Clonal diversity of CTX-M-producing, multidrug-resistant Escherichia coli from rodents

This territory-wide study investigated the occurrence of faecal carriage of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli among wild rodents from the 18 districts in Hong Kong. Individual rectal swabs were obtained from the trapped animals and cultured in plain and selective media. A total of 965 wild rodents [148 chestnut spiny rats (Niviventer fulvescens), 326 Indo-Chinese forest rats (Rattus andamanensis), 452 brown rats (Rattus norvegicus) and 39 black rats (Rattus rattus)] were sampled. ESBL carriage was 0 % in chestnut spiny rats, 0.6 % in Indo-Chinese forest rats, 7.7 % in black rats and 13.9 % in brown rats. Among brown rats, the prevalence of ESBL carriage differed markedly by geographical location: absent in two districts, low (7-10 %) in six districts, moderate (11-19 %) in seven districts and high (21-50 %) in three districts. Nonetheless, there was no correlation between the prevalence of ESBL in brown rats and human population density in the 18 districts. CTX-M-type enzymes were detected in 92.0 % of the ESBL-producing isolates, of which 83.1 % were resistant to three or more non-β-lactam drugs. The CTX-M producing isolates were genetically diverse but a large proportion (47.8 %) were included in six successful clones that are strongly associated with human diseases and CTX-M dissemination, viz. sequence type complex [STC]10/phylogroup A, STC23/phylogroup B1, STC38/phylogroup D, STC155/phylogroup B1, ST405/phylogroup D and ST131/phylogroup B2. In conclusion, our results show that brown rats often carry potentially zoonotic clones of CTX-M producing, multidrug-resistant E. coli. The potential for rats to be a source of CTX-M producing E. coli for humans deserves further consideration.

Increase in the nasopharyngeal carriage of non-vaccine serogroup 15 Streptococcus pneumoniae after introduction of children pneumococcal conjugate vaccination in Hong Kong

This study assessed pneumococcal carriage in the early periods after routine use of 13-valent pneumococcal conjugate vaccine (PCV13) in Hong Kong. Nasopharyngeal swabs were obtained from 1110 children (<5 years) admitted with acute illness during September 2010-August 2013. Pneumococcal carriage rate was 13.5% in unvaccinated children, 14.1% in children who had ≥1 PCV dose and 15.3% in children who had ≥3 PCV doses. Nonv-PCV13 serotypes comprised 56.4% of all isolates. The most common serogroup/types were 15 (15A, 5.1%; 15B, 10.3%; 15C, 9.6%; 15F, 0.6%), 19F (17.9%), 6A (7.1%) and 6C (7.1%). Carriage of serogroup 15 was more common among vaccinated children (4.1% versus 0.6%, P = 0.033). Molecular typing revealed that expansion of several clones (clonal complex, CC63, CC199, CC1262, CC3397) was responsible for the increase in serogroup 15. Almost all CC63 and CC3397 isolates were nonsusceptible to both penicillin and erythromycin. The finding highlights the emergence of serogroup 15 following PCV13 use.

Highly conjugative IncX4 plasmids carrying blaCTX-M in Escherichia coli from humans and food animals

