Abstract
We designed a study to describe the characteristics of sequence type 131 (ST131) lineages, including the H30-Rx sublineage, among a global collection of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates from 9 countries collected from 2000 to 2011. A total of 240 nonrepeat isolates from Canada, the United States, Brazil, the Netherlands, France, the United Arab Emirates (UAE), India, South Africa, and New Zealand were included. Established PCR, sequencing, and typing methods were used to define ST131 lineages, H30 and H30-Rx phylogenetic groups, gyrA and parC mutations, virotypes, and plasmid-mediated quinolone resistance determinants. The majority of the isolates produced CTX-M-15 with aac(6′)-lb-cr, belonged to phylogenetic group B2, and were positive for the H30 lineage with the gyrA1AB and parC1aAB mutations. ST131 showed 15 distinct pulsotypes; 43% of the isolates belonged to four pulsotypes, with a global distribution. Seventy-five percent of the ST131 isolates belonged to H30-Rx; this sublineage was present in all the countries and was associated with multidrug resistance, blaCTX-M-15, aac(6′)-lb-cr, and virotypes A and C. The H41 lineage was negative for the ST131 pabB allele-specific PCR. The multidrug-resistant H30-Rx sublineage poses an important public health threat due to its global distribution, association with virotype C, and high prevalence among ST131 isolates that produce CTX-M-15.
INTRODUCTION
Extended-spectrum β-lactamases (ESBLs) belonging to the TEM and SHV families were the predominant types of ESBLs during the 1980s and early 1990s (1). However, since the late 1990s, CTX-M β-lactamases have emerged worldwide among Enterobacteriaceae, in particular Escherichia coli, and have become the most prevalent and widespread type of ESBL in the world (2). CTX-M-producing E. coli organisms are important causes of community-onset urinary tract infections, bacteremia, and intra-abdominal infections (3). Currently, the most widespread and prevalent type of CTX-M enzyme is CTX-M-15 (4).
In 2008, E. coli sequence type 131 (ST131) containing CTX-M-15 was simultaneously identified in nine countries, spanning three continents (5, 6). The intercontinental dissemination of this ST has contributed immensely to the worldwide emergence of CTX-M-15-producing E. coli (4). Compared to other ESBL-producing E. coli organisms, ST131 isolates with CTX-M-β-lactamases are more likely to be resistant to antibiotics and cause community-acquired urinary tract infections (7). Several in vitro studies suggest that a unique combination of antimicrobial resistance and virulence factors seem to give ST131 a competitive advantage over other E. coli ST, most likely promoting its clonal expansion and dominance over less virulent and/or more susceptible isolates (8, 9).
The global distribution of ST131 reflects the repeated selection of local variants that have acquired certain IncF resistance plasmids carrying genes that encode CTX-Ms (10). However, Johnson and colleagues have shown that the expansion of the H30 lineage within ST131 has contributed significantly to the spread of ST131 among fluoroquinolone-resistant E. coli isolates in the United States (11).
Blanco and colleagues (12) recently introduced a system for classifying ST131 into 4 groups or virotypes (i.e., A, B, C, and D) that is based on the distribution of four distinctive virulence factors, namely, afa FM955459 (Afa/Dr adhesion), iroN (catecholate siderophore receptor), ibeA (invasion of brain endothelium), and sat (secreted autotransporter toxin). They reported that virotypes A and B were associated with multidrug resistance, the presence of CTX-M-15, and the plasmid-mediated quinolone determinant aac(6′)-lb-cr. Virotype C had a global distribution (i.e., was present in 8 countries, including Spain, France, Portugal, Switzerland, the United States, Canada, South Korea, and Lebanon) and was statistically associated with a higher frequency of infection (12).
There is limited information regarding the global distribution, virotypes, and characteristics of ST131 lineages that produce ESBLs. We designed a study to describe the characteristics of ST131 lineages, including the H30-Rx sublineage, from a global collection of ESBL-producing ST131 isolates from 9 countries collected in 2000 and 2011.
MATERIALS AND METHODS
Bacterial isolates.
