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Occurrence of false positive results for the detection of carbapenemases in carbapenemase-negative Escherichia coli and Klebsiella pneumoniae isolates.

Wang P, Chen S, Guo Y, Xiong Z, Hu F, Zhu D, Zhang Y - PLoS ONE (2011)

Bottom Line: The susceptibility rates for imipenem, meropenem, and ertapenem all were 100.0%, 100.0%, and 100.0%, respectively.The MHT gave a positive result for 3.3% (10/301) of the isolates.False positive results can occur when the MHT is used to detect carbapenemase in ESBL-producing isolates and clinical laboratories must be aware of this fact.

View Article: PubMed Central - PubMed

Affiliation: Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China.

ABSTRACT
Adequate detection of the production of carbapenemase in Enterobacteriaceae isolates is crucial for infection control measures and the appropriate choice of antimicrobial therapy. In this study, we investigated the frequency of false positive results for the detection of carbapenemases in carbapenemase-negative Escherichia coli and Klebsiella pneumoniae clinical isolates by the modified Hodge test (MHT). Three hundred and one E. coli and K. pneumoniae clinical isolates were investigated. All produced extended spectrum β-lactamases (ESBLs) but were susceptible to carbapenems. Antimicrobial susceptibility testing was performed by the disk diffusion and agar dilution methods. The MHT was performed using the standard inoculum of test organisms recommended by the CLSI. Genes that encoded ESBLs and carbapenemases were identified by PCR and DNA sequencing. Among the 301 clinical isolates, none of the isolates conformed to the criteria for carbapenemase screening recommended by the CLSI. The susceptibility rates for imipenem, meropenem, and ertapenem all were 100.0%, 100.0%, and 100.0%, respectively. Of the 301 E. coli and K. pneumoniae isolates, none produced carbapenemase. The MHT gave a positive result for 3.3% (10/301) of the isolates. False positive results can occur when the MHT is used to detect carbapenemase in ESBL-producing isolates and clinical laboratories must be aware of this fact.

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Related in: MedlinePlus

False-positive result on MHT.A, K2821 K. pneumoniae (KPC-2 carbapenemase producer). B, 08-438 E.coli. C, 08-97 K. pneumoniae. D, E. coli ATCC 25922.
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pone-0026356-g001: False-positive result on MHT.A, K2821 K. pneumoniae (KPC-2 carbapenemase producer). B, 08-438 E.coli. C, 08-97 K. pneumoniae. D, E. coli ATCC 25922.

Mentions: Of the 301 E. coli and K. pneumoniae isolates, none produced carbapenemase. Genes that encoded the CTX-M-type ESBLs were detected in 280 (93.0%) of the isolates, among which CTX-M-14, CTX-M-15, CTX-M-25, CTX-M-14 coupled with CTX-M-15, and CTX-M-14 coupled with CTX-M-25 type ESBL were found in 135 (48.2%), 112 (40.0%), 2 (0.7%), 28 (10.0%), and 3 (1.1%) of the isolates, respectively. Among 301 isolates, 18.3% were producing more than two types of ESBLs, such as TEM-type and CTX-M-type ESBLs, SHV-type and CTX-M-type ESBLs (Table 2). Although all the isolates were sensitive to carbapenems and carbapenemase-negative, the MHT yielded a positive result (Figure 1) for 3.3% (10/301) of the isolates and all the MHT-positive isolates (except one isolate was SHV-12 type ESBL producer) were CTX-M type ESBL producing (Table 3). Among 18 carbapenem-resistant K. pneumoniae clinical isolates, all were produced KPC-2 type carbapenemase and all were producing a positive result of MHT.


Occurrence of false positive results for the detection of carbapenemases in carbapenemase-negative Escherichia coli and Klebsiella pneumoniae isolates.

Wang P, Chen S, Guo Y, Xiong Z, Hu F, Zhu D, Zhang Y - PLoS ONE (2011)

False-positive result on MHT.A, K2821 K. pneumoniae (KPC-2 carbapenemase producer). B, 08-438 E.coli. C, 08-97 K. pneumoniae. D, E. coli ATCC 25922.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198770&req=5

pone-0026356-g001: False-positive result on MHT.A, K2821 K. pneumoniae (KPC-2 carbapenemase producer). B, 08-438 E.coli. C, 08-97 K. pneumoniae. D, E. coli ATCC 25922.
Mentions: Of the 301 E. coli and K. pneumoniae isolates, none produced carbapenemase. Genes that encoded the CTX-M-type ESBLs were detected in 280 (93.0%) of the isolates, among which CTX-M-14, CTX-M-15, CTX-M-25, CTX-M-14 coupled with CTX-M-15, and CTX-M-14 coupled with CTX-M-25 type ESBL were found in 135 (48.2%), 112 (40.0%), 2 (0.7%), 28 (10.0%), and 3 (1.1%) of the isolates, respectively. Among 301 isolates, 18.3% were producing more than two types of ESBLs, such as TEM-type and CTX-M-type ESBLs, SHV-type and CTX-M-type ESBLs (Table 2). Although all the isolates were sensitive to carbapenems and carbapenemase-negative, the MHT yielded a positive result (Figure 1) for 3.3% (10/301) of the isolates and all the MHT-positive isolates (except one isolate was SHV-12 type ESBL producer) were CTX-M type ESBL producing (Table 3). Among 18 carbapenem-resistant K. pneumoniae clinical isolates, all were produced KPC-2 type carbapenemase and all were producing a positive result of MHT.

Bottom Line: The susceptibility rates for imipenem, meropenem, and ertapenem all were 100.0%, 100.0%, and 100.0%, respectively.The MHT gave a positive result for 3.3% (10/301) of the isolates.False positive results can occur when the MHT is used to detect carbapenemase in ESBL-producing isolates and clinical laboratories must be aware of this fact.

View Article: PubMed Central - PubMed

Affiliation: Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China.

ABSTRACT
Adequate detection of the production of carbapenemase in Enterobacteriaceae isolates is crucial for infection control measures and the appropriate choice of antimicrobial therapy. In this study, we investigated the frequency of false positive results for the detection of carbapenemases in carbapenemase-negative Escherichia coli and Klebsiella pneumoniae clinical isolates by the modified Hodge test (MHT). Three hundred and one E. coli and K. pneumoniae clinical isolates were investigated. All produced extended spectrum β-lactamases (ESBLs) but were susceptible to carbapenems. Antimicrobial susceptibility testing was performed by the disk diffusion and agar dilution methods. The MHT was performed using the standard inoculum of test organisms recommended by the CLSI. Genes that encoded ESBLs and carbapenemases were identified by PCR and DNA sequencing. Among the 301 clinical isolates, none of the isolates conformed to the criteria for carbapenemase screening recommended by the CLSI. The susceptibility rates for imipenem, meropenem, and ertapenem all were 100.0%, 100.0%, and 100.0%, respectively. Of the 301 E. coli and K. pneumoniae isolates, none produced carbapenemase. The MHT gave a positive result for 3.3% (10/301) of the isolates. False positive results can occur when the MHT is used to detect carbapenemase in ESBL-producing isolates and clinical laboratories must be aware of this fact.

Show MeSH
Related in: MedlinePlus