Antibiotic resistance among Enterococcus spp.

Among hospitalized patients resistance to aminoglycosides was prevalent across all species (tables 4.9 and 4.10). The patterns of resistance to aminoglycosides revealed that resistance to streptomycin was most prevalent across all of the isolates.

The observed frequency was highest among isolates of E. faecium (97.3%), followed by E. gallinarum (88.9%), E. faecalis (78.6%), E. durans (78.6%) and E. avium (66.7%).

Among non-hospitalized individuals, resistance to aminoglycosides was lower compared to resistance among species isolated from hospitalized patients.

Among hospitalized patients there were no differences between E. faecalis and E. faecium resistant to Imipenem (18.9%), whereas there were no resistant among E. durans isolates.

E. gallinarum isolates exhibited the highest frequency of resistance to meropenem (33.3%), followed by E. faecium (24.3%) as shown in tables 4.9 and 4.10.

There was an increased resistance among the enterococci isolated from hospitalized patients against cephalospsorins as compared with isolates from non-hospitalized individuals, most especially ceftazidime and ceftriaxone. E. gallinarum isolates were the highest frequency of resistance to cefuroxime (88.9%) followed by E. faecium (75.7%).

Resistance to ciprofloxacin was observed in 77.8% of E. gallinarum   followed by E. faecium (59.5%). E. durans and E. faecalis isolates had similar resistance (50.0%).

Resistance to Vancomycin was more commonly found in E. faecium (86.5%) followed by E. faecalis strains (67.9%) and the lowest percent of resistance was found in E. avium (16.7%). Resistance to teicoplanin was high among E. gallinarum (55.6%).

Resistance to erythromycin was high among E. faecium isolates (74.1%) in group B.

Only a single isolate of E. gallinarum was observed to be resistant to linezolid (11.1%), and a single isolate of E. faecium was observed to be resistant to linezolid (2.7%).

Among group A, 78.4% of E. faecium were observed to be resistant to penicillin G and 67.6% of E. faecium were observed to be resistant to ampicillin. The frequency of resistance was higher among group A compared with group B. 88.9% of E. gallinarum and 81.1% E. faecium, both species were observed to have high resistance rates to co-trimoxazole.

Resistance to chloramphenicol was more commonly found in E. fecalis (92.9%) followed by E. gallinarum (88.9%) strains. The greater resistance of group A compared to group B was observed.      

Table (4.9): Antibiotic resistance pattern among E. fecalis and E. faecium

Antibiotic resistance pattern	E. fecalis		E. faecium
	H* (n=28)	N** (n= 34)	H* (n= 37)	N** (n=27)
Amikacin	17 60.7%	13 38.2%	28 75.7%	13 48.1%
Ampicillin	17 60.7	20 58.8%	25 67.6%	18 66.7%
Penicillin G	19 67.9%	18 52.9%	29 78.4%	18 66.7%
Ceftazidime	17 60.7%	16 47.1%	27 73.0%	17 63.0%
Ceftriaxone	17 60.7%	12 35.3%	24 64.9%	16 59.3%
Cefuroxime	21 75.0%	16 47.1%	28 75.7%	17 63.0%
Cephotaxime	14 50.0%	13 38.2%	22 59.5%	11 40.7%
Chloramphenicol	26 92.9%	24 70.6%	29 78.4%	23 85.2%
Ciprofloxacin	14 50.0%	15 44.1%	22 59.5%	12 44.4%
Co-Trimoxazole	22 78.6%	19 55.9%	30 81.1%	23 85.2%
Erythromycin	18 64.3%	14 41.2%	20 54.1%	20 74.1%
Gentamycin	22 78.6%	18 52.9%	29 78.4%	17 63.0%
Imipenem	4 18.9%	2 5.9%	7 18.9%	0 0.0%
Linezolid	0 0.0	0 0.0%	1 2.7%	0 0.0%
Meropenem	2 7.1%	1 2.9%	9 24.3%	1 3.7%
Methicillin	17 60.7%	12 35.3%	28 75.7%	10 37.0%
Streptomycin	22 78.6%	17 50.0%	36 97.3%	21 77.8%
Teicoplanin	10 35.7%	7 20.6%	20 54.1%	4 14.8%
Tetracycline	20 71.4%	19 55.9%	30 81.1%	22 81.5%
Vancomycin	19 67.9%	13 38.2%	32 86.5%	15 55.6%