We studied a total of 240 nonrepeat ESBL-producing ST131 E. coli isolates recovered between 2000 and 2010, from 9 different countries, spanning 4 continents: Canada (Victoria [n = 5], Vancouver [n = 8], Calgary [n = 62], Edmonton [n = 3], Medicine Hat [n = 4], Regina [n = 12], Winnipeg [n = 11], Toronto [n = 10], Brampton [n = 13], Ottawa [n = 7], Montreal [n = 4]), the United States (Chicago, n = 16), Brazil (Rio de Janeiro, n = 2), the Netherlands (Rotterdam [n = 8], Delft [n = 1], Gouda [n = 5]), France (Paris, n = 4), United Arab Emirates (Abu Dhabi, n = 8), India (Vellore, n = 8), South Africa (Cape Town, n = 12), and New Zealand (Auckland, n = 37). Nonrepeat clinical isolates from previous studies (i.e., from Canada [13, 14], the United States [15], Brazil [16], the Netherlands [17], and South Africa [18]), as well as recently acquired isolates from India, France, the United Arab Emirates (UAE), and New Zealand, were included in this study.
Antimicrobial susceptibility testing.
MICs were determined with the Vitek 2 instrument (Vitek AMS; bioMérieux Vitek Systems, Inc., Hazelwood, MO) that included the following drugs: amoxicillin-clavulanic acid (AMC), piperacillin-tazobactam (TZP), ciprofloxacin (CIP), gentamicin (GEN), tobramycin (TOB), amikacin (AMK), imipenem (IPM), meropenem (MEM), and trimethoprim-sulfamethoxazole (SXT). Throughout this study, the results were interpreted using the 2012 CLSI criteria for broth dilution (19).
ESBL screening and confirmation testing.
The presence of ESBLs was detected in clinical E. coli isolates by using the 2009 CLSI criteria for ESBL screening and confirmation tests (19).
β-Lactamase gene identification.
Isoelectric focusing, PCR amplification, and sequencing for blaCTX-M, blaOXA, blaTEM, and blaSHV were carried out on the isolates with a GeneAmp 9700 thermal cycler (Applied Biosystems, Norwalk, CT) using PCR conditions and primers as previously described (20). The isolates were presumed to produce whichever ESBL was encoded by the ESBL gene they were found to contain.
Plasmid-mediated quinolone resistance determinants, phylogenetic groups, and virotypes.
Amplification of the qnrA, qnrS, and qnrB genes was undertaken in all ESBL-positive isolates with multiplex PCR (21). aac(6′)-Ib and qepA were amplified in a separate PCR using primers and under conditions as previously described (22, 23). The variant aac(6′)-Ib-cr was further identified by digestion with BstF5I (New England BioLabs, Ipswich, MA). The ESBL-positive isolates were assigned to one of the four main E. coli phylogenetic groups (A, B1, B2, or D) by use of a multiplex PCR-based method (24). The 4 main virotypes in ST131 were determined with a multiplex method recently described by Blanco and colleagues (12).
Pulsed-field gel electrophoresis.
The genetic relatedness of the ESBL-producing isolates was examined by pulsed-field gel electrophoresis (PFGE) following the extraction of genomic DNA and digestion with XbaI using the standardized E. coli (O157:H7) protocol established by the Centers for Disease Control and Prevention, Atlanta, GA (25). Cluster designation was based on isolates showing approximately ≥80% relatedness, which corresponds to the “possibly related (4 to 6 bands difference)” criterion of Tenover et al. (26).
Identification of ST131 and fimH, gyrA, and parC sequencing.
Established PCR methods were used to define the ST131 lineages and the H30-Rx sublineage among the ESBL isolates (11, 27, 28). fimH (type 1 fimbrial adhesion), gyrA, and parC subtyping were performed as previously described (11). Multilocus sequence typing (MLST) was undertaken on all isolates using seven conserved housekeeping genes (adk, fumC, gyrB, icd, mdh, purA, and recA) (see http://mlst.warwick.ac.uk/mlst/dbs/Ecoli).
Statistical methods.
Analysis was performed using Stata version 10.0 (StataCorp, College Station, TX). Chi-square and Fisher's exact tests were used to compare group categorical data. P values of <0.05 were considered significant.
RESULTS
Bacterial isolates and susceptibilities.
A total of 240 ESBL-producing E. coli ST131 isolates were included in the study; 91 (38%) were recovered from urine samples, 134 (56%) from blood samples, 2 (1%) from intra-abdominal specimens, 4 (2%) from wound swabs, 2 (1%) from respiratory specimens, and 7 (3%) from rectal swabs. One hundred eighty-one (76%) of these specimens were submitted from community collection sites, and 59 (25%) were from hospitals.
Of the 240 study isolates, 173 (72%) were nonsusceptible (i.e., intermediate or resistant) to SXT, 153 (64%) to AMC, 106 (44%) to TZP, 166 (69%) to TOB, 120 (50%) to GEN, 96 (40%) to AMK, and 226 (94%) to CIP. No resistance to ERT or IPM was detected.
