High Prevalence of CTX-M Beta-Lactamases in Enterobacteriaceae from Healthy Individuals in Guangzhou, China.

This study aimed to determine the prevalence of extended-spectrum beta-lactamases (ESBLs) in Enterobacteriaceae and to characterize the genetic composition of ESBL determinants among Enterobacteriaceae isolates from healthy people in Guangzhou, China. A total of 200 rectal swab samples were collected from healthy asymptomatic individuals and tested for ESBL production using ChromID ESBL agar. Phenotypic ESBL producers were screened for blaCTX-M, blaTEM, and blaSHV genes using PCR and DNA sequencing. The prevalence of ESBL-producing Enterobacteriaceae among rectal swab samples was 69.5%. All ESBL-producing isolates harbored blaCTX-M genes (n=138) except for one isolate that harbored blaSHV-2a. Eleven CTX-M ESBL genes were detected. The most predominant CTX-M-type genes were blaCTX-M-14 (n=82), followed by blaCTX-M-55 (n=19), blaCTX-M-65 (n=10), and blaCTX-M-27 (n=9). Isolates carrying blaCTX-M-38,-3,-15,-14b,-98,-121 and -123 were also identified. Molecular homology analysis of the selected isolates was performed by phylogenetic grouping and multilocus sequence typing and indicated that the predominant clone belonged to A-CC10. This study showed a high rate of CTX-M-type ESBL genes among Enterobacteriaceae isolates from healthy individuals in China.

Epidemiological survey and analysis on an outbreak of gastroenteritis due to water contamination.

OBJECTIVE: To document the investigation and control of an outbreak of gastroenteritis in City G, South China, and provide a reference for preventing future outbreaks. METHODS: An ambispective cohort study was designed. Attack rate (AR) and relative risks (RR) were calculated to identify the causes of gastroenteritis. Investigations using questionnaires included personal interviews with patients and doctors, reviews of medical records, laboratory examinations of fecal specimens and continuous hygiene monitoring of water samples from the waterworks. RESULTS: Overall, 427/71534 (AR=5.97%) cases were identified between October 31 and November 12 2010. Geographic distribution was highly localized, with 80% of cases occurring in the areas supplied by waterworks-A. Consumption of water provided solely by waterworks-A was found to be associated with illness (RR=8.20, 95 CI%:6.12-10.99) compared with that from waterworks-B. Microbiological analyses confirmed the presence of Norovirus in six of eight fecal samples from symptomatic patients, two water samples from waterworks-A and two sewage samples. After taking effective measures, the hygienic indices of waterworks-A met health criteria again on November 9 and no cases were reported 3 days later. CONCLUSION: The outbreak reported here was caused by drinking tap water contaminated with sewage at the source. Early identification of possible contamination sources and awareness of changes that might negatively impact water quality are important preventive measures to protect public health.

Mycobacterium abscessus post-injection abscesses from extrinsic contamination of multiple-dose bottles of normal saline in a rural clinic.

BACKGROUND: We investigated an outbreak of gluteal abscesses following intramuscular (IM) injections given at a clinic in rural China to identify the causative agent, source, and method of exposure. METHODS: We defined a case as an abscess that appeared at the site of an injection given since June 1, 2006. We compared case rates by injection route, medication, and diluents. We reviewed injection practices, and cultured abscesses and environmental sites for mycobacteria. RESULTS: From October through December 2006, 5.8% (n=35) of 604 persons who had received injections at the clinic developed a case. All 35 cases occurred in 184 patients (attack rate=19.0%) who had received IM injections with various drugs that had been mixed with normal saline (NS); risk ratio=infinity; p<0.0001. No cases occurred in the absence of NS exposure. We identified Mycobacterium abscessus from eight abscesses and from the clinic water supply, and observed the inappropriate reuse of a 16-gauge needle left in the rubber septum of 100 ml multiple-dose bottles of NS in the clinic. Fourteen percent (n=527) of the 3887 registered residents of this village had been treated with IM drugs over a three-month period, often for minor illnesses. CONCLUSIONS: This outbreak of M. abscessus occurred from exposure to extrinsically contaminated NS through improper injection practices. Frequent treatment of minor illnesses with IM injections of antibiotics was likely an important contributing factor to the size of this outbreak.

[Application of pulse-field gel electrophoresis analysis in source-tracking of food-borne disease caused by Vibrio parahaemolyticus].