This study investigated the prevalence of IncX plasmid subtypes in commensal and pathogenic Escherichia coli isolates and the biological features of the IncX4 subtype. Two hundred and twenty-five E. coli isolates from multiple sources (47 chickens, 41 pigs, 30 cattle and 107 humans) obtained during the period 2006-2012 were tested for the presence of IncX1 to IncX5. Overall, the prevalence of IncX plasmids in chicken, pig, cattle and human isolates were 21.2 % (10/47), 19.5 % (8/41), 3.3 % (1/30) and 4.8 % (5/107), respectively. IncX4 was the most common subtype, followed by IncX1 and IncX3, while no IncX2 or IncX5 were found. Seven out of 16 (43.8 %) IncX4 plasmids were found to carry blaCTX-M genes and six of them originating from different host sources (four chickens, one pig and one human) had identical or highly similar RFLP patterns. Three IncX4 plasmids carrying blaCTX-M from different host sources were investigated further. It was found that the IncX4 plasmids had little effect on bacterial host growth parameters after their introduction to J53 recipients. Conjugation experiments demonstrated that the IncX4 plasmids could be efficiently transferred at 30-42 °C at rates which were generally 10(2)-10(5)-fold higher than those for the epidemic IncFII plasmid carrying blaCTX-M (pHK01). In conclusion, the IncX plasmids are more common than previously recognized. The efficient transfer of IncX4 plasmid at different temperatures and the lack of fitness burden on bacterial hosts highlight the ability of this plasmid replicon to be an important vehicle for dissemination of antimicrobial resistance.

Prevalence and molecular epidemiology of plasmid-mediated fosfomycin resistance genes among blood and urinary Escherichia coli isolates

A total of 1878 non-duplicate clinical Escherichia coli isolates (comprising 1711 urinary isolates and 167 blood-culture isolates), which were collected from multiple centres in Hong Kong during 1996-2008, were used to investigate the prevalence and molecular epidemiology of plasmid-mediated fosfomycin (fos) resistance genes. Eighteen of the 1878 clinical E. coli isolates were fosfomycin resistant, of which six were fosA3 positive and two were positive for another fosA variant (designated fosKP96). No isolates had the fosC2 gene. The clones of the eight isolates were diverse: sequence type (ST) 95 (n = 2), ST118 (n = 1), ST131 (n = 1), ST617 (n = 1), ST648 (n = 1), ST1488 (n = 1) and ST2847 (n = 1). In the isolates, fosA3 and blaCTX-M genes were co-harboured on conjugative plasmids with F2:A-:B- (n = 2), N (n = 1), F-:A-:B1 and N (n = 1) and untypable (n = 2) replicons. Both fosKP96-carrying plasmids belonged to replicon N. RFLP analysis showed that the two F2:A-:B- plasmids carrying fosA3 and blaCTX-M-3 genes shared the same pattern. Complete sequencing of one of the two F2:A-:B- plasmids, pFOS-HK151325 (69 768 bp) demonstrated it to be >99 % identical to the previously sequenced plasmid pHK23a originating from a pig E. coli isolate in the same region. This study demonstrated the dissemination of fosA3 genes in diverse E. coli clones on multiple blaCTX-M-carrying plasmid types, of which F2:A-:B- plasmids closely related to pHK23a were shared by isolates from human and animal sources.

Dissemination of plasmid-mediated fosfomycin resistance fosA3 among multidrug-resistant Escherichia coli from livestock and other animals

AIMS

To investigate plasmid-mediated fosfomycin resistance related to fosA3 in Escherichia coli isolates collected from different animals in Hong Kong, China, 2008-2010.

METHODS AND RESULTS

In total, 2106 faecal specimens from 210 cattle, 214 pigs, 460 chickens, 398 stray cats, 368 stray dogs and 456 wild rodents were cultured. The faecal colonization rates of fosfomycin-resistant E. coli were as follows: 11.2% in pigs, 8.6% in cattle, 7.3% in chickens, 2.4% in dogs, 0.8% in cats and 1.5% in rodents. The cultures yielded 1693 isolates of which 831 were extended-spectrum β-lactamases (ESBL) producers. Fosfomycin-resistant isolates were more likely than fosfomycin-susceptible isolates to be producers of ESBL and to have resistance to chloramphenicol, ciprofloxacin, cotrimoxazole, gentamicin and tetracycline. Of the 101 fosfomycin-resistant isolates, 97 (96.0%) isolates were fosA3 positive and 94 (93.1%) were bla(CTX) (-M) positive. PCR mapping showed that the fosA3-containing regions were flanked by IS26, both upstream and downstream in 81 (83.5%) isolates, and by an upstream bla(CTX-M-14) -containing transposon-like structure (ΔISEcp1-bla(CTX-M-14) -ΔIS903 or ISEcp1-IS10 -bla(CTX-M-14) -ΔIS903) and a downstream IS26 in 14 (14.4%) isolates. For the remaining two isolates, fosA3 was flanked by a downstream IS26 but the upstream part cannot be defined. In a random subset of 18 isolates, fosA3 was carried on transferable plasmids with sizes of 50-200 kb and the following replicons: F2:A-B- (n = 3), F16:A1:B- (n = 2), F24:A-B- (n = 1), N (n = 1), B/O (n = 1) and untypeable (n = 3).