β-Lactamases, PMQR determinants, and phylogenetic groups.
Of the 240 ST131 ESBL-producing E. coli isolates, 193 (80%) produced CTX-M-15, 40 (17%) produced CTX-M-14, 1 (0.5%) produced CTX-M-24, 2 (1%) produced CTX-M-27, 3 (1%) produced CTX-M-3, and 1 (0.5%) produced TEM-52. One hundred fifty-one (63%) of the ESBL E. coli isolates were positive for aac(6′)-lb-cr, and 6 (3%) were positive for aac(6′)-lb-cr and qnrB1. None of the other types of plasmid-mediated quinolone resistance (PMQR) determinants were detected. All isolates belonged to phylogenetic group B2.
Pulsed-field gel electrophoresis and virotypes.
PFGE identified 15 clusters of E. coli (n = 230) that were designated pulsotypes A (n = 8), B (n = 20), C (n = 11), D (n = 22), E (n = 5), F (n = 7), G (n = 11), H (n = 20), I (n = 10), J (n = 17), K (n = 29), L (n = 38), M (n = 14), N (n = 4), and O (n = 14) (Table 1). The remaining ESBL-producing isolates (n = 10 and referred to as NR [not related]) were not clonally related, i.e., they exhibited PFGE profiles with <60% similarity and did not show patterns similar to those from pulsotypes A to O. Interestingly, certain pulsotypes (e.g., H, J, K, and L) had a global distribution, while other pulsotypes (e.g., A, E, F, and N) tended to be more localized (Table 1). Pulsotypes A to K, N, and O belonged to virotype C, and pulsotypes L and M belonged to virotype A (Table 1). Two isolates from the NR group produced CTX-M-15 and TEM-52 and belonged to virotype D, while the remaining NR isolates belonged to virotype C.
TABLE 1.
The molecular characteristics of different pulsotypes among a global collection of ST131 isolates that produce extended-spectrum β-lactamases
| Pulsotype (n)a | Isolate origin(s) | β-Lactamase(s) (n) | PMQRb determinant(s) (n) | Virotype | fimH lineage | H30-Rx (n) | gyrA allele(s) | parC allele(s) |
|---|---|---|---|---|---|---|---|---|
| A (8) | Canada, New Zealand | CTX-M-15 (8) | aac(6′)-lb-cr (6) | C | H30 | 8 | gyrA1AB | parC1aAB |
| B (20) | Canada, France, South Africa, New Zealand | CTX-M-14 (20) | aac(6′)-lb-cr (2) | C | H30 | 0 | gyrA1AB | parC1aAB |
| C (11) | Canada, India, South Africa | CTX-M-15 (11) | aac(6′)-lb-cr (10) | C | H30 | 11 | gyrA1AB | parC1aAB |
| D (22) | Canada, New Zealand | CTX-M-15 (22) | aac(6′)-lb-cr (22) | C | H30 | 22 | gyrA1AB | parC1aAB |
| E (5) | Canada | CTX-M-14 (2) CTX-M-24 (1) CTX-M-27 (2) | Negc | C | H30 | 0 | gyrA1AB | parC1aAB |
| F (7) | Canada, New Zealand | CTX-M-15 (7) | aac(6′)-lb-cr (4) | C | H30 | 7 | gyrA1AB | parC1aAB |
| G (11) | Canada, United States, South Africa | CTX-M-15 (11) | aac(6′)-lb-cr (8) | C | H30 | 11 | gyrA1AB | parC1aAB |
| H (20) | Canada, United States, South Africa, New Zealand, UAE | CTX-M-15 (20) | aac(6′)-lb-cr (19) | C | H30 | 20 | gyrA1AB | parC1aAB |
| I (10) | Canada, United States, New Zealand | CTX-M-15 (10) | aac(6′)-lb-cr (4) | C | H30 | 10 | gyrA1AB | parC1aAB |
| J (17) | Canada, United States, South Africa, UAE, New Zealand, the Netherlands | CTX-M-15 (12), CTX-M-14 (5) | aac(6′)-lb-cr (10) aac(6′)-lb-cr + qnrB (3) | C | H30 | 12 | gyrA1AB | parC1aAB |
| K (29) | Canada, United States, UAE, South Africa, New Zealand, India | CTX-M-15 (28), CTX-M-14 (1) | aac(6′)-lb-cr (23) | C | H30 | 28 | gyrA1AB | parC1aAB |
| L (38) | Canada, United States, UAE, South Africa, Brazil, the Netherlands, India | CTX-M-15 (36), CTX-M-3 (2) | aac(6′)-lb-cr (30) | A | H30 | 38 | gyrA1AB | parC1aAB |