OBJECTIVE: To apply pulse-field gel electrophoresis analysis(PFGE) in analysing a case of food poisoning caused by Vibrio parahaemolyticus. METHODS: PFGE using restriction enzyme Not I was employed in molecular subtyping of thirty strains of V. parahaemolyticus isolated from a case of food poisoning in Guangzhou city and PFGE patterns were analyzed by using BioNumerics Version 4.0 software to perform cluster analysis. Pattern profiles were compared by using the Dice coefficient and unweighted pair group method with arithmetic averages (UPGMA). RESULTS: Thirty strains were of the same type of pulsotype. CONCLUSIONS: Molecular subtyping by PFGE might disclose the epidemiological relationships of the strains from humans, food and the environment, giving a strong molecular epidemiological evidence and a support for the source-tracking of outbreak events.

[Molecular subtyping of Staphylococcus aureus isolated from a severe food-poisoning].

OBJECTIVE: To study the molecular types of Staphylococcus aureus isolated from a severe food-poisoning and to trace the possible strains. METHODS: Real-time PCR was applied to detect nuc gene as a specific marker for S. aureus, mecA gene encoding methicillin resistance and 5 other genes encoding staphylococcal enterotoxins (sea, seb, see, sed, see). Isolates were also performed with 16S rRNA oligonucleotide sequence analyzing by DNAStar MegAlign 5.0 software and pulse-field gel electrophoresis (PFGE) by BioNumerics Version 4.0 software. RESULTS: The nuc gene was detected from the 10 isolated strains, sea and seb genes were detected from 7 strains. There were 4 16 S rRNA types and 5 PFGE types found from all the strains. CONCLUSIONS: Three relative S. aureus strains were involved in the severe food-poisoning at least. Molecular subtyping might give a molecular epidemiological evidence and support the source tracing of an outbreak.

[Application of pulse-field gel electrophoresis analysis in the source-tracking of cholera epidemics].

OBJECTIVE: To apply pulse-field gel electrophoresis analysis(PFGE) in the analysis of cholera outbreak events and to determine the molecular epidemiological characteristics of Vibrio cholerae ( V. cholerae) isolates. METHODS: PFGE using restriction enzyme Not I was employed in the molecular subtyping of forty-one strains of V. cholerae isolated in cholera outbreak events from 2003 to 2005 in Guangzhou area and PFGE patterns were analyzed by BioNumerics Version 4.0 software to perform cluster analysis. Pattern profiles were compared by utilizing of Dice coefficient and UPGMA(unweighted pair group method with arithmetic averages). Comparison of PFGE typing results was performed with phage-biological typing and pathogenicity-associated genes typing. RESULTS: In cholera outbreak events, PFGE could discriminate epidemiologically related and unrelated strains, having more discriminatory power than phage-biological typing and pathogenicity-associated genes-typing. CONCLUSIONS: Molecular sub-typing by PFGE could disclose the epidemiological relationships of strains from humans and the environment, providing molecular epidemiological evidence and support for the source-tracking of cholera outbreak events.

[Analysis of characteristics of major pathogenicity-related genes of Vibrio cholerae isolated in Guangzhou area from 2001 to 2005].

OBJECTIVE: To apply multiplex polymerase chain reaction (MPCR) assay and sequencing in study of the carrying status of four pathogenicity-related genes of Vibrio cholerae (V.cholerae) and the variation of ctxA. METHODS: Primers targeting cholera toxin sub-unit A gene (ctxA), toxin-coregulated pilus gene (tcpA), accessory cholera enterotoxin gene (ace), zonula occludens toxin gene (zot) were designed and the MPCR method was applied to detect the pathogenicity-related genes of 276 strains of V.cholerae isolates. The amplified fragments of ctxA gene were sequenced and the genetic homology of the amplified fragments of ctxA was analyzed. RESULTS: Of the 276 strains of V.cholerae, 93.9% strains from human sources belong to the pathogenicity-related genes type A (ctxA(+)tcpA(+)ace(+)zot(+) type) and 6.1% belong to pathogenicity-related genes type C (ctxA(-)tcpA(-)ace(-)zot(-) type). Type A strains from clinical sources were isolated from patients with mild to severe symptom and carriers, among which 68.5% were isolated from patients with mild symptom and 21.9% from carriers. All 63.6% of type C strains from clinical sources were isolated from patients with mild symptom and 36.4% from carriers. The proportion of type C strains that caused mild symptom was higher than that of type A strains. Of the 78 strains isolated from the environment, 9.0% strains belong to pathogenicity-related type A and 35.9% belong to the pathogenicity-related genes type B (ctxA(-)tcpA(-)ace(+)zot(+) type), while 55.1% belong to pathogenicity-related genes type C. The sequencing results showed little genetic variation among the amplified fragments for ctxA. CONCLUSION: MPCR disclosed the polymorphic status of pathogenicity-related gene patterns in V.cholerae isolates of Guangzhou, providing effective means for further study on evolution of pathogenicity-related genes among V.cholerae isolates from human and environmental sources. This study also offers significant guidance for effective prevention, control and warning against cholera epidemic in local area.