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J Clin Microbiol. 1979 Jun; 9(6): 654–656.
PMCID: PMC275374

Characterization of anaerobic gram-negative bacilli by using rapid slide tests for beta-lactamase production.


A total of 175 isolates of anaerobic gram-negative bacilli were tested for beta-lactamase production by using a slide test modification of the chromogenic cephalosporin (Nitrocefin, Glaxo, Middlesex, England) assay and the iodometric slide test. Included isolates were Bacteroides melaninogenicus (46), B. fragilis (78), other Bacteroides isolates (21), Fusobacterium (25), and other gram-negative bacilli (5). Both slide tests detected 25 B. melaninogenicus isolates that were beta-lactamase producers (minimal inhibitory concentration of penicillin was greater than 0.78 micrograms/ml). beta-Lactamase produced by the other gram-negative anaerobes could only be detected by the Nitrocefin assay. This assay was positive in 70 or 77 B. fragilis against which the minimal inhibitory concentration of penicillin was greater than 0.78 micrograms/ml. Ten of 11 other species of Bacteroides against which the minimal inhibitory concentration of penicillin was greater than 0.78 micrograms/ml were also Nitrocefin test positive. Minimal inhibitory concentrations of penicillin against all isolates of Fusobacterium and unidentifified gram-negative bacilli were less than or equal to 0.78 micrograms/ml and were Nitrocefin assay negative. beta-Lactamase-producing strains of B. melaninogenicus can be differentiated because both the slide iodometric and Nitrocefin assays will be positive, whereas beta-lactamase produced by other Bacteroides will only be detected by the Nitrocefin assay. Such penicillin-resistant isolates could be detected and reported to clinicians before final identification.

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Selected References

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  • Del Bene VE, Farrar WE., Jr Cephalosporinase activity in Bacteroides fragilis. Antimicrob Agents Chemother. 1973 Mar;3(3):369–372. [PMC free article] [PubMed]
  • Murray PR, Rosenblatt JE. Penicillin resistance and penicillinase production in clinical isolates of Bacteroides melaninogenicus. Antimicrob Agents Chemother. 1977 Apr;11(4):605–608. [PMC free article] [PubMed]
  • O'Callaghan CH, Morris A, Kirby SM, Shingler AH. Novel method for detection of beta-lactamases by using a chromogenic cephalosporin substrate. Antimicrob Agents Chemother. 1972 Apr;1(4):283–288. [PMC free article] [PubMed]
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  • Rosenblatt JE. Isolation and identification of anaerobic bacteria. Hum Pathol. 1976 Mar;7(2):177–186. [PubMed]
  • Rosenblatt JE, Neumann AM. A rapid slide test for penicillinase. Am J Clin Pathol. 1978 Mar;69(3):351–354. [PubMed]
  • Thornsberry C, Kirven LA. Ampicillin resistance in Haemophilus influenzae as determined by a rapid test for beta-lactamase production. Antimicrob Agents Chemother. 1974 Nov;6(5):653–654. [PMC free article] [PubMed]
  • Weinrich AE, Del bene VE. Beta-lactamase activity in anaerobic bacteria. Antimicrob Agents Chemother. 1976 Jul;10(1):106–111. [PMC free article] [PubMed]
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