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the emergence of fosA3-mediated fosfomycin resistance among multidrug-resistant E. coli isolates from various animals. IS26 transposon-like structures might be the main vehicles for dissemination of fosA3.

Molecular epidemiology and nasal carriage of Staphylococcus aureus and methicillin-resistant S. aureus among young children attending day care centers and kindergartens in Hong Kong

OBJECTIVES

To investigate the prevalence and molecular epidemiology of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) nasal carriage in children.

METHODS

We collected nasal and nasopharyngeal swabs from 2211 children aged 2-5 years attending 79 day care centers (DCCs) and 113 kindergartens (KGs) in all 18 geographical districts in Hong Kong.

RESULTS

The overall carriage rates of S. aureus and MRSA were 27.6% (95% confidence interval [CI], 24.8-28.5%) and 1.3% (95% CI, 0.8-1.8%), respectively. Molecular typing (staphylococcal cassette chromosome mec [SCCmec], sequence type [ST], clonal cluster [CC]) showed that all the 28 MRSA isolates had SCCmec IV (n = 13) or V (n = 15) including 12 isolates with community-associated-MRSA genotypes (ST59-IV/V, ST30-IV and ST88-V), 10 isolates with healthcare-associated-MRSA genotypes (ST45-IV/V, CC5-IV and ST630-V) and six isolates with novel genotypes (ST10-V and CC1-IV). Spa typing indicated that there was some within and between DCCs/KGs transmission of certain MRSA and methicillin-sensitive S. aureus strains but this was not extensive.

CONCLUSION

Our findings indicate the potential for DCCs to be a reservoir for emerging MRSA genotypes and highlight the need to enhance education and infection control measures to reduce their cross-transmission in this population.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in residential care homes for the elderly in Hong Kong

This territory-wide study evaluated the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in residential care homes for elderly (RCHEs) in Hong Kong. MRSA colonization was assessed by taking swab culture from anterior nares and active skin lesions. Of 487 RCHEs surveyed, 80 MRSA strains were recovered from 1563 residents, giving a prevalence of 5.1%. Twenty-four isolates had SCCmec II, 2 had SCCmec III, 17 had SCCmec IV, 36 had SCCmec V, and 1 had a composite SCCmec type. Pulsed-field gel electrophoresis typing clustered 75 isolates into 7 clones (HKU10 to 50, HKU80, and HKU90). Two predominant types, HKU30 and HKU50, which together account for 75% of all MRSA strains, were found in 13 and 15 of the 18 geographic districts in Hong Kong, respectively. The main features for HKU50 strains were spa t1081/ST45-IV or V, capsular type 8, agrIV, and hla, seg, sei positive. On the other hand, HKU30 strains had spa t002/ST5-II, capsular type 5, agrII, and were hla, seg, sei positive. HKU30 strains were often multidrug resistant (MDR, involving ciprofloxacin, erythromycin, gentamicin, and tetracycline). In contrast, HKU50 strains exhibit both multidrug resistance (MDR) (involving ciprofloxacin, erythromycin, and tetracycline, but not gentamicin) and non-MDR patterns.

