Bacteroides: A cause of residual abscess?

Bacteroides: A Cause of Residual Abscess? By B. Douglas

and B. Vesey

R

ESIDUAL ABSCESS after appendectomy still remains a problem. Its incidence has not been markedly influenced by the use of parenteral antibiotics.1.2 The cause of residual abscess has never been adequately demonstrated. Various suggestions as to the etiology have been put forward, none more convincing than that of Cooper.3 He demonstrated that if Bacteroides species were present in the peritoneal fluid at operation, there was a 60% chance of a residual abscess developing. If Bacteroides spp. were not present there was very little chance of abscess formation. These findings suggested that Bacteroides spp. might be a significant cause of residual abscess although the evidence was hardly scientific. Leigh4 showed an increase in the isolation of Bacteroides spp. in wound infection after appendectomy from 14% in 197 1 to 8 1% in 1973, although the incidence of wound infection remained the same. If these findings were true, it must follow that we should change our method of treatment. Before attempting a new therapeutic regimen at our hospital, it was necessary to survey our current bacteriologic findings and to correlate these with clinical complications. Such a survey is now presented. METHOD All cases of appendectomy including those done incidentally were studied. These were consecutive appendectomies over a 3-ma period. There were. in all, 54 patients with an age range from 2 days to 14 yr, The operative and pathologic findings were noted and the patients followed closely postoperatively for at least 2 wk. Bacteriologic investigations were performed in every case. three swabs being taken at operation as follows: Swab 1. Peritoneal fluid usually from the right iliac fossa; Swab 2. from the appendix stump; Swab 3. from the lumen of the appendix taken I cm from the tip. Each swab was smeared on to a sterile glass slide and placed into freshly prepared Difco Bacto thioglycollate broth and refrigerated until cultured. Each swab was plated onto: (I) two fresh horse blood agar plates; (2) one MacConkey agar plate (Oxoid No. 2); (3) one neomycin blood agar plate (with a concentration of I00 +g neomycin/ml agar): (4) one bottle of cooked meat medium. One of the blood plates and the neomycin plate were immediately incubated in a Baird and Tatlock anaerobic jar (using 100% hydrogen). The jar was not opened for 2 or 3 days when examples of each colonial type were quickly subcultured and the jars set up again. The original plates were reincubated for at least 3 wk before discarding. having been inspected every 3 to 4 days for new colonies. or prgment production from old colonies. Aerobic bacteria were identified by their morphology and cultural reactions according to Edwards and Ewing.? Cowan and Steele.” and Topley and Wilson.’ As soon as anaerobic organisms were obtained in pure culture, their morphology and cultural reac-

From the Departmenr of Surgerc. .4delaide Children’s H~/~piid. North Adelaide 5006. South AU.G tralia. .Address /or reprint requests: B. Douglas. F.R.A.C.S.. thp Adelaide Children’s Hospital, Inc. 72 King William Road, North Adelaide. 5006. South Australia c 197.5 bv Grune Q Stratton, Inc.

Journal of Pedmtrrc Surgery. Vol 10. No 2 CApnIL 1975

715

216

DOUGLAS

AND VESEY

tions were determined, and they were presumptively identified according to tables in the National Communicable Disease Centre Laboratory Manual ,” Blair, Lennette, and Truant,’ and Bergq~‘s Manual of Determinative Bacteriology.10 For the purposes of this study Bacteroides fiagih was defined as a gram-negative rod, strictly anaerobic, non-spore forming, nonmotile, indole negative, nitrate-reduction negative, gelatinase negative, and oxidase negative. The carbohydrate fermentations were mannitol negative, arabinose negative, glucose, lactose, sucrose, maltose, and xylose-all giving acid. All organisms were identified as accurately as possible. Particular attention was paid to Bacteroides spp. cultures, each being separately identified and each antibiotic sensitivity noted. Chi square was used to test the significance of different infections. RESULTS