| M (14) | Canada, India, South Africa, the Netherlands | CTX-M-15 (14) | aac(6′)-lb-cr (8) aac(6′)-lb-cr + qnrB (2) | A | H30 | 14 | gyrA1AB | parC1aAB |
| N (4) | Canada | CTX-M-15 (4) | aac(6′)-lb-cr (3) | C | H35 | 0 | gyrA1AB | parC1aAB |
| O (14) | Canada, France, the Netherlands, New Zealand | CTX-M-15 (4), CTX-M-3 (1), CTX-M-14 (9) | Neg | C | H41 | 0 | gyrA1AB, gyrA1A | parC3A, parC1b |
| NR (10) | Canada, Brazil, United States, South Africa, New Zealand | CTX-M-15 (6), CTX-M-14 (3), TEM-52 (1) | aac(6′)-lb-cr (2), aac(6′)-lb-cr + qnrB (1) | C, D | H30, H22 | 0 | gyrA1AB gyrA1A | parC1aAB, parC1b |
The isolates that belonged to pulsotypes A to O had >80% similar PFGE profiles among the isolates of each pulsotype. The remaining ESBL-producing isolates referred to as NR (not related) were not clonally related, i.e., they exhibited <60% similar PFGE profiles and did not show patterns similar to those from pulsotypes A to O.
PMQR, plasmid-mediated quinolone resistance.
Neg, negative.
ST131 and fimH, gyrA, and parC sequencing.
The majority of ST131 (220/240 [92%]) isolates belonged to the H30 lineage, and 181/220 (82%) H30 isolates belonged to the H30-Rx sublineage (Table 1). The remaining fimH types belonged to H22 (n = 2), H35 (n = 4), and H41 (n = 14). The H30 lineage comprised 13 different pulsotypes (i.e., A to M), while the H35 and H41 lineages belonged to pulsotypes N and O, respectively (Table 1). The H22 isolates were not clonally related to each other and did not show patterns similar to those from H30, H35, or H41. The H30-Rx sublineage was present in 11 pulsotypes (Table 1).
Among the 240 ST131 isolates, sequence analysis of the gyrA and parC genes identified 2 gyrA alleles and 3 parC alleles (Table 1). The CIP-susceptible isolates (n = 14) were negative for PMQR determinants and belonged to the H41 (n = 13) and H22 (n = 1) fimH lineages. Seven of the CIP-susceptible isolates contained the putative ancestor allele of gyrA (i.e., gyrA1) and the parC variant with 1 silent mutation (i.e., parC1b). The remaining 7 CIP-susceptible isolates (MICs, 0.12 to 0.5 μg/ml) contained the gyrA1A allele (i.e., one amino acid replacement mutation [Ser-83-Leu]) combined with the parC1b allele.
In contrast, the majority of CIP-nonsusceptible isolates were positive for aac(6′)-lb-cr (156/226 [69%]), belonged to the H30 (n = 220), H35 (n = 4), H41 (n = 1), and H22 (n = 1) fimH lineages, and possessed the gyrA allele named gyrA1AB (i.e., differed from gyrA1A by the distinct secondary mutation Asp-87-Asn) and the parC variant named parC1aAB (i.e., parC1a plus the replacement mutations Ser-80-Ile and Glu-85-Val) (11). The H41 CIP nonsusceptible isolate contained the gyrA1AB and parC3A alleles (11).
The antimicrobial susceptibilities, PMQR determinants, ESBL types, and virotypes of ST131, H30, and H30-Rx are shown in Table 2. ST131 was divided into 3 groups according to H30 and H30-Rx status: group 1 was isolates that were negative for H30 (non-H30), group 2 was isolates that were positive for H30 but negative for H30-Rx (H30 non-Rx), and group 3 was isolates that were positive for both H30 and H30-Rx (H30-Rx). H30-Rx isolates were significantly more likely to be resistant to various antimicrobial agents, to be positive for aac(6′)-lb-cr and blaCTX-M-15, and to belong to virotype A (Table 2). H30 non-Rx isolates were more likely to be positive for blaCTX-M-14 and belong to virotype C.
TABLE 2.
