Fc-051 Manual

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Aug 3, 2024, 3:41:20 PM8/3/24

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This passage describes how warnings and alarms are indicated and what actions can be taken to reset them. A warning is indicated by an LED and a code on the display, and remains active until the cause is resolved. An alarm results in the frequency converter tripping and requires resetting once the cause has been rectified. Alarms can be reset in four ways, including via a manual reset, digital input, or serial communication.

If an alarm cannot be reset, it may be trip-locked, in which case the mains supply must be switched off before it can be reset. Table 6.1 provides codes for warnings and alarms, and in some cases, it can specify whether a warning or alarm is to be displayed. After an alarm or trip, the motor coasts and both the warning and alarm flash. Once the problem is resolved, only the alarm continues flashing.

The NCCLS (2004) presented a new methodology to detect, by disk-diffusion agar, oxacillin-resistance using a cefoxitin disk. We identified coagulase-negative staphylococci (SCoN) to the species level and compared the use of cefoxitin disks (30 g) with oxacillin disks (1 g), agar dilution (minimum inhibitory concentration of oxacillin) and mecA gene detection in isolates of coagulase-negative bacteria other than Staphylococcus epidermidis (SCoNne). A total of 238 SCoNne was evaluated; oxacillin-resistance (the mecA gene) was detected in 71% of the isolates. All methods gave 100% sensitivity, based on presence of the mecA gene. The specificity of the cefoxitin disk was 100%, while the oxacillin disk gave a specificity of 91% and agar dilution oxacillin gave a specificity of 88%. We conclude that the cefoxitin disk is an efficient test, and it is an easy method for use in clinical laboratories to detect oxacillin-resistance in staphylococci.

The NCCLS (2004) presented a new methodology to detect, by disk-diffusion agar, oxacillin-resistance using a cefoxitin disk. We identified coagulase-negative staphylococci (SCoN) to the species level and compared the use of cefoxitin disks (30 g) with oxacillin disks (1 g), agar dilution (minimum inhibitory concentration of oxacillin) and mecA gene detection in isolates of coagulase-negative bacteria other than Staphylococcus epidermidis (SCoNne). A total of 238 SCoNne was evaluated; oxacillin-resistance (the mecA gene) was detected in 71% of the isolates. All methods gave 100% sensitivity, based on presence of the mecA gene. The specificity of the cefoxitin disk was 100%, while the oxacillin disk gave a specificity of 91% and agar dilution oxacillin gave a specificity of 88%. We conclude that the cefoxitin disk is an efficient test, and it is an easy method for use in clinical laboratories to detect oxacillin-resistance in staphylococci.

Coagulase-negative staphylococci (SCoN) are common pathogens of the blood stream, being frequently related to nosocomial infections, especially in neonates and immunocompromised patients; transmission usually involves medical devices, such as catheters and prostheses [1-3]. Correct identification of SCoN species has become important in clinical laboratories, since several species have been recognized as potential pathogens, especially in a nosocomial setting [4]. Although Staphylococcus epidermidis causes most SCoN infections, many other species have been identified in association with human infections, for example, Staphylococcus lugdunensis, associated with native valve endocarditis and Staphylococcus haemolyticus, which can be multiresistant, including reduced susceptibility to vancomycin [5-7].

Methicillin-resistant staphylococci are considered important agents of nosocomial infections and have frequently been isolated in hospitals throughout the world, including Brazilian hospitals [8]. Sader et al. reported that 80% of SCoN recovered from blood in Latin America were oxacillin resistant [9]. Susceptibility testing by phenotypic methods can be problematic for the detection of methicillin resistance in SCoN because of heterogeneous expression in many strains, affected by growth conditions and by the nature of the beta-lactam agents that are used [10]. For this reason, mecA gene detection by PCR is considered the gold standard for methicillin resistance detection in Staphylococcus spp. [11].

To improve accuracy in the detection of resistance, NCCLS 2004 recommended that clinical laboratories should use cefoxitin disk (30 g) tests for detection of oxacillin resistance in Staphylococcus spp. [12]. Several studies have been performed to compare results obtained with cefoxitin and oxacillin disks and how they correlate with the presence of the mecA gene in Staphylococcus spp. [13-15]. We identified all SCoN to the species level and compared the use of cefoxitin disks (30 g) with oxacillin disks (1 g), agar dilution (MIC of oxacillin), and mecA gene detection, in isolates of coagulase-negative other than Staphylococcus epidermidis (SCoNne).

A total of 238 samples of SCoNne were analyzed, from a collection of samples of SCoN of the Gram-positive Cocci Laboratory of the UFCSPA, stored in skim milk (Difco, Detroit) at 20C. The samples were obtained from blood cultures collected consecutively, between 2002 and 2004, in the Complexo Hospitalar Santa Casa, Porto Alegre, RS, Brasil.