Clinical Findings

Fifty-four cases of appendectomy were studied. The findings at operation together with the complications are shown in Table 1. It can be seen that in 22 of the 54 cases there was peritonitis at the time of operation, this being judged by the quantity and quality of the peritoneal fluid (20) or by positive culture only (2). There were ten instances of residual abscess, nine of these occurring in patients with peritonitis at the time of operation. For the purposes of this study, a residual abscess is defined as “a palpable mass with a sustained fever over at least 48 hr and which develops at least 4 days postoperatively.” Of the ten abscesses, five were intraperitoneal and five were deep-seated wound abscesses. Table 2 shows the histopathology and its relation to the development of residual abscess in cases with a positive peritoneal culture. As expected, a perforated or gangrenous appendix is more likely to develop postoperative infection complications, but it was of interest that 12 of the 22 cases with a positive culture did not have an obvious perforation or show full-thickness necrosis on histopathology. Table 3 shows the relationship of antibiotic exhibition to the development of residual abscess. The figures are far too small to be of significance but it is interesting to note that preoperative exhibition of antibiotics did not lead to sterile swabs. Also, in the three patients in this category in whom an abscess did not develop tetracycline was used intravenously. Table 1. Operative FIndIngs of Appendix Peritomtis

Findings and Complications Number

Residual Abscess

22

at presentation

9

Acute or chrome inflammation

20

1

Normal

12

0

54

10

histology

Total

Table 2. Hlstopatholoav

of Appendix

Perforated Gangrenous

only

Acute inflammation Total

Positive Peritoneal Number

Swabs (22) Restdual Abscess

5

3

5

4

12

2

22

9

BACTEROIDES

217

Table 3.

Positive Peritoneal

Swabs (22)

Number Pre-

and postoperatwely

Postoperattvely

only

No antiblotlcs

Fiesldual Abscess

4

1

17

7

1

Total

1

22

9

Table 4. All Three Swabs Positive (13) (1) Pentoneum

(2) Stump

(31 TIP

E coli

10

9

12

6 frag1hs

10

7

11

8

4

4

9

11

3

0

0

2

1

3

0

a

7

Streptococci Bacferoides

(all types) spp

(other

than

frag~hsl

Cl. welchii

Pseudomonas

spp.

Other Total

37

Table 5. Positive Peritoneal Total Abscess

No abscess

E

7

38

51

Swabs (22)

fraglhs

E co/i

Streptococc”s

9

8’

7

5

13

3

5

2

‘p < 0.05. Table 6. Antibiotic Sensitivities

of Becteroides

fragilis

Total Tested Lmcomycin

94

97

Tetracycline

92

97

Gentamun

27

91

Chloramphemcol

23

91

Cephaloridine Trtmethopnm

and sulfamethoxazole

Neomycin

24

96

18

90

6

37

Six patients had wound drains inserted after the closure of the peritoneum; wound abscesses developed in five. Bat teriologic Findings

Swabs 2 and 3 did not materially assist the investigation; 2 because it was often sterile and 3 because, although producing large numbers of organisms, it did not reflect the bacteriology of the peritoneal fluid as shown in Swab I. Table 4 shows the bacteriology of the 13 cases in which all three swabs were positive. It can be seen the Bacteriodes spp. considered together are the commonest organisms associated with appendicitis. Table 5 shows the results of the positive peritoneal swabs and the relationship of the common organisms to the development of residual abscess. Although the figures are small, the finding of B. fragifis in the peritoneal fluid at the time of

218

DOUGLAS

AND VESEY

operation is suggestive that that patient is likely to develop a residual abscess (p <0.05). No significance could be attached to any other organisms found individually, although it was of interest that in only one case with the combination of B. fragilis, E. coli. and streptococcus an abscess failed to develop. Five of the 10 cases of residual abscess had this combination in the peritoneal fluid. Table 6 demonstrates the antibiotic sensitivity of the B. fragilis strains found in this survey. As tested, lincomycin and tetracycline were clearly the antibiotics of choice. DISCUSSION