The antimicrobial susceptibilities, plasmid-mediated quinolone resistance determinants, extended-spectrum β-lactamases, and different virotypes of ST131 and its H30 and H30-Rx sublineages
| Isolate characteristica | No. (%) of isolates in sublineageb: |
P | ||
|---|---|---|---|---|
| Non-H30 (n = 20) | H30 non-Rx (n = 39) | H30-Rx (n = 181) | ||
| Collection site | 0.5 | |||
| Hospital | 6 (30) | 9 (23) | 44 (24) | |
| Community | 14 (70) | 30 (77) | 137 (76) | |
| Antimicrobial NS | ||||
| AMC | 4 (20) | 16 (41) | 133 (73) | <0.001 |
| TZP | 2 (10) | 10 (44) | 94 (52) | 0.002 |
| CIP | 10 (50) | 35 (90) | 181 (100) | <0.001 |
| SXT | 1 (5) | 19 (49) | 153 (85) | <0.001 |
| GEN | 2 (10) | 20 (51) | 98 (54) | 0.4 |
| TOB | 3 (15) | 23 (59) | 140 (77) | 0.01 |
| AMK | 1 (5) | 11 (28) | 84 (46) | 0.02 |
| PMQR determinant | ||||
| aac(6′)-lb-cr | 3 (15) | 6 (15) | 142 (78) | <0.001 |
| aac(6′)-lb-cr + qnrB | 1 (5) | 1 (3) | 4 (2) | NAc |
| Virotype | ||||
| A | 0 | 0 | 52 (29) | <0.001 |
| B | 0 | 0 | 0 | |
| C | 18 (90) | 39 (100) | 129 (71) | <0.001 |
| D | 2 (10) | 0 | 0 | NA |
| Type of ESBL | ||||
| CTX-M-14 | 9 (45) | 31 (79) | 0 | <0.001 |
| CTX-M-15 | 9 (45) | 5 (13) | 179 (99) | <0.001 |
| Other CTX-M | 1 (5) | 3 (8) | 2 (1) | NA |
| Other ESBLs | 1 (5) | 0 | 0 | NA |
NS, nonsusceptible, i.e., either intermediate or resistant; AMC, amoxicillin-clavulanic acid; TZP, piperacillin-tazobactam; CIP, ciprofloxacin; SXT, trimethoprim-sulfamethoxazole; GEN, gentamicin; TOB, tobramycin; AMK, amikacin; PMQR, plasmid-mediated quinolone resistance; ESBLs, extended-spectrum β-lactamases.
Non-H30, ST131 E. coli isolate that was negative for H30; H30 non-Rx, ST131 E. coli isolate that was positive for H30 but negative for H30-Rx; H30-Rx, E. coli isolate that was positive for ST131, H30, and H30-Rx.
NA, not available (too many cells with numbers of <5).
DISCUSSION
E. coli ST131 is known to cause extraintestinal infections, as its isolates are fluoroquinolone resistant (FQ-R) and associated with ESBL production most often due to CTX-M-15 (14, 27, 29). ST131 is not a single entity and can be subdivided into different clusters by other typing methods. Previous studies have shown that ST131 isolates with similar pulsotypes (i.e., >80% relatedness) can be present in different regions or countries (6, 10, 30). However, the same studies have also shown that ST131 isolates with different pulsotypes (<80% relatedness) can be present in the same location (6, 30). These studies have included relatively few isolates with limited geographical origins and time periods. Johnson and colleagues (31) addressed these issues when they studied 579 ST131 isolates from various countries and diverse sources (humans, animals, and the environment) that spanned from 1967 to 2009. They concluded that ST131 is highly diverse at the pulsotype level, but a small number of pulsotypes predominate internationally, and these high-frequency pulsotypes had emerged within the last decade (31). A previous study from Calgary, Canada, over an 11-year period (2000 to 2010) showed that a distinct pulsotype of ST131 (named A5 in that study) was responsible for the significant increase in ESBL-producing E. coli isolates that had been causing bloodstream infections since 2007 (14).