H* = Hospitalized, N** = Non-hospitalized

Table (4.10): Antibiotic resistance pattern among E. durans, E. gallinarum and E. avium

Antibiotic resistance pattern	E. durans		E. gallinarum		E. avium
	H* (n=14)	N** (n=3)	H* (n= 9)	N** (n=11)	H* (n= 6)	N** (n=14)
Amikacin	9 64.3%	1 33.3%	8 88.9%	5 45.5%	2 33.3%	4 28.6%
Ampicillin	8 57.1%	2 66.7%	6 66.7%	4 36.4%	4 66.7%	9 64.3%
Penicillin G	9 64.3%	2 66.7%	7 77.8%	4 36.4%	3 50.0%	8 57.1%
Ceftazidime	9 64.3%	1 33.3%	8 88.9%	5 45.5%	2 33.3%	7 50.0%
Ceftriaxone	7 50.0%	1 33.3%	7 77.8%	4 36.4%	1 16.7%	6 42.9%
Cefuroxime	9 64.3%	2 66.7%	8 88.9%	7 63.6%	2 33.3%	9 64.3%
Cephotaxime	7 50.0%	1 33.3%	7 77.8%	5 45.5%	1 16.7%	4 28.6%
Chloramphenicol	10 71.4%	1 33.3%	8 88.9%	8 72.7%	3 50.0%	8 57.1%
Ciprofloxacin	7 50.0%	1 33.3%	7 77.8%	3 27.3%	2 33.3%	6 42.9%
Co-Trimoxazole	11 78.6%	1 33.3%	8 88.9%	9 81.8%	3 50.0%	10 71.4%
Erythromycin	6 42.9%	1 33.3%	5 55.6%	5 45.5%	1 16.7%	9 64.3%
Gentamycin	10 71.4%	2 66.7%	7 77.8%	7 63.6%	2 33.3%	9 64.3%
Imipenem	0 0.0%	0 0.0%	1 11.1%	1 9.1%	1 16.7%	0 0.0%
Linezolid	0 0.0%	0 0.0%	1 11.1%	0 0.0%	0 0.0	0 0.0%
Meropenem	2 14.3%	0 0.0%	3 33.3%	1 9.1%	0 0.0%	1 7.1%
Methicillin	7 50.0%	1 33.3%	8 88.9%	4 36.4%	1 16.7%	3 21.4%
Streptomycin	11 78.6%	1 33.3%	8 88.9%	8 72.7%	4 66.7%	8 57.1%
Teicoplanin	5 35.7%	1 33.3%	5 55.6%	3 27.3%	1 16.7%	2 14.3%
Tetracycline	8 57.1%	1 33.3%	8 88.9%	7 63.6%	2 33.3%	9 64.3%
Vancomycin	7 50.0%	1 33.3%	6 66.7%	4 36.4%	1 16.7%	6 42.9%

H* = Hospitalized, N**= Non-hospitalized

From table (4.11), among hospitalized patients isolates E. faecium has the highest resistance range (32-512) μg/ml while E. durans and E. avium has the lowest range (2-16) μg/ml.

Among non hospitalized isolates MIC range of E. faecium (16-256) μg/ml, while E. gallinarum has the lowest range of MIC (2-8) μg/ml. Figure (4.10) showed two methods for MIC determination figure (A) a photograph of tetrazolium chloride microdilution method and (B) a photograph of conventional microdilution method.

Table (4.11): Enterococcal species isolated from hospital and community specimens and MIC ranges for vancomycin

Sample source Enterococcal species	Hospitalized (n =94)		Non-Hospitalized (n =89)
	Number of isolates n %	MIC vancomycin (μg/ml)	Number of isolates n %	MIC vancomycin (μg/ml)
E. faecalis	28 29.8%	16-256	34 38.2%	16-128
E. faecium	37 39.4%	32-512	27 30.3%	16-256
E. durans	14 14.9%	2-16	3 3.4%	2-16
E. gallinarum	9 9.6%	4-32	11 12.4%	2-8
E. avium	6 6.4%	2-16	14 15.7%	2-16
Total	94 100.0%		89 100.0%