Report of erm(B)⁺ Campylobacter jejuni in the United States

LETTER

Campylobacter is a leading cause of foodborne illness in the United States, causing an estimated 1.3 million illnesses annually (1). Campylobacter usually causes a self-limited diarrheal illness; for patients who are severely ill, immunocompromised, or at the extremes of age, antibiotics may be necessary. When needed, macrolide antibiotics are the preferred treatment (1). Macrolide-resistant Campylobacter isolates have been described in many countries, and resistance is due largely to 23S rRNA mutations. The resistance gene erm(B) and mutations in rplD and rplV contribute to macrolide resistance infrequently (2). First reported in 2014, erm(B)⁺ Campylobacter has been detected primarily in China (2–4). Outside of China, erm(B)⁺ Campylobacter has been isolated only in Spain (5, 6). To the best of our knowledge, erm(B)⁺ Campylobacter has not been reported in the United States.

The CDC's National Antimicrobial Resistance Monitoring System for Enteric Bacteria (NARMS) conducts antimicrobial susceptibility testing (AST) of human Campylobacter isolates from the Foodborne Diseases Active Surveillance Network (FoodNet) sites (7, 8). Sequencing of clinical isolates collected through NARMS surveillance revealed a single erm(B)⁺ C. jejuni isolate (2016AY-0580; Sequence Read Archive accession no. SAMN08098201). A query of the Pathogen Detection page at NCBI (https://www.ncbi.nlm.nih.gov/pathogens/) did not reveal additional erm(B)⁺ C. jejuni strains in the United States prior to the collection date of this isolate. Briefly, 2× 250 NexteraXT genomic DNA libraries underwent Illumina MiSeq sequencing using v3 chemistry (9). Read mapping to detect relevant mutations in gyrA, 23S rRNA, rplD, and rplV revealed a gyrA Thr86Ile substitution. Assembly-based and assembly-free methods (10, 11) identified aadE, aph(2")-If, aph(3′)-III, tet(O), bla_OXA-184, and erm(B) resistance genes. The isolate was resistant to macrolides (azithromycin, clindamycin, erythromycin, and telithromycin), nalidixic acid, ciprofloxacin, gentamicin, and tetracycline but susceptible to florfenicol by NARMS AST (Table 1). Detailed information on testing methodology and interpretation of results can be found in the 2014 NARMS Human Isolates Surveillance Report (7).

TABLE 1.

MICs of and interpretations for tested antimicrobials against strain 2016AY-0580

Antimicrobial	MIC (μg/ml)	Interpretationa
Azithromycin	64	R
Ciprofloxacin	64	R
Clindamycin	>16	R
Erythromycin	>64	R
Florfenicol	4	S
Gentamicin	>32	R
Nalidixic acid	>64	R
Telithromycin	>8	R
Tetracycline	>64	R

^aR, resistance; S, susceptibility. Interpretation was performed using European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cutoff values. Further information on testing and interpretation can be found in the 2014 NARMS Human Isolates Surveillance Report (7).

The erm(B) region shares few genes with previously reported contexts (Fig. 1) (2). Specifically, erm(B) and a 3,708-bp upstream region exhibit 99.8% identity to a portion of Staphylococcus aureus GD1377 (GenBank accession no. CP019595), except for a 210-bp deletion that likely results in constitutive erm(B) expression (12). The regions flanking erm(B) display 99.9% identity to the erm(B)-negative C. jejuni plasmid pCG8245 (accession no. AY701528) (13), isolated from a patient with a history of travel to Thailand (Fig. 1). This novel erm(B) context, designated type IX here, may have been generated by insertion of erm(B) between sat4 and aph(3″)-III of a pCG8245-like plasmid (Fig. 1).

FIG 1.

Comparative analysis of the genetic context of erm(B) in Campylobacter jejuni isolate 2016AY-0580. erm(B) is shown in orange, other resistance genes are shown in blue, transposons are shown in pale gray, and known and predicted genes are shown in yellow and labeled if they are shared with other erm(B) contexts. Truncated genes are indicated by incomplete arrows. The figure was generated using Geneious (10.1.3).

This erm(B)⁺ C. jejuni isolate was cultured from the stool of a 41-year-old woman with symptoms of vomiting, diarrhea, and abdominal cramps in 2016. A standard public health interview was conducted with the patient by the Minnesota Department of Health and reported to FoodNet. The patient reported illness onset after 3 weeks of travel in Malaysia before returning to the United States. She denied contact with animals or ill people during travel but reported consuming a variety of meats, seafood, and fresh produce, as well as undercooked eggs and beef. Her symptoms lasted 12 days; on day 6, she was prescribed a course of azithromycin. The patient was not hospitalized, and no clinical information or follow-up cultures were available.

We describe an erm(B)⁺ C. jejuni isolate with a novel genomic context in the United States. Illness was likely acquired while traveling, consistent with previous reports of erm(B)⁺ Campylobacter found outside the United States. Clinicians should continue to be aware of macrolide resistance in returning travelers, as previous studies have suggested that erythromycin resistance in this population is as high as 6.8% (14). Like other reported erm(B) contexts, this novel context harbors several other determinants conferring resistance to additional drug classes. Clinicians should also be aware of the possibility of coselection of additional resistance among macrolide-resistant Campylobacter strains in travelers with diarrhea.