Our current study identified 15 pulsotypes among 240 human ESBL-producing ST131 isolates recovered from 9 different countries, spanning 4 continents, between 2000 and 2010. Our results were similar to the pulsotype results reported by Johnson et al. (31): 43% of the isolates from our study belonged to four distinct pulsotypes (e.g., H, J, K, and L), with a global distribution (i.e., were present in ≥5 different countries and named international pulsotypes). The remaining 11 pulsotypes tended to be more localized to certain countries and were named localized pulsotypes. We do acknowledge that the localized pulsotypes may actually be more widely disseminated internationally due to sampling bias, as small numbers of isolates were sampled from Brazil, India, France, and UAE. One of the international pulsotypes (i.e., pulsotype L) was identical to the Calgary A5 pulsotype and was present in Canada (i.e., Victoria, Vancouver, Edmonton, Medicine Hat, Regina, Winnipeg, Toronto, Ottawa, Brampton, and Montreal), the United States, UAE, South Africa, Brazil, the Netherlands, and India (Table 1).
Most of the pulsotypes from our study belonged to virotype C (Table 1). Our study supported some of the results reported by Blanco et al. (12); e.g., virotype A from our study was associated with the presence of CTX-M-15 and aac(6′)-lb-cr. However, virotype C was associated with both CTX-M-15 and CTX-M-14 and the H35 and H41 lineages (Table 1). Interestingly, the international pulsotype L, which was responsible for the significant increase in bloodstream infections in Calgary since 2007, belonged to virotype A and was positive for H30-Rx and aac(6′)-lb-cr.
Whole-genome sequencing of 105 ST131 isolates from 5 countries revealed that fluoroquinolone resistance was confined to a single rapidly expanding sublineage designated H30-R (32). Interestingly, H30-R with CTX-M-15 belonged to a single well-defined clade nested within other H30-R isolates, which was named H30-Rx due to its more extensive resistance to antimicrobial agents. A study by Banerjee and colleagues (27) determined the prevalences of ST131 and its sublineages among 267 E. coli isolates from the Chicago region. The authors were able to show that H30-R and H30-Rx were more antimicrobial resistant than and had distinctive virulence profiles compared to those of non-H30 ST131 isolates. Interestingly, the H30-Rx sublineage had the highest virulence scores, implying greater virulence potential and possibly explaining its high prevalence (27).
We believe this is the first study to explore the associations of the H30 lineage and the H30-Rx sublineage of ST131 with different virotypes, resistance phenotypes, ESBL types, and the presence of plasmid-mediated quinolone resistance determinants in a global collection of E. coli ST131 isolates that produce ESBLs. We confirmed the association of the H30-Rx sublineage with multidrug resistance and the presence of CTX-M-15 (Table 2). We uniquely identified the association of H30-Rx with virotypes A and C and the presence of aac(6′)-lb-cr (Table 2). Isolates of the H30 lineage that tested negative for Rx (i.e., H30 non-Rx) were associated with virotype C and the presence of CTX-M-14 (Table 2). The H35 and H41 lineages were linked with virotype C and the presence of CTX-M-14 and CTX-M-15 (Table 2). However, our study did not include a sufficient number of non-virotype C isolates to reasonably conclude that H30-Rx isolates were associated with virotype C. To our knowledge, this is the first report that shows the association of non-H30 with CTX-M-14 due to the H41 lineage.
MLST identified pulsotype O (n = 14) as being from ST131; however, the PCR for the pabB allele, as described by Clermont and colleagues (28), was negative for these isolates. Pulsotype O belonged to the H41 lineage, was positive for virotype C, negative for plasmid-mediated quinolone resistance determinants, and present in Canada, France, the Netherlands, and New Zealand (Table 1). These results were similar to those from a recent study that determined the virulence properties of the H41 lineage and also found an association of the H41 lineage with virotype C (33). The discrepancies observed between the pabB allele-specific PCR and MLST for the H41 lineage of ST131 are noteworthy. The H41 lineage belongs to serotype O16:H5, and a PCR method specific for the detection of this subgroup was recently published (34).
The H30-Rx sublineage of ST131 is a major drug-resistant pathogen among fluoroquinolone-resistant E. coli isolates in the United States (11, 27, 29) and is associated with sepsis (32). Our study shows that H30-Rx also poses an important public health threat due to its global distribution, association with virotype C, and high prevalence among ST131 isolates that produce CTX-M-15. We urgently need well-designed epidemiological and molecular studies to understand the dynamics of the transmission, risk factors, and reservoirs for the E. coli ST131 H30-Rx sublineage. This will provide insight into the emergence and spread of this multidrug-resistant sequence type that will hopefully lead to information essential for preventing the spread of ST131.
ACKNOWLEDGMENTS
This work was supported by a research grant from the Calgary Laboratory Services (10006465).
J.D.D.P. previously received research funds from Merck and Astra Zeneca. The other authors declare no conflicts of interest.
Footnotes
Published ahead of print 21 April 2014
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