The isolates were cultured in Tryptic Soy agar (Oxoid, Basingstoke, UK), supplemented with 5% sheep blood, for 24h at 35C; colony morphology, hemolytic activity and purity were evaluated. Subsequently, phenotypic tests were evaluated by the conventional method proposed by Kloss & Bannerman 1994, and modified by Bannerman 2003, which consists of a set of biochemical tests that determine the utilization of coagulase, catalase, alkaline phospatase, ornithine decarboxylase, urease, PYR (pyrrolidinyl-β-naphthylamide hydrolysis), and acid production from carbohydrates (trehalose, mannitol, mannose, sucrose, maltose, lactose, and cellobiose) [16,17]. Anaerobic growth in thioglycolate and susceptibility to novobiocin, polymyxin B, bacitracin, desferrioxamine and fosfomycin using disk diffusion tests were evaluated [18]. Quality control was performed with S. epidermidis ATCC 12228. The samples that gave variable results in the phenotypic test identifications, or to confirm less frequent species, were run through an automated method of identification (Microscan Walkway; Dade Behringer, Deerfield, IL, USA). The automated results that gave a low percentage certainty of species identification were submitted to determination of the sodA gene by PCR amplification and sequencing with specific primers: d1: 5'CCITAYICITAYGAYYGCIYTIGARCC-3' and d2: 5'ARRTARTAIGCRTGYTCCCAIACRTC-3' [19].

The suspensions were adjusted to a 0.5 McFarland standard for each sample to perform the disk diffusion method (Kirby-Bauer) on Mueller-Hinton agar plates (Difco, Laboratories, Detroit, Mich), using cefoxitin (30 g) and oxacillin (1 g) disks (Oxoid, Basingstoke, UK), according to the criteria recommended by CLSI 2005 [20]. The plates were incubated at 35 C and screened after 24h.

Determination of the minimum inhibitory concentration (MIC) for oxacillin was performed by bacterial suspension (0.5 McFarland), diluted 1:10 in saline solution and inoculated on Mueller-Hinton agar plates supplemented with 2% NaCl by using Steers replicator. Concentrations of 0.125g/mL-4 g/mL of oxacillin (Sigma Chemical Co, St. Louis, USA) were used for determination of the MIC of oxacillin. The plates were incubated at 35 C and screened after 24h.

Detection of PBP2a was performed with the latex agglutination test Slidex MRSA Detection (bioMrieux, l'Etoile, France), following the manufacturer's instructions. This test was performed only for samples that showed discrepant results between cefoxitin and oxacillin in our tests.

The cefoxitin disk test was proposed in 2001 as an option for the detection of oxacillin resistance mediated by the mecA gene, considering that many laboratories do not have a latex agglutination test or a PCR technique for routine use [23]. Earlier studies indicated that the cefoxitin disk is a helpful tool for the detection of oxacillin resistance, with 99%-100% sensitivity and 96% specificity to predict the mecA gene in S. aureus and SCoN [14,24,25].

We evaluated a higher number of isolates of SCoNne than other studies performed in Brazil, and we found high rates of resistance to oxacillin by PCR (71%) in these isolates, though earlier studies also included isolates of S. epidermidis [26-28]. In our study, among the SCoNne isolates, 100 were identified as S. haemolyticus, with 91% presenting a mecA-gene-positive PCR result. Other studies have shown that S. haemolyticus and S. epidermidis are the species most frequently associated with antimicrobial agent resistance [7,8]. A study performed by Palazzo & Darini in 2006 described a sensitivity of 92.5% to both cefoxitin and oxacillin disk tests, a specificity of 98.6% to cefoxitin disks and 96% to oxacillin disks. In this study, six isolates showed a false negative result in the cefoxitin disk test (five isolates of S. epidermidis and one isolate of S. caprae) [29]. Perazzi et al. in 2006 found a lower sensitivity for the cefoxitin disk (84%) than that obtained with the oxacillin disk (87%), in a study performed with isolates of SCoN other than S. saprophyticus. The specificity of the cefoxitin disk was 100% [30].

Among the species for which there were discrepancies between the tests, susceptibility to cefoxitin disk with resistance with oxacillin disk was observed in 44% (4/9) isolates of S. sciuri, all of them giving negative results in a PCR of the mecA gene. Oxacillin resistance was observed in three of these isolates and oxacillin susceptibility in one of them with an agar dilution test. Resistance to oxacillin was observed in 33% (2/6) of S. saprophyticus isolates by the agar dilution test. The PCR results for the mecA gene were negative in these isolates, which showed susceptibility to cefoxitin and oxacillin by disk diffusion. Seventy-five percent (3/4) of the isolates identified as S. cohnii-cohnii, which gave a negative PCR for the mecA gene, had discrepancies with the oxacillin disk and/or agar dilution results. Two of these isolates were resistant to oxacillin by disk and agar dilution, and one of them was resistant only by agar dilution. All of them were susceptible when tested with the cefoxitin disk. Results obtained for the other species did not differ among the methods (Table 2). Pottumarthy et al. in 2005 found 3% of very major errors with the cefoxitin disk test and 4% with the oxacillin disk test [31]. We only found major errors (false-resistance) with the oxacillin disk in 2.5% of the isolates, including S. sciuri, S. saprophyticus and S. cohnii-cohnii. Similar discrepancies between phenotypic and genotypic results have been described for S. saprophyticus, S. cohnii, S. warneri, S. capitis, S. lugdunensis and S. xylosus [32].