaryngologist and ultimately clinically responded to aural debridement and 21 days of topical acetic acid 2% solution.

KPC-producing CRE are the most common carbapenemase-producing CRE (CP-CRE) in the USA [1]. CP-CRE strains other than KPC remain extremely rare as a cause of infections in the USA and are often related with health care exposure outside the USA. In 2013, the first description of two OXA-48-like-producing CRE isolates collected during a surveillance study was published in the USA [6]. OXA carbapenemases have been divided into 14 variants based on amino acid sequences; OXA-232 is a five amino acid variant of OXA-48 first identified in France in 2011 [7]. In 1999, VIM family class B metallo-β-lactamases were initially described in Acinetobacter spp. and P. aeruginosa isolates in Europe. The VIM family has been subsequently detected in Enterobacteriaceae isolates such as Escherichia coli and K. pneumonia. In the USA, a P. aeruginosa isolate carrying bla_VIM, a mobile metallo-β-lactamase gene was first recovered in 2001 from a 58-year-old female with a history of autoimmune hepatitis that required a liver transplant [3]. Following this case, a nosocomial outbreak due to pan-resistant VIM-producing P. aeruginosa isolates was reported in a public teaching hospital in Chicago [8].

Co-producing isolates are a public health risk as they tend to have higher carbapenem minimum inhibitory concentrations than strains harboring individual carbapenemase genes. These isolates can be a source of mobile genetic elements carrying resistance genes and are also easily able to transfer antibiotic resistance to other organisms via mobile elements [9].

This report highlights the importance of hospital staff to be aware of organisms that may produce carbapenemases and of investigating whether a patient has received health care in countries known to have high rates of carbapenemase-producing organisms. Clinical laboratories should have the capacity to provide early detection of carbapenemase-producing bacteria to prevent the spread of these resistant organisms in both community and hospital settings.