The susceptibility to methicillin of 44 Staphylococcus aureus and 120 coagulase-negative staphylococci (CNS) was determined by Etest, agar dilution and presence of the mecA gene. There was agreement between the results of all methods when testing S. aureus. However, discrepancies occurred with CNS when cultural methods were compared with presence of the mecA gene. mecA-positive isolates tested as resistant more often with agar dilution on Columbia agar plus 5% NaCl than by Etest.
SUMMARY The detection of methicillin resistance was examined in 51 strains of Staphylococcus aureus and 135 strains of coagulase negative staphylococci using Isosensitest, Diagnostic Sensitivity Test (DST), Mueller-Hinton (MH), Columbia, and Sensitest agars. MH agar with 5% added sodium chloride incubated at 35°C was the most effective in detecting resistance in S aureus, and Columbia agar with 5% added sodium chloride incubated at 35°C was most effective for coagulase negative staphylococci. For clinical purposes, a provisional report of sensitivity for S aureus could be issued after 18 hours; with coagulase negative staphylococci, only resistant strains could be reported at this time. For definitive results cultures must be examined after 40 hours of incubation.Resistance to methicillin in Staphylococcus aureus is usually heterogeneous and due to the presence of a component which sometimes only manifests resistance if grown on osmotically supportive media' or if cultured at 30'C2 for up to 48 hours.3 Snell et al4 recommended that incubation at 30°C or adding 5% sodium chloride to the medium, or both, be used for methicillin testing. Despite the heterogeneous nature of the resistance in S aureus to methicillin it has been shown to be clinically relevant in that it impairs the response to treatment with methicillin.5 Resistance to methicillin in coagulase negative staphylococci has also been shown to be due to heterogeneous populations and to be enhanced by growth on hypertonic medium or incubation at 30°C or for 48 hours.6In addition to these factors, the detection of methicillin resistance can be affected by the basal test medium used. Hindler and Inderleid7 showed that when MH, an undefined medium, was used from five different manufacturers there were differences in the detection of resistance of S aureus to methicillin.Brown and Kothari8 determined the minimum inhibitory concentration (MIC) of strains of S aureus using MH, DST, Sensitest, and Wellcotest agars, and all gave similar results when incubated at 30°C for 18 hours. In view of the increasing clinical importance of
Shepard (1956) and Shepard, Alexander, Lunceford, and Campbell (1964) reported the isolation from men with non-gonococcal urethritis of a species of mycoplasma which formed very small colonies on culture. The organisms were isolated from 86 per cent. of 79 men in the first study and from 51 per cent. of 64 men in the second. This organism was subsequently called T strain mycoplasma.Ford, Rasmussen, and Minken (1962) and Ford and Duvernet (1963) found that whereas T strain mycoplasmata were isolated from 60 to 79 per cent. of patients with non-gonococcal urethritis, they were found in only 21 to 48 per cent. of normal males. Similar findings were reported by Csonka, Williams, and Corse (1966).These findings suggested that T strain mycoplasma could be an aetiological agent in non-gonococcal urethritis. However, these organisms were also isolated from control groups of patients and the proportions of controls who have yielded this organism have varied considerably. This variation was possibly due to differences in the age and social characteristics of the control groups studied and to difference in the methods used for collecting specimens from the different groups.The present study was undertaken in order to compare the prevalence of T strain mycoplasma in patients suffering from non-gonococcal urethritis and in comparable groups of males not suffering from this disease.
Patients and MethodsThree groups of males were examined. All were over 16 years of age and none gave a history of previous urethritis or prostatitis.(1) Patients with Non-gonococcal Urethritis (45). The diagnosis of non-gonococcal urethritis was made on the basis of a mucopurulent urethral discharge which on * Received for publication June 6, 1966 microscopic examination did not reveal gonococci, and failure to demonstrate Trichomonas vaginalis in the urine. The average age of the patients in this group was 25 years.(2) Normal Controls (54).-These were men seeking reassurance that they had not contracted venereal disease as the result of sexual exposure. Their average age was 29 years.(3) Patients with Gonorrhoea (36).-Men presenting with gonorrhoea were included as an additional control group because of the possibility that the presence of T strain mycoplasmata might simply represent an index of sexual activity. Their average age was 29 years. Collection of Specimens.-These were obtained from all patients by inserting a rigid 4 mm. diameter wire loop 2 inches into the urethra and exerting gentle pressure on the urethral mucosa on withdrawal. The specimens so obtained were inoculated immediately on to a solid medium and into broth. Cultural Methods.-PPLO agar (Difco) supplemented with 10 per cent. horse serum (Burroughs Wellcome No. 3) and 10 per cent. fresh yeast extract and containing 1,000 units penicillin per ml. was used to prepare the solid medium. The liquid medium consisted of Oxoid sensitivity broth to which the same supplements were added. The broth cultures were incubated at 37CC. in an atmosphere of 80 per cent. nitrogen and 20...
Aims-To test 10 culture media for their ability to detect resistance and sensitivity of staphylococci to methicillin by disc diffusion. Methods-Fifty strains of Staphylococcus aureus and 135 strains of coagulase negative staphylococci were tested using Columbia, Diagnostic Sensitivity Test, Mueller Hinton, Sensitest and Isosensitest agars with and without 5% added sodium chloride. Cultures were examined after 18 and 40 hours of incubation. The diameter of the zone and its characteristics were recorded and these media were assessed for their ability to produce clear, readable zones of inhibition. Changes in the variables which determined resistance were investigated. Results were analysed allowing a zone diameter reduction of 8 mm and 10 mm compared with the control in addition to the standard 6 mm.
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