Community emergence of CTX-M type extended-spectrum β-lactamases among urinary Escherichia coli from women

OBJECTIVES

To conduct a territory-wide study of extended-spectrum beta-lactamases (ESBLs) among community isolates of urinary Escherichia coli from women in Hong Kong.

METHODS

Up to 50 consecutive single-patient E. coli isolates, collected from 13 laboratories in 2004, were studied. The ESBLs were characterized by PCR sequencing using specific primers. The epidemiological relationship of the isolates was studied by PFGE and phylogenetic group PCRs.

RESULTS

Forty-two ESBL producers were found among 600 consecutive isolates tested. The ESBL prevalence was 7.3% (15/205) for women aged 18-35 years, 5% (11/219) for women aged 36-50 years, 6.3% (4/63) for women aged 51-64 years and 10.6% (12/113) for women aged >or=65 years (P=0.3). The ESBL-producing isolates were often multidrug-resistant and CTX-M-14 was found in 37 isolates, CTX-M-15 in 3 isolates and CTX-M-3 in 2 isolates. PFGE revealed no significant clusters among the ESBL producers. Overall, CTX-M-14 producers were significantly more likely to belong to group D than non-ESBL producers [18/37 (48.6%) versus 13/57 (22.8%), P=0.009]. However, 7 of 13 (53.8%) CTX-M-14 producers from women aged 18-35 years represented phylogenetic group B2, compared with 7 of 24 (29.2%) for women of all other ages (P=0.1).

CONCLUSIONS

The study documented the community emergence of CTX-M as the predominant ESBL type among urinary isolates from women. The spread of CTX-M enzymes among isolates from young women is concerning and deserves close monitoring.

Decreased levofloxacin susceptibility in Haemophilus influenzae in children, Hong Kong

Among 563 strains of Haemophilus influenzae from young children in Hong Kong, 5 (0.9%) had decreased susceptibility to quinolones. The five strains had a Ser-84-Lys or Asp-88-Asn substitution in GyrA. Pulsed-field gel electrophoresis showed that the isolates are genetically diverse.

Detection and characterization of extended-spectrum β-lactamases among bloodstream isolates of Enterobacter spp. in Hong Kong, 2000–2002

OBJECTIVES

A total of 139 consecutive and non-duplicate bloodstream isolates of Enterobacter spp. collected from inpatients in Hong Kong during 2000-2002 were studied for production of extended-spectrum beta-lactamases (ESBLs).

METHODS

All isolates were evaluated by the modified double-disc synergy test (m-DDST), the combined disc method (CDM) and the three-dimensional (3D) test. The m-DDST and CDM were modified by the use of cefepime discs. beta-Lactamases were characterized by isoelectric focusing and PCR sequencing using specific primers.

RESULTS

ESBLs were identified in nine isolates (overall 6.5%), including seven of 39 (17.9%) Enterobacter hormaechei, one of 27 (3.7%) Enterobacter aerogenes and the only Enterobacter intermedius strain. The E. intermedius strain was positive only in the 3D test but not in the other two tests. The other eight strains were positive in all three tests. No ESBL was detected in the other species, including non-hormaechei members of the Enterobacter cloacae complex (n=61), Enterobacter agglomerans (n=7), Enterobacter gergoviae (n=4) and Enterobacter sakazakii (n=1). The ESBL content included five different CTX-M enzymes (CTX-M-9, CTX-M-13, CTX-M-14, CTX-M-24 and a novel CTX-M-2-like beta-lactamase), SHV-12 (n=2) and unidentifiable ESBLs with a pI of 7.7 or 7.9 in two strains. The seven ESBL-producing E. hormaechei were genotyped by pulsed-field gel electrophoresis and were found to be unrelated to each other. In three of the CTX-M-producing strains, ISEcp1-like elements, including promoters for the beta-lactamase gene, were found.

CONCLUSIONS

Our data underscore the diversity of CTX-M enzymes among Enterobacter spp. in Hong Kong.