Bacteroides spp. are gram-negative rods which are strictly anaerobic and nonspore forming. They are the commonest organisms in the large bowel of man, being up to 100 times more common than E. coli.” It is, therefore, surprising that they have seldom been incriminated as a pathogen after appendectomy or large-bowel surgery. Indeed, it has been suggested that Bacteroides spp. are not major pathogens and are only of low virulence in man. There are many reasons why Bacteroides spp. may not be isolated. They are strictly anaerobic and many will die within an hour of exposure to oxygen. It is imperative that operating room personnel place the swab in a suitable medium as soon as possible after the swab has been taken. The organisms are also sensitive to organic peroxides which form in culture media unless special precautions are taken, so special methods for collecting and culturing specimens must be used. Some Bacteroides spp. take up to 5 days to appear on a blood agar plate by which time plates have often been discarded. Because they grow so slowly they are easily overgrown by other faster-growing organisms-for this reason the neomycin blood agar plate has made isolation easier by suppressing the growth of many of these organisms while allowing the growth of Bacteroides spp. Several strains are nutritionally exacting and some require growth factors which are often supplied by associated bacteria, e.g., Bacteroides melaninogenicus sometimes cannot be isolated unless another organism such as Staphylococcus sp.. Streptococcus sp.. or Clostridium sp. is also present.‘2*‘3 Thus, unless a special endeavor is made to isolate Bacteroides spp. it is likely that its presence will be missed. Our recovery of Bacteroides spp. was high compared to other reported series of appendicitis in children. 14.1fiA recent large series reported by Stone et al.lfi did not demonstrate any anaerobes at all. Our results show that Bacteroides spp. are very commonly associated with appendicitis. Several strains including B. fragilis. B. incommunis, B. oralis, B. variabilis, and B. vulgatus were found in the lumen of the appendix and in the appendix stump. Although most of these were occasionally found in the peritoneal fluid, only B. fragilis occurred significantly in the peritoneal fluid in those cases in which residual abscess later developed. Our findings suggest that if B. fragih is found in the peritoneal fluid at the time of appendectomy, there is a strong possibility of a residual abscess developing. Proof that it was the cause of the abscess by isolation of the microbe is lacking. The intraperitoneal abscesses revolved with intravenous fluids and tetracycline. Three wound abscesses were not cultured and two wound swabs were sent to the routine bacteriology laboratory and were reported as sterile. We, therefore, were unable to demonstrate B. .fragilis in the abscess pus.

EIACTEROIDES

219

However, we feel that the finding of B. fragilis in the peritoneal fluid should alert the surgeon to the possibility of residual abscess development. We also feel that there is sufficient evidence to suggest that an antibiotic to which Bacteroides spp. are sensitive should be used in peritonitis or in residual abscess, should any antibiotic therapy be deemed necessary. It is important to note that Bacteroides spp. are resistant to all antibiotics and sulfonamides routinely used as prophylaxis for large-bowel surgery. The antibiotics of choice in the treatment of Bacteroides spp. infections are tetracycline and lincomycin and clindamycin. Prevention of the residual abscess will, however, require therapy other than parenteral antibiotics. It may be that peritoneal lavage with appropriate antibiotics as well as wound lavage will be required. Much work has been done demonstrating that peritoneal lavage before, during, and after operation has done much to reduce the mortality of peritonitis, though the problem of residual abscess has been barely studied.17-1$’ SUMMARY

Bacteroides fragilis as a cause of residual abscess has not been previously demonstrated. This clinical and bacteriologic study of 54 consecutive cases of appendectomy in children suggests that if B. fragilis is found in the peritoneal fluid at the time of operation there is a strong possibility of residual abscess development. Special collection and culture methods are necessary to obtain positive cultures of this strictly anaerobic organism. ACKNOWLEDGMENT This work was financed by the Research Trust Foundation at the Adelaide Children’s Our thanks to the Department of Bacteriology for advice and material assistance.

Hospital.

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AND

VESEY

pancreatitis. irrigation.

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