In vivo emergence of ceftaroline resistance during therapy for MRSA vertebral osteomyelitis

Sir,

Ceftaroline, the active metabolite of ceftaroline fosamil, was approved by the US FDA in 2010 and by the European Commission in 2012 for the treatment of acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia.¹ This medication has also been reported to be used for the sporadic treatment of other severe MRSA infections, including osteomyelitis² and epidural abscesses.³

A middle-aged man with diabetes mellitus was admitted for incision and drainage of a septic left wrist. Source control was achieved. Tissue cultures grew MRSA (strain 89, Table 1), with ceftaroline MIC of 0.75 mg/L by broth microdilution (incremental dilution steps).⁴ Vancomycin was initiated, but was switched to ceftaroline fosamil due to rising serum creatinine and impending cardiac catheterization for a myocardial infarction. He improved and was discharged on renally adjusted ceftaroline fosamil 600 mg every 12 h. During his hospitalization, the patient complained of chronic sciatica back pain. Physical examination was notable for no spinal tenderness. However, back pain progressed post-discharge, and MRI showed vertebral osteomyelitis and collections in bilateral psoas muscles. He was readmitted for CT-guided aspiration of the right psoas fluid collection, which grew MRSA (strain 91) with ceftaroline MIC 4–6 mg/L (Table 1) and antibiotics were changed to vancomycin. Peripheral blood cultures revealed two MRSA isolate morphologies (strains 86 and 88). He underwent laminectomy and facetectomy for epidural abscess drainage with lumbar debridement, fusion and fixation. Cultures from the epidural abscess again grew MRSA. Trans-thoracic echocardiogram was negative for vegetations. The patient was discharged and completed 12 weeks of intravenous antibiotics followed by 12 months of oral doxycycline after inflammatory markers normalized. More than 1 year after surgery the patient was ambulating independently with a cane and living at home, and inflammatory markers had remained normal for >4 months after completing antibiotics. The patient gave verbal and written informed consent for the publication of this case report.

Table 1.

Series of MRSA isolates included in the study

Isolate	Specimen	Collection date	Time frame (days/weeks)a				Ceftaroline MIC (mg/L)	PBP2a amino acid residue number			Clonal typec
				Genome comparisonb				nPBD	PBD
				SNPs	InDels	total			447	601
89	wound (wrist)	1/2/14	NA	NA	NA	NA	0.75/0.75/0.75	WT	Glu	Ala	ST5-II
91	wound (lumbar spine)	1/3/14	28/4	104	70	174	4/4/6	WT	Lys	Ser	ST5-II
86	blood (colony 1)	13/3/14	40/6	93	64	157	8/8/8	WT	Lys	Ser	ST5-II
88	blood (colony 2)	13/3/14	40/6	92	59	151	4/6/6	WT	Lys	Ser	ST5-II

nPBD, non-penicillin-binding domain.

^aPeriod after recovery of baseline MRSA isolate.

^bNumbers of SNPs, insertions and deletions (InDels) compared with baseline genome.

^cCombination of MLST (ST) type and SCCmec type. All isolates were spa type t002/TJMBMDMGMK (Ridom/Kreiswirth).

The baseline MRSA (strain 89) and subsequent ceftaroline-resistant isolates (strains 86, 88 and 91) were subjected to WGS. Genome sequence data were utilized to extract epidemiological information related to isolate ST, spa and SCCmec determination, as previously described.⁵ The DNA genes and/or regions obtained from the baseline MRSA (strain 89) were considered as the reference for comparison purposes with the three selected follow-up isolates included in the study. The following proteins were investigated: PBP1, PBP2, PBP2a, PBP3 and PBP4. Other DNA sequence regions analysed were mecI, mecR and the mecA ribosomal binding site and the vraSR regulation network (cell wall stress response operon). All downstream DNA analysis was performed using the Lasergene^® package (DNAStar).

All four isolates belonged to ST5, had a spa type t002 and carried an SCCmec type II, associated with MRSA USA100 clone.⁶ Follow-up isolates showed Glu447Lys and Ala601Ser alterations in the penicillin-binding domain (PBD) of PBP2a. The additional alteration observed at the PBD (Ala601Ser) has not been previously reported and the role of this mutation in the phenotype associated with decreased susceptibility to ceftaroline needs further investigation. However, the adjacent amino acid (Glu602) is involved in a conformational change caused by the ceftaroline R1 segment, which is associated with a broader conformational change linked to opening the active site.⁷ Thus, it can be speculated that the Ala601Ser mutation may be associated with decreased ceftaroline binding to the active site. In addition, the Glu447 amino acid is adjacent to the critical Tyr446 in the cephalosporin binding pocket, which closely interacts with the R2 group of ceftaroline and ceftobiprole.^6,7 Therefore, the resistant strains described here may have possessed two mutations affecting binding at both the R1 and R2 ceftaroline groups. The other PBP amino acid sequences and other DNA sequence regions investigated were unchanged in the three follow-up isolates compared with the reference strain 89. In summary, clinical failure with ceftaroline may indicate emerging resistance. The role of this newly described resistance mutation in MRSA needs further investigation.

Funding

This work was partially supported by funds from Actavis PLC. E. S. is supported by NIH grant #5T32 AI055412-09.

Transparency declarations

G. M. A. has the following declarations: speaker's bureau Merck, research funding Merck, consulting with Coram Home Infusion Company, consultant Nuo Therapeutics, consultant scPharmaceuticals, Infectious Disease Society of America committee member. R. E. M. and H. S. S. have no personal declarations but are employees of JMI Laboratories, which has received research and educational grants in 2012–2014 from: Achaogen, Actelion, Affinium, American Proficiency Institute (API), AmpliPhi Bio, Anacor, Astellas, AstraZeneca, Basilea, BioVersys, Cardeas, Cempra, Cerexa, Cubist, Daiichi, Dipexium, Durata, Exela, Fedora, Forest Research Institute, Furiex, Genentech, GlaxoSmithKline, Janssen, Johnson & Johnson, Medpace, Meiji Seika Kaisha, Melinta, Merck, Methylgene, Nabriva, Nanosphere, Novartis, Pfizer, Polyphor, Rempex, Roche, Seachaid, Shionogi, Synthes, The Medicines Co., Theravance, ThermoFisher, Venatorx, Vertex, Waterloo, Wockhardt and some other corporations. Some JMI employees are advisors/consultants for Astellas, Cubist, Pfizer, Cempra, Cerexa-Forest, and Theravance. E. H. S. has none to declare.